INSTITUTEFORCOSMIC RAY RESEARCH
THE UNIVERSITY OF TOKYOANNUAL REPORT(APRIL 2013 – MARCH 2014)

Editorial Board
MIYOKI, Shinji
YOSHIKOSHI, Takanori
BAI, Lili
HAYASHIDA, Misato

c Institute for Cosmic Ray Research, The University of Tokyo
5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8582, Japan
Telephone: (81) 4-7136-3102
Facsimile: (81) 4-7136-3115
WWW URL: http://www.icrr.u-tokyo.ac.jp/

TABLE OF CONTENTS
PrefaceResearch Divisions.........................................................................................

1

Neutrino and Astroparticle Division2

High Energy Cosmic Ray Division

24

Astrophysics and Gravity Division51.........................................................................

Observatories and a Research Center

73

Norikura Observatory

74

Akeno Observatory

80

Kamioka Observatory

83

Research Center for Cosmic Neutrinos

84.............................................................

86..............................................................................

88..........................................................................

88

Appendix A.

ICRR Workshops and Ceremonies

Appendix B.

ICRR Seminars

Appendix C.

List of Publications(a) Papers Published in Journals(b) Conference Papers(c) ICRR Reports
Appendix D.

Doctoral Theses.............................................................................

98

Appendix E.

Public Relations.............................................................................

98(a) ICRR News(b) Public Lectures(c) Visitors
Appendix F.

Inter-University Researches..................................................................

102

Appendix G.

List of Committee Members.................................................................

106(a) Board of Councillors(b) Advisory Committee(c) Inter-University Research Advisory Committee
Appendix H.

List of Personnel...........................................................................

107

PREFACE
This report summarizes the scientific activities of the Institute for Cosmic Ray Research (ICRR) of the
University of Tokyo in the Japanese FY 2013.
ICRR is an inter-university research institute for studies of cosmic rays. The headquarters of ICRR islocated in Kashiwa, Chiba prefecture, Japan. In order to promote various cosmic-ray-related studies efficiently,
ICRR has three research divisions; Neutrino and Astroparticle division, High Energy Cosmic Ray division, andAstrophysics and Gravity division. ICRR has 3 observatories in Japan; Kamioka Observatory (Kamioka underground, Gifu prefecture), Norikura Observatory (2770 meters above sea level, Mt. Norikura, Gifu prefecture),
and Akeno Observatory (Yamanashi prefecture), together with 1 research center; Research Center for Cosmic
Neutrinos (Kashiwa, Chiba prefecture). In addition, there are 2 major experimental facilities outside of Japan.
They are located in Utah in USA, and Yangbajing in Tibet, China.
Many researchers from various Japanese institutions as well as those from overseas are involved in the
research programs of ICRR. It should be noted that most of the scientific outputs from this institute are theresults of the collaborative efforts by many scientists from various institutions. In order to produce outstanding
results, it is very important to carry out an experiment by an international collaboration composed of toplevel researchers all over the world. Hence, most of the experimental collaborations that ICRR is involved areinternational ones. For example, the number of collaborators in the Super-Kamiokande experiment is about
120; about a half of them are from abroad (USA, Korea, China, Poland, Spain and Canada).
Many exciting scientific activities of ICRR are described in this report. One of the highlights in FY 2013is the results from the Tibet AS gamma experiment, which studied the solar magnetic field using the cosmic
ray shadow of the Sun for the first time. It should be noted that the Super-Kamiokande and T2K (which uses
Super-Kamiokande as the far detector) experiments have been continuously producing impressive results onneutrino oscillation physics. Another highlight is the construction of the large-scale cryogenic gravitational
wave telescope (KAGRA), which intends to detect gravitational waves for the first time and open a new fieldof gravitational wave astronomy.
As an inter-university research institute, ICRR is reviewed by the top-level researchers in the field. Furthermore, future projects of ICRR are evaluated by a committee composed of top-level researchers from various
nearby fields. The report from the ICRR Future Project Evaluation Committee was released in September 2013.
The Committee evaluated various possible future projects of ICRR. Several projects have been recommended
highly. Among them, joining the CTA project, which is a global TeV gamma ray astronomy project, has been
recommended as the top priority ICRR future project. The review report from the External Review Committee,
which was released in May 2013 (please see the Annual Review of the last year), also supported joining CTA.
ICRR is going to make every endeavor to realize the CTA project as an important international partner of thisproject.
We hope that this report is useful for the understanding of the current research activities of ICRR. Finally,
we appreciate very much the strong support of our colleagues in this research field, the University of Tokyoand the Japanese Ministry of Education, Culture, Sports, Science and Technology. They are indispensable forthe continuing, and exciting scientific outcome of ICRR.

Takaaki Kajita,
Director,
Institute for Cosmic Ray Research,
The University of Tokyo

The ICRR building at Kashiwa,
Chiba, Japan.

The inner detector of SuperKamiokande-III during the fullreconstruction. The purified wateris under filling.

XMASS detector using 835 kg ofliquid xenon.
Radiations areshielded and cosmic-ray muons canbe vetoed by a water-Cherenkov detector outside.

The system of four imaging atmospheric Cherenkov telescopesof 10m diameter of CANGAROO
project for detection of very highenergygamma-rays The whole system is in operation since March
2004 in Woomera, South Australia.

Tibet-III air shower array (37000
m2 ) at Yangbajing, Tibet (4300 m
in altitude).

Air fluorescence telescopes (left)
and a scintillator surface detector(right) of the Telescope Array experiment in Utah, USA to explore
the origin of extremely high energy
cosmic rays.

Cryogenic mirror sysytem for KAGRA with a cryostat and a cryocooler.

A public lecture held by ResearchCenter for Cosmic Neutrinos.

Organization

Number of Staff Members (As of May 1, 2013)

Neutrino and Astroparticle Div.
High Energy Cosmic Ray Div.
Astrophysics and Gravity Div.
Administration
Total

Scientific
Staff

Technical
Staff

Research
Fellows

24
18
14
0
56

4
11
0
0
15

1
5
5
0
11

Administrators
andSecretaries
17
2
8
12
39

Total

46
36
27
12
121

FY 2007–2013 Budget
Personnel
expenses
Nonpersonnel
expenses
Total

2007

2008

2009

2010

2011

2012

2013

624 000

632 000

590 000

576 000

653 000

658 000

687 000

1 253 000

1 121 000

1 292 000

1 048 000

1 400 000

1 172 000

1 034 000

1 877 000

1 753 000

1 882 000

1 624 000

2 053 000

1 830 000

1 721 000

(in 1 000 yen)

1

RESEARCH DIVISIONS
Neutrino and Astroparticle Division
Overview
Super-Kamiokande
XMASS ExperimentHyper-Kamiokande
T2K ExperimentHigh Energy Cosmic Ray Division
Overview
Cherenkov Cosmic Gamma-Ray Group
TA: Telescope Array Experiment
Tibet ASγ Project
The Ashra ProjectHigh Energy Astrophysics Group

Astrophysics and Gravity Division
Overview
Gravitational Wave GroupGravitational Wave Project Office
KAGRA Project
CLIO Project

Observational Cosmology Group
Primary Cosmic Ray Group
Theory Group
Particle Phenomenology
Astrophysics and Cosmology

2

NEUTRINO AND ASTROPARTICLE DIVISION
Overview
This division aims to study particle physics with prime interests in physics of neutrinos and proton decay, and astroparticle physics with the use of underground experimental facilities.
Our most important facility is the Super-Kamiokande (SK)detector. It is a 50 kton water Cherenkov detector using 11,129
50 cm-diameter photomultipliers (PMTs) for its inner detector
and 1,885 20 cm-diameter PMTs for its outer detector. The
data taking of SK started in April 1996. The neutrino oscillations in atmospheric neutrinos were discovered in 1998 andthereby demonstrating that neutrinos have a finite mass. In
2001, the accurate measurements of the 8 B solar neutrino flux
by SK and SNO discovered that neutrino oscillations are thesolution of the solar neutrino problem beyond doubt. After
those discoveries, precise measurements of atmospheric neutrinos and solar neutrinos have been performed and they unraveled various phenomena of neutrino oscillations. Recently,
excess of events induced by ντ appearance was observed in atmospheric neutrinos, and the day/night difference of the solar
neutrino flux, which is expected from the matter effect of neutrino oscillations, was observed in the precise solar neutrino
measurement.
The search for nucleon decay at SK gives the current best
limit which strongly constrains the grand unification scenario
of particle interactions. SK has been searching for neutrinos
from supernovae by two methods, one is a search for burst
neutrinos originate from nearby supernovae, another is socalled supernova relic neutrinos, which is an accumulated supernova burst neutrinos from the beginning of the universe.
A high intensity neutrino beam experiment using the JPARC accelerator (T2K) was started in 2009. The T2K experiment uses the SK detector as the far detector. Electron
neutrino appearance (the effect of the mixing angle θ13 ) andthe high precision measurement of oscillation parameters aremain physics subjects in T2K. An indication of electron neutrino appearance was found in June 2011, and the significanceof the appearance has been greatly improved in 2013.
Another activity of the Neutrino and Astroparticle division is a multi-purpose experiment using liquid xenon aiming
at the detection of cold dark matter, neutrino absolute massusing neutrinoless double beta decay, and low energy solar
neutrinos. The construction of a 800 kg liquid xenon detector
was completed at the end of 2010 and subsequent commissioning run continued by June 2012. With the commissioning
data, low-mass WIMPs, annual modulation of event rate, andaxions were studied. In 2013, detector refurbishment to reduce the surface background had been performed.
In addition to those on-going projects, some R&D projects
are also proceeded. GADZOOKS! is a project to add 0.1%
of gadolinium into the Super-K tank in order to tag neutronsfor ν¯e detection. It should enable us to detect supernova relicneutrinos. A feasibility study for GADZOOKS! has been per-formed using a 200 ton tank which mimics the Super-K detector. The Hyper-Kamiokande (Hyper-K) detector is proposed
as a next generation underground water Cherenkov detector.
The detector is approximately 20 times larger in volume thanSuper-K and has discovery potential of leptonic CP violationand proton decays. New photosensor R&D and physics potential studies for Hyper-K has been performed in 2013.

SUPER-KAMIOKANDE[Spokesperson : Masayuki Nakahata]
Kamioka Observatory, ICRR, The University of Tokyo
Search for nucleon decay
Proton decays and bound neutron decays (nucleon decays
in general) is the most dramatic prediction of Grand Unified
Theories (GUTs) in which three fundamental forces of elementary particles are unified into a single force. Super-Kamiokande (SK) is the world’s largest detector to search for nucleon decays. Various nucleon decay modes have been looked
for, but we have found no significant signal excess so far. In
2013, lifetime limits of major proton decay modes, p → e+ π 0
and p → ν̄K + , were updated with 260 kton·year exposure. In
addition to them, some of nucleon decay modes which violatebaryon and lepton number by two have been newly studied.
Figure 1 shows summary of nucleon lifetime limits of various
decay mode which we have investigated in SK data.
A proton decay into one positron and one neutral pion
(p → e+ π 0 ) is one of the most popular decay modes. This
decay mode is mediated by super-heavy gauge bosons anddiscovery of the signal would give us the information of themass of the gauge mesons. To discriminate the signal from theatmospheric neutrino background, we reconstruct the number of particles (Cherenkov rings) and reconstruct the total
visible energy corresponding to parent proton mass and total
momentum corresponding to the proton’s Fermi momentum.
If a proton decays in an oxygen with this mode, generated
π 0 is affected by various interactions (scattering, absorption,
charge exchange, multi pion production) with nucleus before
go out from the oxygen. In 2012, we have studied pion interaction cross sections which have been measured by otherexperiments and re-tune final state interaction of pion, which
is important also for atmospheric ν analysis (details in theprevious annual report). As a result, the selection efficiency
for p → e+ π 0 is estimated to be decreased from 45 % to 40% dominantly due to increasing cross section of pion charge
exchange and large angle scattering. Signal and BKG simulations for all period (SK1-SK4) have been regenerated, anddata set was also updated until February 2013 corresponding

3

Fig. 1. Nucleon lifetime limits with 90% CL for decay modes

which have been investigate by SK. Red histograms shows
updated mode and green show new decay mode whichhave been studied in 2013.

SK1
SK2
SK3
SK4

kton·yr
91.7
49.2
31.9
87.3

Efficiency
39.2±0.7%38.5±0.7%40.1±0.7%39.5±0.7%

BKG
0.27
0.15
0.07
0.22

Table 1. Results of p → e+ π 0 mode.

to 260 kton·year exposure, as summarized in Table 1. No
candidate has been observed so far and a lower lifetime limit(90% CL) of proton is estimated to be 1.4×1034 years.
Total expected background events in 260 kton·year exposure is 0.71 events. In order to keep good sensitivity evenin future, it is important to reduce background. A new algorithm to tag neutrons, which are captured in water and emit
2.2 MeV gamma ray, are under developing to distinguish neutrino and anti-neutrino interaction. The neutron tagging is also
expected to be useful to reduce atmospheric neutrino background in proton decay searches.
Some GUT models incorporating with Super-symmetry
theory, SUSY, favored decay modes which include K mesonsin the final state, p → ν̄K + . In this mode, we tag the signal by
decay products from K + . The momentum of K + is below theCherenkov threshold, and is stopped in the water and decay
into µ + ν or π + π 0 with monochromatic momenta. The residual nucleus after proton decay emits γ ray ( 40% probability)
and it is also useful to tag proton decay signal. There were several improvements in 2012 as described in the previous annual
report. Signal and background MC in all period have been reprocessed based on the new analysis, and the exposure of data
has been updated to 260 kton·years. There are no candidates

for methods tagging proton decay by using µ with prompt γ
and π + π 0 from K+ decay, and no excess can be observed inµ momentum distribution. The results are summarized in Table 2 and estimated lower limit of lifetime for this decay modeis 5.9×1033 years.
In case of above two decay modes, B-L are conserved
where B and L are baryon and lepton number, respectively.
Trilepton decay modes such as p → e+ νν and p → µ + νν,
which are based on SO(10) GUT model, can violate B-L by
two, | ∆(B − L) |=2. Final states of these two modes should besingle ring e- or µ- like event which has momentum in characteristic band due to three body decay. Thus momentum distributions of single ring fully contained (FC1R) events have been
examined to check distortions which come from proton decay
into three leptons. Figures 2 show momentum distribution of
FC1R e-like and µ-like events of data with 273 kton·year exposure, atmospheric ν MC, and proton decay MC. There wereno clear bumps made by proton decays. The data was fitted byatmospheric ν MC and proton decay MC, and lower limit ofproton lifetimes are estimated to be 1.7×1032 and 2.0×1032
years for p → e+ νν and p → e+ νν, respectively.
If two nucleons decay into meson simultaneously, B-L is
not conserved also. In past, pp → e+ e+ , µ + µ + , K + K + havebeen studied and it is natural extensions to study two nucleons
decay into pions. As a first step, pp → π + π + has been juststarted to investigate. The difficult point than other modes
studied in the past is that charged pions with high momentum can loose their energy by hadronic interactions which
may not be observed by Chrenkov light, which is usually used
for estimation of momentum, consequently distributions of total momentum and invariant mass become broader than othermodes. ”Boosted Decision Tree” analysis has been introduced
for this analysis to overcome the difficulty. Once the analysis
method is established, it will be extended to pn → π + π 0 and
nn → π 0 π 0 .
Atmospheric neutrinos
Cosmic ray interactions in the atmosphere produce neutrinos via the decay products of secondary hadrons, such aspions and kaons, emerging from these interactions. The atmospheric neutrino flavor ratio, (νµ + ν̄µ )/(νe + ν̄e ), is expected to be approximately two based on the structure of thepion decay chain. Though the uncertainty on this ratio is estimated to be only 5 % or less, the absolute scale of the flux for
all neutrino species is much less understood and its prediction
carries an uncertainty of at least 20 %. It should be noted that
despite this uncertainty, above a few GeV where the effects ofthe geomagnetic field are negligible, the fluxes of upward- anddownward-going neutrinos are nearly equal and therefore provide a useful constraint in the study of these neutrinos. SuperKamiokande has been observing atmospheric neutrinos since1996 and has accordingly made several important measurements, including the discovery of neutrino oscillations [1, 2].
Three flavor oscillations and the neutrino mass hierarchy
The SK atmospheric neutrino data are described at leading order by two-flavor νµ → ντ oscillations with maximal
mixing (θ23 =π/4). However, sub-leading contributions via νµ4Exp.(kton·yrs)
Prompt γ

Pµ spec.
π +π 0SK-I
91.7
7.9±0.10.08
033.9±0.3193
177
7.8±0.1
0.18
0Eff.(%)BKG
OBS
Eff.(%)BKG
OBS
Eff.(%)
BKG
OBS

SK-II
49.2
6.3±0.10.14
030.6±0.3
94.3
78
6.7±0.1
0.17
0SK-III31.9
7.7±0.10.03
032.6±0.3
69.0
85
7.9±0.1
0.09
0

SK-IV
87.3
9.1±0.10.13
037.6±0.3223.1
22610.0±0.1
0.18
0Table 2. Summary of the proton decay search p → ν̄K + with selection efficiencies and expected backgrounds for each detector

period.

900
1200

DATA
Signal 90CL
ATM + Signal (best fit)

700
600

800

EventsEvents1000

SK I-IV µ-like800

SK I-IV e-like
DATA
Signal 90CL
ATM + Signal (best fit)

600

500
400
300

400

200
100

0

0

100
50
0
-50
-100
100

100
50
0
-50
-100
200

EventsEvents

200

200

300

400

500

600

700

800

900

1000

300

Momentum (MeV/c)

400

500

600

700

800

900

1000

Momentum (MeV/c)

Fig. 2. Reconstructed momentum distribution for 273.4 kton · years of combined SK data (black dots), the best fit result for the atmospheric
neutrino background (solid line) and the 90% confidence level allowed amount of nucleon decay signal (hatched histogram) for p → e+ νν(left) and p → µ + νν (right).

SK-I+II+III+IV, 4581 Days

Number of Events

1000

1500 Prediction

300

1000

200

500

0
-1

SK Data

Sub-GeV e-like8994 Events
0

1

600

500 νµ → ντ
Sub-GeV µ-like9359 Events
0
-1
0

100

1

0
-1

UpStop µ1286 Events
-0.5

0

1000
1000

400
500
500
200

0
-1

Multi-GeV e-like2463 Events
0

1

0
-1

Multi-GeV µ-like + PC
5068 Events
0

1

0
-1

UpThrough µ5475 Events-0.5

0cos zenith

Fig. 3. Zenith angle distributions of SK atmospheric neutrino data. The horizontal axis indicates the cosine of the reconstructed zenith angle(cos θ =-1 corresponds to the upward-going direction). The data are shown by the black points with error bars and the MC predictions
without oscillations and with two flavor νµ → ντ oscillations are shown by the blue and red lines, respectively.

5→ νe oscillations induced by the mixing angle θ13 as wellas the “solar” mixing parameters (∆m212 , θ12 ) provide the ability to probe currently unknown aspects of the standard neutrino oscillation paradigm, such as the existence of leptonic
CP violation and the neutrino mass ordering (hierarchy). Understanding these open questions may bring important insight
into larger questions, such as the origin and evolution of today’s matter-dominated universe.
Several sub-leading oscillation effects are expected to appear in atmospheric neutrinos:days of FC/PC and 1646+828+636+1775 days of upwardgoing muon data have been analyzed. Zenith angle distributions for six data subsamples are shown in Fig. 3. An oscillation analysis considering all mixing parameters from the
PMNS framework, including the CP violating term, δcp , andthe effects of the earth’s matter on neutrino propagation, hasbeen performed assuming that θ13 is constrained to the measured value from reactor neutrino experiments, sin2 θ13 =0.025.
It should be noted, however, that the uncertainty on this measurement is included as a systematic uncertainty in this analysis. Fig. 4 shows the allowed region of the atmospheric• Resonant enhancement of νµ → νe oscillations due to mass squared difference (∆m2 ) and θ parameters obtained
2332
the effects of matter occur at energies between 2 and from the analysis. Though accelerator experiments such as
10 GeV and will manifest as an excess of upward-going T2K and MINOS give more stringent constraints, the atmoelectron-like events in the atmospheric sample.
spheric neutrino measurements are consistent with these re2• This enhancement exists for either νe or ν̄e depending sults. Comparing the minimum absolute χ values between
on the mass hierarchy. Therefore the mass hierarchy fits to the normal and inverted hierarchy hypotheses indicate
have a weak preference for the normal
can be probed by understanding the relative amount of that the Super-K data
2 = χ 2 − χ 2 = -0.9. In order to immass
hierarchy,∆χNH
IH
neutrino and antineutrino interactions in the detector.
prove sensitivity to the mass hierarchy the analysis has been
• The combination of the solar oscillation parameters and extended to include external constraints from the T2K exthe octant of sin2 θ23 , may enhance or suppress the event periment. T2K is modeled using atmospheric neutrino MC
rate, and to some extent alter the spectral shape, of Sub- reweighted to the beam spectrum and incorporates publicly
GeV electron-like data the due to νµ ↔ νe oscillations available data and systematic error information for the analythey induce.
sis [4, 4]. The modeled T2K data samples are then fit in conjunction with the atmospheric neutrino data including relevant• The CP violating term, δcp , induces several sub-dominantsystematic error correlations. In this fit the normal hierarchy
oscillation effects which are predicted to appear acrosspreference is strengthened to ∆χ 2 = −1.2. The best fit oscillamany of the SK atmospheric neutrino samples.
tion parameters and minimum χ 2 values from these analyses
Super-Kamiokande has studied the effects of these oscil- are shown in Table 3. It should be noted that the data show a◦lations on atmospheric neutrino data separated into fully-cont- slight preference for δcp = 220 but include sinδcp = 0 at theained (FC) events, partially-contained (PC) events, and upward- 90% C.L. in all fits.
going muon topologies. Fully-contained events are characterized by a primary interaction vertex that is located inside the Neutron tagging
22.5 kton fiducial volume of the detector and whose visible
With SK-IV’s upgraded electronics it is now possible toparticles stop within the inner detector. On the other hand, record all PMT hit information in the 500µs after an event
though the primary vertex position of PC events is within the is triggered within the detector. This feature is particularly
fiducial volume, they are characterized by having at least one important for the study of neutrons, which are ordinarily uncharged particle escaping the inner detector and depositing seen within Super-K. Indeed, neutron capture on hydrogenlight in the outer detector. In most cases the escaping particle produces a 2.2 MeV γ ray, via p(n, γ)d, which is just above
is a muon. Upward-going muons originate from high energy threshold and therefore difficult to detect in isolation amidst
muon-neutrino interactions in the rock surrounding the detec- the various radioactive backgrounds occurring in the detector. Since all other particles are lost to interactions in the rock, tor. However, using the 500µs data following a primary trigonly the muon is penetrating enough to reach the detector and ger it is possible to correlate and tag signals consistent with
be identified. The FC sample is separated into electron-like neutron capture on water with neutrino interactions. Amongand muon-like subsamples by applying a particle identifica- water Cherenkov detectors this ability is unique to SK and hastion algorithm to the most energetic Cherenkov ring of each the potential to improve separation of charged current neutrino
event. Since PC and upward-going events are predominantly interactions, which dominantly produce a secondary proton,
produced by muon neutrinos, no particle identification is ap- from antineutrino interactions, which dominantly produce aplied. Though SK cannot distinguish on an event-by-event secondary neutron. At increasing energies additional hadronicbasis neutrino and antineutrino interactions, since the effect of interactions may produce further neutrons and therefore charthe mass hierarchy lies in the difference of their oscillations, acterization of this production is an important input for MC
statistical separation of multi-GeV electron-like subsamples generators.
is performed. A likelihood method designed to enhance the
The Super-K neutron tagging algorithm is two stage prokinematic differences between neutrino and antineutrino in- cedure applied to fully contained neutrino interactions using
teractions is applied to separate the events into νe -like and a few simple precuts followed by a neural network-based seν̄e -like subsamples.
lection to define the final neutron candidates. During the preThe atmospheric neutrino data accumulated during SK-I,- selection, a search is made for time-clustered PMT hits after
II,-III,and -IV and corresponding to 1489+799+518+1775

6

Fig. 4. Allowed regions in the atmospheric mixing plane, ∆m223,31 and sin2 θ23 , at the 90% C.L. as measured by Super-Kamiokande atmospheric
neutrinos (red), MINOS (purple) [3], and T2K [4] (cyan). Fits to the normal and inverted hierarchy hypotheses are shown in the left and rightfigures, respectively.

SK only (NH)SK only (IH)
SK+T2K (NH)
SK+T2K (IH)

sin2 θ13
0.025
0.025
0.025
0.025

δCP
3.84
3.84
4.19
4.19

sin2 θ23
0.57
0.57
0.55
0.55

∆m232 (× 10−3 )
2.6
2.5
2.5
2.5

χ2
559.8
560.7
578.2
579.4

Table 3. Best fit oscillation parameters obtained by the three flavor oscillation analysis. Fits are conducted for both the normal (NH) and inverted(IH) hierarchy assumptions for the atmospheric neutrino data (“SK only”) and including constraints from the T2K experiment(“SK+T2K”). Allfits are performed assuming sin2 θ13 =0.025.

a time-of-flight correction relative to the neutrino interaction
vertex has been applied. All clusters with more than seven
PMT hits within a 10 ns time window and less than 50 (200)hits within a 10(200) ns window which occurring during the
18-535µs after the initial neutrino interaction are selected as
candidates for the neural network. The neural network is composed of 16 variables designed to exploit the following expectations from the signal. Hits from a neutron capture gamma
should be produced from a single electromagnetic shower andshould therefore have an opening angle near 42◦ , the critical angle in water, should exhibit low isotropy, and have atight timing profile. Further, since the majority of neutrons
thermalize and capture within 200 cm of the neutrino interaction, hits from a neutron capture have a higher likelihood of
occurring on PMTs closer to the initial interaction and their
total energy should be consistent with 2.2 MeV. Optimizing
the neural network for these criterion, Super-K has achieved
20.5% selection efficiency with an estimated background of
0.018 events per neutrino event. Without applying the neural network these numbers are 33.2% and 4.45% respectively,
clearly demonstrating the power of this selection. Applying
this algorithm to the atmospheric neutrino data sample a clear
neutron capture signal with an exponential time constant of
205.3µs is observed and shown in Fig. 5. This measurementcompares well with the expectation of 204.8 µs [13]. The
right panel of the figure shows a comparison between data andMC of the average tagged neutron multiplicity as a functionof the initial neutrino’s total visible energy. Impressive agreement across most of the energy range has been obtained andestablishes the robustness of the method. Future analyses will
use this tagging to reduce atmospheric neutrino backgrounds
in the SK search for proton decay and to improve the separation between the νe - and ν̄e -like oscillation analysis samples.
Search for sterile neutrino
Though the standard three flavor oscillation scheme has
been established by a wide range of experiments, there remain “anomalies” which are not consistent in this picture;
For example, the LSND experiment observed ν̄e appearance
over a short baselines, which when interpreted as an oscillation signal suggests a mass difference inconsistent with the results of solar and atmospheric neutrino measurements, ∆m2s ∼1eV2 [6]. The MiniBooNE experiment, which was designed
to study this anomaly, reported a similar excess of ν̄e events [7].
Due to the strong constraint on the number of neutrinos from
LEP measurements, the additional neutrino suggested by thisnew mass difference must not participate in weak interactions.
These non-interacting neutrinos are therefore called “sterile.”
If there is indeed a heavy fourth neutrino state, the effects ofthe extra oscillation channel atop the dominant νµ → ντ oscillations are expected to be visible in the atmospheric neutrino
flux.
The atmospheric neutrino data has been fit searching for205.2 ± 3.7

τ

800
700
600
500
400

Average Neutron Multiplicity per event

7

SK-IV Data
MC
10

1

300
200
100
0
0

100

200

300

400

500
dt (µs)

10-1
1.5

2

2.5
3
3.5
4
4.5
5
Neutrino Interaction Visible Energy Log(Evis MeV)

Fig. 5. Time difference between the primary neutrino interaction and tagged neutron capture gamma ray candidates (left) and the averagetagged neutron multiplicity as a function of the total visible energy of the neutrino interaction (right). In the latter, the red line indicates the
expectation from the Super-K MC.

∆m241

10

1

10-1

99% C.L.

10-2

10-1
2

|U |
µ4

Fig. 6. (Left) Super-Kamiokande’s limit on |Uµ4 |2 at the 90% confidence level. (Right) Upper limits on |Uµ4 |2 vs |Uτ4 |2 at 90% and 95% C.L.
are shown by the solid and dashed lines, respectively. The light gray region is excluded at 90 % and the dark gray region is disallowed byunitarity.

evidence of these oscillations. However, at large masses atmospheric neutrino oscillations become insensitive to the exact value of the mass splitting and are primarily sensitive tothe additional mixing matrix elements between the active andsterile states, Uµ4 and Uτ4 . More importantly, the data areinsensitive to the precise number of additional sterile neutrinos, a feature unique to atmospheric neutrino studies, so theanalysis is performed using a model with only one additional
neutrino (the “3+1” model) [9]. The results of two fits, one
for Uµ4 with standard matter effects only and one for Uµ4 andUτ4 including sterile matter effects only, are shown in Fig. 6.

Tight constraints on both parameters have been obtained, with
|Uµ4 |2 < 0.21 and |Uτ4 |2 < 0.22 at 90% C.L., and a large portion of the allowed region from [9] has been ruled out.
Limits on Lorentz invariance violation
Symmetry of physical systems under Lorentz transformations is a fundamental feature of both the Standard Model ofparticle physics and the General Theory of Relativity. Accordingly, violation of this symmetry, termed Lorentz invariance violation (LIV), would provide striking evidence for new
physics and has been the focus of many experiments. Neu-

8

Fig. 7. Contours showing the 95 % confidence level allowed regions for the Lorentz invariance violating parameters aTeτ (solid), aTeµ (solid), aTµτ
(dot-dashed) appear in the left figure and those for cTeτT (solid), cTeµT (dashed), cTµτT (dot-dashed) are shown in the right figure. Best fit points
from the six fits are also shown.

trino oscillations are sensitive to two types of LIV phenomena: sidereal effects, in which oscillations are seen to vary as
the earth rotates through its sidereal day, and spectral anomalies, which induce oscillation effects whose frequency is proportional to the neutrino pathlength or the product of the neutrino pathlength with its energy. At Super-K LIV is studied
within the context of the standard model extension (SME) [12]which introduces a LIV term,HLV , into the standard neutrino
Hamiltonian,
H = UMU † +Ve + HLV ,lack of a positive signal, the SK constraints on the existenceof LIV phenomena in neutrino oscillations improve on existing limits [10] for aT and cT T by four and seven orders ofmagnitude, respectively.

Indirect WIMP searches
Astronomical and cosmological observations point conclusively to the existence of dark matter and though invisible
to electromagnetic probes, it is thought to represent 26% of
the matter-energy content of the universe. Weakly Interact2
where U is the PMNS mixing matrix, M is the neutrino mass ing Massive Particles (WIMPs), GeV/c -scale particles which
matrix and Ve is the earth matter potential. Though HLV can have only gravitational and weak interactions, are a favoredhave many possible complex coefficients corresponding to high- candidate to explain the existence of this as yet unknown mater dimensional LIV operators, the present analysis focuses ter. Though direct dark matter detection experiments search
only on the isotropic dimension-three and dimension-four con- for the elastic scattering interactions of these proposed particles with ordinary baryonic matter, it is also possible that
tributions,
WIMPs decay or annihilate into Standard Model particles which




T
T
TT
TT
0
aeµ
aeτ
0
ceµ
ceτ
can then be detected to give indirect evidence for WIMPs.
T
∗
T
T
T
∗
T
T
0
aµτ
)
0
cµτ
HLV = ± (aeµT )∗− E (ceµ
.
∗
T ∗
T ∗
(aeτ )
(aT
0
(cT
(cT
0
If WIMPs become trapped in the gravitational potential of a
µτ )
eτ )
µτ )
massive system, such as the center of the Milky Way or the
The diagonal elements of HLV have been neglected since they sun, their density may become sufficient for large numbers
cannot be observed in neutrino oscillations. Though this ma- of these particles to annihilate into particles which then detrix represents the neutrino Hamiltonian, antineutrino propa- cay into neutrinos. In this case the neutrinos pass undeflectedgation is described by changing the sign of the first matrix and through the universe and would therefore create an additional
taking the complex conjugate of the aT and cT T parameters.
neutrino signal with a characteristic energy spectrum emergIt should be noted that this is the first analysis to approach ing from a common direction.
the problem of LIV in the SME without introducing approxiAt Super-K, though the search for these particles is dommations. Indeed, the usual perturbative conditions introduced inated by the atmospheric neutrino background, the expectato simplify analysis in this framework are invalid for the high tion that they are produced at a common location in the sky isenergy Super-K atmospheric neutrino data, so the complete a powerful discriminant. Accordingly, the atmospheric neuneutrino evolution equation has been solved when computing trino data are binned in both lepton momentum and the reoscillation probabilities. After performing oscillation fits in- constructed angle to either the galactic center or to the sun tocluding these effects, no evidence for LIV is seen. As a result, search for the presence of an extra neutrino signal from thoseSuper-K has set limits on the isotropic parameters aT and cT T directions. Since there is no knowledge of WIMP interactions,in the eµ, µτ, and eτ sectors as shown in Fig. 7. Despite the9Fig. 8. The 90% C.L. upper limits on the velocity averaged WIMP self-annhilation cross section from a search for WIMP annihilation from thedirection of the Galactic Center as a function of WIMP mass. Upper limits assuming branching ratios of 100% for WIMP annihilation into:χ χ → ν ν̄ (black), µ + µ − (green), W +W − (red), and bb̄ (blue) are shown. Limits from the IceCube experiment appear in magenta [11].

Fig. 9. The 90% C.L. upper limits on the spin-dependent (left) and spin-independent (right) WIMP-nucleon scattering cross section based ona search from WIMP-induced neutrinos coming from the direction of the sun are shown as a function of WIMP mass. These limits arecalculated assuming WIMP annihilation into τ + τ − (red solid), bb̄ (red dashed), W +W − (red dot-dashed), with 100% branching fraction.
Limits and allowed regions from other experiments are also shown.

the analysis proceeds by separately assuming annihilation into
each of ν ν̄, bb̄, t t¯, and W +W − with 100% branching fraction. For each assumed WIMP mass the expected neutrinoenergy distribution emerging from the decay chains of theseparticles is computed and used to define the signal spectrum

at Super-K. In contrast to previous studies, the entire atmospheric neutrino data set is used and therefore gives access
WIMP masses in the range of several GeV/c2 to TeV/c2 . No
evidence for a neutrino signal on top of the atmospheric neutrino background has been found in the direction of either the

10

Bibliography[1] Y. Fukuda et al., “Evidence for Oscillation of Atmospheric Neutrinos”, Phys. Rev. Lett. 81 1562 (1998).
[2] Y. Fukuda et al. [Super-Kamiokande Collaboration],
Phys. Rev. Lett. 81, 1562 (1998) [hep-ex/9807003].
[3] P. Adamson et al. [MINOS Collaboration], Phys. Rev.
Lett. 112, 191801 (2014) [arXiv:1403.0867 [hep-ex]].
[4] K. Abe et al. [T2K Collaboration], Phys. Rev. Lett. 112,
181801 (2014) [arXiv:1403.1532 [hep-ex]].
[5] K. Abe et al. [T2K Collaboration], Phys. Rev. Lett. 112,061802 (2014) [arXiv:1311.4750 [hep-ex]].
[6] A. Aguilar-Arevalo et al. (LSND Collaboration),
Phys.Rev. D64, 112007 (2001), arXiv:hep-ex/0104049[hep-ex].

0.35

Events/day/kton/bin

galactic center or the sun. The resulting limits on the velocity
averaged WIMP self-annihilation cross section for the galactic
center search appear in Fig. 8. Limits on the WIMP-nucleon
spin-dependent and spin-independent scattering cross sections
from the search for events from the sun are shown in Fig. 9.

0.3

SK-IV 1668.8 days 3.5 - 19.5 MeV(kin.)
Signal = 31945.1 + 282.9 - 281.0(stat.) events
8

6

B Flux = 2.303 ± 0.020(stat.) ± 0.039(syst.) [× 10 /cm2/s]
8

0.25(with Winter06 B spectrum)

0.2

0.15
0.1
0.05
0
-1 -0.8 -0.6 -0.4 -0.20

0.2 0.4 0.6 0.8 1
cosθSunFig. 10. Solar angle distribution for 3.5-19.5 MeV. θsun is the angle between the incoming neutrino direction and the reconstructed recoil
electron direction. Black points are data while the blue and red
histograms are best fits to the background and signal plus background, respectively.

energy solar neutrinos (pp, 7 Be, pep, CNO and lower energy 8 B neutrinos) arise only from vacuum oscillations, which
limits the average electron flavour survival probability to ex[7] A. Aguilar-Arevalo et al. (MiniBooNE Collaboration), ceed 50%. The transition from the matter dominated oscilPhys.Rev.Lett. 110, 161801 (2013).
lations within the sun, to the vacuum dominated oscillations,
8[8] P. Huber,
Phys.Rev. C84,024617 (2011), should occur near 3 MeV, making B neutrinos the best choice
when looking for a transition point within the energy specarXiv:1106.0687 [hep-ph].
trum. A second signature unique to oscillations arises from
[9] J. Kopp, P. A. N. Machado, M. Maltoni, and T. Schwetz, the effect of the terrestrial matter density on solar neutrino osJHEP 1305, 050 (2013).
cillations. This effect is tested directly by comparing solar
neutrinos which pass through the Earth at nighttime to those[10] V. A. Kostelecky, N. Russell and R. Tso, Phys. Lett. B
which do not during the daytime. Those neutrinos which pass
716, 470 (2012) [arXiv:1209.0750 [hep-th]].
through the Earth will in general have an enhanced electron[11] R. Abbasi et al. [IceCube Collaboration], neutrino content compared to those which do not, leading toan increase in the nighttime electron elastic scattering rate (orarXiv:1210.3557 [hep-ex].
any charged-current interaction rate), and hence a negative[12] V. A. Kostelecky, Phys. Rev. D 69, 105009 (2004) [hep- “day/night asymmetry”. SK detects 8 B solar neutrinos overth/0312310].
a wide energy range in real time, making it a prime detector[13] D. Cokinos and E. Melkonian, Phys. Rev. C 15, 1636 to search for both solar neutrino oscillation signatures.
The start of physics data taking of SK-IV occurred on Oc(1977).
tober 6th, 2008, with this report including data taken until January 31st, 2014. The total livetime is 1668.8 days. The entire
data period was taken using the same low energy threshold,Solar Neutrinos
with about 85% triggering efficiency at 3.5-4.0 MeV kinetic
Solar neutrino flux measurements from Super-Kamiokandeenergy, 99% at 4.0-4.5 MeV kinetic energy and 100% above(SK) [1] and the Sudbury Neutrino Observatory(SNO) [2] have
4.5 MeV kinetic energy. In the case of ν-e interactions of soprovided direct evidence for solar neutrino flavour conversion.
lar neutrinos in SK, the incident neutrino and recoil electron
However, there is still no clear evidence that this solar neudirections are highly correlated. Fig.10 shows the cos θsun distrino flavour conversion is indeed due to neutrino oscillations
tribution for events between 3.5-19.5 MeV. In order to obtainand not caused by any other mechanism. Currently there are
the number of solar neutrino interactions, an extended maxtwo testable signatures unique to neutrino oscillations. The
imum likelihood fit is used. This method is also used in thefirst is the observation and precision test of the MSW resoSK-I [1], II [4], and III [5] analyses. The red line of Fig.10
nance curve [3]. Based on oscillation parameters extracted
is the best fit to the data. The blue line shows the backgroundfrom solar neutrino and reactor anti-neutrino measurements,
component of that best fit.
there is an expected characteristic energy dependence of the
The combined systematic uncertainty of the total flux inflavour conversion. The higher energy solar neutrinos (higher
SK-IV is found to be 1.7% as the quadratic sum of all com8
energy B and hep neutrinos) undergo complete resonant conponents. This is the best value seen throughout all phases ofversion within the sun, while the flavour changes of the lower

0.7

Blue:Total uncertainty
Red:Energy-uncor. Sys.
: Energy-cor. Sys.

0.6
0.5
0.4

All SK phase are combined without regard toenergy resolution or systematics in this figure(total # of bins of SKI - IV is 83)

0.56

Solar+KamLAND
Solar
quadratic ﬁtexponential ﬁt

0.54
0.52

χ2
70.13
68.14
67.67
66.54

MSW is slightly disfavored by ~1.7
using the Solar+KamLAND best fit
parameters, and ~1.0 using the Solar
best fit parameters.

0.5
0.48
0.46
0.44

(statistic error only)
preliminary

0.42
0.4

4

e, 2014

6

8

10

12

14

16

Neutrino 2014

SK-IV Energy Spectrum
4

6

8
10
12
14
16
18
20
Recoil electrons kinetic energy[MeV]Fig. 11. SK-IV energy spectrum. The horizontal dashed line gives the
SK-IV average. Error bars shown are statistical plus energy-uncorrelated systematic uncertainties. Energy-correlated systematic
uncertainties are shown separately as shaded region.

E

18
in MeVkin

Fig. 12. All SK phase combined energy spectrum and fitted functions.

bitrary parameter. The extended maximum likelihood fit to
extract the solar neutrino signal is expanded to allow timevarying signals. The likelihood is then evaluated as a functionof the average signal rates, the background rates and the scaling parameter which is called the “day/night amplitude”. The
equivalent day/night asymmetry is calculated by multiplying
the fit scaling parameter with the expected day/night asymmetry. In this manner the day/night asymmetry is measured
more precisely statistically. Because the amplitude fit depends
on the assumed shape of the day/night variation, it necessarily depends on the oscillation parameters, although with very
little dependence expected on the mixing angles (in or near
the large mixing angle solutions and for θ13 values consistent
with reactor neutrino measurements [7]).

p

0.3
0.2

0.6

0.58

Day/Night Asymmetry (%)

DATA/MC(unoscillated)

SK, much improved over 2.2% in SK-III. The main contributions to the reduction come from improvements in the uncertainties arising from the energy-correlated uncertainties (energy scale and resolution), the vertex shift, trigger efficiency
and the angular resolution. SK-III data below 6.0 MeV recoil electron kinetic energy has only about half the livetimeas the data above, while SK-IV’s livetime is the same for allenergy bins. As a consequence, the energy scale and resolution uncertainties lead to a smaller systematic uncertaintyof the flux in SK-IV than in SK-III. The higher efficiency of
SK-IV between 5.0 and 6.0 MeV (kinetic) of SK-IV and the
addition of the 3.5 to 4.5 MeV data lessens the impact of energy scale and resolution uncertainty on the flux determination even further. The number of solar neutrino events (between 3.5 and 19.5 MeV) is 31, 945+283−281 (stat.) ± 543(syst.).
8
This number corresponds to a B solar neutrino flux of Φ8 B =(2.303 ± 0.020(stat.) ± 0.039(syst.)) × 106 /(cm2 sec), assuming a pure νe flavor content.
Fig.11 shows the resulting SK-IV energy spectrum. SKIV has Nbin = 23 energy bins; 20 bins of 0.5 MeV width between 3.5-13.5 MeV, two energy bins of 1 MeV between 13.5
and 15.5 MeV, and one bin between 15.5 and 19.5 MeV.

Data/MC (unoscillated)

11
SK I/II/III/IV LMA Spectrum

y

20

0

-20
expected

To test the expected “upturn” below ∼6 MeV from the-40 m221=4.84x10-5 eV2
MSW resonance effects, the best fit oscillation parameters ofsin212=0.311
solar experiments and solar + KamLAND (described later)
5
10
15
were fitted to all the SK-I to SK-IV spectra, and it is disfaRecoil Electron Kinetic Energy (MeV)
4vored by 1σ and 1.7σ respectively so far. Fitted results areshown in Fig.12.
Fig. 13. SK combined energy dependence of the fitted day/night
The SK-IV livetime during the day (night) is 799.7 days
asymmetry (measured day/night amplitude times the expected(869.1 days). The solar neutrino flux between 4.5 and 19.5
asymmetry (red)) for ∆m221 = 4.84 × 10−5 eV2 , sin2 θ12 = 0.311 andsin2 θ13 = 0.025. The error bars shown are statistical uncertainties
MeV and assuming no oscillations is measured as ΦD = (2.25±
6
2
only.
0.03(stat.) ± 0.38(sys.)) × 10 /(cm sec) during the day and62ΦN = (2.36±0.03(stat.)±0.40(sys.))×10 /(cm sec) during
The day/night asymmetry coming from the SK-I to IV
the night. A more sophisticated method to test the day/nightcombined
amplitude fit can be seen as a function of recoil
effect is given in [1, 6]. For a given set of oscillation paramelectron
kinetic
energy in Fig.13, for ∆m221 = 4.84 × 105 eV2 ,eters, the interaction rate as a function of the solar zenith an2
2
gle is predicted. Only the shape of the calculated solar zenith sin θ12 = 0.311 and sin θ13 = 0.025. The day/night asymmeangle variation is used, the amplitude of it is scaled by an ar- try in this figure is found by multiplying the fitted day/night

12

amplitude from each energy bin, to the expected day/night
asymmetry (red distribution) from the corresponding bin.
SK-I/II/III/IV Combine Day/Night Asymmetry
Day/Night Asymmetry (%)

1

sin212=0.311, sin213=0.025

preliminary
1 Solar1 KamLAND

0

3.0

2.9

2.8
expected-1-2

SK-I,II,III,IV best fit
-3

-4

-5

2

4

6

8

10

12

14

16

18

m

2 20
21

22
-5
2
(10 eV )Fig. 14. Dependence of the measured day/night asymmetry (fitted day/night amplitude times the expected day/night asymmetry (red)) on ∆m221 (light gray band=stat. error, dark grayband=stat.+syst. error) for sin2 θ12 = 0.311 and sin2 θ13 = 0.025.
Overlaid are the allowed ranges from solar neutrino data (greenband) and KamLAND (blue band).

Fig. 15. Allowed contours of ∆m221 vs. sin2 θ12 from solar neutrino data
(green) at 1, 2, 3, 4 and 5 σ and Kam-LAND data (blue) at the
1, 2 and 3 σ confidence levels. Also shown are the combined
Fig.14 shows the ∆m221 dependence of the SK all phases
results in red. For comparison, the almost identical results of the
combined day/night asymmetry for sin2 θ12 = 0.311 and sin2 θ13
SK+SNO combined fit are shown by the dashed dotted lines. θ13= 0.025. Here the day/night asymmetry is also found by mulis constrained by sin2 θ13 = 0.0242 ± 0.0026.

tiplying the fitted day/night amplitude by the expected day/night
asymmetry (red curve). The point where the best fit crosses
the expected curve represents the value of ∆m221 where the slightly disfavor the MSW resonance curves, but are consismeasured day/night asymmetry is equal to the expectation. tent with MSW prediction within 1 ∼ 1.7σ . SK data proSuperimposed are the allowed ranges in ∆m221 from the global vide the first indication (at 2.8 ∼ 3.0σ ) of terrestrial mattersolar neutrino data fit (green) and from KamLAND (blue). effects on 8 B solar neutrino oscillation. This is the first obThe amplitude fit shows no dependence on the values of θ12 servation using a single detector and identical neutrino beams
that matter affects neutrino oscillations [8]. These SK mea(within the LMA region of the MSW plane) or θ13 .
We analyzed the SK-IV elastic scattering rate, the recoil surements strongly constrain neutrino oscillation parameters:
electron spectral shape and the day/night variation to constrain SK uniquely selects the Large Mixing Angle MSW region by
the solar neutrino oscillation parameters. We then combined > 3σ , gives world’s best constraint on ∆m221 using neutrinos,
the SK-IV constraints with those of previous SK phases, as and significantly contributes to the measurement of θ12 .
well as other solar neutrino experiments. The allowed contours of all solar neutrino data (as well as KamLAND’s con- Bibliography
straints) are shown in Fig.15 and 16. In Fig.15 the contours[1] J.Hosaka et al., Phys. Rev. D73, 112001 (2006).
from the fit to all solar neutrino data are almost identical to theones of the SK+SNO combined fit. In the right panel some[2] Q.R.Ahmad et al., Phys. Rev. Lett. 87 071301 (2001).
tension between the solar neutrino and reactor anti-neutrino[3] S.P.Mikheyev and A.Y.Smirnov, Sov. Jour. Nucl. Phys.
measurements of the solar ∆m221 is evident. This tension is42, 913 (1985); L.Wolfenstein, Phys. Rev. D17, 2369
mostly due to the SK day/night measurement. Even though(1978).
the expected amplitude agrees well within 1σ with the fitted
2
amplitude for any ∆m21 in either the KamLAND or the SK[4] J.P.Cravens et al., Phys. Rev. D 78, 032002(2008).
range, the SK data somewhat favor the shape of the variation predicted by values of ∆m221 that are smaller than Kam[5] K.Abe et al., Phys. Rev. D 83 052010 (2011).
LAND’s. The best fit values are sin2 θ12 = 0.308 ± 0.013,+0.19[6] M.B.Smy et al., Phys. Rev. D. 69, 011104(R) (2004).
∆m221 = 7.50−0.18
× 10−5 eV2 , and sin2 θ13 = 0.027+0.016−0.014 . The
significance of non-zero θ13 is about 2σ .
[7] F.P.An et al., arXiv:1210.6327 (2012); J.K.Ahn et
In summary, the analysis threshold was successfully lowal., Phys.Rev.Lett. 108 191802 (2012); Y.Abe etered to 3.5 MeV kinetic recoil electron energy in SK-IV andal.,Phys.Rev. D86 052008 (2012).
by adding SK-IV data, ∼70,000 solar neutrino interactions
has been observed in ∼4,500 days, by far the largest sample[8] A.Renshaw et al., Phys. Rev. Lett. 112, 091805 (2014).
of solar neutrino events in the world. SK spectrum results

Number of events

13

30

relic
all background
νµ CC

25

20

νe CC
NC elastic
µ/π

SK-I

15

10

5

0

25
50
75
20-38 degrees (MeV)

25
50
75
38-50 degrees (MeV)

25
50
75
78-90 degrees (MeV)

Fig. 17. SK-I best fit result, assuming Ando et al’s LMA model. The
relic best fit is negative, so a relic fit of 0 is shown. SK-II and SK-III
have small but positive relic best fits.
Fig. 16. Allowed contours of sin2 θ13 vs. sin2 θ12 from solar neutrino
data (green) at 1, 2, 3, 4 and 5 σ and KamLAND measurements(blue) at the 1, 2 and 3 σ confidence levels. Also shown are the
combined results in red.

committee members meet via TV conference system, and discuss to make a decision for a prompt announcement to outside researchers and the press. We practice this drill as if
a real supernova happened. We also have SK shift training
by illuminating an LED in the SK detector a few times evSupernova neutrinos
ery month. SK shift members are notified by a dummy alarm
In 1987, the observation of supernova 1987a by Kamiokande that SNWATCH makes when the LED is illuminated. The
and IMB etc. opend the neutrino astronomy. This observa- shift members then call to the SNWATCH experts and give ation confirmed that the energy released by neutrinos is about report. The SK collaborators will be ready for the real superseveral×1053 ergs. However, the core collaple supernova mech- novae through the drill and the training.
anism is not fully understood yet. Super-Kamiokande would
Not only the supernova burst, signals from Supernova Relicbe able to detect several thousand neutrino events if a super- Neutrinos (SRNs) are also searched at SK. The SRN signal isnova happened near the centre of our galaxy. Such an obser- the diffuse supernova neutrino background from all the supervation would enable us to investigate in detail the mechanics novae in the past. This signal has never been detected, but itof the supernova explosion.
is expected to be detectable in the 16-30 MeV energy region,
A online program called SNWATCH searches for time which is the gap between the energy ranges of solar neutrinos
clustered events. The current criteria of SNWATCH are (1) and atmospheric neutrinos. Our published result utilizes SKmore than or equal to 7 events within 0.5 sec, (2) more than I, II and SK-III data with analysis energy threshold 16MeV.
or equal to 8 events within 2 sec, and (3) more than or equal A maximum likelihood search was performed in multiple reto 13 events within 10 sec. When at least one of these criteria gions of the Cherenkov angle distribution to extract the mostare met, SNWATCH reconstructs vertex position and energy accurate flux limit(Fig.17). The obtained flux limit is betweenof the events together with neighbouring cosmic ray muons. 2.7 and 3.0 ν̄cm−2 s−1 (positron energy > 16 MeV), which acIn most cases, these clusters are due to spallation products tually depends on the shape of the neutrino spectrum assumed.
whose vertex positions are aligned with their parent cosmic This result currently provides the world’s best limit on SRN
ray muon. Since all the SNWATCH processes are now run- flux. Furthermore, a new method of presenting the SRN flux
ning on online machines, if a supernova happens, we will be limit is also ready which is of great use to theorists and does
able to detect it within about one minute.
no depend on any particular model (Fig.18).
If SNWATCH finds an event cluster whose vertex spread islarger than a given criterion, an alarm signal is sent to experts
by e-mail and an automatic call to their cellphones. Then, R&D for the gadolinium project
the experts check whether it is a real supernova signal or not
As mentioned above, although at SK a few SRN events aby looking at various plots which are uploaded to a secured year are expected, SRNs have not been detected yet becausesite accessible from the Internet. These alarms are usually the large backgrounds constrain our search. The main goal
due to the accidental coincidence of two cosmic ray induced of our research is to reduce these backgrounds and be able toclusters. We have a supernova drill at least once per year. So detect SRNs. The observation of SRNs in general or neutrifar, no real supernova neutrino burst signal has been observed nos from distant supernovae in particular, would give us someat Super-Kamiokande.
information about the universe, for example the core collapse
In the drill, the SNWATCH conveners and the executive

53

SN νe Energy in 10 erg

14

3

SK 1497+794+562 Days
Excluded (E>16MeV)
νe→e+ (90%C.L.)

2

1

0
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0
Tν in MeV
Fig. 18. Results plotted as an exclusion contour in SN neutrino luminosity vs. neutrino temperature parameter space. The green
and blue contours show IMB and Kamiokande allowed areas for
1987a data, respectively. The red shows our new 90% c.l. result.
The dashed line shows the individual 90% c.l. results of each temperature considered separately, which is not a true 2-D exclusion
contour.

Fig. 19. In the new cavern the Gd pre-mixing and pre-treatment 15
ton tank (front left), the selective filtration system (front right) andthe 200 ton tank (rear of the hall) have been installed.

rate from SRNs, and about the neutrino itself too, for example
its lifetime. Since most of the neutrinos that can be detected
at SK undergo inverse beta decay, electron anti-neutrinos are
the most copiously detected neutrinos:ν̄e + p → e+ + n(1)

Presently, the SK detector can only detect the positrons efficiently but if we could detect the neutrons, we could greatly
reduce the backgrounds that constrain our SRN search. This
could be attained by the coincidence detection of positron andneutron (in space, vertices within tens of cm and in time,with the neutron capture delayed about 20 µsec). By adding
0.2% of gadolinium (Gd) sulfate into the water tank we could
achieve this goal. Gadolinium has a neutron capture cross section of 49.000 barns (about 5 orders of magnitude larger thanof protons) and emits a gamma cascade of 8 MeV that can beeasily detected at SK.
We want to show that adding Gd into the SK water, SK
will become an electron anti-neutrino detector, able to tag inverse beta decays, while keeping all its previous capabilities
in the other analyses like solar and atmospheric neutrinos.
The EGADS (Evaluation Gadolinium’s Action on Detector Systems) project was funded in 2009. Since then, a newhall near the SK detector has been excavated and a 200 tontank with its ancillary equipment has been installed, see Fig.19,
to mimic the conditions at SK. Of special importance is the selective water filtration system, that filters out water impurities
while it keeps the Gd in the water.
From January 2010 to July 2011 we circulated pure water through the 200 ton tank and proved that our water systemis stable and achieves a high water quality. In 2013, fromFebruary 6th to April 20th, the 200 ton tank has been stepwise loaded with Gd until the final 0.2% concentration wasreached. By measuring Gd concentration at some detector positions, we confirmed that the Gd sulfate dissolves homogeneously in the 200 ton tank, and we can achieve and maintaina good water quality.
In summer 2013, we installed 240 photomultipliers andthe data taking has started from September without Gd. Afterthe water quality became good and stable, detector caibrations
were performed. At the end of March, few batches of Gd weredissolved into water corresponding 115 ppm Gd concentration. Soon after that, the first signal from Gd neutron capture
was detected with a Am/Be (gamma and neutron source) installed at the detector center. Figure 20 (left) shows the timedifference between the prompt gamma event and the delayed
neutron capture event. The time constant is obtained as 123µsec which is in good agreement with our expectation (120.8µsec). Am/Be data were also taken with 230 ppm Gd concentration, and it was confirmed that the time difference became
shorter due to a higher neutron capture rate by Gd (Figure 20).
Next year, we will make a final configuration with 0.2% Gd
concentration and provide detailed information, such as thewater transparency and its uniformity, PMT signal stability,
Rayleigh scattering measurement using EGADS detector, andthe neutron capture rate. Aftre all these evaluations finished,
EGADS will become a detector with instant supernova detection capabilities.

XMASS EXPERIMENT[Spokesperson : Yoichiro Suzuki]
Kavli IPMU, University of TokyoXMASS experiment
XMASS is a multi-purpose experiment (detection of dark
matter, neutrino-less double beta decay, and 7 Be/pp solar neutrinos) using ultra-pure liquid xenon [1]. The first stage of
XMASS experiment (XMASS-I) is to look for dark matter
using 800 kg liquid xenon (100 kg fiducial mass).

χ2 / ndf
const
τ

800
700

113.6 / 44931.3 ± 15.4
215.4 ± 3.4

600
500
400

Number of events / 10 µs

Number of events / 10 µs

15χ2 / ndf
const
τ

5000

4000

195.4 / 39
6229 ± 53.5
130.9 ± 0.9

3000

2000

300
200

1000

100
0

50

100 150 200 250 300 350 400 450 500∆ T ( µs)

050

100 150 200 250 300 350 400 450 500∆ T ( µs)

Fig. 20. Time difference between a prompt event and a delayed event obtained in Am/Be calibration in 115 ppm (left) and 230 ppm (right) Gd
concentration. Back shows data and blue line shows fitted line.

• Physics analysis using commissioning data. We have
The existence of dark matter is recognized through gravachieved the lowest energy threshold, and the largest
itational effects in astronomical observations. It is indicatedtarget mass. The level of background without rejecthat the universe contains a large amount of nonbaryonic darktion of e/gamma events are modest. Therefore the data
matter. One of the most plausible candidates for the nonbaryonic dark matter is a weakly interacting massive particle
from the world largest detector, XMASS-I, is valuable
to search for low-mass WIMPs, solar axions, inelastic(WIMP) conceived by the supersymmetry in the form of ascattering by WIMPs, and bosonic super-WIMPs. We
lightest supersymmetric particle. WIMPs can be directly dehave conducted these searches.
tected through their elastic scattering off target nuclei in a detector. The XMASS-I searches for the WIMP-xenon nucleus• Refurbishment. Based on the investigation with cominteraction in liquid xenon.
missioning data, we devised a plan to reduce background.
Two phase liquid xenon detectors achieve low backgroundCovering the contaminated parts by copper covers andby removing electron and gamma ray events, but XMASS
plates, we could reduce background more than one oraims at realizing low background even with electron and gamma
der of magnitude. This strengthen our understanding of
ray events. This introduces a unique advantage in a search forbackground and reinforces the future design of XMASS
dark matter particles through electromagnetic interactions as
detectors.
well. This is particularly important since no indications ofsupersymmetric particles have obtained so far even from the We succeeded the background reduction of the XMASS-I delarge hadron collider. Dark matter particles other than WIMPs tector. However, in order to get into the new regime, we need
are also quite interesting. In parallel to the search for WIMP- more sensitive detectors. We are designing XMASS-1.5 dexenon nucleus interactions, ability to detect e/gamma events tector as described in following section.
enables us to search for broad range of dark matter particles.
For example, axion-like particles, bosonic super-WIMPs, in- XMASS-I detector
elastic scattering by WIMPs can be searched for with our
The construction of the XMASS-I detector was started
unique detector.
in April 2007 and was completed in September 2010. The
As the first stage of the XMASS experiment, the XMASS- XMASS-I detector uses a cylindrical water tank with 72 50 cm
I detector was constructed. In the following sections, we de- PMTs and spherical liquid xenon detector with 642 2 inch
scribe:PMTs is placed at the center of the water tank as shown in Fig.
21. This is the first case to adopt a pure-water tank as an active• Construction and commissioning data taking. After theand passive shield for dark matter experiments. The sphericalconstruction of the detector, we took data to understandarray of PMTs is arranged in a double wall vessel. The vesthe performance of the XMASS-I detector. By introsel consisting of inner and outer vacuum chamber (IVC andducing radioactive sources, number of photoelectrons
OVC) is made from oxygen free high conductivity copper.
per keV was measured. Vertex reconstruction algorithm
The layer between IVC and OVC is kept vacuum for thermal
was confirmed to work properly. Origins of backgroundisolation.
were also investigated and found one of the parts used
After the construction, commissioning data was taken fromin photomultipliers contained natural radioactivity more
October 2010 to May 2012. Based on calibration data, wethan expected.
found that the detector has the largest photoelectron yield (≈14

16

OFHC copper vessel
Refrigerator
10.5m
642
PMTs
835kg
xenon
10m

~1.2m

72 50cm PMTs (veto)

Asymptotic cross section (σasI ) [pb]

Fig. 21. Schematic view of the water tank and the liquid xenon vessel.

SD WIMP - neutron cross section [cm2]Electronics
hut

Water tank

10-34
10-35
CDM

S

ASS
XM

10-37

ZEP

I

10-36

10-38

-III

LIN

100

ON

XEN

XENON10

10-39
10-40

102

103
WIMP mass [GeV]102
Fig. 23. The thick line and dots represent our limit on the spin-dependent cross section of WIMPs on neutron using two different recent
calculations of form factors. The gray shaded part of the thick line
shows systematic uncertainty. The dashed, dotted, dash-dotted,
and long dash-dotted lines represent experimental constraints on
spin dependent WIMP nucleon cross sections extracted from elastic scattering data. Our own limit is the first derived exclusively
from data on inelastic scattering.

10

102

103
WIMP mass [GeV]

Fig. 22. The black solid line is our 90% C.L. upper limit on the asymptotic cross section σIas for inelastic scattering on 129 Xe (black solidline) using the same form factors as DAMA. The gray band covers its variation with our systematic uncertainty. The dotted line isthe limit obtained by the DAMA group that was derived after statistically subtracting background. Our low background allows us
to derive this limit without such background subtraction. Observed
energy spectrum and predictions for various mass of dark matter.

log(α’/α)

1

-18
-19
-20
-21
HB stars-22-23

photoelectrons/keV). This enables us to realize low-energy
threshold which is important for dark matter search. We also
conducted various performance tests on XMASS-I, such as reconstruction by scintillation patterns. The details of these aredescribed in Ref. [2].

Ge (solar)Ωh2=0.1

-24
-25
-26

Diffused γ

XMASS

Results using commissioning data-27
We analyzed the commissioning data to search for low20
40
60
80 100 120 140
mass dark matter and solar axions [3, 4]. In our recent analyvector boson mass (keV)sis, we have achieved an unprecedented low-background levelof 3 × 10−4 kg−1 keV−1 kg−1 in the energy range around a few
Fig. 24. Our first experimental limit on coupling constants between
10’s of keV close to our ultimate goal at 5 keV. This backelectrons and vector bosons in 90% C.L. (thick solid line) assuming
ground level was one order of magnitude lower than XENON100
dark matter consists of the vector bosons. The thin black line corresponds to the coupling constant required to reproduce the oband LUX before their e/γ rejection. This results demonstrated
served dark matter abundance through thermal production mechthe unique feature mentioned above.
• A search for inelastic scattering of WIMPs on the isotope 129 Xe [5]. WIMPs are expected to cause inelastic scattering on nucleus 129 Xe has an excited state at
39.58 keV that can be excited through spin-dependentanism. The green and blue dotted lines correspond to the upper
limit from He-burning lifetime in horizontal branch (HB) stars andfrom the γ ray background from 3γ decays in the Galaxy, respectively. The purple line shows an experimental constraint derived ina search for particles produced in the Sun. See text for details.

17• A search for vector boson super-WIMPs [6]. We havesearched for superweakly interacting particles (superWIMPs), with 40-120 keV mass. These particles are
motivated since they soften some problems in the cold
dark matter models 3 . In particular, the vector superWIMPs in this mass range are not experimentally constrained and are a good candidate for thermally generated dark matter in the Universe. Interestingly, thebosonic nature of the particles means that they cause
a monochromatic peak at the rest mass when they areabsorbed in the target. In the 165.9 days data no signal was observed and stringent limits on the electron
coupling with a mass in the 40-120 keV range were obtained. For vector bosons in some of this mass range
our direct detection limit (Fig. 24) surpasses existing
astrophysical constraints, covering new territory.
Refurbishment of XMASS-I
In the commissioning data we found that majority of the
background was from the radioactive contamination in thealuminum seal of PMT windows. Some radioactive contamination on the inner wall of the detector was also identified.
Since the understanding of the origins of background is essentially important for future design of the detector, we decided
to refurbish the detector. By covering the aluminum using
copper rings and copper plates, we can demonstrate the correctness of the understandings and reduce background of the
XMASS-I detector. The actual modification of the detector
are shown in Fig. 25. The copper rings and plates are expected
to stop scintillation lights and radiations practically caused by
the radioactive contamination.
The refurbishment was completed in November, 2013, anddata taking was resumed. The comparison before and after the
refurbishment is presented in Fig. 26. It is clearly seen that
numbers of event in lower energy region (5-10 keV) are reduced around one order of magnitude. Further analysis basedon event reconstruction is expected to give better background
reduction.
*1 P. Belli et al.. Phys. Lett. B 387, 222 (1996); R. Bernabei et al., New J.
Phys. 2, 15 (2000).
*2 L. Baudis et al., Phys. Rev. D 88, 115014 (2013); J. D. Vergados,
H. Ejiri, and K. G. Savvidy, Nucl. Phys. B 877, 36 (2013).
*3 M. Pospelov, A. Ritz, and M. Voloshin, Phys. Rev. D 78 (2008) 115012;
J. Redondo, M. Postma, J. Cosm. Astropart. Phys., 02 (2009) 005;
R. Horvat, D. Kekez, M. Krčmar, Z. Krečak, A. Ljubičić, Phys. Lett.
B 721 (2013) 220.

PMT before attaching a ring

After thin plates installation

PMT after attaching a ring

Fig. 25. Left two photographs show PMTs before and after installinga copper ring. Right two photographs show the inner wall of thedetector before and after the refurbishment.

dru

coupling. A peak at 39.58 keV with a high-energy tailis expected since the scintillation lights from gamma
rays emitted after the excitation 1 and from the additional nuclear recoil cannot be separated. Using a restricted target mass (∼41 kg of LXe at the center of ourdetector) we observed no significant excess of events in
165.9 live days of data. Our background reduction allowed us to derive our limits as shown in Fig. 22 for the
WIMP-nucleus cross section and Fig. 23 for the spindependent cross section on neutron 2 . These limits havebeen the first derived exclusively from data on inelastic
scattering.

Before the refurbishment

1

10-1

6

8

10

12

14

16

18

20

scaledE[keV]

Fig. 26. Energy spectrum before the refurbishment(black) and after(red) is respectively plotted after a set of simple noise reduction
is applied.

XMASS-1.5
We are planning to build the next stage detector, XMASS1.5, with 1 ton fiducial mass. Increasing the fiducial mass is
indispensable to examine cross sections smaller than current
constraints for standard WIMPs. The basic design of the detector is same as the one for the 100 kg fiducial mass detector
but with an essential improvement of the discrimination between the surface background and the inner events. For that
purpose, we are developing a new type of PMTs. They have
convex-shape photocathodes which has advantage to detect
direct light from the inner surface of the detector. As shownin Fig. 27 (left), the dome-shaped PMTs are more efficientfor detecting scintillation photons originated at the inner surface of the detector than the flat-shaped PMTs used for the
XMASS-I detector. In fact, our simulation shows that three
PMTs surrounding the event vertices on the surface should
detect 40%–50% of photoelectrons. This strongly indicatesthat reducing surface events is much easier and more reliable.
With this improvement, we can search for heavy WIMPs withcross sections less than 10−46 cm2 even for the same background level of the XMASS-I. Figure 27 (right) shows the
expected sensitivity of this detector.
It is noteworthy that the XMASS-1.5 has an unique featurethat it has a very low energy threshold as well as high sensitivity for other types of dark matter. The low energy threshold is essentially important for a low mass WIMP search andachieved by the high light yield as confirmed in the XMASS1 detector. The detector is sensitive to axion-like particles aswell as bosonic super-WIMPs as discussed above because thedetector is designed to realize low background even withoute/γ rejection. These unique features are particularly important to have a detector sensitive to broad range of dark mattercandidates.

18

Fig. 27. (Left) Response to surface events of PMT with flat photocathode and a dome-shaped photocathode. Because the dome-shaped
photocathode has a large acceptance for scintillation light from the inner surface of the detector, identification of surface events is much
more efficient with the dome-shaped PMTs. (Right) Expected sensitivity with the XMASS-1.5 detector.

Bibliography[1] Y. Suzuki et al., “Low energy solar neutrino detection byusing liquid xenon”, Aug. 2000, hep-ph/0008296.
[2] K. Abe et al., Nucl. Instr. Meth. 716 (2013) 78[3] K. Abe et al., the XMASS collaboration, Phys. Lett. B
719 (2013) 78.
[4] K. Abe et al., the XMASS collaboration, Phys. Lett. B
724 (2013) 46.
[5] H. Uchida et al., the XMASS collaboration, Prog. Theor.
Exp. Phys. 2014, 063C01.
[6] K. Abe et al., the XMASS collaboration, arXiv:
1406.0502.

HYPER-KAMIOKANDE PROJECT[Project Leader: Masato Shiozawa]
Kamioka Observatory, ICRR, The University of Tokyo
The Hyper-Kamiokande is the third generation nucleon
decay and neutrino detector at Kamioka, that aims to explore
unification of elementary particles and full picture of neutrino
masses and mixings [1, 2]. The schematic view of the HyperK detector is illustrated in Fig. 28 and 29.
A letter of intent [3] of the Hyper-Kamiokande project has
been released, in which the baseline design of the detector
and physics potential of Hyper-K are described. The water
Cherenkov detector with the mass of 1 million tones has capability to search for the nucleon decays with sensitivity ofFig. 28. Schematic view of the Hyper-Kamiokande. The detector consists of two cylindrical tanks holding ∼ 500 kton ultrapure water(∼ 1 Mton in total). The each tank is divided by segmentation walls
every 50 m.

10 times longer than the lifetime limits given by the SuperKamiokande. For example, the sensitivity for the decay modep → e+ π 0 is expected to be beyond 1 × 1035 years [3]. The
detector also aims to study neutrino properties, such as Dirac
CP phase δCP , mass hierarchy, octant of θ23 , by using a highpower accelerator based neutrino beam and atmospheric neutrinos. In particular, the neutrino oscillation physics sensitivities of Hyper-K with J-PARC neutrino beam and atmospheric
neutrinos have been updated and compiled in a proposal, andthat has been submitted to J-PARC Physics Advisory Committee in 2014. Fig. 30 shows the expected size of allowed
regions for the parameter space of θ13 and δCP by using upgraded J-PARC neutrino beam with the power of 0.75 MW
×10 years and the Hyper-Kamiokande detector with the fiducial volume of 0.56 Megaton. Hyper-K has a good sensitivity
in the whole relevant θ13 and δCP parameter space. The highstatistics data sample of atmospheric neutrinos obtained byHyper-K will also allow us to extract information on the mass
hierarchy and the octant of θ23 (Fig. 31). With a full 10 year
period of data taking, the significance for the mass hierarchyδcp Uncertainty

30
25
20
15
10

3σ

5

2σ

0

0.4

0.45

0.5
sin2θ230.55

0.6∆ χ 2 Wrong Octant Rejection∆ χ2 Wrong Hierarchy Rejection19
δcp Uncertainty

30
25
20
15
10

3σ

5

2σ

0

0.4

0.45

0.5
sin2θ 23

0.55

0.6

Fig. 31. Atmospheric neutrino sensitivities for a ten year exposure ofHyper-K assuming the mass hierarchy is normal. Left: the ∆χ 2
discrimination of the wrong hierarchy hypothesis as a function of
the assumed true value of sin2 θ23 . Right: the discrimination between the wrong octant for each value of sin2 θ23 . The uncertainty
from δCP is represented by the thickness of the band.

δCP

Fig. 29. The cross section of the Hyper-Kamiokande water tank.

150

Normal mass hierarchy

100
50
0
-50
-100

Hyper-K
Hyper-K + reactor

-150
0.04

0.06

0.08

0.1

0.12

0.14

0.16
2

0.18

The results highly encourage and boost the activities towardrealization of the future detector.
For Hyper-K R&D, design studies and constructing a detector prototype, five years Grant-in-Aid has been approved
and started in 2013. Hyper-Kamiokande project has been selected as one of top 27 important large-scale projects in the“Master plan 2014” [5] of Science Council of Japan.
International Hyper-Kamiokande Working Group consistsof about 240 people in 67 institutes from 12 countries. The
working group intensively develop various aspects of HyperK project such as geological surveys at the detector candidate
sites, design of cavern and tank, water purification and circulation system design, new photon-sensor and DAQ system, detector calibration system, analysis software, and physics sensitivities. A technical design report of Hyper-K cavern andtank constructions has been written up, and that will be released in near future. Although the detector baseline design
and the physics sensitivities studies of Hyper-K assume to use
Super-K style 20-inch PMTs, new photo-sensors that are potentially lower-cost and higher-sensitivity are pursued since
the photo-sensor is a major cost driver in Hyper-Kamiokande
project. Hyper-Kamiokande Working Group has been developing new photo-sensor candidates, hybrid photo-detector(HPD) and high quantum efficiency (HQE) PMT. Prototypesof these photo-sensors have been produced, and eight 8-inch
HPDs and five HQE 20-inch PMTs were installed in a 200ton water Cherenkov detector (EGADS detector, Fig. 32) toevaluate the basic performance and a long term stability of thephoto-sensors. The testing with the 200-ton detector is well

Photosensor Test
in Water Tanksin 2θ13

2

Fig. 30. Expected sensitivity for sin 2θ13 and CP phase δCP (normal
mass hierarchy case). Red (blue) lines show the result with Hyper-K only (with sin2 2θ13 constraint from reactor experiments).

determination is expected to reach 3σ or greater as is shownin left panel of Fig. 31.
T2K has observed νµ → νe oscillations (electron neutrino
appearance) with more than 7σ significance [4]. The T2K
result with the world average value of θ13 disfavored somevalues of δCP and showed a slight preference for δCP ∼ −π/2.

20-inch High20’’ Quantum
high-QE
Super-K
PMT
Efficiency
PMT
8’’ normal-QE
8-inch Hybrid
PhotoHPD
detector (HPD)

7

Fig. 32. Photo of 200-ton water Cherenkov detector in which new photo-sensor prototypes have been installed and filled with ultrapure
water.

20

progressing, and it is confirmed that new photo-sensors havebetter performances than Super-K style PMTs. Other typesof photo-sensors, such as box and line dynode PMT, are also
being developed. 20-inch prototypes for these photo-sensors
will be available and their performances will be evaluated in
2014. Hyper-Kamiokande Working Group plans to publish atechnical paper summarizing the results of new photo-sensor
R&D. Several other R&D and studies are also making good
progresses. Hyper-Kamiokande Working Group holds ‘Open
Meeting for Hyper-Kamiokande Project’ once in about every
six months to discuss the progresses of studies and various
aspects of the project face to face.

Table 4. T2K data taking periods and integrated numbers of protons
on target (POT) for SK (off-axis ND280) used in the neutrino oscillation analyses. References for T2K results from each data update
are also listed.

Period
Run 1
Run 2
Run 3
Run 4

Dates
Jan.2010 - Jun.2010
Nov.2010 - Mar.2011
Mar.2012 - Jun.2012
Oct.2012 - May.2013

×1020 POT (ND)
0.32 (0.17)
1.11 (0.79) [5],[6]1.58 (1.56) [7],[8]3.56 (3.38) [9],[10]background, produced in the decays muons as well as thesehadrons, represents less than 1% of the neutrino flux around
Bibliography[1] M. Shiozawa, “The Hyper-Kamiokande project,” Nucl. the beam’s peak energy. T2K is the first long-baseline experi-◦ment to adopt an off-axis beam [2]. The beam is directed 2.5
Phys. B (Proc. Suppl.) 237-238, 289-294 (2013).
away from the direction to Super-K, which creates a narrow[2] M. Diwan, R. Edgecock, T. Hasegawa, T. Patzak, M. Sh- muon neutrino energy spectrum peaking around 0.6 GeV, theiozawa and J. Strait, “Future long-baseline neutrino fa- location of the first oscillation maximum for the T2K baseline.
cilities and detectors,” Adv. High Energy Phys. 2013,
The near detector (ND) site located 280 m from the T2K
460123 (2013).
target consists of two detector complexes one each on andoff the beam axis. The on-axis interactive neutrino grid (IN[3] K. Abe, T. Abe, H. Aihara, Y. Fukuda, Y. Hayato, GRID [3]), composed of an array of iron scintillator sandK. Huang, A. K. Ichikawa and M. Ikeda et al., “Letter of wiches, monitors the neutrino beam intensity, direction andIntent: The Hyper-Kamiokande Experiment — Detec- profile. The off-axis detector (ND280) is situated along the
tor Design and Physics Potential —,” arXiv:1109.3262 same direction to SK and measures the neutrino beam flux,[hep-ex].
composition and energy spectrum prior to neutrino oscilla[4] K. Abe et al. [T2K Collaboration], “Observation of Elec- tions. ND280 provides important information on the neutrino
tron Neutrino Appearance in a Muon Neutrino Beam,” flux and interaction models, both of which are essential to
Phys. Rev. Lett. 112, 061802 (2014) [arXiv:1311.4750 T2K’s oscillation measurements.
The far detector, SK [4], is a 50 kton water Cherenkov[hep-ex]].
detector which uses timing information synchronized to the[5] “Master plan 2014” of Science Council of Japan
Global Positioning System (GPS) to records events coincident
http://www.scj.go.jp/ja/info/kohyo/pdf/kohyo-22-t188with the operation of the T2K beam. All data within ±500 µs
1.pdf (in Japanese)of the beam arrival time at SK are recorded for use in later
analysis.
This report uses T2K neutrino data collected during thefour run periods listed in Table 4 and corresponds to 6.57 ×1020 protons on target (POT) in total. The proton beam reachedT2K EXPERIMENTan intensity of 220 kW during this period and produced 1.2 ×
1014 protons per pulse. The expected number of events at
ND280 and SK is calculated using a flux, cross section and de[Spokesperson : Takashi Kobayashi]
tector simulation assuming a certain oscillation parameter set.
High Energy Accelerator Research Organization (KEK)
The systematic uncertainties in this prediction are largely reduced by measurements using the T2K near detectors, whose
The T2K (Tokai-to-Kamioka) experiment [1] is a 295 km
data constrain the neutrino flux and interaction model paramlong-baseline neutrino oscillation experiment, employing a higheters used throughout the experiment.
intensity muon neutrino beam sent from the Japan Proton AcThe neutrino flux is calculated with a Monte Carlo (MC)celerator Research Complex (J-PARC) in Tokai to the Supersimulation considering the T2K beamline and measurements
Kamiokande (SK) water Cherenkov detector in Kamioka. Theof the primary proton beam profile, the magnetic fields proprimary goals of the experiment are to observe electron neuduced by the focusing horns, and hadron production data fromtrino appearance in this muon neutrino beam and thereby meathe NA61/SHINE measurements [11, 12]. Neutrino interacsure the last unknown mixing angle, θ13 , as well as to pretions are then simulated based on the flux predictions at both2
cisely determine the oscillation parameters, ∆m32 and θ23 , by
the ND280 and SK sites using the NEUT framework [13].
simultaneously observing muon neutrino disappearance.
Parameters in the neutrino interaction model are constrained
The T2K beam is composed primarily of muon neutrinos,
with three control samples from ND measurements [14]. Chargwhich are produced in the decays of charged pions and kaons
ed current (CC) samples were selected at the ND280 using
created in the interactions of 30 GeV protons from the J-PARC
tracking information from its FGD and TPC subdetectors andaccelerator striking a graphite target. An electron neutrino

21

δCP (π)δCP (π)Number of νe candidate events

further divided based on pion multiplicity into a (i) CC-0π
Datasample with no identified pions and therefore enriched in CCQE
8Best fitinteractions, a (ii) CC-1π + sample with only one identified
Background component
π + to constrain CC resonant pion production and a (iii) CC20
6other sample with all other CC events. Using 5.90 × 10 POT
Fit region < 1250 MeV(c.f. Table 4) the observed event rates for these samples were17369, 4047, and 4173 events, respectively.
4
Charged current quasi-elastic (CCQE) scattering at SK,
νl + N → l + N 0 , is a dominant interaction in the T2K energy
2
region, which produces a single charged lepton (l = muon,or electron) from an initial nucleon, N, with a final state nucleon, N 0 . This processes appears as a single Cherenkov ring
0
>2000
0
500
1000
1500
at SK and the parent neutrino energy can be inferred using thisReconstructed neutrino energy (MeV)
ring’s reconstructed information. For this reason events with
only one Cherenkov ring are selected at SK and the T2K anal- Fig. 33. Observation and best fit reconstructed neutrino energy distribution (sin2 2θ13 = 0.144, δCP = 0, normal hierarchy). The contribuysis studies oscillations using in two independent data samtion from νe appearance is shown by the white histogram.
ples separated by particle identification: νµ → νe with singlering e-like events, and νµ → ν(X6=µ) with single-ring µ-likeevents. Neutral current (NC) production of a single pion is a1
main background source in these single-ring events.
The value of θ13 has been evaluated using the observation
0.5
of electron neutrino appearance at SK. The analysis sample isenriched in νe CCQE by selecting fully contained single-ring∆m232>0e-like events consistent with the T2K beam timing and located0
within the SK fiducial volume. Residual νµ events generating
68% CL
90% CLdecay-electrons which can mimic the CCQE signal and pion
-0.5
Best fitbackgrounds from NC interactions are reduced by requiring
PDG2012 1σ rangethat there are no delayed decayed electrons observed and that-1
the reconstructed momentum of electron exceeds 100 MeV/c.
1Furthermore, requiring the reconstructed neutrino energy beless than 1250 MeV is used to elected to avoid a small amount0.5
of high-energy electron neutrinos intrinsic to the beam. A new
SK event reconstruction algorithm, fiTQun, was introducedin the 2013 analysis in order to improve the rejection of π 0 s0that are misidentified as a single electron ring. FiTQun uses
all photomultiplier hit information in its fit and achieves im∆m232<0-0.5
proved background rejection while maintaining good signal
efficiency.
In the Run 1-4 data, out of 377 fully contained fiducial-1
volume neutrino candidates at Super-K 28 events passed all of
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4
the selection cuts [9]. Compared to the prediction of 4.92 ±sin22θ13
0.55 events assuming θ13 = 0, this is a significant excess.
intervals for sin2 2θ13 scanned
Two independent analyses were performed, one using the Fig. 34. The 68% and 90% confidence
over values of δCP assuming sin2 θ23 = 0.5 Results from a fit to thereconstructed energy of the neutrino and one using both thenormal hierarchy (top) and inverted hierarchy (bottom) are shown.
momentum and the angle of the observed electron direction
relative to the beam direction, and both gave consistent results. Figure 33 shows the reconstructed neutrino energy dis- 7.6 × 10−5 eV2 , sin2 θ23 = 0.5 and ∆m232 = 2.4 × 10−3 eV2 .
tribution assuming all events underwent CCQE interactions, The best fit values of sin2 2θ13 with the 68% confidence inter+0.045
where the solid line represents the expected distribution at the vals are evaluated to be sin2 2θ13 = 0.140+0.038−0.032 (0.170−0.037 )best fit for θ13 assuming fixed values of the oscillation param- at δCP = 0 for the normal (inverted) hierarchy assumption.
eters: sin2 θ12 = 0.306, ∆m221 = 7.6 ×10−5 eV2 , sin2 θ23 = 0.5, The 28 observed νe events are a clear indication of electron∆m232 = 2.4 × 10−3 eV2 and δCP = 0. The parameter δCP de- neutrino appearance and non-zero θ13 with 7.3σ significance.
scribes a CP (charge parity) phase, where the CP conservation Therefore, the νµ → νe oscillation mode has been definitely
in leptonic sector is unknown. The prediction agrees well with discovered by T2K using its data up until 2013.
the observed distribution.
As the precision of the T2K measurement improves, unThe best fit as well as 68% and 90% confidence intervals certainties in the other oscillation parameters become increasfor sin2 2θ13 from the momentum and angle binned analysis ingly important and have been included in the subsequent analare shown at each fixed value of δCP in Fig. 34 and with the ysis. The measured values of θ23 and ∆m232 from the T2K
following parameter assumptions: sin2 θ12 = 0.306, |∆m221 | = νµ disappearance analysis [8], corresponding to 3.01 × 1020

-2∆lnL22654∆m232>0∆m232<090% CL ( ∆m232>0)
90% CL ( ∆m232<0)

3
2
1
0
-1

-0.5

0

0.5

1

δCP (π)Fig. 35. The −2∆lnL and 90% CL of δCP obtained by incorporating
results of the T2K νµ disappearance result (3.01 × 2020 , 2012) andaverage value of θ13 from reactor experiments in the appearance
analysis.

+0.051
POT, are sin2 2θ13 = 0.136+0.044−0.033 (0.166−0.042 ) in the case of
the normal (inverted) hierarchy at δCP = 0.
The first evaluation of the allowed region of δCP in T2K
was performed with the help of precision measurements ofθ13 by reactor ν̄e disappearance experiments. The value ofsin2 2θ13 value was to 0.098 ± 0.013 based on the PDG2012
average [15]. The −2∆lnL curve as a function of δCP is shownin Fig. 35 with a 90% confidence level (CL) determined with
the Feldman-Cousins method [16]. T2K data indicate at the
90% CL that δCP is excluded between 0.19π and 0.80π (−πand −0.97π, and −0.04π and π) assuming a normal (inverted)hierarchy.
The T2K νµ disappearance analysis is performed separately on a νµ CCQE enriched sample by selecting singlering µ-like events with cuts on the reconstructed muon momentum (pµ > 200 MeV/c) and the number of delayed signals from Michel electrons (less than or equal to one). In the
Run 1-4 data 446.0±22.5 events are expected without neutrino oscillations, while just 120 events have been observed[10]. The best fit MC expectation and data as a function ofreconstructed neutrino energy are shown in the top portionof Fig. 36. The bottom panel shows the ratio of the observation and best fit expectation relative to the expectation fromthe null oscillation hypothesis, clearly demonstrating the presence of νµ → ν(X6=µ) oscillations in the data. In Fig. 37, theT2K allowed regions for the parameters sin2 θ23 and ∆m232 (or∆m213 ) for both hierarchy assumptions are shown. T2K has
achieved the most stringent constraint on θ23 , surpassing the
SK atmospheric neutrino measurement.
T2K data sets are also used to determine neutrino crosssections. The result of the measurement for νµ inclusive charged current interactions was published [17]. The first measurement of the neutrino-oxygen neutral current quasi-elastic(NCQE) cross section was also reported [18]. With 3.01 ×
1020 POT, a search for γ-ray events from nuclear de-excitation
following NC interactions in Super-K has yielded 43 eventswith energy between 4-30 MeV and corresponds to a fluxaveraged NCQE cross section measurement of 1.35+0.59−0.29 ×
−38
2
10
cm .

Fig. 36. The reconstructed energy spectrum of single-ring µ-likeevents at SK for the Run 1-4 data with the best fit MC expectation broken down by neutrino flavor and interaction type appears
in the top panel. The ratio of the observed and best-fit MC expectations from the top figure relative to the no oscillation hypothesis
is shown in the bottom panel.

Fig. 37. The 68% and 90% confidence region from the T2K νµ disappearance measurement for both hierarchy assumptions. The 1-d
profile likelihoods for each parameter are separately shown at the
top and right of the figure with the 68% and 90% confidence levels
determined using the Feldman-Cousins method.

Although the discovery of electron neutrino appearance
and the most constraining measurement of θ23 have been achieved the current T2K exposure is still only 8% of the design
goal. The T2K experiment has also analyzed both the appearance and disappearance samples simultaneously incorporating
parameter correlations and the first preliminary result was obtained using the Run 1-4 data. In 2014, an anti-neutrino run
with a ν̄µ beam will start. This will allow T2K to independently study νe and ν̄e oscillations and improve sensitivity to
the CP violating parameter, δCP .

Bibliography[1] K. Abe et al. [T2K Collaboration], Nucl. Instrum. Meth.
A 659, 106 (2011) [arXiv:1106.1238 [physics.ins-det]].

23[2] D. Beavis, A. Carroll, I. Chiang, et al., Long Baseline
Neutrino Oscillation Experiment at the AGS (Proposal
E889), 1995. Physics Design Report, BNL 52459.
[3] M. Otani, N. Nagai, D. Orme, A. Minamino, K. Nitta,
O. Drapier, F. Moreau and M. Besnier et al., Nucl. Instrum. Meth. A 623, 368 (2010).
[4] Y. Fukuda et al. (Super-Kamiokande Collaboration),
Nucl. Instrum. Meth. A501, 418 (2003).
[5] K. Abe et al. [T2K Collaboration], Phys. Rev. Lett. 107,041801 (2011) [arXiv:1106.2822 [hep-ex]].
[6] K. Abe et al. [T2K Collaboration], Phys. Rev. D 85,
031103 (2012) [arXiv:1201.1386 [hep-ex]].
[7] K. Abe et al. [T2K Collaboration], Phys. Rev. D 88,
032002 (2013) [arXiv:1304.0841 [hep-ex]].
[8] K. Abe et al. [T2K Collaboration], Phys. Rev. Lett. 111,
211803 (2013) [arXiv:1308.0465 [hep-ex]].
[9] K. Abe et al. [T2K Collaboration], Phys. Rev. Lett. 112,061802 (2014) [arXiv:1311.4750 [hep-ex]].
[10] K. Abe et al. [T2K Collaboration], Phys. Rev. Lett. 112,
181801 (2014) [arXiv:1403.1532 [hep-ex]].
[11] N. Abgrall et al. [NA61/SHINE Collaboration], Phys.
Rev. C 84, 034604 (2011) [arXiv:1102.0983 [hep-ex]].
[12] N. Abgrall et al. [NA61/SHINE Collaboration], Phys.
Rev. C 85, 035210 (2012) [arXiv:1112.0150 [hep-ex]].
[13] Y. Hayato, Nucl. Phys. (Proc. Suppl.) B112, 171 (2002).
[14] K. Abe et al. [T2K Collaboration], Phys. Rev. D 89,
092003 (2014) [arXiv:1403.2552 [hep-ex]].
[15] J. Beringer et al. [Particle Data Group], Phys. Rev. D 86,
010001 (2012).
[16] G.J. Feldman and R.D. Cousins, Phys. Rev. D 57, 3873
(1998).
[17] K. Abe et al. [T2K Collaboration], Phys. Rev. D 87,
092003 (2013) [arXiv:1302.4908 [hep-ex]].
[18] K. Abe et al. [T2K Collaboration], arXiv:1403.3140[hep-ex].

24

HIGH ENERGY COSMIC RAY DIVISION
Overview

tension of the air shower array was completed in 1995 and an
There are three major experimental research activities in emulsion chamber has been combined with this air shower arthe High Energy Cosmic Ray Division, the study of high en- ray since 1996 to study the primary cosmic rays around theergy gamma rays and the development of the next generation knee energy region. After successive extensions carried out
gamma-ray telescopes by the Cherenkov Cosmic Gamma Ray in 1999, 2002 and 2003, the total area of the air shower argroup, the study of extremely high energy cosmic rays by the ray amounts to 37,000 m2 . The sun’s shadow in cosmic rays
Telescope Array (TA) group, and the study of very high en- affected by the solar magnetic field was observed for the firsttime in 1992, utilizing its good angular resolution at multiergy cosmic rays and gamma rays by the Tibet ASγ group.
Other activities, such as experiments utilizing the Akeno TeV energy region.
A new type of detector, called Ashra (all-sky survey highobservatory, the Norikura observatory, the Mt. Chacaltaya observatory (jointly operated with Bolivia) are closely related to resolution air-shower detector), was developed. The first-phaseinter-university joint research programs. Also an all-sky high stations were installed near the Mauna Loa summit in the
resolution air-shower detector (Ashra) is in partial operation Hawaii Island and high-efficiency observation is continuing.
on the Hawaii island. The High Energy Astrophysics group It monitors optical and particle radiation from high-energy
created in the fiscal year 2009 aims to explore various high transient objects with a wide field-of-view.
The High Energy Astrophysics group is conducting theenergy astrophysical phenomena, through theoretical and oboretical researches on fundamental processes responsible forservational approaches.
The CANGAROO telescopes had been in operation in South non-thermal particle acceleration in various astrophysical enAustralia since 1992, with a 3.8 m small telescope and then vironments, including first-order diffusive shock acceleration,with four 10 m telescopes. The major scientific objective was second-order stochastic acceleration in shock downstream rethe study of Very High Energy (VHE) gamma-ray sources in gions, modification of shock structure by pick-up interstellar
our galaxy in the southern hemisphere. The mission of these neutrals, as well as injection processes of suprathermal partitelescopes was completed and the CANGAROO observation cles. In addition to these theoretical works, R/D studies forradio observations of pulsars and cosmic ray air showers aresite was closed in 2011.
For further development of VHE gamma-ray astronomy, also being made.
the Cherenkov Cosmic Gamma Ray group is working on thedesign study and development of the next generation international ground-based gamma-ray observatory CTA which willoffer an order of magnitude better sensitivity than currently Cherenkov Cosmic Gamma-Ray Grouprunning Cherenkov telescopes, three times better angular resolution, and wider energy coverage from 20 GeV to 100 TeV
or higher.
CTA Project (Cherenkov Telescope Array)
At the Akeno observatory, a series of air shower arrays of
increasing geometrical sizes were constructed and operated to CTA-Japan Consortium
observe extremely high energy cosmic rays (EHECRs). The [Spokespersons : M.Teshima and H.Kubo]
Akeno Giant Air Shower Array (AGASA) was operated from Collaboration list:
1991 to January 2004 and covered the ground area of 100 km2 Institute for Cosmic Ray Research, The University of Tokyo,
as the world largest air shower array. In 13 years of opera- Chiba, Japan; Department of Physics, Aoyama Gakuin Unition, AGASA observed a handful of cosmic rays exceeding versity, Tokyo, Japan; Department of Physics, Hiroshima Unithe theoretical energy end of the extra-galactic cosmic rays versity, Hiroshima, Japan; Hiroshima Astrophysical Science
Center, Hiroshima University, Hiroshima, Japan; Faculty of(GZK cutoff) at 1020 eV.
The Telescope Array (TA), a large plastic scintillator ar- Science, Ibaraki University, Ibaraki, Japan; Institute of Partiray with air fluorescence telescopes, has been constructed in cle and Nuclear Studies, High Energy Accelerator ResearchUtah, USA, which succeeds AGASA and measures the EHE- Organization (KEK), Ibaraki, Japan; Department of Physics,
CRs with an order of magnitude larger aperture than that of Konan University, Hyogo, Japan; Faculty of Medical EngiAGASA for the further study of EHECRs. The full-scale TA neering and Technology, Kitasato University, Kanagawa, Japan;
is accumulating data as the largest array viewing the north- Graduate School of Science and Technology, Kumamoto Uniern sky and observed the energy spectrum with high statistics, versity, Kumamoto, Japan; Department of Physics, Kyoto University, Kyoto, Japan; Department of Applied Physics, Uniwhich is in good agreement with the GZK suppression.
An air shower experiment aiming to search for celestial versity of Miyazaki, Miyazaki, Japan; Department of Physics,
gamma-ray point sources started in 1990 with Chinese physi- Nagoya University, Aichi, Japan; Solar-Terrestrial Environcists at Yangbajing (Tibet, 4,300 m a.s.l.). This international ment Laboratory, Nagoya University, Aichi, Japan; Kobayashicollaboration is called the Tibet ASγ Collaboration. An ex- Maskawa Institute, Nagoya University, Aichi, Japan; Depart-25

Fig. 1. Artist view of the CTA observatory. CTA consists of three types of telescopes, Large Size Telescopes (23m diameter), Mid Size
Telescopes (12m) and Small Size Telescopes (4m), and covers the broad energy band from 20GeV to 100TeV.

ment of Earth and Space Science, Osaka University, Japan;
Department of Physics, Kinki University, Osaka, Japan; Astrophysical Big Bang laboratory, RIKEN, Wako, Japan; Department of Physics, Saitama University, Saitama, Japan; Institute of Space and Astronautical Science, JAXA, Kanagawa,Japan; Department of Physics, Tokai University, Kanagawa,Japan; Department of Radiation Oncology, Tokai University,
Kanagawa, Japan; Faculty of Integrated Arts and Sciences,
The University of Tokushima; Department of Astronomy, The
University of Tokyo, Tokyo, Japan; Department of Physics,
The University of Tokyo, Tokyo, Japan; Faculty of Scienceand Engineering, Waseda University, Tokyo, Japan; Department of Physics, Yamagata University, Yamagata, Japan; Faculty of Management Information, Yamanashi Gakuin University, Yamanashi, Japan; Center for Cosmology and AstroParticle Physics, Ohio State University, Ohio, USA; Max-PlanckInstitute for Physics, Munich, Germany [1].
CTA Project
During the past several years, Very High Energy (VHE)
gamma-ray astronomy has made spectacular progress and has
established itself as a vital branch of astrophysics. To advance
this field even further, we propose the Cherenkov Telescope
Array (CTA) [2], the next generation VHE gamma ray observatory, in the framework of a worldwide, international collaboration. CTA is the ultimate VHE gamma ray observatory,
whose sensitivity and broad energy coverage will attain an order of magnitude improvement above those of current Imaging Atmospheric Cherenkov Telescopes (IACTs). By observing the highest energy photons known, CTA will clarify many
aspects of the extreme Universe, including the origin of thehighest energy cosmic rays in our Galaxy and beyond, thephysics of energetic particle generation in neutron stars andblack holes, as well as the star formation history of the Universe. CTA will also address critical issues in fundamental
physics, such as the identity of dark matter particles and thenature of quantum gravity.
VHE gamma rays from 100GeV to 10TeV can be observedwith ground-based IACTs. The history of VHE gamma ray astronomy began with the discovery of VHE gamma rays fromthe Crab Nebula by the Whipple Observatory in 1989. To
date, the current generation IACTs featuring new technologies, such as H.E.S.S., MAGIC, VERITAS, and CANGAROO, have discovered more than 100 Galactic and extragalactic sources of various types.
CTA is designed to achieve superior sensitivity and performance, utilizing established technologies and experience
gained from the current IACTs. The project is presently in its
preparatory phase, with international efforts from Japan, theUS and EU. It will consist of several 10s of IACTs of three different sizes (Large Size Telescopes, Mid Size Telescopes, andSmall Size Telescopes). With a factor of 10 increase in sensitivity (1m Crab ∼ 10−14 erg s−1 cm−2 ), together with a muchbroader energy coverage from 20GeV up to 100TeV, CTA willbring forth further dramatic advances for VHE gamma ray astronomy. The discovery of more than 1000 Galactic and extragalactic sources is anticipated with CTA.
CTA will allow us to explore numerous diverse topics inphysics and astrophysics. The century-old question of the origin of cosmic rays is expected to be finally settled through detailed observations of supernova remnants and other Galactic
objects along with the diffuse Galactic gamma ray emission,
which will also shed light on the physics of the interstellar
medium. Observing pulsars and associated pulsar wind nebulae will clarify physical processes in the vicinity of neutronstars and extreme magnetic fields. The physics of accretion

26

onto supermassive black holes, the long-standing puzzle of theorigin of ultrarelativistic jets emanating from them, as well as
their cosmological evolution, will be addressed by extensive
studies of active galactic nuclei (AGN). Through dedicatedobserving strategies, CTA will also elucidate many aspects ofthe mysterious nature of gamma ray bursts (GRBs), the mostenergetic explosions in the Universe. Detailed studies of both
AGNs and GRBs can also reveal the origin of the highest energy cosmic rays in the Universe, probe the cosmic history ofstar formation including the very first stars, as well as provide
high precision tests of theories of quantum gravity. Finally,
CTA will search for signatures from elementary particles constituting dark matter with the highest sensitivity yet. Realization of the rich scientific potential of CTA is very much feasible, thanks to the positive experience gained from the current
IACTs.
The CTA-Japan consortium [1] is aiming at contributing inparticularly to the construction of the Large Size Telescopes(LSTs) and is involved in their development. The LST covers the low energy domain from 20GeV to 1000GeV and is
especially important for studies of high redshift AGNs and
GRBs. The diameter and area of the mirror are 23m and
400m2 , respectively, in order to achieve the lowest possibleenergy threshold of 20GeV. All optical elements/detectors require high specifications, for example, high reflectivity, highcollection efficiency, high quantum efficiency and ultra fast
digitization of signal, etc. For this purpose, CTA-Japan is developing high quantum efficiency photomultipliers, ultrafast
readout electronics and high precision segmented mirrors. On
the strength of their experience gained from construction of
the MAGIC telescope, the Max-Planck-Institute for Physics
in Munich is responsible for the design of the 23m diametertelescope structure, based on a carbon fiber tube space frame.
The LSTs require very fast rotation (180 degrees/20seconds)
for promptly observing GRBs.
The Cherenkov Cosmic Gamma Ray group is also operating the MAGIC Telescopes [6] on La Palma, Canary Islands.
This facility is used not only for scientific observations but
also for technological development toward the future observatory CTA.

Fig. 2. Large Size Telescope (23m diameter) designed by Max–
Planck-Institute for Physics. CTA Japan is contributing to the design and prototyping of the imaging camera at the focal plane, ultrafast readout electronics, and high precision segmented mirrors.

Fig. 3. Camera cluster for the Large Size Telescope (LST) developedby CTA-Japan. This cluster consists of seven high quantum efficiency photomultipliers (R11920-100), CW High Voltages, pre-amplifier, Slow Control Board, DRS4 Ultra fast waveform recording
system and Trigger. The LST camera can be assembled with 265of these clusters, cooling plates and camera housing.

Bibliography[1] CTA
Consortium
website:cta-observatory.jp/ andcta-observatory.org/.

http://www.
http://www.

[2] Design Concepts for The Cherenkov Telescope Array,
The CTA Consortium, Exper. Astron. 32 (2011) 193316.
[3] Status of Very High Energy Gamma Ray Astronomy and
Future Prospects, M. Teshima, The Astronomical Herald, 104 (2011) 333-342.
[4] Design Study of a CTA Large Size Telescope,Proc. of ICRC2012 at Beijing China, M. Teshima,
arXiv:1111.2183.
[5] Introducing the CTA Concept, B. Acharya et al., Astroparticle Physics, 34 (2013) 3.

Fig. 4. The high precision segmented mirrors for the Large Size Telescope (LST) developed by CTA-Japan in cooperation with Sanko
Co.LTD. The mirror is made of a 60mm thick aluminum honeycomb
sandwiched by 3mm thin glass on both sides. A surface protection coat consisting of the materials SiO2 and HfO2 is applied toenhance the reflectivity and to elongate the lifetime.

27

Fig. 5. MAGIC Stereo System with two Cherenkov telescopes of 17m
diameters, so far achieved the threshold energy of 25GeV. It locates near the mountain top of the Roque de los Muchachos on
the Canary Island of La Palma. Two telescopes are located withthe distance of 85 meters.

[6] MAGIC Collaboration website:
mppmu.mpg.de/.

Fig. 6. Akeno atmospheric Cherenkov telescope with 18 segment
mirrors readjusted as the Davies-Cotton optics.

http://magic.

MAGIC
The MAGIC Collaboration has built in 2002 / 2003 a firstlarge atmospheric imaging Cherenkov telescope, MAGIC-I,
with a mirror surface of 236 sq.m. and equipped with photomultiplier tubes of optimal efficiency. In 2009, a second
telescope of essentially the same characteristics was added;
MAGIC-II was installed at a distance of 85m from MAGICI. With the accent of these instruments on large mirror surface and best light collection, cosmic gamma-rays at an energy threshold lower than any existing or planned terrestrial
gamma-ray telescope have become accessible. So far achieved
has been a threshold of 25 GeV. The Japanese group has joined
the MAGIC collaboration since 2010, and contributed to theoperation, observations and data analysis. The MAGIC telescopes are operated by an international collaboration of 17
institutes from 8 countries.
The recent highlights from MAGIC are, 1) the successful
observation of pulsed gamma ray signal from the Crab pulsar up to TeV regime [1], 2) the discovery of the most distant blazer 3S 0218 + 35 with the redshift of 0.944 above
100GeV [2], 3) the observation of the very fast flare of 1mintime scale from the blazar inside Perseus cluster, IC310 [3].
These results brought new questions on the pulsar emission
mechanism, the EBL energy density, and gamma ray emission mechanism from the supermassive blackholes or vicinityof them.

Bibliography[1] Phase-resolved energy spectra of the Crab pulsar in therange of 50-400 GeV measured with the MAGIC telescopes, the MAGIC Collaboration, Aleksić et al. A&A
540 (2012) A69.
[2] ATEL 6349.
[3] ATEL 4583.
Other Activities
As a test bench for domestic R & D activities of future
ground-based gamma-ray observatory projects, a used atmospheric Cherenkov telescope of a 3 m diameter was obtained

and placed at the Akeno Observatory in November 2010. Thisis currently the only atmospheric Cherenkov telescope locatedin Japan. In the fiscal year 2013, we readjusted the telescope
optics consisting of 18 segment mirrors, which had been recoated by 2012 at the Okayama Astrophysical Observatory(OAO), the National Astronomical Observatory of Japan (NAOJ)(Fig. 6). An R & D system of 32 pixel (PMT) imaging camera and electronics were installed to the telescope, and test
observations of air-shower events are going to be carried out
with this system in the next fiscal year [1, 2]. Test observations with some prototype imaging cameras for CTA are alsoplanned with the telescope in the near future.

Bibliography[1] M. Ohishi et al., Proc. of 33rd Internat. Cosmic Ray
Conf. (Rio de Janeiro), in press (2013).
[2] T. Yoshikoshi et al., Proc. of 32nd Internat. Cosmic Ray
Conf. (Beijing), 9, 226–229 (2011).

TA: Telescope Array Experiment[Spokespersons: H. Sagawa1 , G. B.Thomson2 ]1 : ICRR, The Univ. of Tokyo, Kashiawa, Chiba 277-8582
2 : Dept. of Physics, University of Utah

Collaborating Institutions:
Chiba Univ., Chiba, Japan; Earthquake Research Institute, Univ.
of Tokyo, Tokyo, Japan; Ehime Univ., Matsuyama, Japan;
Ewha W. Univ., Seoul, Korea; Hiroshima City Univ., Hiroshima,
Japan; Hanyang Univ., Seoul, Korea; ICRR, Univ. of Tokyo,
Kashiwa, Japan; INR, Moscow, Russia; IPMU, Univ. of Tokyo,
Kashiwa, Japan; Kanagawa Univ., Yokohama, Japan; KEK/
IPNS, Tsukuba, Japan; Kinki Univ., Higashi-Osaka, Japan;
Kochi Univ., Kochi, Japan; Kyoto Univ., Kyoto, Japan; Nat.
Inst. of Rad. Sci., Chiba, Japan; Osaka City Univ., Osaka,
Japan; RIKEN, Wako, Japan; Ritsumeikan Univ., Kusatsu,

28

1025

3

Overview and Status of TA
The Telescope Array (TA) is the largest Ultra-High-Energy
Cosmic-Ray (UHECR) observatory in the Northern Hemisphere, located in the West Desert in Utah, USA (latitude 39.3◦
N, longitude 112.9◦ W, altitude ∼1400 m). TA is designed
to observe extensive air showers (EAS) induced by UHECRs
with energies from ∼1018 to ∼1020.5 eV, and measures the energy spectrum, mass composition, and arrival direction distribution of UHECRs, and searches for ultra-high-energy photon
and neutrino primaries. The aim of these measurements is to
explore the origin, propagation and interaction of UHECRs.
The TA detector consists of an air shower surface detector(SD) array of plastic scintillation counters to measure the lateral distribution of secondary particles on the ground, and fluorescence detectors (FDs) to measure the longitudinal development of the EAS in the atmosphere. The SD array consistsof 507 counters with an area of 3 m2 , which were deployed ona square grid of 1.2-km spacing, covering ∼700 km2 . Three
FD stations are located at the periphery, looking inward over
the SD array. The Middle Drum (MD) FD site is located to thenorth of the SD array, and is instrumented with 14 refurbishedtelescopes from the High-Resolution Fly’s Eye (HiRes) station. The Black Rock Mesa (BRM) and Long Ridge (LR)FD sites are located to the southeast and southwest of the SD
array, respectively. They are each instrumented with 12 newtelescopes. TA is operated by an international collaborationof researchers from Japan, USA, Korea, Russia, and Belgium.
Hybrid observations using both SDs and FDs commenced in
March 2008.

relationship, where the SD energy must be reduced by 27% toagree with the FD energy.
The resulting energy spectrum is shown together with themeasurements of other experiments in Figure 7. Using a broken power-law fit, we found the two breaks at (5.04 ± 0.27) ×
1018 eV and (5.68 ± 1.05)×1019 eV. These are consistent withthe ankle and the GZK suppression [2, 3], respectively. We
observed 26 events above the suppression, whereas a linear
extrapolation of the power law below the break predicts 68.1
events above the break. This result provides evidence for theflux suppression with a statistical significance of 5.74σ . The
Auger spectrum after energy-scale shift by +10% agrees with
the TA spectrum below the suppression, whereas the suppression points differ between the two spectra.
We check the compatibility of the measured TA spectrum
above 1018.2 eV using the MC code for cosmic-ray propagation (CRPropa) with modifications [4] by setting the injection
spectral index (p for E p ), the source evolution (m for (1+z)m )and energy scale as free parameters, where z is the red shift.
We obtain the preliminary best fit χ 2 /d.o. f . = 12.5/17 with
+1.7
+0.03
p = 2.21+0.15−0.10 , m = 6.6−1.2 , and ∆logE = −0.03−0.02 . Similar results are obtained for the isotropic model and the largescale structure (LSS) model, and the difference is included asa systematic error. The LSS model used in this analysis is
explained in Section .

I(E) E [eV2/m2/s/sr]

Japan; Rutgers Univ., Piscataway, NJ, USA; Saitama Univ.,
Saitama, Japan; Tokyo City Univ., Tokyo, Japan; Tokyo Inst.
of Tech., Tokyo, Japan; Tokyo Univ. of Science, Noda, Japan;
ULB, Brussels, Belgium; UNIST, Ulsan, Korea; Univ. of
Utah, Salt Lake City, UT, USA; Univ. of Yamanashi, Kofu,
Japan; Waseda Univ., Tokyo, Japan; Yonsei Univ., Seoul, Korea

1024

Auger combined
Auger combined (x1.1)
TA-SD

Results
Energy Spectrum
The energy spectrum for four years of TA SD data has
been published [1]. Here, we update this energy spectrum using the SD data for the five years of observations from May
2008 to May 2013 with an exposure of ∼4500 km2 sr yr. The
Monte Carlo (MC) data were generated by a CORSIKA air
shower simulation with the QGSJET-II-03 model. A GEANT4
simulation was used for the detector simulation. We use thecorrelation of S800 , which is the charge density at a distanceof 800 m from the shower core, and zenith angle with primary energy from the MC study for the first estimation of thecosmic-ray energy.
The energy scale uncertainty in the SD MC simulation canbe large, mainly due to the modeling of hadronic interactions.
The energy scale uncertainty is experimentally controlled for
the FD, because the energy measurement is calorimetric. We
correct our energy scale to the TA FD using events detected byboth the FD and SD. The observed differences between the FD
and SD events are well described by a simple proportionality

17.5

18

18.5

19

19.5

20

20.5
log (E/eV)
10Fig. 7. The preliminary TA SD spectrum together with the spectrafrom other experiments: the TA SD (blue closed squares), AGASA(black open squares), Auger [5] (red closed circles), HiRes (black
open triangles). Red open circles are Auger spectrum after energy-scale shift by +10%. .

With each of the three sites acting independently, the FD
measurement of the spectrum in “monocular” mode [6] provides a larger dynamic range of energy measurements anda bolometric measurement of the EAS energy, but the duty
cycle is only ∼10% due to its operation being restricted tomoonless nights. The geometrical reconstruction of the EAS
is also poorer than with the SD alone. The “hybrid” measurement [7, 8] combines the bolometric FD measurements withthe geometrical precision of the SD at the cost of the duty
cycle and reduced dynamic range of each method. For the
monocular and hybrid measurements of the spectra, two separate analyses were performed, and these separate analyses are
combined appropriately to allow us to present a TA monocular29

spectrum and a TA hybrid spectrum. Figure 8 shows the preliminary results for the combined monocular spectrum, combined hybrid spectrum, and SD spectrum [9]. These spectra
are consistent with each other.

10

2

5

SD, Monocular and Hybrid Spectra
JE (eV 2 m2 s sr)-1

18.4 - 18.6

15

4

0
400
1025

20

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6600
800 1000
Xmax [g/cm 2]

1200

600
800 1000
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20

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20

0
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15
10

10

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5
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600
800 1000
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1200

600
800 1000
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1200

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1024

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15

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10

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18.4

18.6

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5

5

SD Spectrum
Monocular Spectrum
Hybrid Spectrum
18

0
400

0
400
19.4

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20.2 20.4
log (E /eV)

600
800 1000
Xmax [g/cm 2]

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10

1200

19.6 - 19.8

Search for Ultra-high-energy Photons
It is expected that a photon-induced shower would have a
deeper shower maximum than a hadronic shower and exhibit
a larger shower-front curvature on the ground. We present results from the TA 5-year SD data set [12]. Figure 12 shows
the distribution of Linsley curvature parameter for events withzenith angles between 45◦ and 60◦ . For each event, we determined the percentile rank below the observed Linsley parameter value for photon primaries. The distribution of thispercentile rank for photon primaries is flat between 0 and 1,
whereas the actual distribution in the data is strongly nonuniform (mostly below 0.5). Based on this, the obtained 95%

1

1
600
800 1000
Xmax [g/cm 2]

1200

0
400

600
800 1000
Xmax [g/cm 2]

1200

Fig. 9. The preliminary reconstructed Xmax distributions for the stereo
data (points) with QGSJET-II-03 MC simulation for eight energy
regions between 1018.2 and 1019.8 eV. The red and blue histograms
are the proton and iron predictions, respectively.

900
850
800
<X max >Mass Composition
The dependence of shower maximum depth, Xmax , on the
primary energy is used to determine the mass composition.
The HiRes result is consistent with proton-dominated composition for E > 1018 eV [10], whereas the Auger result iscompatible with mixed composition [5].
The events observed simultaneously at two new FD stations (stereo events) from November 2007 through November 2012 are presented [11]. The distribution of reconstructed
Xmax for the TA data is in agreement with the QGSJET-II-03
proton distribution in each energy range as shown in Figure 9.
Here the Xmax values include reconstruction and acceptancebias both for the TA data and MC simulation. The evolutionof the average Xmax with energy for TA stereo data is shownwith the MC simulation in the energy range of 1018.2 to 1019.8
eV in Figure 10. The TA stereo data are in agreement with theproton prediction.
A similar result was obtained using the MD hybrid data for
four years (2008–2012) [8]. The evolution of the average Xmax
with energy is shown with the MC simulation in the energy
range of 1018.2 to 1019.6 eV in Figure 11. The MD hybrid data
are in agreement with the proton prediction.

1200

2

2
0
400

600
800 1000
Xmax [g/cm 2]

19.4 - 19.6

3

Fig. 8. The TA combined monocular FD spectrum, TA combined hybrid spectrum, and TA SD spectrum (preliminary).

0
400

750

45
24

59

61

24

7
11

51

700
650
600
18

18.2 18.4 18.6 18.8 19 19.2 19.4 19.6 19.8
log(E/eV)20

Fig. 10. The preliminary average reconstructed Xmax (black points) as
a function of energy for the TA stereo data. The red lines are thepure proton predictions with three interaction models: QGSJET-01(solid line), QGSJET-II-03 (dot-dash line), and SYBILL (dottedline). The blue lines show the iron predictions.

CL upper limits on the photon fluxes are 0.019, 0.0097, and
0.0071 km−2 sr−1 yr−1 @ for Eγ > 1019 , 1019.5 and 1020 eV,
respectively.
Search for Ultra-high-energy Neutrinos
Neutrino-induced showers are expected to produce young
showers for all zenith angles. For each event, we count the
total number of peaks in SD waveforms over the upper andlower layers of all detectors. Very inclined hadronic showers
are old, and contain mostly muons. These propagate recti-

Data<Xmax>
Proton MC
Iron MC

1100
1000
900
800

7

5
4
3

700

2

600

1

500

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data

6

peaks / layer

XMAX [g/cm2]

30

ν

0
18

18.5

19

19.5

20
20.5
log E (eV)10Fig. 11. The preliminary result of Xmax vs. energy for the TA MD-hybrid
data. The gray points show the distribution of Xmax measurementsof the data as a function of energy. The black points with error
bars are the average Xmax measurements of the data for the various energy slices. The red line is the pure proton prediction withQGSJET-II-03 model. The blue line is the iron prediction.

Linsley curvature parameter

Fig. 12. Linsley curvature parameter distribution for zenith angle region between 45◦ and 60◦ for reconstructed Eγ > 1019 eV. Black
points refer to the data and the red histogram represents a photon
MC simulation with E−2 spectrum.

linearly, producing mostly single-peaked waveforms. On thecontrary, young showers produce long, indented waveforms.
Figure 13 shows the number of peaks per layer versus zenith
angle for the TA 5-year data [13]. There are no apparent neutrino candidates in the data set. We define the percentile rankof the number of peaks per layer for neutrino primaries, andobtain the following preliminary differential flux limit at 1020
eV: E2 Φνe < 5×10−5 GeV cm−2 s−1 sr−1 (90% CL).
Anisotropy in Arrival Directions of UHECRs
We have published an analysis of UHECRs for correlations with Active Galactic Nuclei (AGNs), as well as for autocorrelations and correlations with the LSS for a 40-month TAdata set [14]. Here, we update the anisotropy results using thefull 5-year TA data, which contains 2130 events with E > 1019
eV, 132 events with E > 4×1019 eV, and 52 events with E >5.7×1019 eV for zenith angles below 55◦ for autocorrelationsand LSS correlations. There are 42 events with E > 5.7×1019

10

20

30

40
50
60
Zenith angle

70

80

90

Fig. 13. The number of peaks per layer in the TA data set. Young
inclined neutrino-induced showers are expected to lie within thecircle.

eV for zenith angles below 45◦ for AGN correlations [15, 16].
For the 40-month TA data set, we published the result of thesearch for the correlations of the arrival directions of UHECRs
with extragalactic objects for several catalogs [17].
Correlations with AGNs
Auger reported correlations between the arrival directionsof UHECRs with E > 5.7×1019 eV and the positions of nearby
AGNs from the Véron 2006 catalog with 0< z ≤0.018 in2007 [18]. They reported the probability that correlations forangular separations of less than 3.1◦ occurred by chance is
1.7×10−3 . The number of correlating events was 9 out of 13,
which is about 69%. The Auger analysis has been updated,
and it was found that the number of correlating events was 21
out of 55, which corresponds to about 38% of events [19].
We searched for AGN correlations using the same requirements as Auger, and found 17 correlating events (40%) out of
42 total events with E > 5.7×1019 eV . The number of random coincidences expected for this total number of events is
10. Using a binomial distribution with a single-event correlation probability of piso = 0.24, the probability of this excess
occurring by chance is 1.4%, assuming an isotropic distribution.
Autocorrelations
Figure 14 shows the dependence of the p-value, P(δ ), on
the pair separation angle, δ , for events with zenith angles below 55◦ for two energy thresholds: 4×1019 eV and 5.7×1019
eV. There is no excess of small-scale clusters. For energies
above 5.7×1019 eV, there is a hint of some grouping of eventsat angular scales with a minimum p-value of about 0.2% in
the angular range between 20◦ and 30◦ .
Correlations with LSS
We use galaxies at distances of 5 to 250 Mpc and with Ks
magnitudes of less than 12.5 in the 2MASS Galaxy Redshift
Catalog (XSCz) [20]. This catalog provides the most accurate information about the three-dimensional distribution ofgalaxies. We assume that UHECRs are protons, and that the31
1

E > 40 EeV

P(δ )

0.1

1e−2

E > 57 EeV
1e−3
0

20

40

60

80

100

120

140

160

180

δ
Fig. 14. The dependence of the p-value, P(δ ), on the pair separation
angle, δ , for two energy thresholds: 4×1019 eV and 5.7×1019 eV(upper blue and lower red lines, respectively).

effects of galactic and extragalactic magnetic fields on each arrival direction can be approximated by a Gaussian probability
density function with an angular resolution (called a smearing angle) of θ , which is treated as a free parameter. The
data above 5.7×1019 eV is compatible with the LSS model,of which p-value is about 10%, and is incompatible with theisotropy model, of which p-value is about 0.1% at a smearing
angle of 6◦ .
Hotspot for highest-energy cosmic rays
We search for intermediate-scale anisotropy of cosmic-ray
events with energy greater than 5.7×1019 eV [21]. Here weuse the event selection somewhat looser than the above analyses in order to increase the number of events with maintaining
reasonable energy and angular resolution. By the looser cuts,of which major change is abolishing the cut of the SD arrayedge, we obtain 72 cosmic-ray events. Figure 15 (a) shows asky map in equatorial coordinates of these events. A clusterof events that we call a “hotspot” appears in this map centerednear right ascension ∼150◦ and declination ∼40◦ , with a diameter of ∼30◦ to 40◦ . In order to estimate the significance of
this hotspot, we use oversampling with a 20◦ radius. Figure 15(b) shows a significance map of the events above 5.7×1019 eV.
The maximum excess in our Field-of-View (FoV) appears as
a hotspot centered at right ascension of 146.7◦ and declinationof 43.2◦ with a statistical significance of 5.1σ (the number ofobserved events = 19, and the number of events expected in
an isotropic cosmic-ray sky = 4.49). The probability of such a
hotspot appearing by chance in an isotropic cosmic-ray sky isestimated to be 3.7×10−4 (3.4σ ).
Search for point-like sources and large-scale anisotropy ataround EeV
We search for steady point-like sources of neutral particles
around EeV energy observed by the TA SD [22]. The airshower reconstruction and data selection are optimized for the
EeV air showers. The number of air showers above 0.5 EeV isincreased by ∼10 times, which corresponds to 172,125 events,
after the optimization. In order to search for the point-likesources, the Equi-Zenith Angle method is adopted to these
cosmic-ray air showers taken by the TA SD during the period

Fig. 15. Aitoff projection of the UHECR maps in equatorial coordinates. The solid curves indicate the galactic plane (GP) and supergalactic plane (SGP). Our FoV is defined as the region above
the dashed curve at declination of −10◦ . (a) The points show thedirections of the UHECRs with E > 5.7 × 1019 eV observed by the
TA SD array, and the closed and open stars indicate the Galactic
center (GC) and the anti-Galactic center (Anti-GC), respectively.
(b) Significance map using oversampling with a 20◦ radius. Color
scale denotes significance value.

between 2008 May and 2011 October. As a result, we findoverall no significant excess above 0.5 EeV in the northernsky. Hence, we set upper limits at 95% C.L. on the neutron
flux, which is an averaged flux 0.067 km−2 yr−1 above 1 EeV
in the northern sky. This is the most stringent flux upper limit
in the northern sky survey assuming the point-like sources.
We search also for the large-scale cosmic-ray anisotropy
in the energy region between 1018.0 eV and 1018.4 eV basedon the dataset taken during the period between 2008 May and2012 October [23]. The number of analyzed air shower events
is approximately 1.6 times larger than that of the AGASA observation which claimed the presence of the large-scale anisotropies before. In order to estimate the significance, we use
oversampling with a 20◦ radius. We find no such excesses ordeficit in the TA SD data.
TA SD burst events in association with lightning
By SD shower trigger, we record events that are detectedby not less than three neighboring SDs, of which trigger rateis ∼5×10−3 per second. Contrarily to this average triggerrate, we detected 10 bursts that consisted of not less than three
events recorded by SD shower triggers generated within 1 millisecond in the 5-year SD data. The chance probability ofobtaining such burst event rate was 10−4 . The SDs of each
event spread over up to about 10 km2 . Some events were reconstructed using cosmic-ray air-shower reconstruction program, and we found some differences of the event characteristics from the usual air-shower events induced by cosmic rays.

32

And we observed temporal and spatial correlations between
the burst events and lightning. Figure 16 shows a burst example with reconstructed SD events in association with lightning.

Burst 120706 014911

Height above
ground (m)at 3000 m

North

184307Ps

Intra-cloud

Y (m)184122us

South

300 m
Reconstructedaxis of TA event
Core position(on the ground)of TA events

184219Ps

X (m)

West

mentioned fluorescence spectrum is normalized to the yieldmeasured by Kakimoto et al. [25]. This model is used in theanalysis of air showers by the TA. The second is a combinedmodel for air fluorescence yield [26] proposed by the dedicated working group of the UHECR2012 symposium [27].
This model adopts the fluorescence spectrum measured by
AIRFLY. This spectrum is normalized for the air fluorescence
yield at 337 nm measured by AIRFLY [28].
The air fluorescence yield is measured by comparing the
ELS data with the MC simulation. The average fluorescence
yield ratios of the data to the MC simulation for the first andsecond models were presented at ICRC2013 [29] and the updated preliminary results are 1.18 ± 0.01 (stat) ± 0.18 (sys)and 0.96 ± 0.01 (stat) ± 0.15 (sys).
In addition, the ELS is being used by groups from aroundthe world to calibrate a new telescope that is under development [36], and to search for radio signals from cosmic ray
showers. Several groups are searching for molecular bremsstrahlung signals [30, 31] and radar echoes.

East
1 km

Fig. 16. Geometrical information of reconstructed SD events in the
burst at 01 hr. 49 min. 11 sec. on July 6 in 2012 UTC in association with lightning. The vertical and horizontal axes show thenorth-south and east-west directions, respectively. The unit of thecoordinates is meter, and the values are measured from the Central Laser Facility (CLF) in the TA site. The blue circle with 300-m
radius denotes median location error of the lightning flash and theblue cross mark is its measured position provided by the National
Lightning Detection Network (NLDN) in US. The red points denote the core positions on the ground of the two reconstructed SD
events. The axes show the directions of the two reconstructed
showers. The blue ends show the x-y positions at 3,000 m above
ground level. The six digits of three values in µsec correspond to
the timing of the lightning flash and two SD events.

TA and Auger Joint Studies
The TA and Auger collaborations began a program of joint
studies in order to understand the differences of the TA andAuger results for the energy spectrum, Xmax , and arrival directions. The following progress reports were presented at
ICRC2013 [32]:• The light source developed by the Auger collaboration
was brought to the TA site and measured by the TA FD
in 2012 and 2013.
• A large-scale anisotropy result with full sky coverageusing the TA and Auger data above 1×1019 eV was reported by developing a method to combine the two data
sets.

Prospects
We present preliminary results from the ELS, and outline
the status of joint studies by the TA and Auger collaborations.
We also describe extensions, proposals, and R&D of future
detectors.

• The Xmax analysis of ad hoc data that is compatible with
the Auger composition model via TA reconstruction is
being studied in order to know how well the TA detector distinguishes between the Auger mixed composition
and the pure proton composition.

The Electron Light Source: Measurement of Fluorescence
Yield
The basic idea of the end-to-end calibration of the FD with
the ELS is to compare measured ADC values with those froma MC simulation, and then correct the MC simulation for thedifference from the data, which affects the energy scale. The
beam energy is measured with an accuracy of less than 1%
using a bending magnet. We worked for the precise measurement of the beam charge using a Faraday cup, and checked therelevant geometry with GEANT4 simulation. The first step ofcalibrating the TA FD using the ELS involves measuring the
air fluorescence yield. This requires all of the FD calibration
parameters. For this purpose, we select the following two air
fluorescence models described.
The first model uses a fluorescence spectrum measured
by the FLASH experiment [24] for 300–420 nm. The fluorescence yield integrated over 300–400 nm in the above-

Low Energy Extension
The TA Low Energy Extension (TALE) will enable detailed studies of the energy spectrum and composition from1016.5 eV upwards. Previous experiments reported the second
knee in the cosmic-ray spectrum around the 1017 -eV decade.
The energy scales of these detectors differed by about a factorof two, so the energy at which this spectral break occurs isquite uncertain. There is a possibility that the transition fromgalactic cosmic rays to extragalactic cosmic rays occurs in thisenergy region. Thus we expect to observe the transition fromheavier to lighter composition. A 14-TeV center-of-mass collision at the LHC corresponds to a proton of about 1017 eVcolliding with another proton at rest. The cosmic-ray data observed by TALE could be compared with the air shower MC
simulation tuned by the results of the LHC experiments.
Ten additional TALE FDs view 31◦ –59◦ in elevation angle, and are constructed from refurbished HiRes-II telescopes.

33

The TALE infill SD array consists of approximately 100 scintillation counters, which are identical to those of the TA SD
array. These counters have graded spacings, ranging from 400
m near the FD to 600 m further away, which merge with the
TA SD array at its northwestern corner. The TALE FD operation was commenced in the spring of 2013. About one thirdof the surface detectors were deployed at this time. Figure 17
shows an air shower event recorded with the combined TA
MD and TALE FDs, and TALE SDs.
The Non-Imaging CHErenkov (NICHE) array is proposed
to cover an energy range of 1015.8 to 1018 eV [33]. With anarray of simple Cherenkov counters (PMTs looking upwards)
deployed within the TALE infill array, we can use counter timing to reconstruct the shower geometry, counter pulse heights
to reconstruct the shower energy, and counter signal widths toreconstruct Xmax .
TA×4 proposal
The TA result is consistent with the proton LSS modelwith GZK suppression, and there are some indications of anisotropy of arrival directions of highest-energy cosmic rays at alevel of 3σ . Based on this picture, we propose TA×4, whichquadruples the SD array by building additional 500 countersof the current TA SD design, and deploying them in a squaregrid with 2.08-km spacing [34]. Including the existing TA SD,
this array would reach an overall design size of ∼3000 km2 .
The new array would need an FD overlooking it to confirm
the energy scale and increase the number of hybrid events.
This FD will be formed from additional reconditioned HiRes
telescopes. The layout of TA×4 is shown in Figure 18. Assuming two-year construction and three-year observation for
additional SD array and FD and five-year observation by thecurrent TA, we expect the equivalent of 20 and 14 years of TA
SD and hybrid exposures, respectively, by adding the 6-year
data recorded so far, After five years, the recorded data will
clarify anisotropy of arrival directions of highest-energy cosmic rays, which can be originated from the matter structure
or extreme phenomena in the nearby universe, with a significance greater than 5σ if the correlation continues at the current level.
R&D for future detectors with larger aperture
To collect much better statistics at the highest energies,
significantly larger detectors are needed to identify sources
via anisotropy studies. Because of the prohibitive cost, it may
be difficult to build a sufficiently large detector using existing
technologies. Hence, it is important to explore new detection
techniques.
It is advantageous that the FD on the ground detects air
showers at a distance, but the FD has only a 10% duty cycle. Radio echoes from EASs have not been proven to be a
successful technology. The TA RAdar Experiment (TARA)
provides a controlled test of the bistatic radar technique, andis now operating a 40-kW transmitter at 54.1 MHz in the TA
site, with receivers located 40 km away, west of the SD [35].
This project aims to look for coincidences between radar signals and either the SD or FD of TA.

Fig. 17. An air shower event recorded with the combined TA MD and
TALE FDs, and TALE SDs. In the first panel, the top two cameras correspond to the TALE and the bottom two cameras correspond to the TA MD. The circles represent the PMTs that were hit,
whereas the points represent PMTs that were not hit. The solidline shows the reconstructed shower-detector plane. The second
panel shows the corresponding SD hit map. The arrow and thecross point denote the arrival direction and the core position of thereconstructed shower, respectively.

JEM-EUSO is a new type of observatory that will utilize
very large volumes of the earth’s atmosphere as a detector of
the highest-energy cosmic rays in the Universe. It will bemounted to the International Space Station (ISS) at an altitudeof approximately 400 km. The sensor is a very wide-field,
very fast, and large telescope, and observes brief UV flashes inthe earth’s atmosphere caused by highest-energy cosmic rays.
In ICRR, we preliminarily set up the calibration system ofMulti-Anode PMTs (MAPMT) which will be used at the focal
surface detector of JEM-EUSO [36]. The test of JEM-EUSO
prototype is been performed at a TA FD site.

34

Additional SD
for TAx4
TALE FDTA MD FDTALE SD

For the future detectors with larger aperture,the R&D of
a new technology investigating the detection of radio echoesfrom EASs (TARA) and JEM-EUSO prototype test are been
performed in the TA site. The preliminary calibration test of
JEM-EUSO MAPMTs has just started in ICRR.

Bibliography[1] T. Abu-Zayyad et al., Astrophys. J. Lett. 768 (2013) L1(5pp).

TA LR FD

[2] K. Greisen, Phys. Rev. Lett. 16 (1966) 748-750.
[3] G.T. Zatsepin and V.A. Kuz’min, JETP Lett. 4 (1966) 7880.

TA SD

TA BR FD

Additional FD
for TAx4[4] O.E. Kalashev and E. Kido, arXiv:1406.0735 [astroph.HE].
[5] A. Aab et al., arXiv:1307.5059.
[6] T. Abu-Zayyad et al., Astropart. Phys. 48 (2013) 16-24.

Fig. 18. The layout of the proposed TA×4. The array of 507 SDs(red filled circles inside a blue closed curve) is the current TA SD
array. There are three TA FD stations (MD to the north, LR to thewest, and BRM to the east of the TA array). The array of surface
detectors (yellow filled circles inside an orange closed curve) to thenorth of the TA SD array is the TALE SD array. An additional arrayof 500 surface detectors (rouge filled circles inside a red curve)
for TA×4 is located to the east of the TA SD array. An additional
FD station with refurbished HiRes telescopes for TA×4 is locatedat the BRM FD site and views to the southeast as denoted by reddashed lines.

[7] D. Ikeda et al., ICRC 2013 #0358.
[8] M. Allen et al., ICRC 2013 #0794.
[9] D. Bergman et al., ICRC 2013 #0221.
[10] R.U. Abbasi et al., Phys. Rev. Lett. 104 (2010) 161101.
[11] Y. Tameda et al., ICRC 2013, #0512.
[12] T. Abu-Zayyad et al., Phys. Rev. D 88 (2013) 112005.

Summary
The TA confirmed flux suppression above 5.68 × 1019 eV,
which is consistent with the GZK suppression expected for
protons, with a statistical significance of 5.74σ and the ankle
at 5.04 × 1018 eV. The preliminary Xmax measurement above
1018.2 eV is consistent with QGSJET-II-03 proton model. We
found an indication of a cluster of cosmic rays with energy
greater than 5.7×1019 eV by oversampling using 20◦ -radius
circles. Its significance appearing in an isotropic cosmic-ray
sky is 3.7×10−4 (3.4σ ). Analyses of these highest-energy
cosmic-ray arrival directions for correlations with AGNs, correlations with the LSS proton model, and autocorrelation showa hint of anisotropy at a level of 2σ to 3σ .
The TA results suggest that anisotropy of arrival directionsof highest-energy cosmic rays could be related to the matter
distribution or extreme phenomena in the nearby universe. We
propose to build TA×4, an extension of the SD area by a factor
of four and one FD station. After five years, the expanded
array will provide 20 years of TA SD data and 14 years ofTA hybrid data by adding 6 years of TA data taken before
TA×4. The signal at a level of 3σ in the current anisotropy
studies is expected to result in an observation at more than 5σ .
And we will have more events for the measurement of energy
spectrum and Xmax .
TA, TALE, and the proposed TA×4 and NICHE will provide important measurements of the spectrum, composition,
and anisotropy from the knee region up over five decades inenergy, with a single energy scale calibrated with the ELS.

[13] G. Rubtsov et al., ICRC 2013, #0149.
[14] T. Abu-Zayyad et al., Astrophys. J. 757 (2012) 26(11pp).
[15] P. Tinyakov et al., ICRC 2013, #0935.
[16] P. Tinyakov et al., ICRC 2013, #1033.
[17] T. Abu-Zayyad et akl., Astrophys. J. 777 (2013) 88(8pp).
[18] J. Abraham et al., Science 318 (2007) 939; J. Abraham
et al., Astropart. Phys. 29 (2008) 188-204.
[19] P. Abreu et al., Astropart. Phys. 34 (2010) 315-326.
[20] T. Jarrett, arXiv:astro-ph/0405069.
[21] R.U. Abbasi et al., Astrophys. J. Lett. 790 (2014) 21.
[22] K. Kawata et al., ICRC 2013, #0310.
[23] K. Kawata et al., ICRC 2013, #0311.
[24] R. Abbasi et al., Astrophys. J. 29 (2008) 77.
[25] F. Kakimoto et al., Nucl. Instrum. and Meth. Phys. Res.
A 372 (1996) 527.
[26] B. Keihauer et al., arXiv:1210.1319.

35
Tibet III Air Shower Array (2003)[27] http://www.epj-conferences.org/
index.php?option=com_toc&url/articles/epjconf/abs/2013/14/contents/
contents.html

36,900 m2[28] M. Ave et al., Astropart. Phys. 42 (2013) 90.
[29] T. Shibata et al., ICRC 2013, #0507.
[30] R. Engel et al., ICRC 2013, #1200.
[31] T. Yamamoto et al., ICRC 2013, #1003.
[32] T. Abu-Zayyad et al., arXiv:1310.0647 [astro-ph.HE].
[33] J. Krizmanic et al., ICRC 2013, #0365.
[34] H. Sagawa et al., ICRC 2013, #0121.
[35] J. Belz et al., ICRC 2013 #1192.
[36] M. Casolino et al. ICRC 2013, #1213.
15 m

FT Detector (512)FT Detector w/ D−PMT(249)
Density Detector (28)789 detectors

Tibet ASγ Project[Spokespersons : M. Takita]
ICRR, The Univ. of Tokyo, Kashiawa, Chiba 277-8582

Experiment
The Tibet air shower experiment has been successfully operated at Yangbajing (90◦ 31’ E, 30◦ 06’ N; 4300 m above sea
level) in Tibet, China since 1990. It has continuously made awide field-of-view (approximately 2 steradian) observation ofcosmic rays and gamma rays in the northen sky.
The Tibet I array was constructed in 1990 and it was gradually upgraded to the Tibet II by 1994 which consisted of
185 fast-timing (FT) scintillation counters placed on a 15 m
square grid covering 36,900 m2 , and 36 density (D) countersaround the FT-counter array. Each counter has a plastic scintillator plate of 0.5 m2 in area and 3 cm in thickness. All
the FT counters are equipped with a fast-timing 2-inch-indiameter photomultiplier tube (FT-PMT), and 52 out of 185
FT counters are also equipped with a wide dynamic range 1.5inch-indiameter PMT (D-PMT) by which we measure up to
500 particles which saturates FT-PMT output, and all the Dcounters have a D-PMT. A 0.5 cm thick lead plate is put on the
top of each counter in order to increase the counter sensitivity by converting gamma rays into electron-positron pairs inan electromagnetic shower. The mode energy of the triggered
events in Tibet II is 10 TeV.
In 1996, we added 77 FT counters with a 7.5 m lattice interval to a 5,200 m2 area inside the northern part of the Tibet II
array. We called this high-density array Tibet HD. The modeenergy of the triggered events in Tibet HD is a few TeV.
In the late fall of 1999, the array was further upgraded byadding 235 FT-counters so as to enlarge the high-density areafrom 5,200 m2 to 22,050 m2 , and we call this array and further
upgraded one Tibet III. In 2002, all of the 36,900 m2 area wasFig. 19. Schematic view of Tibet III.

covered by the high-density array by adding 200 FT-countersmore. Finally we set up 56 FT-counters around the 36,900 m2
high density array and equipped 8 D-counters with FT-PMT
in 2003. At present, the Tibet air shower array consists of 761
FT-counters (249 of which have a D-PMT) and 28 D-counters
as in Fig. 19.
The performance of the Tibet air shower array has been
well examined by observing the Moon’s shadow (approximately 0.5 degrees in diameter) in cosmic rays. The deficit
map of cosmic rays around the Moon demonstrates the angular resolution to be around 0.9◦ at a few TeV for the Tibet III
array. The pointing error is estimated to be better than ∼0.01◦ ,as shown in Fig. 20, by displacement of the shadow’s centerfrom the apparent center in the north-south direction, as theeast-west component of the geomagnetic field is very small at
the experimental site. On the other hand, the shadow center
displacement in the east-west direction due to the geomagnetic field enables us to spectroscopically estimate the energy
scale uncertainty at ±12 % level, as shown in Fig. 21. Thus,
the Tibet air shower experiment introduces a new method forenergy scale calibration other than the conventional estimation by the difference between the measured cosmic-ray flux
by an air shower experiment and the higher-energy extrapolation of cosmic-ray flux measured by direct measurements bybaloon-borne or satellite experiments.
Physics Results
Our current research theme is classified into 4 categories:(1) TeV celestial gamma-ray point/diffuse sources,(2) Chemical composition and energy spectrum of primarycosmic rays in the knee energy region,

Sunspot number

36

North

Energy (TeV) / Z
0.1

2.94 4.20 6.46 11.4

21.6

45.4

0

180

a

140
100
60
20

South

Sun’s shadow
Deficit (%)

−0.1
−0.2
−0.3
−0.4

Moon’s shadow
Deficit (%)

Displacement (degrees)

−1

Data
MC

−0.5

Data Best fit

100

1000

Fig. 20. From [1]. The Moon’s shadow center displacement fromthe apparent position in the north-south direction as a function ofenergy, observed by Tibet III.

Energy (TeV) / Z
East
Displacement (degrees)West

2.94 4.20 6.46 11.4

21.6

PFSS Rss=2.5R
CSSS Rss=2.5R
CSSS Rss=10R

−5
−6
−1

c

−2
−3
−4
−5
−6
1998

2000

2002

2004

2006

2008

2010

−0.1
−0.2
−0.3
−0.4

Data
MC
MC Best fit
MC +−10%

−0.5
−0.6
100

Fig. 23. From Ref. [2]. Temporal variations of (a) the monthly meansunspot number, (b) the deficit intensity due to the Sun’s shadowand (c) the deficit intensity due to the Moon’s shadow. The open
squares in the panel (b) are the observed central deficit (Dobs ). The
blue triangles, green squares and red circles indicate the central
deficits (DMC ) by the MC simulations assuming the PFSS (Rss =2.5RJ ), the CSSS (Rss = 2.5RJ ) and the CSSS (Rss = 10.0RJ )models, respectively. The dashed lines in the panels (b) and (c)are the deficits expected from the apparent angular size of the Sun
and the Moon.

45.4

0

−0.7
10

−4

Year

Σρ FT

0.1

−3

1996

−0.6
−0.7
10

b

−2

1000

Σρ FT
Fig. 21. From [1]. The Moon’s shadow center displacement from theapparent positionin the east-west direction as a function of energy,
observed by Tibet III.

(3) Cosmic-ray anisotropy in the multi-TeV region with highprecision,(4) Global 3-dimensional structure of the solar and interplanetary magnetic fields by observing the Sun’s shadow in cosmicrays.
We will introduce a part of the results obtained in this fiscal year.
An understanding of the structure of the Sun’s magnetic
field between it and the Earth is essential if humanity is to venture into space. However, it is extremely difficult to directly
observe the coronal magnetic structure within the Earth’s or-bit, and while spacecraft such as Voyager and Ulysses havecarried out some observations, the solar neighborhood is anextremely harsh environment characterized by high temperatures and high levels of radiation. Even the latest spacecraft
cannot get close to the Sun, and as a result our understandingof this region is limited.
The Tibet AS γ experiment observed the Sun’s shadow ofcosmic rays at 10 TeV energies from 1996 to 2009, created
when it shields galactic cosmic rays reaching the Earth, as isshown in Fig. 22.
The coronal magnetic field deflects these charged particles as they pass near the Sun, causing variation in the formof the Sun’s shadow. The analyzed data were recorded overthe 14-year period from 1996 to 2009, and a correlation was
discovered between the 11-year solar cycle and this variation,
as shown in Fig. 23. The stable size of the Moon’s shadow incosmic rays over the same period demonstrates that the systematic uncertainty is negligible.
We have also developed and performed numerical simulations of the Sun’s shadow in galactive cosmic rays, based on
two major coronal magnetic field models - the Potential Field
Source Surface (PFSS), and the Current Sheet Source Surface(CSSS). The PFSS model leaves out the effect of the electric
current in the vicinity of the Sun on the structure of the coronal magnetic field, while the CSSS model assumes the effectof the electric current. The magnetic field lines near the Sun
are drawn in Fig. 24 in both cases.
The simulation of the trajectories of galactic cosmic rays
based on the two models found that the CSSS model better
describes the size variation of the Sun’s shadow, as shown in
Fig. 23.
This is the world’s first and most successful analysis of
the coronal magnetic structure using the data obtained by theobservation of the cosmic ray shadow of the Sun. This re-North

2

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1
0

South

GSE latitude (deg.)

37

−1

−2
2

1

East

0

−1

−2

West

GSE longitude (deg.)−6.0 −5.0 −4.0 −3.0 −2.0 −1.00

Dobs (%)

Fig. 22. From Ref. [2]. Year-to-year variation of the observed Sun’s shadow between 1996 and 2009. Each panel displays a 2 dimensional
contour map of the observed flux deficit (Dobs ).The map in 2006 is omitted because of insufficient statistics for drawing a map.

Physical Review Letters (PRL) in 2013. The American Physical Society (APS) also featured this paper on its website withshort summary: Synopsis: Catching Rays in the Sun’ Shadow.

a
PFSS

b
CSSS

Other Activities
The emulsion-pouring facilities can meet the demands formaking any kind of nuclear emulsion plates which are used
for cosmic ray or accelerator experiments. The thermostatic
emulsion-processing facilities are operated in order to develop
nuclear emulsion plates or X-ray films. Using these facilities, it is also possible to make and develop emulsion pellicles in 600-micron thickness each. In this way, these facilities
have been open to all the qualified scientists who want to carryout joint research programs successfully. Of recent, however,the shrinking demand for the facilities let us decide that weshould suspend calls for joint research programs to utilize theemulsion-pouring facilities, starting from 2012.

Future Plans(1) Chemical composition of primary cosmic rays making theknee in the all-particel energy spectrum
Fig. 24. From Ref. [2]. Magnetic field line structures calculated using (a) the PFSS model and (b) the CSSS model in CR1910 (Year1996), in a region between the photosphere and the source surface at 2.5RJ , represented by the inner and outer spheres, respectively. The red (blue) lines represent the field lines directing
away from (toward) the photosphere.

search provides a new approach to exploring the Sun’s magnetic structure and, with future increased in accuracy, should
provide even more detailed knowledge of the magnetic filed
between the Sun and the Earth. This research employed thephenomenon that the path of charged cosmic rays is bent when
it passes through a magnetic field, and was made possible by
the long-term accumulation of cosmic radiation data over a
period of 14 years, and is a major step forward in the longterm observation of cosmic radiation. The paper from thisresult was highlighted as one of the “Editor’s Suggestions” in

We have measured the energy spectra of primary cosmicray protons, heliums, all particles around the knee energy region. The main component responsible for making the knee
structure in the all particle energy spectrum is heavier nulei
than helium. The next step is to identify the chemical component making the knee in the all particle energy spectrum. We
have a plan to install an Yangbajing Air shower Core detector
array (YAC) around the center of Tibet III to distinguish thechemical component making the knee. We completed construction of YAC2 (∼100 detectors over ∼160m2 in area), as
is shown in Fig. 25, and started data-taking in March 2013.
YAC2 aims at mainly studying the energy specta of protonand helium components in the knee energy region.
Currently, we are planning to set up YAC3 (∼400 detectors over ∼5000m2 in area) to measure the iron flux in theknee energy region.

38

Fig. 25. YAC2 set up at Yangbajing.

(2) Gamma-ray astronomy in the 100 TeV region

Fig. 26. Tibet AS + MD (red curve) integral flux sensitivity (5σ or 10
events/1yr) for a point source.

We have a plan[3] to construct a large (∼ 10, 000 m2 ×1.5m
deep) underground (∼ 2.5 m soil+concrete overburden) water Cherenkov muon detector array (Tibet MD) around an extended version (Tibet AS, ∼83,000 m2 ) of Tibet III. By Tibet AS + MD, we aim at background-free detection of celestial point-source gamma rays in the 100 TeV region (10 TeV –1000 TeV) with world-best sensitivity and at locating the origins of cosmic rays accelerated up to the knee energy region
in the northern sky. The measurement of cut off energies inthe energy spectra of such gamma rays in the 100 TeV region
may contribute significantly to understanding of the cosmicray acceleration limit at SNRs. Search for extremely diffuse
gamma-ray sources by Tibet AS + MD, for example, fromthe galactic plane or from the Cygnus region may be very intriguing as well. Above 100 TeV, the angular resolution of
Tibet AS with 2-steradian wide field of view is 0.2◦ and thehadron rejection power of Tibet MD is 1/10000. The proposed
Tibet AS + MD, demonstrated in Fig. 26, has the world-best
sensitivity in the 100 TeV region, superior to HESS above 10- Fig. 27. The 5 shaded squares represent the constructed 5 MD pools.
20 TeV and to CTA above 30-40 TeV.
In addition to unknown point-like sources, we expect to sonably.
detect established sources in the 100 TeV region: TeV J2032
In March 2013, construction of 5/12 of the full-scale MD,+ 4130, HESS J1837-069, Crab, MGRO J2019+37, MGRO as is shown in Fig. 27, was successfully completed and dataJ1908+06, Milagro candidate sources, Mrk421, Mrk501 are taking started. One of the detector cell filled with water issufficiently detectable and Cas A, HESS J1834-087, LS I+63 303,demonstrated in Fig. 28
IC443 and M87 are marginal.
Furthermore, our integral flux sensitivity to diffuse gamma
rays will be the world-best as well. The diffuse gamma raysfrom the Cygnus region reported by the Milagro group and Bibliography
also diffuse gamma-rays from the galactic plane will be clearly Papers in refereed journals
detected. Diffuse gamma-rays of extragalacitic origin may be
an interesting target as well.
[1] “Multi-TeV Gamma-Ray Observation from the CrabIn fall, 2007, a prototype underground muon detector, comNebula Using the Tibet-III Air Shower Array Finely
posed of two 52m2 water pools, was successfully constructed
Tuned by the Cosmic-Ray Moon’s Shadow”, M.
in Tibet to demonstrate the technical feasibility, cost estimate,
Amenomori et al., Astrophysical Journal, 692 , 61-72
validity of our Monte Carlo simulation. Data analyses demon(2009).
strate that our MC simulation reproduces real data quite rea-39
7 Institute of Modern Physics, SouthWest Jiaotong University,

Chengdu 610031, China
8 Faculty of Engineering, Kanagawa University, Yokohama 2218686, Japan
9 Faculty of Education, Utsunomiya University, Utsunomiya
321-8505, Japan
10 Department of Physics, Konan University, Kobe 658-8501,
Japan
11 Research Institute for Science and Engineering, Waseda University, Tokyo 169-8555, Japan
12 Faculty of Engineering, Yokohama National University, Yokohama 240-8501, Japan
13 Department of Physics, Shinshu University, Matsumoto 3908621, Japan
Fig. 28. PMTs mounted in a MD cell filled with water.
14 Institute for Cosmic Ray Research, University of Tokyo,
Kashiwa 277-8582, Japan[2] “Probe of the Solar Magnetic Field Using the “Cosmic- 15 School of Information Science and Engineering, Shandong
Ray Shadow of the Sun”, M. Amenomori et al., Physical Agriculture University, Taian 271018, China
16 Saitama University, Saitama 338-8570, Japan
Review Letters, 111 , 011101-1-011101-5 (2013).
17 National Institute of Informatics, Tokyo 101-8430, Japan[3] “Exploration of a 100 TeV gamma-ray northern sky us- 18 Sakushin Gakuin University, Utsunomiya 321-3295, Japaning the Tibet air-shower array combined with an un- 19 Tokyo Metropolitan College of Industrial Technology, Tokyo
derground water-Cherenkov muon-detector array”, T.K. 116-8523, Japan
Sako et al., Astroparticle Physics, 32 , 177-184 (2009).
20 Max-Planck-Institut für Physik, München D-80805, Deutschland
21 College of Industrial Technology, Nihon University, Narashino
Papers in conference proceedings
275-8576, JapanThe Tibet ASγ Collaboration
22 Shonan Institute of Technology, Fujisawa 251-8511, Japan
1
2
3
4
2
M. Amenomori, X. J. Bi, D. Chen, T. L. Chen, W. Y. Chen, 23 Japan Atomic Energy Agency, Tokai-mura 319-1195, Japan
S. W. Cui,5 Danzengluobu,4 L. K. Ding,2 C. F. Feng,6 Zhaoyang 24 School of General Education, Shinshu University, MatsumotoFeng,2 Z. Y. Feng,7 Q. B. Gou,2 Y. Q. Guo,2 H. H. He,2 Z. T. He,5 390-8621, Japan
K. Hibino,8 N. Hotta,9 Haibing Hu,4 H. B. Hu,2 J. Huang,2
H. Y. Jia,7 L. Jiang,2 F. Kajino,10 K. Kasahara,11 Y. Katayose,12
C. Kato,13 K. Kawata,14 Labaciren,4 G. M. Le,2 A. F. Li,15,6,2
H. J. Li,4 W. J. Li,2,7 C. Liu,2 J. S. Liu,2 M. Y. Liu,4 H. Lu,2 The Ashra Project
X. R. Meng,4 K. Mizutani,11,16 K. Munakata,13 H. Nanjo,1M. Nishizawa,17 M. Ohnishi,14 I. Ohta,18 S. Ozawa,11
X. L. Qian,6,2 X. B. Qu,2 T. Saito,19 T. Y. Saito,20 M. Sakata,10 [Spokesperson: Makoto Sasaki]
T. K. Sako,12 J. Shao,2,6 M. Shibata,12 A. Shiomi,21 T. Shirai,8 ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
H. Sugimoto,22 M. Takita,14 Y. H. Tan,2 N. Tateyama,8 S. Torii,11 In collaboration with the members of:
H. Tsuchiya,23 S. Udo,8 H. Wang,2 H. R. Wu,2 L. Xue,6
ICRR, University of Tokyo, Kashiwa, Japan; Toho UniverY. Yamamoto,10 Z. Yang,2 S. Yasue,24 A. F. Yuan,4 T. Yuda,14 sity, Funabashi, Japan; University of Hawaii at Manoa, HonL. M. Zhai,2 H. M. Zhang,2 J. L. Zhang,2 X. Y. Zhang,6olulu, USA; University of Hawaii at Hilo, Hilo, USA; Nagoya
Y. Zhang,2 Yi Zhang,2 Ying Zhang,2 Zhaxisangzhu,4University, Nagoya, Japan; Kanagawa University, Yokohama,
X. X. Zhou7
Japan
1 Department of Physics, Hirosaki University, Hirosaki 036-

8561, Japan
2 Key Laboratory of Particle Astrophysics, Institute of HighEnergy Physics, Chinese Academy of Sciences, Beijing 100049,
China
3 National Astronomical Observatories, Chinese Academy of
Sciences, Beijing 100012, China
4 Department of Mathematics and Physics, Tibet University,
Lhasa 850000, China
5 Department of Physics, Hebei Normal University,
Shijiazhuang 050016, China
6 Department of Physics, Shandong University, Jinan 250100,
China

Overview
Ashra (All-sky Survey High Resolution Air-shower detector) [1, 2, 3, 4] is a project to build an unconventional opticaltelescope complex that images very wide field of view, covering 77% of the sky, yet with the angle resolution of a few
arcmin, sensitive to the blue to UV light with the use of image
intensifier and CMOS technology.
Detection of PeV-EeV neutrinos (ν’s) is direct evidence
for the acceleration of hadrons into the EeV range and ofphoto-pion interactions in a violent object such as GRBs[5].
The earth-skimming tau neutrino technique, which detects extensive air showers [6], has the advantage of providing a large

40Fig. 30. The Ashra main and sub stations at the Mauna Loa site (top),
and a light collector towards Mauna Kea (bottom).

target mass. The technique uses air shower produced by decay
particles of tau leptons in the atmosphere as the observed signal. The air shower emits intense Cherenkov lights in front,
which could be detected by the mountain or the ground faced
detector (Figure 29). The method is realized by Ashra-1 experiment [7]. The air shower also emits isotropic fluorescencelights. In order to enhance the tau neutrino detectability, thedetector should be capable of detecting fluorescence signal.
The observatory firstly consists of one main station having
12 detector units and two sub-stations having 8 and 4 detector
units. One detector unit has a few light collecting systems
with segmented mirrors. The main station and one of the sub
stations were constructed on Mauna Loa (3,300 m) on Hawaii
Island in 2007 as shown in Figure 30.
Since January 2012, we highly efficiently made physics
observation runs (Observation03) with triple types of triggers
for Cherenkov tau showers induced by earth-skimming tau
neutrinos, Cherenkov cosmic ray showers, and optical flashes
from transient objects like GRBs.

Vertical [deg]Fig. 29. Conceptual drawing of Cherenkov τ shower method. The
right mountain is Mauna Kea and the left is Mauna Loa.

B ' 13 mag, for which we expect 3-σ signals.
The split image is transported a trigger device via the 4mlong optical fiber bundle. The bundle is made of 500 µm φ optical fiber. 64 × 64 optical fibers are arranged to have 32mm ×32mm square cross section. Central position of each fiber isarranged according to 500 µm lattice within the accuracy ofless than 100µm. The transmittance is measured to be greaterthan 85% including coupling loss at each end of the fiber.
One end of the bundle is connected to multi-anode PMTs.
PMT signal is injected to the custom made trigger LSI . Each
LSI chip has 16 × 16 pixels, each size of those is 500 µm
× 500 µm. Total 4096 channels of 16 LSI chips are implemented on the ceramic board. In order to process different time scale lights, Cherenkov light and fluorescence light,
band-pass frequency of the filter is designed to be adjustableby external voltage. The threshold level on each pixel can bechosen from 8 levels to compensate pixel-to-pixel sensitivity
discrepancy.
“Wired OR” signal, summed signal of 64 pixels alongaxes, are sent to the FPGA based trigger circuit. Decisionof the first level Cherenkov trigger is based on geometricalcriteria. The aperture of one trigger pixel is ∼ 0.65◦ × 0.65◦ ,adjacent two of which well contain Cherenkov lights from an
air shower.

20
15
10
5
0
trajectory of GRB081203A-5-10

Ashra detector
All-sky survey high-resolution air-shower detector (Ashra)is designed to hold 77% of the entire night sky in the field ofview with a resolution of a few arcminutes. Ashra detector
is a complex of unconventional optical light collectors (LCs), each of those has 42◦ diameter field of view. An image ofthe optical collector is focused on the large electrostatic lens[8] followed by the image pipeline, which is shown in Figure 31. The image pipeline split and transport the image toboth a trigger device and a high-gain, high-resolution complementary metal-oxide semiconductor image sensor.
Ashra will acquire optical images every 1 second with 1second exposure without dead time. This enables us to explore
optical transients, possibly associated with gamma ray bursts(GRBs), flares of soft gamma-ray repeaters (SGRs), supernovae explosion, and so on, in so far as they are brighter than

-15
-20
-20

-15

-10

-5

0

5

10

15

20

Horizontal [deg]Fig. 31. Schematic view of Ashra image pipeline (top), trigger pixel
configuration in FOV (bottom left) and real image of triggered
200ns-expusure for an air-shower (bottom right).

The calibration chain is designed to obtain not only an
absolute energy scale to air shower measurement, but also
uniformed sensitivity over the large field of view (positional)
and in time (temporal). Environmental monitors systems, acloud monitor, weather monitors, a far Lider and a near Lidar have already been installed or are ready for installation.
Especially Ashra detector observes stars in the view every 1
second, which would give us an absolute calibration of thetransparency of atmosphere. LED flasher system was developed in order to obtain positional and temporal flat calibration

41of the detector sensitivity.
LED flasher is composed of a LED, a photo diode and optical lenses in a black box. Collimated light of λ = 405nm is
divided by a half mirror in two directions. One illuminates a
photo diode monitoring LED luminous intensity and the otherilluminates the input window of the photoelectric tube via off-focusing optical lenses. Thermal variations of LED luminosity and photo diode sensitivity were carefully studied using
a thermostatic chamber. LED luminosity variable coefficient(Photo diode output variable coefficient) was measured to be 0.21ppc/◦C( -0.07ppc/◦C ) in the temperature range from 35◦C
to 47◦C. Radiance uniformity was also measured to be sufficiently flat in the view; namely the variation was less than 1%.
Experiment and Observation
Experiment of the Cherenkov light trigger was carried out
at Ashra observational site on Mauna Loa in Hawaii. The trigger LSI module and the trigger board were installed on one
LC and a half of the PMT channels are read out in place ofold handmade discriminator module. The LC which dedicates
Mauna Kea and the above sky to the view allows to observe
the earth skimming tau neutrino and also extensive air showers. Pilot observation was carried out for a total of 44.4 hours
in 2008 December [5, 7] Data was also taken in the 3rd observation period from January 2012 to end of February 2013,
more than 1720 hours.
Arrays of trigger pixels and their aperture are shown in
the field of view of the detector (Figure 31). Cherenkov lightobservation was carried out using this trigger pixel configuration. In Figure 31, shown are the boundary (large red circle)
between the inside (open circle) and outside (hatched area) of
the FOV of the Ashra-1 light collector, which faces MaunaKea, and the layout of trigger pixel FOVs and blue boxes for
Cherenkov τ shower observation [7]. We repositioned arrayof the trigger pixel FOVs (upper blue boxes) to check the detection sensitivity with ordinary cosmic-ray air showers at ahigher elevation. Firing trigger pixels (thick blue boxes) of anobserved image of a cosmic-ray air shower readout along thetrigger (points) is overlaid. An extended portion of the trajectory of GRB081203A counterpart (circular arc), the segmentof this trajectory used in the ντ search (thick circular arc), theridge lines of Mauna Kea (red) and Mauna Loa (green) mountains, the horizon, and Mauna Kea access road are shown.
Observed cosmic-ray flux was consistent with Monte Carlosimulation in PeV to EeV region [7].
Gamma-ray bursts (GRBs) eject the most energetic outflows in the observed universe, with jets of material expanding relativistically into the surrounding interstellar matter witha Lorentz factor Γ of 100 or more. Energy dissipation processes involving nonthermal interactions between particles arethought to play an important role in GRBs. The GRB standard
model [9], which is based on internal/external shock acceleration, has been used to describe the general features of a GRB,
but the jet structure and particle acceleration details remain
observationally unresolved. In the context of the GRB standard model, the interaction of an expanding relativistic shellwith the intersteller medium (ISM) involves two shocks: theforward shock, which explains observed multi-wavelength afterglow, and the reverse shock, which is predicted to produce a

Satellite
Swift
Fermi
Fermi
Swift
Fermi
Swift
Fermi
Fermi
Fermi
Swift
Fermi
Swift
Fermi
Fermi

GRB Name
GRB081203A
GRB090428
GRB090429C
GRB091024
GRB100216A
GRB100906A
GRB120120
GRB120129
GRB120327
GRB120911
GRB121019
GRB121212A
GRB130206
GRB130215

tinFOV −t0 [sec]-1.2×104 – 5.6×103-8.1×103 – 5.9×103-4.1×103 – 1.7×103-1.6×103 – 3.3×102-4.0×103 – 1.1×104-1.0×104 – 4.0×103-1.4×103 – 8.9×103-1.6×103 – 6.7×103-9.9×103 – 8.2×101-2.4×104 – 6.8×101-1.7×103 – 7.3×103-5.8×103 – 2.6×104-3.3×103 – 7.5×104-2.7×103 – 4.3×102

Table 1. Summary of coincidence events with satellite GRB triggers[16, 17]. List of gold-plated events which must be observable geometrically within the FOV of our light collector at satellite triggers
during our observation time.

strong optical flash [10, 11]. The explanation of optical flashes
by the reverse shock has led to some estimates of the initial
Lorentz factor η [11, 12]. The presence of accelerated protons at the GRB site must be a reality. The detection of PeV–
EeV neutrinos (νs) from a GRB provides direct evidence forthe acceleration of hadrons into the EeV range, and of photopion interactions in the GRB. Even the non-detection of neutrino can provide valuable information about GRB’s key physical parameters such as the emission radius Rd , and the bulk
Lorentz factor Γ [13].
Ashra-1 acquires optical images every 1∼6 s with shortreadout deadtime. This enables us to explore optical transients, possibly associated with violent objects such as GRBs
in so far as they are brighter than B = 12 ∼ 13 mag, for which
we expect 3σ signals assuming 4 s exposure. The unique advantage is the on-time detection of the events without resorting to usual satellite alerts. In each detector unit FOV, 1∼2
events per year are expected in coincodence with the Swiftgamma-ray events. The total Ashra field of view that is wider
than satellite instruments allows to detect more optical transients, including an interesting possibility for an optical flash,not visble with gamma-rays.
The earth-skimming tau neutrino (ντ ) technique, which
detects extensive air showers [6], has the advantage of a large
target mass, since it uses air showers produced by decay particles of tau leptons (τs) in the atmosphere as the observed
signals. τs emerge out of the side of the mountain or the
ground facing the detector; they are the product of interactions
between VHE ντ and the earth matter they traverse. Above
1 EeV, air fluorescence observations based on the earth-skimming ντ technique have been reported [14]. Ashra-1 has reported the first observational search for ντ from a GRB basedon the earth-skimming ντ technique with air showers inducedby τ decays (hereafter referred to as the Cherenkov τ shower
method) [15]. It can achieve sufficient detection sensitivity in
the PeV–EeV region to be useful in the search for νs originating from hadrons accelerated to EeV at astronomical objects.

42

Additional advantages of the Cherenkov τ shower method are
its perfect shielding of cosmic-ray secondary particles, highly
precise arrival direction determination for primary ντ and negligible background contamination by atmospheric νs in the
PeV–EeV energy range.
Two of the Ashra-1 light collectors has been used for optical flash observation, of which FOV centers are in the direction of 60◦ (0◦ N) and 12◦ (22.5◦ N) in the elevation (azimuthal) angles respectively. We recorded more than 3 million
non-trigger reccuring images of the FOV of 0.83 sr for 5637 hr
of 1121 night runs between June 28 in 2008 and March 23 in
2013. The observation time corresponds to 20 % of all time Fig. 32. NTA Observatory layout (left) and NTA detector unit of foursame LCs (right).
without the shutdown period for the maintenance and 95 %of the maximum observable time defined by the solar and thelunar conditions where the altitudes of the sun and the moonmust be lower than -18◦ and 0◦ respectively with the moon
fraction less than 0.2.
To investigate GRB optical emission, we define three specific observational time domains with respect to satellite triggers; precursor (0<t0 -te <24 hr), prompt (ts <t0 <te ), and afterglow (0<ts -t0 <3 hr ) where t0 is a satellite trigger time, ts
is the time when the trajectry of the center position of GRB
counter part object triggered by the satellite enters into a FOVof an Ashra-1 light collector and te is the time when it ex17
its the FOV. Throughout the above observation time for op- Fig. 33. Simulated event with Eντ = 10 eV: (left) fluorescence track
image by Site0; (right) Cherenkov track image by Site1. Trigger
tical flashes and afterglows, we preselected and categolized
pixel and fine image FOV angles are 0.5◦ and 0.125◦ , respectively.
32 (86), 6 (21), and 1 (4) GRBs triggers by Swift (Fermi)
satellite, which were circulated through The Gamma-ray Coordinates Network (GCN) [16, 17], into the three time do- Prospects
mains respectively as optical transient cadidates. Futhermore,In this Ashra-1 experiment, we were performing device
we selected gold-plated samples of 14 prompt GRB candidate installation and specific observation in a step-by-step way toevents for our cross observation with Swift or Fermi satellites enhance the scientific impacts as shown in the previous secrequiring the events triggered are reported as trigger type of tions. We have already made a referee journal publication
GRB as summarized in Table1.
of PeV-EeV tau neutrino search [20] as important physics reOne of the Ashra light collectors built on Mauna Loa has sults with the Ashra-1 detector unit adding to publications on
the geometrical advantages of not only facing Mauna Kea, al- the detector or methodorogical developments and circulations
lowing it to encompass the large target mass of Mauna Kea in [8, 21, 22]. We are now preparing for a few physics publicathe observational FOV, but has also an appropriate distance tions from the optical observation data of the 2.5 years fromof ∼30 km from Mauna Kea, yielding good observational the Obs01 to Obs02 as well as keeping highly efficient obefficiency when imaging air-shower Cherenkov lights which servation runs in Obs03 for optical transients, VHE CRs andare directional with respect to the air-shower axis. Using the tau neutrinos. Adding that, the R&D for the direct Cherenkov
advanced features, we performed commissioning search for method applied to Ashra-1 has been granted and under develCherenkov τ showers for 197.1 hr between October and De- opment.
cember of 2008 and have already published [15]. We served
The planned full Ashra (Neutrino Telescope Array (NTA))
limited 62 channels of photomultiplier tubes (PMTs) as trig- observatory consists of four sites: Site0-3, as shown in Fig. 32
ger sensors prepared for the commissioning runs to cover the (left), with the x-y-z coordinates and corresponding FOV covview of the surface area of Mauna Kea, maximizing the trigger erage. Site1-3 form a 25 km triangle, observing the total air
efficiency for Cherenkov τ showers from Monte Carlo (MC) mass surrounded by Mauna Loa, Mauna Kea, and Hualalai.
study. Adjacent-two logic was adopted to trigger the fine The central Site0 has full-sky coverage. Each site has a group
imaging, by judging discriminated waveform signals from each of detector units each of which has several LC systems (Fig. 32
pixel of the multi-PMT trigger sensor. During the commis- (right)) instrumented with segmented mirrors. Performancesioning search period, ∼2 hr before the trigger of GRB081203A was studied based on Ashra-1 experience. Detailed design[21]. We accumulated nealy 44 million images with the air- studies for the NTA detector are currently underway.
shower Cherenkov light triggers for 1863 hr of 323 night runs
The z-axis points to zenith and y-axis points north, with zof the ντ search between January 12 in 2012 and March 23 in coordinates determined from topography data. Site1-3 are the2013.
vertices of an equilateral triangle of side length 25 km, with
Site0 at their geometric center. Site1 is located at ML-OS (onMauna Loa) and Site2 at 25 km distant from ML-OS in the
direction of the Kilohana Girl Scout Camp. To simulate the43performance of the Ashra NTA detector, we assume each LC
has 32◦ × 32◦ total FOV, 0.5◦ × 0.5◦ for trigger pixel FOV, and0.125◦ × 0.125◦ image sensor pixel FOV. The Site0 system
consist of 12 LCs in the lower, 8 LCs in the middle, and 4 LCs
in the higher elevation angle regions which together cover the
full-sky solid angle of 2π sr. The remaining sites have only
12 LCs in the lower elevation angle region covering π sr. The
bottom edge of the lower elevation angle region is defined tobe −9◦ (below the horizon).
In our simulation program, we take density profile of the
Earth, use the ντ distribution from CTEQ4 citeGandhi96, inelasticity parameter from [29], and parameterize energy loss
in Earth by citeTseng03,Dutta2001. We use τ decay fromTAUOLA and air-shower generation of Gaisser-Hillas + NKG[30]. We use a constant average ντ energy fraction of 40%(lab frame) from τ decays. The error from this approximation is found negligible. For detector simulation, we incorporate light collection and throughput with simplified triggering
logic. Event reconstruction is not yet implemented. All candidate events must satisfy the trigger conditions (1) numberof detected photoelectrons per LC > 61; (2) S/N estimatedin track-associated 4 pixels × 64 pixels box (air-shower track
included) >4 [31].
A simulated event with primary ντ energy Eντ = 1017 eV
consistent with the above conditions is shown in the r.h.s. ofFig. 33. The error for ντ arrival direction reconstruction is
0.08◦ . Fig. 34 shows estimated effective detection areas simulated for ντ from point source with azimuthal arrival direction. NTA can survey ντ point source objects with the bestyet sensitivity in the detection solid angle for ντ defined as−30◦ < θelev < 0◦ and 0◦ < φazi < 360◦ , and for 10 PeV <Eντ < 1 EeV. The location of NTA on Hawaii Island allows
us to survey the galactic center for more than several hundred
hours each year.

Further discussion on angular resolution and backgroundsimulation can be found in the LOI, which is to be published.
Preparation for Observation 4
We are now preparing for the fourth observation period(Obs04) as a next step during the long shutdown after the
Obs03 as well as proceeding several physics analysis streams
using observed data. The aim of the Obs04 is primarily acommissioning of Ashra-1 as a fluorescence detector for holizontal air-showers with good sensitivity and well establisheddetector calibration of statistically dominating further events.

Fig. 35. PLI (left) and PIP (right) mounted on LC.

The photoelectric lens imaging tube (PLI) installed on thefacul sphere of the Ashra-1 optical system and the image pipeline(PIP) following PLI have worked stably so far at the Mauna
Loa observational site (Figure 35).

Fig. 36. Trigger decision board

Fig. 34. Estimated effective detection areas simulated for ντ frompoint source with azimuthal arrival direction φ2 of the Mauna Loa
summit with respect to the central Site0, and dip angles 2.0◦ (black
open circle), −2.0◦ (green star), −5.0◦ (blue filled box), −10.0◦ (redfilled circle), −20.0◦ (yellow filled triangle), and −30.0◦ (black filled
triangle).

For the readout of images from PLI and PIP, we uses a trigger decision processing board with programmable two fieldprogrammable gate arrays (FPGAs) and one Digital Signal
Processor (DSP). During Obs03, we used a trigger condition
for Cherenkov light of air-shower image requring adjacent
two triggered pixels as the first level and a global readout of
the image just after the trigger decision. For the aim of fluorescence trigger and readout, we need to implement more
complicated trigger logic to adapt to long sustained fluorescence signal with the typical duration of several micro seconds. We have been developing such control programs to be
implemented onto the combination of the FPGAs and DSP installed on the board (Figure 36). The trigger decision processing board includes a function of automatic adjustment of the44threshold of the 1st level (exposure control) trigger to keep thetotal trigger frequence stable even if the night sky backgroundchange time to time due to natural weather or/and artificial
conditions. The trigger decision processing board sends, tothe fine image sensor with trigger (FST) as described later, thedecided triggers of the 1st and 2nd levels with the addresses
corresponding to 64×64 cell regions of FOV.

Fig. 37. Fiber bundles attached to PIP trigger ports (top), images offiber ends before (bottom left) and after (bottom right) fine polishwith the achieved transmittance more than 95%.

The PIP can split and relay the same image from the output of PLI into the trigger pixel sensor and fine image sensor
with trigger (FST). To transmit the trigger image into trigger
pixel sensor, we use the 64×64 optical fiber bundle with 4m
length. The fiber bundles have been developed and assembled by Ogawa group of Toho University (Figure 37 top). The
fabrication and assembling process has been established well.
Particularly the technique of alignment and polish of the endof each optical fiber is essential. Now we have confirmed thatthe alignment accuracy is achieved to be within 0.1 mm andtransmission of the 4m-length fiber to be more than 95% after
the original technique of polishing the end of fibers (Figure 37
bottom).

(FST), which can start exposure of any of 64×64 subdivided
cell regions on the sensor after the 1st level (exposure control) trigger signal and start readout to data acquisition computer through a Camera Link cable after the 2nd level (readout control) trigger signal sent from the trigger processor as
described before. The FST chip with 2048×2048 pixels on
19 mm×19 mm area mounted on the camera box as shown in
Figure 38 has been tested in a laboratory. The achieved parameters are the saturation capacity of more than 4500 electrons,
the dark current of about 600 electrons/s, the temporal darknoise of 16 electrons, the total quantum efficiency of 58.3% atwave length of 525 nm, the dark signal non-uniformity of 4%,
and the photoresponse non-uniformity of 7%, where the last
two types of non-uniformity can be eliminated after carefuloff-chip fixed pattern noise correction as usual CMOS sensor
technology. The FST sensor mounted on the control camera
box is now ready for integration tests in a laboratory and useof the field test observation after the total integration on theLC.

Fig. 39. LED flusher (left) and the schematic view of the installation
on LC (right).

As a basic step of the Ashra-1 gain calibration chain, theimportance and the function of the LED flusher (Figure 39)
has been already described before. The achieved status is asfollows. To ensure the uniform lights on the focal sphere of
the PLI input window, the spot size of the virtual point sourceis required to be small and the numerical aperture of the output
light to be large after the output of the LED flusher opticalsystem. The measured HWHM spot size at the output windowof the LED flusher is 300 µm without any spiky structure.
We have also measured the non-uniformity on the PLI input
window surface to be less than 1%. The optical system insideof the LED flusher box may cause some systematic error of
the alightment. We measured the misalignment error to beless than 23 µm which corresponds to 1.7 mrad (0.1◦ ). We
can expect the LED flusher can be used even every second
during the observation to confirm the stability of the total gainof the readout system and calibrate it time to time if necessary.

Fig. 38. FST CMOS sensor chip (left) and camera control box (right).

Comparing with Cherenkov image trigger, the fluorescence Fig. 40. Shelters for a laser and LC (left) and LC (right) in the shelter.
image trigger requres the trigger process to reduce the contamination of night sky background more severely. For the reaWe have already set up the test facility to integrate theson, we have developed custom fine image sensor with trigger readout system on the LC for test in a shelter at Akeno Ob-

45

servatory (Figure 40). The LC for test is ready for mounting
and integrating the trigger and readout system. A 355 nm and532 nm YAG laser system with 130 mJ/puse has been installedin the next shelter, which will be used for virtual fluorescencesignals for test. The YAG laser pulse at the appropriate distance yields Rayleigh scattering light, some of which reaches
the puple of the optical system of Ashra-1 LC, corresponds tothe emission of fluorescence light from an air-shower with theprimary energy up to several 1019 eV. The integratin test of
the trigger and readout procedure with the facilities at Akeno
observatory will be useful just before the installation and thecommissioning at the Ashra-1 Mauna Loa observatory.

[25] Kobayashi, S. and Zhang, B., 2003, ApJ, 582, 641

Bibliography[31] M. Sasaki, J. Phys. Soc. Jpn. 70 (Suppl. B) (2001) 129.

[26] http://gcn.gsfc.nasa.gov/other/081203A.gcn3[27] Asaoka, Y. and Sasaki, M., 2013, Astropart. Phys., 41, 7[28] Sasaki, M., Manago, N., Noda, K., Asaoka, Y., GCN
Circ. 3421, 2005.
[29] R. Gandhi, C. Quigg, M.H. Reno and I. Sarcevic, Phys.
Rev. D 58 (1998) 093009.
[30] M. Sasaki, Y. Asaoka, M. Jobashi, Astropart. Phys. 19(2003) 37.

[1] http://www.icrr.u-tokyo.ac.jp/∼ashra[2] Sasaki, M., Progress of Theoretical Physics Supplement,
151, 192 (2003).
[3] Sasaki, M., et al., Proc. 29th Int. Cosmic Ray Conf.
(Pune, India), Vol. 8, 197-200, 2005.
[4] M. Sasaki, 30th Intl. Cosmic Ray Conf. (Merida),
ID1232, 2007.
[5] M. Sasaki et al., in 32th International Cosmic Ray Conference, Rio de Janeiro 2013.
[6] D. Fargion, ApJ, 570:909, 2002.
[7] Y. Aita et al. ApJ, 736:L12, 2011.
[8] Y. Asaoka and M. Sasaki, Nucl. Instr. and Meth. A647,
34, 2011.
[9] Mésźaros, P. 2006, Rep. Prog. Phys., 69, 2259
[10] Mésźaros, P., & Rees, M.J. 1997, ApJ, 476, 232[11] Sari, R., & Piran, T., 1999. ApJ, 517, L109
[12] Mésźaros, P., & Rees, M.J. 1999, MNRAS, 306, L39[13] Gao, S., et al. 2013, arXiv:1305.6055

High Energy Astrophysics Group[Spokesperson: T. Terasawa]
ICRR, Univ. of Tokyo, Kashiawa, Chiba 277-8582

Overview
Since its creation in December 2009, the high energy astrophysics group has been making theoretical and observational studies of violent astrophysical phenomena in which
nonthermal cosmic ray particles are being accelerated. In April
2013, new members, a research associate and a postdoc, joined
the group, who have been contributing to extend the group activity significantly. Targets of the group’s study include highenergy astrophysical objects such as supernova remnants/pulsar
magnetospheres, giant flares and repeating bursts of magnetars, a giant galactic explosion called ‘Fermi bubble’, neutron star merger events, fast radio bursts (FRBs), jets from
active galactic nuclei (AGN), as well as mysterious gamma
ray bursts (GRBs). Research works on the origin of ultra highenergy cosmic rays (UHECRs) are also within the coverage ofthe group.

[14] Abraham, J., et al. 2008, Phys. Rev. Lett., 100, 211101[15] Aita, Y., et al. 2011, ApJL, 736, L12[16] http://gcn.gsfc.nasa.gov/swift grbs.html[17] http://gcn.gsfc.nasa.gov/fermi grbs.html[18] Antoni, T., et al. 2005, Astropart. Phys., 24, 1[19] Amenomori, M., et al. 2008, ApJ, 678, 1165
[20] Y. Aita et al., ApJL736, L12 (2011).
[21] Y. Aita et al., GCN Circ., 8632 (2008).
[22] Y. Asaoka et al., GCN Circ., 11291 (2010).
[23] Bertin, E. and Arnouts, S. 1996, A&AS, 117, 393[24] Hφ g, E., et al., 2000, A&A, 355, L27

Research topics: 1. Particle acceleration and emissions in GRBs and AGNs
The origin of ultra high-energy cosmic-rays (UHECRs)
is one of the most important research targets in ICRR. The
sources may be ultra-relativistic jets such as gamma-ray bursts(GRBs) or acitive galactic nuclei (AGNs). The physical condition to produce UHECRs can be verified via studies of electromagnetic emission, in which the information on the acceleration mechanism and efficiency is concealed. The first stepto unveil the UHECR sources is the identification of the photon emission processes in relativistic jets.
In the standard model of GRB, electrons are accelerated
via shocks, and emit synchrotron photons. In such a situation,
protons should be accelreated to ultra high-energies. However, several alternative models have been proposed by many
authors. In the photosphere model, one of such alternative

46

ε

ε

ε

1032erg s-1-121031erg s-1-14

d =1 3
0 3

erg

s -1

-16

Ls

models, thermal emission is a main spectral component. In
the high photon density of this model, the UHECR production is difficult owing to the cooling due to the photopion production. However, our time-dependent simulations show thatthe photosphere model is hard to reconcile with the observed
GRB spectra [3]. In another study [5], based on the standard
picture, we quantitatively estimate the UHECR and neutrino
production rates from GRBs with our numerical simulations.
As shown in Figure 41, our results indicate that GRBs are still
possible UHECR sources avoiding the neutrino limit by IceCube.
On the other hand, there are several open questions in the
wide-band photon spectra of AGN jets. Generally electrons
are supposed to be accelerated via shocks in jets. However,
the maximum energy of electrons is comparable to that inyoung supernova remnants in spite of stronger magnetic fields
in AGN jets. The spectra show curved feature, while the simple shock acceleration theory predicts power-law spectra. We
try to fit wide-band spectra assuming the stochastic acceleration by turbulences instead of shocks. The spectra for 1ES
1101-232 and Mrk 421 are well fitted by our models [4]. If thestochastic acceleration is common mechanism in AGN jets,
the UHECR production seems to be difficult.

Fig. 42. The γ − θpl diagram of the pulsar wind where γ is the Lorentz
factor of the pulsar wind and θpl is the inclination angle with respect
to the propagation direction of the radio pulses [8]. Here, we do
not consider the gray region. The black solid line of τLC = 1 means
the optical depth for induced Compton scattering of unity. The
blue region corresponds τLC < 1, i.e., the radio pulses are allowed
to escape from the scattering by the pulsar wind. The fuctional
form of τc = 1 is not shown in the diagram because it depends onthe magnetization of the pulsar wind and the size of the emission
region of the radio pulses.

log Pdot [s/s]Fig. 41. Fluxes of UHECRs and neutrinos from GRBs calculated with
time-dependent simulations of the hadronic cascade processes[5]. The results are consistent with the upper-limit of the neutrino
flux (IC40+59) and observed UHECR flux (AUGER).

-18

Research topics: 2. Theoretical studies of pulsars

-2

-1

0

1

log P [s]2a: Pulsar wind properties
High energy emissions from pulsars and their nebulae areunambiguous evidences that the pulsars generate high energy
particles, i.e., cosmic rays. However, because of their extreme
physical condtions, we have not fully understood the particle acceleration and creation processes at the pulsar magnetosphere. We do not even achieve consensus on the physicalconditions, such as the number density, the kinetic energy andthe magnetization of the high energy particles which is called

Fig. 43. Synchrotron radiation death lines (thick solid and dashedlines) on the P-Ṗ diagram, where P is the period and Ṗ is its derivative (Kisaka and Tanaka, in press). The thin dot-dashed lines
denote the spin-down power of Lsd = 1033 , 1032 and 1031 erg s−1 .
Each large cross denotes X-ray detected old pulsars. Four of oursamples locate in the filled region (below the death lines) so thatthe synchrotron radiation model does not explain their non-thermal
X-ray emissions.

47

2b: High energy emission from old pulsars
Observationally, pulsars are characterized by their spin period and its derivative. We obtain the characteristic age andthe spin-down power from them. We know the young energetic pulsars are efficient particle accelerator and emit brightnon-thermal radiation mostly in X-rays and γ-rays. However,a dozen of old (typically > 1 Myr) and less energetic pulsars have been also detected in X-rays. Their non-thermal
X-ray signatures give a great opportunity to study the evolution of how and where to accelerate particles. We study the
non-thermal X-ray emission from old pulsars based on synchrotron radiation models which are usually considered as the
non-thermal X-ray emission mechanism for young pulsars.
Figure 43 shows X-ray emission death lines for the one offour types of synchrotron radiation model which we considered. The death line means that the significant non-thermal
X-ray emission is not expected for the pulsars below this line.
Although we consider fairly optimistic model of synchrotron
X-ray emission, the detected X-ray flux for some old pulsars
is not explained by the synchrotron radiation. In addition, we
require the different particle acceleration process from that ofyoung pulsars even for the pulsars above the death line. Our
results indicate that the particle acceleration and creation processes at pulsar magnetospheres significantly change around
1 Myr.
2c: Electric field screening and particle ejection in a pulsar
magnetosphereWe study the screening of the rotationally induced electric field above pulsar polar caps including backflow-particles
from the outer gap region. We apply a simple numerical modelfor the dynamics of the charged particles using Particle-inCell methods. Although the field-line footpoints of the outergap are considered to the return current region where the signof the average current density flowing along the magentic field
line j and the Goldreich-Julian current density jGJ = cρGJ is
opposite ( j/ jGJ < 0), we find that the electric field can bescreened without pair creation under the certain conditions.
For the arbitrary value of current density, we find that if another backflow components with small average Lorentz factorγ̄ ∼ 1 are come into the polar cap, the development of the electric field is prevented. If ions are extracted from the surface,

1000

n

800

600

400

200

0
8000

10000

12000

14000

16000

18000

20000

t

Fig. 44. Periodic ejection of particles into a pulsar magnetosphere.
The number of particles through the outer domain boundaries asa function fo the compultational time. The value of the vertical axis
is normalized by 0.01nGJ , where nGJ is the Goldreich-Jullian density. The colors show the number of injected particles ninj /nGJ =0.1 (red), 0.2 (light green), 0.4 (blue), 0.6 (purple), 0.8 (light blue)and 1.0 (black) from the outer boundary (Kisaka, Asano, and Terasawa, in preparation).

40
35-315keV event rate [count/sec]

pulsar wind. We study the induced Compton scattering off radio pulses of the pulsar by the pulsar wind generated by thepulsar itself to constrain the physical conditions of the pulsar
wind. One of our results are shown in Figure 42, the γ − θpldiagram of a pulsar wind, where the Lorentz factor γ and theinclination angle with respect to the radio pulse θpl . In Figure 42, blue region is allowed for escaping the radio pulses
from scattering and tells us the allowed pulsar wind velocity
characterized by γ and θpl . For example, when γ and θpl are
sufficiently high, radio pulses escape from induced Compton
scattering. In terms of the number density, sufficiently low
density is required for escaping of the radio pulses from scattering. We find the small value of the Lorentz factor and also
the large value of the number density of the pulsar wind compared with the study by Wilson & Rees (1978) are allowed
when we consider the inclined pulsar wind with respect to theradio pulses.

1200

35
30
25
20
15
10
5
0
-5

-0.4

-0.2

0
Phase [period]

0.2

0.4

Fig. 45. The pulse profile of the Crab pulsar for soft γ-ray photons(35-315 keV, the average photon energy ∼113 keV), observed with
the HXD/GSO sensor on board of the Suzaku satellite. Red dotsshows the count rates folded over only the periods simultaneouswith GRPs, while black dots shows those accumlated only for non–
GRP periods. We estimate the upper limit on soft-gamma-ray flux
enhancement (1σ ) concurrent with the GRPs to be ∼ 10%, which
is more stringent than the previous value (∼ 19%, Lundgren et al.,1995). Phase 0 correspond to the main peak of radio pulses.

the bunches of particles are ejected to the outer region quasiperiodically (Figure 44). We suggest that this behavior may
be one of the origin of pulsar radio emission.

Research topics: 3. Observational study of the CrabpulsarCrab pulsar, the remnant of the supernova explosion in
1054 A.D., is one of the most studied neutron stars. While its
physical properties have been investigated for more than 40
years since its discovery, there remains an enigma about theorigin of giant radio pulses (GRPs). While for a long time theCrab’s GRPs had been regarded as a pulsar phenomenon lim-

48

Fig. 46. Energy spectrum of diffuse gamma-rays by Fermi (M. Ackermann et al. 2012) and an expectation of CALET 5-year observation.

ited to the radio frequency, a 3% enhancement of the opticalemission at the GRP timing was discovered recently (Shearer
et al., 2003; Strader et al. 2013). However, in other frequency
bands, no significant flux enhancement was found and only
the upper limits were set. We have been making simulatenous
observations of the Crab pulsar at the GHz frequency range
and X-ray/soft-gamma-ray energy ranges. Figure 45 shows anexample, where we made the correlation study between GRPs
and the soft-gamma-ray pulses.

Research topics: 4. CALET project — a R/D study
CALET, CALorimetric Electron Telescope, is a new mission for the Japanese Experiment Module-Exposed Facility(JEM-EF) on the International Space Station. The CALET
mission aims at revealing unsolved problems in high energy
phenomena of the Universe by carrying out accurate measurements of high energy spectra of electrons, gamma-rays
and nuclei. The instrument will be flown in JFY 2014, andis scheduled to be operated for five years. CALET is focused on investigating the high energy total electron spectrum
into the trans-TeV energy range. CALET can also performa gamma-ray all-sky survey, complementing Fermi and atmospheric Cerenkov telescope, to detect intense high energy
sources, study the diffuse component. CALET has an imaging
and deep calorimeter with 30 radiation lengths for electromagnetic particles, which provides superior energy resolution and
excellent separation between hadrons and electrons/gammarays and between charged particles and gamma-rays. We developed analysis methods such as particle identification andarrival direction, and evaluated detection performance such as
angular resolution, energy resolution and point spread function, using Monte Carlo simulations and CERN-SPS beam
test data. Figure 46 shows energy spectrum of diffuse gammarays expected by CALET 5-year observation. We note that
CALET can make an important contribution by extending the
Fermi gamma-ray observations to energies above ∼ 100 GeV.

Fig. 47. A multi-point observation of forward scattering meteor echomade on 30 July 2013 at 02:45:07 JST (29 July 2013 at 17:45:07
UT). In this example, we utilized three transmitters (solid blackdots) and eight receivers (solid red dots) making possible to derive
meteor parameters, such as the radiant position (RA=5.96±0.18
hour, DEC=47.90±6.04 deg) and the meteor velocity (32.31±0.95km/s), from which we concluded that this meteor was a sporadic
meteor not belonging to any known meteor shower group. The
contour curves represent the error residuals in the parameter–
fitting procedure, where a open black dot shows the geographical position giving the error minimum (longitude=138.4±0.2 deg,
latitude=35.9±0.3 deg). An arrow starting from there shows themeteor velocity direction projected to the horizontal plane.

Research topics: 5. R/D study for radar detection of
UHECRs and extraterrestrial grains
Wide attention has been attracted to the detection of ultra high energy cosmic rays (UHECRs) with radio techniques,
either passive and active, towards future large-scale UHECR
observatory on the ground. Collaborating with the TA groupof ICRR, we have made a R/D study of the active method,
namely, the detection of radar echoes from extensive air showers of UHECRs (UHECR echoes, hereafter) [13]. Parallel tothe above R/D study, we have also made a radar research research project for extraterrestrial grains (meteors). Despite
more than three orders of magnitude difference in the echo
duration between UHECR echoes (<∼ µs, expected but not
yet identified) and meteor echoes (several - several tens of ms,
observed), the know-how developed in the latter project (Figure 47) can provide a technical basis for the former.

Bibliography
Papers in refereed journals
1. Ackermann, M., M. Ajello, K. Asano et al. The First
Fermi LAT Gamma-Ray Burst Catalog, ApJS 209, 11(90pp) (2013)
2. Ackermann, M., M. Ajello, K. Asano et al., Fermi-LAT
Observations of the Gamma-Ray Burst GRB 130427A,

49

Science Vol. 343, 42-47 (2014)
3. Asano, K., and P. Meszaros. Photon and Neutrino Spectra of Time-Dependent Photospheric Models of GammaRay Bursts, JCAP 09, 008 (2013)
4. Asano, K., F. Takahara, M. Kusunose, K. Toma, and
J. Kakuwa, Time-Dependent Models for Blazar Emissions with the Second-Order Fermi Acceleration ApJ
780, 64(12pp) (2014)
5. Asano, K., and P. Meszaros, Neutrino and Cosmic-Ray
Release from Gamma-Ray Bursts: Time-Dependent Simulations, ApJ 785, 54 (2014)
6. Mikami, R., T. Terasawa, S. Kisaka, H. Miyamoto, K.
Asano, N. Kawai, Y. Yamakoshi, K. Nagata, R. Kataoka,
K. Takefuji, M. Sekido, H. Takeuchi, H. Odaka, S. Sato,
Y. T. Tanaka, Search for a correlation between giant radio pulses and hard X-ray emissions in the Crab pulsar,
JPS Conf. Proc., 1, 015106 (2014)
7. Takamoto, M., Kisaka, S., Suzuki, T., and T. Terasawa,
The Evolution of High Temperature Plasma in Magnetar Magnetospheres and its Implications for Giant Flares,
ApJ, in press (2014)
8. Tanaka, S. J., and Takahara, F., Constraint on Pulsar
Wind Properties from Induced Compton Scattering off
Radio Pulses, PTEP 12, 123E01 (2013)
9. Yatsu, Y., K. Asano, N. Kawai, Y. Yano, and T. Nakamori,
Spatially Resolved Spectroscopy of a Pulsar Wind Nebula in MSH 15-56 ApJ 773, 25(14pp) (2013)
10. Yokota, S., Y. Saito, K. Asamura, M. N. Nishino, T. I.
Yamamoto, H. Tsunakawa, H. Shibuya, M. Matsushima,
H. Shimizu, F. Takahashi, M. Fujimoto, and T. Terasawa, Kaguya observation of the ion acceleration arounda lunar crustal magnetic anomaly, Planetary and Space
Science, 93-94, 87-95 (2014)
ThesisSokolsky, H. Takai, T. Terasawa, and G. B. Thomson,“TARA: Forward-scattered radar detection of UHECR
at the telescope array”, EPJ Web of Conferences 53,
08012 (2013)15 Fujisawa, K., and S. Kisaka, “Axisymmetric and stationary magnetic field structures in neutron star crusts
under various boundary conditions”, Proceedings of IAU
Symposium 302, Magnetic fields throughout stellar evolution (2013)
16. Guzik, T., for the CALET collaboration, “The CALorimetric Electron Telescope (CALET) ground data handling and processing system”, Proceedings of the 33rd
International Cosmic Ray Conference (2013)
17. Kisaka, S., and T. Terasawa, “Electric field screening
at the pulsar polar cap”, Proceedings of SKA Science
Workshop in East Asia (2013)
18. Marrocchesi, P. S., for the CALET collaboration, “CALET
measurements with cosmic nuclei and performance ofthe charge detectors”, Proceedings of the 33rd International Cosmic Ray Conference (2013)
19. Marrocchesi, P. S., for the CALET collaboration, “CALET
Measurement of Ultra-Heavy Cosmic Rays”, Proceedings of the 33rd International Cosmic Ray Conference(2013)
19. Mikami, R., T. Terasawa, S. Kisaka, K. Asano, S. J.
Tanaka, M. Sekido, K. Takefuji, H. Takeuchi, H. Odaka,
T. Sato, Y. T. Tanaka and N. Kawai, “Hard X-ray observations with Suzaku HXD at the time of giant radio
pulses from the Crab pulsar”, Proceedings of SUZAKU- MAXI conference (2014)
20. Moiseev, A., for the CALET collaboration, “CALET
perspectives in high-energy gamma-ray observations”,
Proceedings of the 33rd International Cosmic Ray Conference (2013)

21. Mori, M., for the CALET collaboration, “Expected Performance of CALET as a High Energy Gamma Ray Ob11. Higuchi, C., “Statistical study of lightning activity: Peservatory”, Proceedings of the 33rd International Cosriodicity and possible link with solar activity”, (in Japanese),mic Ray Conference (2013)
Master thesis, Department of Physics, Tokyo Institute
22. Niita, T., and the CALET collaboration, “CALET Calof Technology (2014)ibration on ISS Orbit Using Cosmic Rays”, Proceedings of the 33rd International Cosmic Ray Conference
Conference papers(2013)
12. Akaike, Y., for the CALET collaboration, “CALET ob23. Rauch, B., for the CALET collaboration, “CALET Positronservational performance expected by CERN beam test”,/ Electron Measurements Using the Geomagnetic Field”,
Proceedings of the 33rd International Cosmic Ray ConProceedings of the 33rd International Cosmic Ray Conference (2013)
ference (2013)
13. Asano, K., “Wide-Band Spectra of Prompt Emission”,
25. Tamura, T., for the CALET collaboration, “Particle Beam
EAS Publications Series, 61, 115 (2013)
Tests of the Calorimetric Electron Telescope”, Proceed14. Belz, J., M. Abu Bakr Othman, C. Allen, E. Barcikowski,
ings of the 33rd International Cosmic Ray Conference
D. Besson, B. Farhang-Boroujeny, D. Ikeda, W. Han(2013)
lon, S. Kunwar, J. P. Lundquist, I. Kravchenko, S. Larson, I. Myers, T. Nakamura, J. S. Rankin, H. Sagawa, P.

50

26. Tanaka, S. J., “Broadband Emission Structure of Pulsar
Wind Nebulae”, Proceedings of the 33rd International
Cosmic Ray Conference (2013)
27. Tanaka, S. J., “High Energy Emission from Spherically
Symmetric Pulsar Wind Nebulae”, Proceedings of SUZAKUMAXI Conference (2014)
28. Tanaka, S. J., and S. Kisaka, “Synchrotron Emission
from Old Pulsars”, Proceedings of SUZAKU-MAXI Conference (2014)
29. Tanaka, Y. T., M. Hayakawa, Y. Hobara, J. Raulin, Y.
Takahashi, M. Sato, and T. Terasawa, T. ELF and VLF
observations of ionospheric disturbances caused by extraterrestrial origin, American Geophysical Union, Spring
Meeting, SM24A-03 (2013)
30. Torii, S., for the CALET collaboration, “The Calorimetric Electron Telescope (CALET) for High Energy Astroparticle Phsycis on the International Space Station”,
Proceedings of the 33rd International Cosmic Ray Conference (2013)
31. Ueyama, Y., for the CALET collaboration, “The CALET
Structure and Thermal Model used for beam test at CERN”,
Proceedings of the 33rd International Cosmic Ray Conference (2013)
32. Yamaoka, K., for the CALET collaboration, “CALET
Gamma-ray Burst Monitor (CGBM)”, Proceedings ofthe 33rd International Cosmic Ray Conference (2013)

51

ASTROPHYSICS AND GRAVITY DIVISION
Overview• coordination of collaboration meetings

Astrophysics and Gravity Division consists of Gravitational
Wave Group, The Observational Cosmology Group, Primary
Cosmic Ray Group and Theory Group. The Gravitational
Wave Group conducts experimental research of gravitational
wave with researchers of gravitational wave experiment andtheory in Japan. The main items are the construction of thelarge scale cryogenic interferometer(KAGRA) at Kamioka underground and the operation of CLIO.
The Observational Cosmology Group studies the cosmic
history based on deep multi-wavelength observations in collaboration with worldwide researchers. This group has started
a new optical deep survey project with the wide-field imagerof Hyper Suprime-Cam mounted on the Subaru telescope.
Theory Group conducts both theoretical study of the Universe and astroparticle physics.

• technical supports for the KAGRA construction• support for education of graduate students• bridging collaboration members and ICRR administration office• others

Head

Head of Kamioka
Branch2 technical staffs

Gravitational Wave GroupGravitational Wave Project Office (GWPO)

4 researchers

Administration
staff and 2
secretaries

3 technical staffs
and 2 technicians

6 researchersand 2 PDs

3 secretaries

Fig. 1. Organization of the Gravitational Wave Project Office in 2013

[Spokesperson : Kazuaki KURODA]
ICRR, The Univ. of Tokyo, Kashiwa, Chiba 277-8582

Activity in FY 2013
Overview
We supported the collaboration meetings held in Kashiwa
Gravitational wave project office was established at the be- campus. They were two face-to-face international collaboraginning of the financial year of 2011 to assist the construction tion meetings5 and four KAGRA collaobration remote meetof KAGRA4 gravitational wave telescope. The organization ings (two international and two domestic) 6 . We supported theof this office is illustrated in Fig. 1. Main office is set in KAGRA council meeting on 17th, September, Program AdviKashiwa campus and its Kamioka branch is in Kamioka. It is sory Board meeting on 2nd-3rd, November and 2nd ELiTES
an internal office belonging to Astrophysics and Gravity Divi- general meeting held at Euro Tokyo delegation house on 4th,sion of ICRR.
December and at Sanjo Conferene Hall on 5th, December.
KAGRA project is hosted by ICRR, which means the fundWe took care of travel supports for the following events:
ing comes through the University of Tokyo and all procure- - External Peer Review of KAGRA in April, 2014 (which wasments are made through ICRR. However, the number of re- for FY2014 but had to be processed in FY 2013)searchers working for KAGRA construction belonging to other - 4th Korea-Japan Workshop on 10th-11th, June in Osaka Uniorganizations is larger than the staffs belonging to ICRR. There- versity
fore, three collaboration members of KEK are recruited as - 5th Korea-Japan Workshop in Seoul on 29th-30th, Novemguest researchers of ICRR and one research staff is temporar- ber
ily moved to ICRR from NAOJ.
The role of this office is to support execution of KAGRA
We supported the execution of research programs adopted
project by ICRR staffs together with these collaboration mem- as ICRR collaborative researches listed in Table 1 in processbers. Main works are
ing invoices for experimental goods and domestic travels.
• finance planning• management of collaboration• support for the execution of KAGRA budget*4 nicknamed in January, 2012 by public contribution for LCGT

*5 http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA/Meeting/F2F*6 http://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA/Meeting/Collaboration

52

Title
Research and Development for the ultra highsensitivity quantum interferometer in KAGRA
Development of optical cavities forultranarrow stable laser
Gravitational Wave Detector in Kamioka (XII)
Data analysis using CLIO data (IV)
Application of geophysical observations in the
Kamioka mine to the dynamics of snow and water
Study for LCGT data analysis and Research
for its System (III)Development of beam position minitoring andcontroling systems for KAGRA
The development of a super sensitive shadow sensor
for a gravitational antenna
Research on ultra-low frequency anti-vibration
system for KAGRA
Research of Large-scale Gravitational wave Telescope(III)
Development of Sapphire Mirror Suspension for
KAGRA(LCGT) (X)Development of Very Low Vibration Cryo-Cooler System
Gravitational Wave Detection using Non-Harmonic Analysis
Characterization of Sapphire mirror for KAGRA using
electron spin resonanceR&D for the intensity stabilization of the laser system
in KAGRA
Development of the output mode-cleaner for
KAGRA
Development of precision profiler for mirrors of LCGTinterferometer 3
Development of a stabilization system for the KAGRA
laser source
Real time control for interferometer using computers(II)
Numerical simulation of Electric-Magnetic Wave Propagationin Gravitational wave Detector
Research on cryogenic payload for KAGRA

Representative
Yutaka Shikano

Affiliation
IMS

Tetsuya Ido

NICT

Masatake Ohashi
Hirotaka Takahashi
Yuichi Imanishi

ICRR, UTokyo
Nagaoka U TEC
ERI, UTokyo

Nobuyuki Kanda

Osaka CU

Takashi Sato

Niigata U

Ruggero Micheletto

Yokohama CU

Ryutaro Takahashi

ICRR/NAOJ

Kazuaki Kuroda

ICRR, UTokyo

Toshikazu Suzuki

KEK/ICRR

Nonuhiro Kimura
Shigeki Hirobayashi
Yukinori Ono

KEK/ICRR
Univ. of Toyama
Univ. of Toyama

Fusakazu Matsushima

Univ. of Toyama

Kentaro Somiya

TITEC

Toshiyuki Takatsuji

AIST

Norikatsu Mio

PSC, UTokyp

Osamu Miyakawa

ICRR, UTokyo

Shinji Miyoki

ICRR, UTokyo

Kazuhiro Yamamoto

ICRR, UTokyo

Table 1. List of research titles adopted as ICRR Cooperative researches in FY 2013

Kamioka branch of GWPO
The manpower of the Kamioka branch consists of 5 research staffs, one adminstration staff, 2 secretaries and 2 technicians as shown in Fig. 1, which is increased from the previous year.
The data acquisition & Analysis building was designed
and constructed by the end of this financial year as shown in
Fig. 2. The building is jointed to the adjacent Hokubu Kaikan
building where the office & laboratory rooms for Kamioka
branch of GWPO are located (refurbished part from previous
Kinder garten).
The Kamioka branch mainly executes the following works:• Supporting research activity for KAGRA project• Planning coordination and schedule of the KAGRA construction• Making liason with the construction company, Kamioka
Observatory and local government for condcuting KAGRA construction• Outreach activity with local communities• Accepting visitors from various fields
The Kamioka branch held an exchange meeting with local
residents in collaboration with the Kamioka Observatory on
12th, July and had an information session about the construction and schedule of KAGRA for local residents on 20th, August. Research staffs gave lectures at several weekends from
April to July at Public Exposition Hall of Inotani as listed inAppendices.

53

Fig. 3. Ultimate sensitivity limit of KAGRA.

Fig. 2. Data acquisition & analysis building for KAGRA

lowing:• The excavation of the tunnel was completed.

KAGRA Project Status[Spokesperson : Seiji KAWAMURA]
ICRR, The Univ. of Tokyo, Hida, Gifu 506-1205• A building for data analysis was built in the Mozumi
area.
• Various kinds of cooling tests with the cryostats, including measuring the cooling time of the mirror and measuring the vibration level caused by the cryo-coolers
were performed successfully.

Overview
KAGRA, Large-scale Cryogenic Gravitational wave Tele• Some of the mirrors/beam splitter were polished andscope, aims at detection of gravitational waves for the firstcoated successfully.
time and establishing a new astronomy, gravitational wave astronomy, by a 3 km baseline laser interferometer with a cryo• The prototype test of the inverted pendulum, which is
genic mirror system placed underground at Kamioka. The
an important element of the advanced seismic isolation
KAGRA development is divided into two stages: the initialsystem, was successfully finished, and the payload proKAGRA (iKAGRA) and baseline KAGRA (bKAGRA). The
totype was assembled.
iKAGRA detector will be a simple Fabry-Perot Michelson interferometer with mirrors at room temperature and a simple• The digital control system and the data acquisition sysseismic isolation system. We plan to operate the iKAGRA detem were completed.
tector by the end of 2015 with a one-month observation run
at the end of the stage. Then we will proceed to bKAGRA.
We also enhanced the international and domestic collabThe bKAGRA detector will employ a Resonant Sideband Ex- orations with the Einstein Telescope (ET) project, LIGO andtraction (RSE) interferometer with cryogenic mirrors and an Virgo, the Korean and other Asian groups, and Toyama Uniadvanced Seismic Attenuation System (SAS). The bKAGRA versity by exchanging researchers and having international
detector should attain the sensitivity high enough for the de- workshops.
tection of gravitational waves with the help of the RSE interThe rapidly progressing status of KAGAR were presented
ferometer to reduce the quantum noise, the cryogenic mirrors in several international conferences.[1] Some papers about theto reduce the thermal noise, and the SAS to reduce the seis- progress of KAGRA were also published.[2] We also premic noise. We plan to start operating the bKAGRA detector sented activities in our web-page.[3]by the end of 2017, then repeat short-time observation runs
and noise hunting to improve the sensitivity until it reaches
Bibliography
the aimed sensitivity of KAGRA.
[1] Seiji Kawamura for the KAGRA collaboration,
Fig. 3 shows the estimated ultimate sensitivity limits of”Progress and Challenges of KAGRA”, 10th Amaldi
KAGRA where incoherent sum of the fundamental noise sources
Conference on Gravitational Waves, July 7-13, 2013,is assumed. The observation range for an inspiral and merger
Uniwersytet Warszawski, Warsaw, Poland.
of neutron-star binary with the ultimate sensitivity limit of
KAGRA is about 173Mpc. It should be noted that the def[2] Yoichi Aso, et al. (The KAGRA Collaboration), ”Interinition of the observation range, which used to be different
ferometer design of the KAGRA gravitational wave defrom the one used by LIGO and Virgo, was changed to be thetector”, Phys. Rev. D 88 (2013) 043007.
same as LIGO and Virgo to avoid possible confusion.
Major milestones we had accomplished and important progress[3] http://gwcenter.icrr.u-tokyo.ac.jp/en/
we had made between April 2013 and March 2014 are the fol-

54

Tunnel for KAGRA

The vibration isolation is a very important system for the
successof KAGRA. It should provide the seismic noise at[Spokesperson : Takashi UCHIYAMA]
tenuationin the detection band and should reduce the mirror
ICRR, The Univ. of Tokyo, Hida, Gifu 506-1205
speed at low frequencies. It consist of several components inKAGRA is a laser interferometric gravitational-wave de- cluding the pre-isolator, the mechanical filters based on the getector with a 3 km arm length. It is to be constructed in tun- ometric anti-spring (GAS) filter, and the socalled ”payload”,
nels of Kamioka mine (Hida, Gifu, Japan). The use of an which includes the mirror and all the components required forunderground site for small seismic motion is a key feature of its suspension and control. Schematic view of the system is
KAGRA. Kajima corporation (Kajima) in Japan carried out shown in figure 6.
KAGRA tunnel excavation work from 22th May, 2012 to the
The control of the inverted pendulum (IP) in the pre-isolator
end of March, 2014. The total length and the total volume of prototype was tested. The resonancies were inertially damped
the tunnels are 7,697 m and 156.301 m3 , respectively. Kajima by the active control system successfully. The payload proused the New Austrian Tunneling Method.
totype was assembled and tested. The dummy test mass was
Figure 4 shows a location map of the KAGRA tunnels. suspended by two-loop wires with 10-mm gap so as to makeThe tunnels have been excavated in Mt. Ikenoyama of Kamioka the pitch mode frequency be lower (∼ 1 Hz). The optical senmine, whose top is at about 1,300 m. There are two 3,000 m sor and electro-magnetic actuator module (OSEM) is used toarm tunnels connected perpendicularly. One arm tunnel in control the test mass. Four OSEMs are attached onto the renorth-east direction is called Xarm; the other arm tunnel is coil mass, and the sensors and actuators were diagonalized tocalled Yarm. The Center area, Xend area and Yend area, three degrees of freedom (transverse pitch, and yaw) successwhere some experiment rooms exist are located at the con- fully.
necting corner of the arm tunnels and at the end of both arm
tunnels, respectively. All of the areas are inside at more than
200 m from the surface of the mountain, in order to obtain a Bibliography[1] R. Takahashi, ”Vibration Isolation System for Mirrors”,
quiet seismic motion environment as we expected at the unJ. Vac. Jpn 54 (2011) 24-27.
derground site. Both arm tunnels are tilted by 1/300 for natural water drainage. The Xend area is at the highest altitude
of about 382 m, and the Yend area is at the lowest altitude
of about 362 m.The altitude of the Center area is 372 m. The Fabrication of cryostat and R&D for cryogenic items
KAGRA tunnels have two entrances: New Atotsu entrance [Spokesperson : Kazuhiro YAMAMOTO]
and Mozumi entrance. The New Atotsu entrance was newly ICRR, The Univ. of Tokyo, Kashiwa, Chiba 277-8582
constructed for the KAGRA tunnels, whose dimensions are awidth of 4 m and a height of 4 m. The cross section of the
New Atotsu entrance is the same of standard cross section of Outlines A key feature of KAGRA is the operation of the interferometer mirrors made from sapphire at cryogenic temperthe arm tunnels.
Figure 5 shows how to conduct the excavation work. Ex- atures. This mirror is a part of the cryogenic payload and thiscavation work must be done at multi working positions by payload is cooled. In 2013, a cooling test of KAGRA cryostats
multi worker groups. The first blast was conducted at the was performed and we studied radiation shield vibration andMozumi access tunnel by a worker group that entered from initial cooling time of a cryogenic payload in this cooling test.
the Mozumi entrance on 22th May, 2012. This worker group Other R&D research (cryogenic duct and sapphire suspension
proceeded with the excavation work of the Mozumi access and so on) is also in progress. In the following, the details oftunnel, the Yend area, and the Yarm tunnel, and stopped at the these items and an international collaboration (ELiTES) are
Ikenoyama fault because of spring water. All work from the explained.
Mozumi entrance was completed on 27th April, 2013. Another worker group started excavation of the New Atotsu ac- Cooling test of KAGRA cryostat in 2013 In fiscal year 2012,cess tunnel on 18th June, 2012, and reached the Center area all four KAGRA cryostats were fabricated by Toshiba Keihinon 1st October, 2012. This worker group completed the 1st Product Operations and the cooling test of the all KAGRA
floor of the Center area in 2012, and then started excavation cryostats themselves was conducted. We tried the cooling testof the Xarm tunnel and the Yarm tunnel on 24th December, for one cryostat again in 2013 at Toshiba Keihin Product Op2012 and on 9th January, 2013, respectively. The Yarm tun- erations. The main purposes of this test were to measure thenel was completed on 5th December, 2013. The Xarm tun- radiation shield vibration around 10 K and evaluate the initial
nel was completed on 1st March, 2014. After completing the cooling time of a cryogenic payload with heat links.
Any vibration of the radiation shield could contaminate
Xarm tunnel, excavation of the Xend area and the bypass tunnel started. All the excavation work for the KAGRA tunnels the gravitational wave signal, being introduced through theheat links that is necessary to cool the mirrors as well as throughwas completed by the end of March, 2014.
scattered light. In order to evaluate this noise, the horizontal and vertical cryogenic accelerometers were developed at
Vibration Isolation Subsystem
ICRR and University of Rome La Sapienza, respectively. We[Spokesperson : Ryutaro TAKAHASHI]
measured the vibration of the radiation shield around 10K.
NAOJ, Mitaka, Musashisakai 181-8588
After this measurement, we derived the noise by the vibration

55

Fig. 4. Location map of the KAGRA tunnels. The tunnels are in Mt. Ikenoyama of Kamioka mine, whose top is at about 1,300 m. There are two
3,000 m arm tunnels connected perpendicularly. One arm tunnel in the north east direction is called Xarm; the other arm tunnel is called
Yarm. The Center area, Xend area and Yend area, contain some experiment rooms, which are located at the connecting corner of the arm
tunnels and at the end of both arm tunnels, respectively. All of the areas are inside at more than 200 m from the surface of the mountain inorder to obtain the quiet seismic motion environment that we expected to be achieved at the underground site. Both arm tunnels are tilted
by 1/300 for natural water drainage. The Xend area is at the highest altitude of about 382 m, and the Yend area is at the lowest altitude ofabout 362 m.The altitude of the Center area is 372 m.

via heat links from our measurement. We found that extra
pendulums are necessary to reduce the vibration via the heatlinks. The details of these pendulums will be considered. We
submitted the paper about this investigation to Classical andQuantum Gravity.
In the cooling test of 2012, we installed a half size cryogenic payload prototype without heat links in order to investigate the cooling time by radiation. In the cooling test of
2013, we installed the prototype cryogenic payload with purecopper heat links in order to evaluate the cooling time by thethermal conduction in the heat links. We found that the thermal conductivity of pure copper was not as high as that we
expected. However, our other experiment showed annealing
increases the thermal conductivity. We calculated the initialcooling time of a KAGRA cryogenic payload based on theseexperiment results. It is about 1 month. We submit the paper
about this study to Classical and Quantum Gravity. We musttake the thermal resistance at both ends of the heat links into
account. The investigation is in progress.
Cryogenic duct The radiation shields should have two large
holes for the laser beam which are comparable in size withthe diameter of the cooled mirror (220 mm). Through theseholes, 300 K radiation will invade the radiation shield. Cryogenic ducts with baffles are necessary to prevent the propagation of 300 K radiation. We measured the heat transfer by thiscryogenic duct and found that it is enough small for KAGRA
as our calculation result (using ZEMAX). The scattered lightby these cryogenic ducts could contaminate the output of KAGRA interferometer. We calculated the scattered light noise(again, using ZEMAX) with some assumptions. Fortunately,
it is smaller than the KAGRA goal. However, for more precise
evaluation, we have plans to measure cryogenic duct vibration
and amplitude of the scattered light.
1/4 cryostat Since the cryogenic payload is a complicatedsystem, a test is necessary before the installation in the Kamioka
mine. The 1/4 cryostat for this test was delivered on the September.
Sapphire suspension The cooled mirror will be suspended
by four sapphire fibers. These fibers must have nail heads
on the fiber ends. MolTech GmbH and IMPEX HighTech
GmbH (both of them are German companies) delivered thesapphire fibers with the nail heads. These sapphire fibers musthave a high thermal conductivity to extract heat from the mir-

56

Fig. 5. Schematic view of the KAGRA tunnels. Arrows indicate the progress direction of excavation. Excavation work has been done at multi
working positions by multi worker groups. A worker group entered from the Mozumi entrance and excavated the Mozumi access tunnel, theYend area, and the Yarm tunnel of 1,200 m. Another worker group entered from the New Atotsu entrance and excavated the New Atotsu
access tunnel and the Center area. After completing the 1st floor of the Center area, excavation of the Xarm and the Yarm has started.
Excavation of the Xend area and the bypass tunnel was completed in the final period.

ror and high Q-values for small thermal noise. We measured
these values and found that IMPEX fibers satisfy the requirements. The result of the thermal conductivity experiment was
published (Classical and Quantum Gravity 31(2014)105004).
Institute for Gravitational Research, University of Glasgow
investigated the strength of the fibers and they are enoughstrong. The nail head in above experiments is a cylinder.
However, for connection with the mirror, a square nail headis better. The fibers with the square nail heads were delivered
and the investigation is in progress.
Sapphire blade springs are necessary to compensate thedifference of the sapphire fibers. This spring was designed
based on the strength test of sapphire plates at Glasgow. These
springs are delivered soon and will be checked performance.
For connection between each part, bonding techniques arenecessary. We are studying the Hydroxide Catalysis Bonding
and Indium Bonding. The Hydroxide Catalysis Bonding is
adopted in the room temperature gravitational wave detectors,
Advanced LIGO and Advanced Virgo. The Indium Bonding is
also necessary because the fibers and mirror can be taken apartwhen the fibers are broken. We tried the strength test of theHydroxide Catalysis Bonding and the analysis is in progress.
We are measuring thermal resistance of the bonding and haveplans to investigate mechanical loss of bonding at cryogenic
temperature.
ELiTES ELiTES (ET-LCGT interferometric Telescope Exchange of Scientists) is a European grant (European 7th Framework Programme Marie Curie action between Mar. 2012 andFeb. 2016) for the collaboration between KAGRA and Einstein Telescope (European future project). People in Europe
visit Japan for KAGRA. In 2013, a total of 25 visitors (fromGermany, Netherland, U.K., Italy) were supported by ELiTES.
Many of them helped the development of the sapphire suspension; the development of an automatic measurement system (and measurement with this system) of the thermal conductivity and Q-values of sapphire fibers and so on, sapphirefiber and plate strength tests, the lecture about how to makethe Hydroxide Catalysis Bonding, the investigation of how tomake the Indium Bonding, strength tests of Hydroxide Catalysis Bonding, the measurement of thermal resistance and mechanical loss of the Hydroxide Catalysis Bonding and Indium

57

Fig. 6. Schematic view of the seismic attenuation system. The system for the cryogenic mirror has additional two filters (Filter2 and 3).

Bonding. Some other people supported the measurement of
the radiation shield vibration, the development of the vibration isolation system at room temperature, the investigation of
annealed tungsten, the control system for cryogenic payload,
the measurement of the reflective coating mechanical loss at
low temperature, the study of the reflective coating on the mirror with smaller thermal noise, the ponderomotive squeezing
experiment, environmental sensors and so on.
Moreover, ELiTES stimulated Japanese graduate students
to visit Europe. Three graduate students in Ph.D. course of our
project office stayed at University of Glasgow and FriedrichSchiller-Universitaet Jena, NIKHEF (Amsterdam), Universityof Rome La Sapienza, respectively, within a few months.
Data aqcuisition and control[Spokesperson : Osamu MIYAKAWA]
ICRR, The Univ. of Tokyo, Hida, Gifu 506-1205

KAGRA collects many signals from all of subsystems in
the interferometer, not only for a main gravitational wave sig-

Fig. 7. A test piece of the sapphire fiber with nail heads (a whitebar with a white nail head on the right hand side). This piece isinstalled in an apparatus to measure the thermal conductivity. The
actual KAGRA fibers to suspend the mirror are about 300 mm inlength.

58

nal but also additional control signals for length and alignment of optics, physical environmental monitor signals fromsensors and so on. The total number of signals will be morethan 2000 channels. These signals are collected into a dataacquisition (DAQ) system. In this fiscal year, we have constructed and tested a full scale DAQ system for KAGRA asa preparation of installation into the mine (see Fig.8). DAQ
system consists of 3 parts, Data Concentrator (DC), Network
Data Service (NDS) and Frame Writer (FW). All the data fromKAGRA is collected into the DC server once, and it is distributed into the NDS and FW servers through 10GB networkwith a low latency protocol. The NDS server works as a data
manager which is responsible for requests from users or data
analysis software. The FW server stores some selected data
as DAQ channels into disks. We have prepared 200 TB disk
storage for the initial operation of KAGRA for one month full
data and one-two years commissioning data for full KAGRA.
Whole KAGRA may require several Peta-byte class data storage for observation in several years.

of control. Signals from sensors in an interferometer are collected by ADC, then they are filtered in computers, and finally they are fedback to mirrors to actuate the interferometer.
A transmission of control signals among computers is very
critical. Even a small delay which may happen in the general network protocol can break control loops easily. To establish a very low latency connection, the reflective memory(RFM) networks are used in this system. Memories of remotecomputers are immediately reflected on memories of the local
computer through the RFM.
We have tested connections between multiple RTFM computers and above the DAQ system, and we verified that all
the data from computers is collected in the DC server andtransmitted into downstream with 10GB speed. This system
is called a Large scale Network System (LNS) in altogether.
This LNS is a preparation of KAGRA’s control system which
has been constructed outside of the mine, and the whole system of this LNS will be directly moved into the mine. It will
be used as an actual full scale KAGRA’s control system withsome additional RTFE computers connected into subsystemsof KAGRA, e.g. vibration isolation system or photo detectors.
Between the digital system and subsystem, or to makesubsystem itself work, many analog circuits will be used in
KAGRA. The total number of circuit will be more than 800
boxes. We are designing and manufucturing the circuits. Recently we have just started providing the circuits to people
who need circuits for their subsystem.
Combined system with analog and digital will provide us
not only to control the interferometer but also to establish a
total monitoring/diagnostic system for an observation of thegravitational waves in the future.
Collaboration research with the Korean gravitational wave
group
[Spokesperson : Seiji KAWAMURA]
ICRR, The Univ. of Tokyo, Hida, Gifu 506-1205

Fig. 8. Part of DAQ system for KAGRA. All data from KAGRA is collected into these computers. The DAQ system and real time front-end computers are synchronized by timing system shown in blue
chassis in this picture.

Another important part of KAGRA’s control system is thereal time front-end (RTFE) which consists of a server classcomputer, PCIe extension chassis, ADC (analog to digital converter) and DAC (digital to analog converter) modules. ADC
is a front-end of DAQ, on the other hand DAC is a front-end

We have a close collaboration on KAGRA with the Korean
gravitational wave group since 2012. We exchanged someresearchers to perform some collaboration research with thehelp of the JSPS core-to-core program we obtained startingfrom April, 2013. For the instrument development, Tai Hyun
Yoon (Korea University) spent two months in the summer of2013 at ICRR as a visiting professor to develop the fiber ringcavity with his student and another student of Norikatsu Mio(University of Tokyo). He successfully stabilized the laser
frequency using the fiber ring cavity. Later in the KAGRA
input/output optics group led by Seiji Kawamura (ICRR) we
discussed and decided to use the technology for iKAGRA if
the frequency stability attained is satisfactory. Then it was decided and approved that Tai Hyun Yoon will visit ICRR again
for two months in the summer of 2014 as a visiting professor
to refine the system and measure the stability. For the data
analysis led by Hideyuki Tagoshi (Osaka University), as oneof the collaboration research between Japan and Korea, we
worked on the Bayesian parameter estimation method of thegravitational waves from colasescing compact binaries in the
KAGRA data analysis. From the Korean side, Hyung Won
Lee (Inje University), Jeongcho Kim (Inje University), and59

Chunglee Kim (Seoul National University) participated thisresearch. We had been working on the research of basic papers on the Bayesian parameter estimation methods and the
profiling the pipeline used in the LIGO data analysis. For
the detector characterization led by Kazuhiro Hayama (Osaka City University), in order for KAGRA to reach its design sensitivity quickly, one of important activities was to develop a system to localize noise sources to be suppressed using information from the auxiliary instrumental channels. We
collaborated with the Korean detector characterization group,
involving John J. Oh (NIMS), Sang-Hoon Oh (NIMS), Edwin J. Son (NIMS), and Young-Ming Kim (PNU), to develop
the system based on the multi-channel analysis method basedon the artificial neural network (ANN) algorithm, which the
Korean group had developed. The Japanese members were
granted accounts to access the KISTI cluster in Korea andstart collaborating development using the LIGO S5 auxiliary
channel data on the cluster. We have been integrating the
ANN based multi-channel analysis software package into ourdetector-characterization software package called HasKAL.
For the data management, we considered the data tier plans,
including usage of GRID computing. We also contacted Japanese and Korean astronomers who were working on opticalobservations, or X- and Gamma-Ray detectors. Between April,2013 and March, 2014, we had two Korea-Japan workshops
on KAGRA and we discussed the past activities and future
plan in details.

CLIO Project[Spokesperson : Masatake Ohashi]
ICRR, The Univ. of Tokyo, Kashiwa, Chiba 277-8582

In collaboration with members of: KEK, Tsukuba; Kyoto-U,
Kyoto; ERI of UT, Tokyo
Overview of CLIO
CLIO (Cryogenic Laser Interferometer Observatory) is a
100 m-baseline underground cryogenic interferometer at the
Kamioka Mine. CLIO forms a bridge connecting the CLIK
(7 m prototype cryogenic interferometer at Kashiwa campus)
and the KAGRA (3 km cryogenic interferometer at Kamioka).
The site of CLIO, near the Super-Kamiokande neutrino detector, is shown in Fig. 9. The tunnel was dug in 2002, and astrain meter for geophysics was installed in 2003 [1]. The
construction of CLIO began in late 2003, and installation of
the mode cleaner vacuum system was reported in the annual
report (2003–2004). Four sets of cryostats and whole vacuum
system were installed (annual report 2004–2005). We started
the operation of CLIO in 2006 (annual report 2006).
The prime purpose of CLIO is to demonstrate mirror thermal noise reduction with cryogenic mirrors. We achieved thedesign sensitivity at the room temperature after noise hunting taken in 2008 (Annual report 2008) [2, 3]. After then, we
started out cooling the mirrors and noise hunting with the mirrors under 20K had been done. We firstly observed the sensitivity improvement due to the mirror thermal noise reduction.
CLIO sensitivity curve with cooled mirrors (cryogenic sensitivity) and without cooling (300K sensitivity) are shown in

Fig. 10. Overview of the CLIO interferometer.

Fig. 12 with estimation curves of the mirror thermal noise.
The 300K sensitivity and the cryogenic sensitivity were measured at 2008/11/5 and at 2010/03/20, respectively. When the
cryogenic sensitivity was measured, two front mirrors werecooled and the rest of two end mirrors were at the room temperature. Temperature of the front mirrors were 17K and 18K.
Modifications possibly affecting the sensitivity at the cryogenic sensitivity measurement are exchange of final suspension wires and addition of heat link wires to the suspension
systems. Cooling the mirror took about 250 hours and vacuum
pressure was better than 10−4 Pa for both sensitivity measurements.
The noise floor level of the cryogenic sensitivity from 90Hz
to 240Hz is below the 300K sensitivity. Observation range
for GWs from neutron star binary coalescence was also improved to 159kpc from 148kpc for the optimum direction.
This is the first observation of sensitivity improvement by thecryogenic mirrors.
√ The noise floor at 165Hz√ was reduced to
2.2 × 10−19 m/ Hz from 3.1 × 10−19 m/ Hz after coolingthe front mirrors. Amount of this noise floor reduction is consistent with the estimation of mirror thermal noise reduction
due to cooling. This achievement has been published in 2012
[4].
Digital control in CLIO
Since KAGRA will have a very complicated control topology in its optical configuration called as RSE (resonant sideband extraction). A digital control system using multiple computers will be used since the computer based human interface
provides us a very good flexibility to control such a complicated interferometer, and it is expected to reduce noise hunting
time for KAGRA.
We are continuously developing a standalone based digital controls system in CLIO. CLIO is a very good test bench
for the control system since we can use a whole function of
the begin operated interferometer, and the gravitational wave
data and the control signal data produced by CLIO are quite
similar as KAGRA’s data. Advanced lock acquisition techniques were tested with this system and it was shown that thenoise performance using whitening/dewhitening filters was almost the same as the analog control servo. Recently some data
monitoring system and timing synchronization have been de-

60Fig. 9. Location of the CLIO interferometer.

!

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9 76504321/0/.-,+*)(!

3:!!A3*/1*)2)B)2@
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8

Fig. 11. A sapphire mirror and cryogenic suspension systemveloped and tested, and the results are ready to be used in alarger scale control systems for KAGRA.
Study for the next generation techniques
Although construction of KAGRA is on going, researches
and developments of techniques to realize much more sensitive detectors are still important. Since CLIO still maintains
the sensitivity, CLIO is a suitable apparatus to test techniques:; ' & %$!!

8:

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Fig. 12. Comparison of CLIO sensitivity curves. 300K sensitivity (solid
blue line) and Cryogenic sensitivity (solid red line) show CLIO sensitivity curves without cooling mirrors measured at 2008/11/05 andwith front mirrors under 20K measured at 2010/03/20, respectively.
300K mirror thermal noise (dot dash gray line) and Cryogenic mirror thermal noise (dot dash blue line) show estimation curve of
mirror thermal noise corresponding to the each sensitivity measurements.

which need a cryogenic laser interferometer. Two study topics
using CLIO for the next generation techniques are on going.
One is development of low-loss optical coating. Another isdevelopment of a high finesse Fabry-Perot cavity using NQD
method[5].

61The mirror thermal noise is still a serious fundamental
noise even using the cryogenic mirror. Dissipation in opticalcoatings on a mirror surface will be dominate the amplitudeof the thermal noise in cryogenic temperature. Purpose of thedevelopment of low-loss mirror coatings is to reduce the mirror thermal noise further more. The current status of the study
is looking for a recipe of a low-loss optical coatings using dissipation measurements of samples of coatings made by an Ion
Beam Spattering machine at NAOJ Mitaka. After finding therecipe, we will make mirrors whose substrates are monolithic
sapphire, dimensions are the same as the mirrors of CLIO.
The mirrors will be installed in CLIO and we will investigate
the mirror thermal noise reduction in cryogenic temperature.
A Fabry-Perot cavity having a high finesse and a long cavity length is important to realize Resonant Sideband Extraction (RSE) method with a higher gain. The high gain RSE provides not only a sensitivity improvement in high frequency region, but also decreasing heat generation in test masses causedby laser absorption in substrates. The decreasing heat generation is important for cooling test masses at cryogenic temperature. The most difficult issue to realize a Fabry-Perot cavity
having a high finesse and a long cavity length is a lock acquisition for an optical cavity to resonance. Since we have alreadydeveloped NQD method[5] to solve this issue using the Mode
Cleaner optical cavity of CLIO, we will apply this method to
the 100 m arm cavity of CLIO to demonstrate a Fabry-Perotcavity having a high finesse and a long cavity length. We
are making new test masses made of sapphire as well as thecurrent test masses of CLIO, and new test masses will havelaser reflection coating whose reflection ratio of 0.99999 instead of the current value of 0.999. We will exchange new
test masses with high reflection with the current test masses,
and construct Fabry-Peort cavities whose length is 100 m andFinesse is 300,000 instead of the current Finesse of 3,000.

Bibliography[1] S. Takemoto, et al., Journal of Geodynamics 41 (2006)
23.
[2] S. Miyoki, et al., Journal of Physics: Conference Series
203 (2010) 012075.
[3] T. Uchiyama and S. Miyoki, ”Experimental Demonstration of Cryogenic Mirror Technique - Achievements of
CLIO-”, J. Cryo. Super. Soc. Jpn., 46 (2011) 392-399.
[4] Takashi Uchiyama, Shinji Miyoki, Souichi Telada,
Kazuhiro Yamamoto, Masatake Ohashi, Kazuhiro Agatsuma, Koji Arai, Masa-Katsu Fujimoto, Tomiyoshi
Haruyama, Seiji Kawamura, Osamu Miyakawa, Naoko
Ohishi, Takanori Saito, Takakazu Shintomi, Toshikazu
Suzuki, Ryutaro Takahashi, Daisuke Tatsumi, ”Reduction of thermal fluctuations in a cryogenic laser interferometric gravitational wave detector”, Phys. Rev. Lett.
108, 141101 (2012) [5 pages].
[5] S. Miyoki, S.Telada and T.Uchiyama, “Expansion of linear range of Pound-Drever-Hall signal”, Applied Optics,
Vol. 49, Issue 28, pp.5217-5225 (2010) .

Observational Cosmology Group[Spokesperson : Yoshiaki Ono]
ICRR, The Univ. of Tokyo, Kashiwa, Chiba 277-8582

An Intensely Star-Forming Galaxy at z ∼ 7 with Low
Dust and Metal Content Revealed by Deep ALMAand HST Observations [1]
In collaboration with the members of The University of Tokyo,
Kavli Institute for the Physics and Mathematics of the Universe, California Institute of Technology, The Graduate University for Advanced Studies, Joint ALMA Observatory, HarvardSmithsonian Center for Astrophysics, and National Astronomical Observatory of Japan.
We report deep ALMA observations complemented by associated HST imaging for a luminous (mUV = 25) galaxy,“Himiko”, at a redshift z = 6.595. The galaxy is remarkablefor its high star formation rate, 100M yr−1 , which has been
securely estimated from our deep HST and Spitzer photometry, and the absence of any evidence for strong AGN activity
or gravitational lensing magnification. Our ALMA observations probe an order of magnitude deeper than previous IRAM
observations, yet fail to detect a 1.2 mm dust continuum, indicating a flux of < 52µJy, which is comparable to or weaker
than that of local dwarf irregulars with much lower star formation rates (Figure 13). We likewise provide a strong upper limit for the flux of [C II ] 158µm, L[CII] < 5.4 × 107 L ,which is a diagnostic of the hot interstellar gas that is often
described as a valuable probe for early galaxies. In fact, ourobservations indicate that Himiko lies off the local L[CII] –starformation rate scaling relation by a factor of more than 30.
Both aspects of our ALMA observations suggest Himiko is aunique object with a very low dust content and perhaps nearly
primordial interstellar gas. Our HST images provide uniqueinsight into the morphology of this remarkable source, highlighting an extremely blue core of activity and two less extreme associated clumps. Himiko is undergoing a triple major
merger event whose extensive ionized nebula of Lyα emittinggas, discovered in our earlier work with Subaru, is poweredby star formation and the dense circumgalactic gas. We arelikely witnessing an early massive galaxy during a key periodof its mass assembly close to the end of the reionization era.

Bibliography[1] Ouchi, M., et al. 2013, Astrophys. J., 778, 102

Evolution of the Sizes of Galaxies over 7 < z < 12
Revealed by the 2012 Hubble Ultra Deep Field Campaign [2]In collaboration with the members of The University of Tokyo,
Kavli Institute for the Physics and Mathematics of the Universe, University of Edinburgh, California Institute of Tech-62

Fig. 13. Optical to far-infrared SED of Himiko in the observed frame.
The filled square shows the upper limit from our deep ALMA Band
6 observations and the filled circles represent photometry from
HST/WFC3 J125 and H160 photometry and Spitzer SEDS 3.6 and4.5µm. The filled pentagons indicate the UKIDSS-UDS DR8 J, H,
and K photometry. The cross and plus symbols denote HST/WFC3
F098M and Suprime-Cam NB921 photometry that includes Lyαemission and the Gunn-Peterson trough in their bandpasses. The
open circles and arrows are data points and the upper limits takenfrom the literature. The open diamond with an arrow shows theupper limit from the IRAM observations. The red, magenta, green,
and blue lines represent the SEDs of local galaxies, Arp220, M82,
M51, and NGC6946, respectively, redshifted to z = 6.595. SEDsof local dwarf irregular galaxies similarly redshifted are presented
with cyan lines. All local galaxy SEDs are normalized in therest-frame UV, where Himiko’s SED is reliably determined. This
figure is reproduced by permission of the AAS.

nology, University of Arizona, Space Telescope Science Institute, Institut d’Astrophysique de Paris, and University ofCalifornia.
We analyze the redshift- and luminosity-dependent sizesof dropout galaxy candidates in the redshift range z ∼ 7 − 12
using deep images from the 2012 Hubble Ultra Deep Field(UDF12) campaign, which offers two advantages over thatused in earlier work. First, we utilize the increased signalto-noise ratio offered by the UDF12 imaging to provide improved measurements for known galaxies at z ' 6.5 − 8 in
the HUDF. Second, because the UDF12 data have allowed theconstruction of the first robust galaxy sample in the HUDF
at z > 8, we have been able to extend the measurement of
average galaxy size out to higher redshifts. Restricting ourmeasurements to sources detected at > 15σ , we confirm earlier indications that the average half-light radii of z ∼ 7 − 12galaxies are extremely small, 0.3 − 0.4 kpc, comparable tothe sizes of giant molecular associations in local star-forming
galaxies. We also confirm that there is a clear trend of decreasing half-light radius with increasing redshift, and provide the first evidence that this trend continues beyond z ' 8(Figure 14). Modeling the evolution of the average half-lightradius as a power-law, ∝ (1 + z)s , we obtain a best-fit index+0.12
of s = −1.30−0.14
over z ∼ 4 − 12. A clear size-luminosity
relation is evident in our dropout samples. This relation can

Fig. 14. Left: evolution of the half-light radius across the redshift range∗ . The filled circles show the average
from z ∼ 2 to 12 in (0.3 − 1)Lz=3
sizes of our z850 -dropouts and Y105 -dropouts, and the size of thez ∼ 12 object. The open symbols are taken from the literature Afterexcluding the sample overlaps, we fit simple functions of (1 + z)s
with the data in both luminosity bins, and obtain s = −1.30+0.12−0.14 .
which is shown as the solid line. The dotted and dashed lines
correspond to the case of s = −1.0 and −1.5, respectively. Right:
evolution of the half-light radius across the redshift range from z ∼ 4∗ . The open and filled black symbols denoteto 8 in (0.12 − 0.3)Lz=3
the same as those in the top panel. The gray filled circles are∗ .
dropout galaxies in the fainter luminosity bin, (0.048 − 0.12)Lz=3
The solid, dotted, and dashed lines are the same as those in theleft panel. This figure is reproduced by permission of the AAS.

be interpreted in terms of a constant surface density of star
∗ . Theformation over a range in luminosity of 0.05 − 1.0Lz=3
average star formation surface density in dropout galaxies is
2 − 3 orders of magnitude lower than that found in extreme
starburst galaxies, but is comparable to that seen today in thecenters of normal disk galaxies.

Bibliography[2] Ono, Y., Ouchi, M., et al. 2013, Astrophys. J., 777, 155

What is the Physical Origin of Strong Lyα Emission?
I. Demographics of Lyα Emitter Structures [3]
In collaboration with the members of The University of Tokyo,
The University of Tsukuba, and Kavli Institute for the Physics
and Mathematics of the Universe.
We present the results of structure analyses for a large
sample of 426 Lyα emitters (LAEs) at z ∼ 2.2 that are observed with HST/ACS and WFC3-IR during deep extra-galactic
legacy surveys. We confirm that the merger fraction and theaverage ellipticity of LAE’s stellar component are 10 − 30%
and 0.4 − 0.6, respectively, that are comparable with previous
study results. We successfully identify that some LAEs havea spatial offset between Lyα and stellar-continuum emission
peaks, δLyα , by ∼ 2.5 − 4 kpc beyond our statistical errors. To
uncover the physical origin of strong Lyα emission found in
LAEs, we investigate the Lyα equivalent width (EW) dependences of three structural parameters: merger fraction, δLyα ,and ellipticity of stellar distribution in the range of EW (Lyα) =20 − 250 Å. Contrary to expectations, we find that the merger
fraction does not significantly increase with Lyα EW (Figure15). We reveal an anti-correlation between δLyα and EW (Lyα)
using a Kolmogorov–Smirnov (K-S) test. There is a trend that
the LAEs with a large Lyα EW have a small ellipticity. This

Merger Fraction

Number63
40
20

Asymmetry, I814

Asymmetry, H160

0
300
200
100
0

Close−pair, I814

Close−pair, H160

0.6
0.5
0.4
0.3
0.2
0.1
0
0

Close−pair, I814
Asymmetry, I814

50
H160
H160

100

150

200

250

EW(Lyα) [Å]Fig. 15. Merger fraction of z = 2.2 LAEs as a function of Lyα EW. The
blue and red symbols indicate the merger fractions in I814 and H160 ,respectively. The filled and open circles denote the merger fraction in the close-pair method and the A classification, respectively.
Error bars in each plot include the Poisson statistical error. Error
bars in Lyα EW indicate the bin widths. The symbols are slightly
shifted along the x-axis for the sake of clarity. There are no LAEs
in H160 in the highest EW bin for the A classification, because no
mergers are found in this EW bin. The histograms in the upperand middle panels show the number of LAEs in each Lyα EW bin
in the A classification and the close-pair method, respectively. This
figure is reproduced by permission of the AAS.

is consistent with the recent theoretical claims that Lyα photons can more easily escape from face-on disks having a small
ellipticity, due to less inter-stellar gas along the line of sight,
although our KS test indicates that this trend is not statistically significant. Our results of Lyα-EW dependence generally support the idea that an H I column density is a key
quantity determining Lyα emissivity.

Fig. 16. Emission line flux ratio [O III]/[O II] vs. R23-index for ourz = 2.2 LAEs (CDFS-3865: the solid red circle; COSMOS-30679:
the open red circle) and non-LAEs (the blue symbols); the metal-poor BX galaxy at z = 2.3 (the open pentagon), lensed galaxies at z ∼ 2 (the crosses, the open diamonds, and the open
square), the lensed galaxy at z = 3.4 (the solid star), and z ∼ 3
LBGs (the solid pentagons, the solid squares), as well as thestar-forming galaxies at 0.47 < z < 0.92 (the black open triangles),and local star-forming galaxies in the low-metallicity range (7 .
12+log(O/H) . 8.5: the gray diamonds) and high-metallicity range(12 + log(O/H) & 8.2: the gray dots). The values on this plot are
not corrected for dust extinction, except for the local data points.
For CDFS-3865 and COSMOS-30679, effects of their extinction
corrections are indicated by the red small arrows. The black gridshows photoionization model calculations. For reference, the relations of qion = 3 × 108 , 8 × 107 , and 2 × 107 cm s−1 are shown,linked to each other at same metallicities, which are denoted by
12 + log(O/H) values with dots. This figure is reproduced by permission of the AAS.

108 cm s−1 ) and a low oxygen abundance (12 + log(O/H) =7.84+0.24−0.25 ) in contrast with moderate values of other high-z
galaxies such as Lyman break galaxies (LBGs). COSMOS30679 also possesses a relatively high ionization parameter
7−1
Bibliography(qion = 8+10
−4 × 10 cm s ) and a low oxygen abundance (12 +[3] Shibuya, T., Ouchi, M., et al. 2014 Astrophys. J., 785, 64 log(O/H) = 8.18+0.28 ). Both LAEs appear to fall below the−0.28
mass-metallicity relation of z ∼ 2 LBGs. Similarly, a low
metallicity of 12 + log(O/H) < 8.4 is independently indicatedFirst Spectroscopic Evidence for High Ionization State for typical LAEs from a composite spectrum and the [N II]/Hα
and Low Oxygen Abundance in Lyα Emitters [4]index. Such high ionization parameters and low oxygen abunIn collaboration with the members of The University of Tokyo, dances can be found in local star-forming galaxies, but thisKavli Institute for the Physics and Mathematics of the Uni- extreme local population occupies only ∼ 0.06% of the SDSS
verse, Space Telescope Science Institute, and Observatories spectroscopic galaxy sample with a number density ∼ 100
times smaller than that of LAEs. With their high ionizationof the Carnegie Institution of Washington.
parameters and low oxygen abundances, LAEs would repreWe present results from Keck NIRSPEC and Magellan sent an early stage of galaxy formation dominated by masMMIRS follow-up spectroscopy of Lyα emitters (LAEs) at sive stars in compact star-forming regions. High-qion galaxies
z = 2.2 identified in our Subaru narrowband survey. We suc- like LAEs would produce ionizing photons efficiently with acessfully detect Hα emission from seven LAEs, and perform high escape fraction achieved by density-bounded HII regions,a detailed analysis of six LAEs free from AGN activity, two which would significantly contribute to cosmic reionization atout of which, CDFS-3865 and COSMOS-30679, have [O II] z > 6.
and [O III] line detections. They are the first [O II]-detected
LAEs at high-z, and their [O III]/[O II] ratios and R23-indices
Bibliography
provide the first simultaneous determinations of ionization parameter and oxygen abundance for LAEs (Figure 16). CDFS- [4] Nakajima, K., Ouchi, M., et al. 2013 Astrophys. J., 769, 33865 has a very high ionization parameter (qion = 2.5+1.7−0.8 ×

64
(a)

(b)

Fig. 17. NB816, NB816 corr , and Rz images of O IIB 1. North is up
and east is left. Each panel is 1500 × 1500 (corresponding to 124
kpc ×124 kpc at z = 1.19) with the O IIB at the center. The spatial
scale is indicated in the NB816 images. The yellow contours in
the Rz images show the isophotal area above 2σ arcsec−2 in the
NB816 corr image. This figure is reproduced by permission of the
AAS.

First Systematic Search for Oxygen-Line Blobs at
High Redshift: Uncovering AGN Feedback and StarFormation Quenching [5]In collaboration with the members of The University of Tokyo,
Liverpool John Moores University, Tohoku University, andUniversity of Tsukuba.
We present the first systematic search for extended metalline [O II]λ λ 3726,3729 nebulae, or [O II] blobs (O IIBs), atz = 1.2 using deep narrowband imaging with a survey volume of 1.9 × 105 Mpc3 on the 0.62 deg2 sky of Subaru–XMM
Deep Survey (SXDS) field. We discover a giant O IIB, dubbed“O IIB 1” (Figure 17), with a spatial extent over ∼ 75 kpc at
a spectroscopic redshift of z = 1.18, and also identify a totalof 12 O IIBs with a size of > 30 kpc. Our optical spectrumof O IIB 1 presents [Ne V]λ 3426 line at the 6σ level, indicating that this object harbors an obscured type-2 AGN. The
presence of gas outflows in this object is suggested by two
marginal detections of Fe IIλ 2587 absorption and Fe II∗ λ 2613
emission lines both of which are blueshifted at as large as
500−600 km s−1 , indicating that the heating source of O IIB 1
is AGN or associated shock excitation rather than supernovae
produced by starbursts. The number density of O IIB 1-type
giant blobs is estimated to be ∼ 5 × 10−6 Mpc−3 at z ∼ 1.2,
which is comparable with that of AGNs driving outflow at
a similar redshift, suggesting that giant O IIBs are produced
only by AGN activity. On the other hand, the number density of small O IIBs, 6 × 10−5 Mpc−3 , compared to that ofz ∼ 1 galaxies in the blue cloud in the same MB range, may
imply that 3% of star-forming galaxies at z ∼ 1 are quenching star formation through outflows involving extended [O II]
emission.

Bibliography[5] Yuma, S., Ouchi, M., et al. 2013, Astrophys. J., 779, 53

log

Kennicutt 98
Bigiel et al. 08
This work

log
Fig. 18. K-S plot on 500 pc scale, (a) without and (b) with BG subtraction, for our 10 sample galaxies. The dot-dashed lines are SFEs of
10−8 , 10−9 and 10−10 yr−1 , from top to bottom. The green and bluelines are the best-fit results taken from the literature. The light purple lines are the best-fit linear regressions through our data, yielding slopes of 1.3 (a) and 1.8 (b), respectively. The overlaid black
contours are density distributions of the data points. We also plot
all data points below 3σ as black dots. This figure is reproducedby permission of the AAS.

University, University of Cambridge, Japan Aerospace Exploration Agency, University of Massachusetts, California Institute of Technology, and Joint ALMA Observatory.
We report a super-linear correlation for the star formation
law based on new CO(J = 1–0) data from the CARMA andNOBEYAMA Nearby-galaxies (CANON) CO survey. The
sample includes 10 nearby spiral galaxies, in which structures at sub-kpc scales are spatially resolved. Combined withthe star formation rate surface density traced by Hα and 24µm images, CO(J = 1–0) data provide a super-linear slopeof N = 1.3 (Figure 18a). The slope becomes even steeper(N = 1.8) when the diffuse stellar and dust background emission is subtracted from the Hα and 24 µm images (Figure18b). In contrast to the recent results with CO(J = 2–1) thatfound a constant star formation efficiency (SFE) in many spiral galaxies, these results suggest that the SFE is not independent of environment, but increases with molecular gas surface density. We suggest that the excitation of CO(J = 2–1) islikely enhanced in the regions with higher star formation anddoes not linearly trace the molecular gas mass. In addition, thediffuse emission contaminates the SFE measurement most in
regions where the star formation rate is low. These two effects
can flatten the power-law correlation and produce the apparent linear slope. The super-linear slope from the CO(J = 1–0) analysis indicates that star formation is enhanced by nonlinear processes in regions of high gas density, e.g., gravitational collapse and cloud-cloud collisions.

Bibliography[6] Momose, R., et al. 2013, Astrophys. J. (Letters), 772, L13

Star Formation On Subkiloparsec Scale Triggeredby Non-linear Processes in Nearby Spiral Galaxies[6]
In collaboration with the members of The University of Tokyo,
National Astronomical Observatory of Japan, Stony Brook

65

BBN, which leads to constraints on the new particles and theparticle physics models.
The grand unified theories (GUT) predict that our universe
Theory Group
undergoes several vacuum phase transitions. In the courseof phase transitions topological defects (monopoles, cosmic
Overview
strings and domain walls) are generally produced depending
We have theoretically studied particle physics (mainly par- on symmetries of the vacua. Our group has studied evolution
ticle physics phenomenology) and astroparticle physics (mainly of various topological defects.
particle cosmology).
2013 was one of the important milestone for the particle
Particle Phenomenology
physics and the cosmology. The observed ”Higgs-like scalarparticle” in the mass region around 126 GeV has been con- [Spokesperson : M. Ibe]firmed to be ”the Higgs boson” consistent with the standard ICRR, The Univ. of Tokyo, Kashiwa, Chiba 277-8582
model of particle physics, and also the AMS-02 experimenthas reported an excess of the cosmic-ray positron fraction, Dark Matter, Inflation
which is consistent with the previous observations. The lat• Recent Result of the AMS-02 Experiment and Decaying Gravter result would give a considerable clue to find dark matteritino Dark Matter in Gauge Mediation
candidate. BICEP2 experiment has given us a significant impact by reporting the observation of B-mode polarization of In collaboration with the members of ICRR, IPMU and Unithe cosmic microwave background (CMB), which might be a versity of Tokyo
fingerprint of the inflationary universe. While these experiThe AMS-02 collaboration has recently reported an excess
ments make us confirm the standard model of particle physics
ofcosmic-ray
positron fractions, which is consistent with preand Big bang Universe, they also give us many implications
vious
results
at
PAMELA and Fermi-LAT experiments. The
for extensions of the standard scenarios.
resultindicates
the existence of new physics phenomena to
The supersymmetric (SUSY) extension of the standard
providetheoriginof the energetic cosmic-ray positron. We
model (SM) in the particle physics is considered to be one
pursuethepossibility
that the enhancement of the positronof the most promising models beyond the standard model. It
fraction
is
due
to
the
decay
of gravitino dark matter. We dissolves the naturalness problem for the Higgs boson mass term
cuss
that
such
a
scenario
viablyfits into the models in whichin the standard model, and it is also compatible with the grand
the
soft
SUSY
breaking
parameters
are dominantly from gaugeunified theories (GUTs). Our group has been studying phemediation
mechanismwithsuperparticle
masses of around 10
nomenological and cosmological aspects of the SUSY modTeV.
Ourscenarioiscompatible
with126
GeV Higgs boson,els.
negativesearchesfor
SUSY
particles,
andnon-observation
of
Recent cosmological observations including the Planck data
anomalous
FCNC
processes.
We
also
point
out
that
the
scedetermine precisely the mean densities of matter and baryon
in the Universe, and existence of non-baryonic dark matter is nario will be tested in near future by measuring the electric
established. Weakly interacting massive particles (WIMPs) dipole moment of the electron and the lepton flavor violating
are considered to be good candidates of the dark matter. They decay of the muon.
act as the cold dark matter in the structure formation of theuniverse. Our group has been studying model building fordark matter and detectability in direct and indirect search experiments.
For understanding of the early universe, a role of the elementary particle physics is crucial. Recent progress in the particle physics such as grand unification theories and supersymmetry leads us to a more deeper insight into the fundamental
aspects of the early universe. In the inflationary universe, thequantum fluctuations of the scalar field which drives the inflation become the density fluctuations and lead to formation of
the structure observed in the present universe. On the other
hand cosmology and astrophysics are used to test new theories in particle physics. Such particle cosmology is one ofmain subjects of our group.
Big Bang Nucleosynthesis (BBN) is one of the most important subjects in modern cosmology. Predicted abundancesof the light elements are very sensitive to the cosmologicalscenario. On the other hand, physics beyond the standard
model predicts the new particles which would have existed
at the BBN epoch. Such particles may spoil the success of• AMS-02 Positrons from Decaying Wino in the Pure Gravity
Mediation ModelIn collaboration with the members of ICRR, IPMU and UC
Berkeley
The AMS-02 collaboration has recently reported an excess of the cosmic-ray positron fraction, which turned out tobe consistent with previous results reported by the PAMELA
and Fermi-LAT collaborations. A decaying dark matter withthe mass around 1 TeV can be responsible for the excess of thepositron fraction when it is interpreted as a dark matter signal.
Interestingly, the pure gravity mediation model provides sucha dark matter, namely an almost pure neutral wino dark matter, when a tiny R-parity violation through LLE c interactions
is introduced. We show that the decaying wino dark matter
well reproduces the energy spectrum of the fraction with being consistent with constraints from cosmic-ray anti-protonand gamma-ray observations.

66• Mixed (Cold+Warm) Dark Matter in the Bino-Wino co-annihilation
scenario
2 ton-year
4 ton-year
10 ton-year
30 ton-year

1.0

f p" fn

0.5
0.0

!0.5

.6 ton-year.2 ton-year
7.0

7.2

7.4

7.6
7.8
8.0
Log10!MDM"GeV#

8.2

8.4

Fig. 19. The required effective exposures for a 90%C.L. exclusion of
the isospin violation dark matter for a given hypercharged dark
matter mass. Isospin preserving dark matter corresponds tof p / fn = 1, and Z-mediated scattering (this model) is shown as
the dashed line. The shaded region has been excluded by the
XENON100 experiments.

• Hypercharged Dark Matter and Direct Detection as a Probeof Reheating
In collaboration with the members of ICRR, and IPMU
The lack of new physics at the LHC so far weakens the argument for TeV scale thermal dark matter. On the other hand,heavier, non-thermal dark matter is generally difficult to test
experimentally. Here we consider the interesting and genericcase of hypercharged dark matter, which can allow for heavy
dark matter masses without spoiling testability. Planned direct
detection experiments will be able to see a signal for masses
up to an incredible 1010 GeV, and this can further serve toprobe the reheating temperature up to about 109 GeV, as determined by the non-thermal dark matter relic abundance. The
Z-mediated nature of the dark matter scattering may be determined in principle by comparing scattering rates on different
detector nuclei, which in turn can reveal the dark matter mass.
We will discuss the extent to which future experiments may
be able to make such a determination (see Fig. 19).
• Lower Bound on the Garvitino Mass m3/2 > O(100) TeV in
R-Symmetry Breaking New Inflation
In collaboration with the members of ICRR, and IPMU
In supersymmetric theories, the R-symmetry plays a uniquerole in suppressing a constant term in the superpotential. In
single chiral field models of spontaneous breaking of a discrete R-symmetry, an R-breaking field can be a good candidate for an inflaton in new inflation models. In this paper, we
revisit the compatibility of the single-field R-breaking new inflation model with the results of the Planck experiment. As
a result, we find that the model predicts a lower limit on thegravitino mass, m3/2 > O(100) TeV. This lower limit is consistent with the observed Higgs mass of 126 GeV when themasses of the stops are of order the gravitino mass scale.

In collaboration with the members of ICRR, and IPMU
We study phenomenological aspects of the bino-wino coannihilation scenario in high-scale supersymmetry breaking
models. High-scale SUSY breaking scenarios are considered
to be promising possibility after the discovery of the Higgs
boson with a mass around 126 GeV. In this paper, we discuss
the bino lightest supersymmetric particle (LSP) accompaniedby the at most around 30 GeV heavier wino. With the suitablemass splitting between the bino and the wino, the bino LSP
has the correct relic abundance of dark matter. For the smaller
mass splitting, the late-time decay of the gravitino can provide
the correct abundance of the bino dark matter. It is extremely
challenging to find signals from the bino dark matter in direct
and indirect detections. By utilizing multi-jets plus missing
transverse momentum events at the LHC, we can constraint
the gluino mass and thus probe the bino-wino co-annihilation
scenario indirectly. The collider experiment, however, can notsearch the bino dark matter directly. In this paper, we suggest
the direct probe of the bino dark matter. We show that the bino
dark matter leaves imprints on the small-scale matter power
spectrum when the bino dark matter is produced by the decayof the gravitino. The non-thermal bino dark matter behaves as
mixed (cold+warm) dark matter.
• Dynamical Chaotic Inflation in the Light of BICEP2
In collaboration with the members of ICRR and IPMU
The measurement of a large tensor-to-scalar ratio by the
BICEP2 experiment, r = 0.20 (-0.05)(+0.07), severely restricts
the landscape of viable inflationary models and shifts attention once more towards models featuring large inflaton fieldvalues. In this context, chaotic inflation based on a fractional
power-law potential that is dynamically generated by the dynamics of a strongly coupled supersymmetric gauge theory
appears to be particularly attractive. We revisit this class of
inflation models and find that, in the light of the BICEP2
measurement, models with a non-minimal gauge group behind the dynamical model seem to be disfavored, while themodel with the simplest group, i.e. SU(2), is consistent withall results. We also discuss how the dynamical model can be
distinguished from the standard chaotic inflation model basedon a quadratic inflaton potential.
• High-Scale SUSY Breaking Models in light of the BICEP2ResultIn collaboration with the members of ICRR and IPMU
The large value of the tensor-to-scalar ratio in the cosmic
microwave background radiation reported by the BICEP2 collaboration gives strong impact on models of supersymmetry(SUSY). The large ratio indicates inflation with a high-energy
scale and thus a high reheating temperature in general, andvarious SUSY models suffer from the serious gravitino andPolonyi problems. In this article, we discuss a class of thehigh-scale SUSY breaking models which are completely free67

from those problems. With especially focusing on the dark
matter relic abundance, we examine how the BICEP2 result
narrows down the parameter space of the models, assuming
the simplest chaotic inflation model. We find that the mass ofthe dark matter is predicted to be less than about 1 TeV thanks
to the non-thermal production in the early universe throughthe decay of abundant gravitinos produced after the reheatingprocess. We also discuss implications in some details to dark
matter searches at collider and indirect dark matter detection
experiments.

Bibliography[1] M. Ibe, S. Iwamoto, S. Matsumoto, T. Moroi and
N. Yokozaki, JHEP 1308, 029 (2013) [arXiv:1304.1483[hep-ph]].
[2] M. Ibe, S. Matsumoto, S. Shirai and T. T. Yanagida,
JHEP 1307, 063 (2013) [arXiv:1305.0084 [hep-ph]].
[3] B. Feldstein, M. Ibe and T. T. Yanagida, Phys. Rev. Lett.
112, 101301 [arXiv:1310.7495 [hep-ph]].
[4] K. Harigaya, M. Ibe and T. T. Yanagida, Phys. Rev. D
89, 055014 (2014) [arXiv:1311.1898 [hep-ph]].

• Peccei-Quinn symmetry from a gauged discrete R symmetry
In collaboration with the members of ICRR, and IPMU
The axion solution to the strong CP problem calls for an
explanation as to why the Lagrangian should be invariant under the global Peccei-Quinn (PQ) symmetry, U(1)PQ, to sucha high degree of accuracy. In this paper, we point out that
the U(1)PQ can indeed survive as an accidental symmetry in
the low-energy effective theory, if the standard model gauge
group is supplemented by a gauged and discrete R symmetry,
ZNR, forbidding all dangerous operators that explicitly breakthe Peccei-Quinn symmetry. In contrast to similar approaches,
the requirement that the ZNR symmetry be anomaly-free forces
us, in general, to extend the supersymmetric standard modelby new matter multiplets. Surprisingly, we find a large landscape of viable scenarios that all individually fulfill the current experimental constraints on the QCD vacuum angle aswell as on the axion decay constant. In particular, choosing
the number of additional multiplets appropriately, the order Nof the ZNR symmetry can take any integer value larger than 2.
This has interesting consequences with respect to possible solutions of the problem, collider searches for vectorlike quarks
and axion dark matter.

[5] M. Ibe, A. Kamada and S. Matsumoto, Phys. Rev. D 89,
123506 (2014) [arXiv:1311.2162 [hep-ph]].

• A Closer Look at Gaugino Masses in Pure Gravity Mediation Model/Minimal Split SUSY Model[6] K. Harigaya, M. Ibe, K. Schmitz and T. T. Yanagida,
Phys. Lett. B 733, 283 (2014) [arXiv:1403.4536 [hepph]].

In collaboration with the members of ICRR, and IPMU

[7] K. Harigaya, M. Ibe, K. Ichikawa, K. Kaneta and S. Matsumoto, arXiv:1403.5880 [hep-ph].

Supersymmetric extensions of the Standard Model• Non-Universalities in Pure Gravity Mediation
In collaboration with the members of ICRR, IPMU and Minnesota U.
The simplest model of pure gravity mediation contains
only two free parameters: the gravitino mass and tan β . Scalarmasses are universal at some high energy renormalization scaleand gaugino masses are determined through anomalies anddepend on the gravitino mass and the gauge couplings. This
theory requires a relatively large gravitino mass (m3/2 & 300
TeV) and a limited range in tan β ' 1.7 − 2.5. Here we generalize the theory to allow for non-universality in the Higgs
soft masses. This introduces zero, one or two new free parameters associated with Higgs soft masses. This generalization
allows us to greatly increase the allowed range in tan β and it
allows one to find viable solutions with lower m3/2 . The latter is important if we hope to find a low energy signal fromgluinos. Some special cases of these non-universalities aresuggestive of Higgs bosons as Nambu-Goldstone bosons ora partial no-scale structure for the Higgs doublets. Thus, weprobe signatures at the weak scale and structures at the GUT
and/or Planck scale.

We take a closer look at the gaugino masses in the context
of pure gravity mediation models/minimal split SUSY models. We see that the gaugino mass spectrum has a richer structure in the presence of vector-like matter fields even when they
couple to the supersymmetry breaking sector only throughPlanck suppressed operators. For example, the gluino masscan be much lighter than in anomaly mediation, enhancing thedetectability of the gluino at the LHC experiments. The richgaugino spectrum also allows new possibilities for dark matter
scenarios such as the bino-wino co-annihilation, bino-gluino
co-annihilation, or even wino-gluino co-annihilation scenarios, which affects future collider experiments as well as dark
matter search experiments.
• One-loop anomaly mediated scalar masses and (g − 2)µ in
pure gravity mediation
In collaboration with the members of ICRR, IPMU and Minnesota U.
We consider the effects of non-universalities among sfermion generations in models of Pure Gravity Mediation (PGM).
In PGM models and in many models with strongly stabilized
moduli, the gravitino mass may be O(100) TeV, whereas gaugino masses, generated through anomalies at 1-loop, remain
relatively light O(1) TeV. In models with scalar mass universality, input scalar masses are generally very heavy (m0 'm3/2 ) resulting in a mass spectrum resembling that in split
supersymmetry. However, if one adopts a no-scale or partial
no-scale structure for the Kähler manifold, sfermion masses
may vanish at the tree level. It is usually assumed that the

68leading order anomaly mediated contribution to scalar masses
appears at 2-loops. However, there are at least two possible
sources for 1-loop scalar masses. These may arise if PauliVillars fields are introduced as messengers of supersymmetry breaking. We consider the consequences of a spectrum inwhich the scalar masses associated with the third generation
are heavy (order m3/2 ) with 1-loop scalar masses for the firsttwo generations. A similar spectrum is expected to arise in
GUT models based on E7 /SO(10) where the first two generations of scalars act as pseudo-Nambu-Goldstone bosons. Explicit breaking of this symmetry by the gauge couplings thengenerates one-loop masses for the first two generations. In
particular, we show that it may be possible to reconcile the(g − 2)µ discrepancy with potentially observable scalars andgauginos at the LHC.

• Testing the Minimal Direct Gauge Mediation at the LHC
In collaboration with the members of ICRR, IPMU and University of Tokyo
We reexamine the models with gauge mediation in view ofthe minimality. As a result, we arrive at a very simple modelof direct gauge mediation which does not suffer from the flavor problems nor the CP problems. We show that the parameter space which is consistent with the Higgs boson mass ataround 126 GeV can be tested through the stable stau searches
at the 14TeV run of the LHC. The gravitino is a viable candidate for a dark matter. We also give a short discussion on
a possible connection of our model to the recently discovered
X-ray line signal at 3.5 keV in the XMM Newton X-ray observatory data.

• Flat Higgs Potential from Planck Scale Supersymmetry BreakBibliographying[1] J. L. Evans, K. A. Olive, M. Ibe and T. T. Yanagida, Eur.
In collaboration with the members of ICRR, and IPMU
Phys. J. C 73, 2611 (2013) [arXiv:1305.7461 [hep-ph]].
The observed Higgs boson mass poses a new puzzle inaddition to the longstanding problem of the origin of the electroweak scale; the shallowness of the Higgs potential. The
Higgs quartic coupling even seems to vanish at around the
Planck scale within the uncertainties of the top quark massand the strong gauge coupling. We show that the shallownessof the Higgs potential might be an outcome of supersymmetry
breaking at around the Planck scale. There, the electroweak
fine-tuning in the Higgs quadratic terms leads to an almost
vanishing quartic coupling at around the Planck scale.
• Peccei-Quinn Symmetric Pure Gravity Mediation
In collaboration with the members of ICRR, IPMU and Minnesota U.
Successful models of Pure Gravity Mediation (PGM) withradiative electroweak symmetry breaking can be expressedwith as few as two free parameters which can be taken as
the gravitino mass and tan β . These models easily support
a 125 − 126 GeV Higgs mass at the expense of a scalar spectrum in the multi-TeV range and a much lighter wino as thelightest supersymmetric particle. In these models, it is alsoquite generic that the Higgs mixing mass parameter, µ, which
is determined by the minimization of the Higgs potential isalso in the multi-TeV range. For µ > 0, the thermal relic density of winos is too small to account for the dark matter. The
same is true for µ < 0 unless the gravitino mass is of order
500 TeV. Here, we consider the origin of a multi-TeV µ parameter arising from the breakdown of a Peccei-Quinn (PQ)
symmetry. A coupling of the PQ-symmetry breaking field,
P, to the MSSM Higgs doublets, naturally leads to a value ofµ ∼ hPi2 /MP ∼ O(100) TeV and of order that is required in
PGM models. In this case, axions make up the dark matteror some fraction of the dark matter with the remainder madeup from thermal or non-thermal winos. We also provide solutions to the problem of isocurvature fluctuations with axion
dark matter in this context.

[2] K. Harigaya, M. Ibe, K. Schmitz and T. T. Yanagida,
Phys. Rev. D 88, no. 7, 075022 (2013) [arXiv:1308.1227[hep-ph]].
[3] K. Harigaya, M. Ibe and T. T. Yanagida, JHEP 1312, 016(2013) [arXiv:1310.0643 [hep-ph]].
[4] J. L. Evans, M. Ibe, K. A. Olive and T. T. Yanagida, Eur.
Phys. J. C 74, 2775 (2014) [arXiv:1312.1984 [hep-ph]].
[5] M. Ibe, S. Matsumoto and T. T. Yanagida, Phys. Lett. B
732, 214 (2014) [arXiv:1312.7108 [hep-ph]].
[6] J. L. Evans, M. Ibe, K. A. Olive and T. T. Yanagida,
arXiv:1402.5989 [hep-ph].
[7] K. Hamaguchi, M. Ibe, T. T. Yanagida and N. Yokozaki,
arXiv:1403.1398 [hep-ph].

Particle Cosmology[Spokesperson : M. Kawasaki]
ICRR, The Univ. of Tokyo, Kashiwa, Chiba 277-8582
Inflation and Thermal History in the early Universe• Heavy gravitino in hybrid inflation
In collaboration with the members of ICRR, IPMU and University of Tokyo
It is known that supersymmetric hybrid inflation model
may require severe tunings on the initial condition for large
gravitino mass of order 100 − 1000 TeV due to the constantterm in the superpotential. We propose a modified hybrid inflation model, where the constant term is suppressed during
inflation and generated after inflation by replacing a constantterm with dynamical field. In this modified model, successful
inflation consistent with large gravitino mass takes place without severe tunings on the initial condition. Constraint fromcosmic strings is also relaxed [1].

69

• Domain wall and isocurvature perturbation problems in axion models
In collaboration with the members of ICRR and IPMU
Axion models have two serious cosmological problems,domain wall and isocurvature perturbation problems. In orderto solve these problems we investigate the Linde’s model inwhich the field value of the Peccei-Quinn (PQ) scalar is large
during inflation. In this model the fluctuations of the PQ fieldgrow after inflation through the parametric resonance and stable axionic strings may be produced, which results in the domain wall problem. We study formation of axionic strings
using lattice simulations. It is found that in chaotic inflation the axion model is free from both the domain wall andthe isocurvature perturbation problems if the initial misalignment angle θa is smaller than O(10−2 ). Furthermore, axions
can also account for the dark matter for the breaking scalev ' 1012−16 GeV and the Hubble parameter during inflation
Hinf . 1011−12 GeV in general inflation models [2].

result in single field slow-roll inflation. We also describe thealgorithm for numerical calculations of the curvature perturbations in more general inflation models [4].

Bibliography[1] M. Kawasaki,
N. Kitajima,
K. Nakayama
and T. T. Yanagida, JCAP 1306, 037 (2013)[arXiv:1301.6281, arXiv:1301.6281 [hep-ph]].
[2] M. Kawasaki, T. T. Yanagida and K. Yoshino, JCAP
1311, 030 (2013) [arXiv:1305.5338 [hep-ph]].
[3] M. Kawasaki and M. Yamada, arXiv:1311.0985 [hepph].
[4] T. Fujita, M. Kawasaki, Y. Tada and T. Takesako, JCAP
1312, 036 (2013) [arXiv:1308.4754 [astro-ph.CO]].

Dark Matter, Baryogenesis, Big-Bang nucleosynthesis• Decay rates of Gaussian-type I-balls andBose-enhancement effects in 3+1 dimensions
In collaboration with the members of ICRR and IPMU.
I-balls/oscillons are long-lived spatially localized lumps
of a scalar field which may be formed after inflation. In thescalar field theory with monomial potential nearly and shallower than quadratic, which is motivated by chaotic inflationary models and supersymmetric theories, the scalar field configuration of I-balls is approximately Gaussian. If the I-ballinteracts with another scalar field, the I-ball eventually decays into radiation. Recently, it was pointed out that the decayrate of I-balls increases exponentially by the effects of Boseenhancement under some conditions and a non-perturbative
method to compute the exponential growth rate has been derived. In this paper, we apply the method to the Gaussiantype I-ball in 3 + 1 dimensions assuming spherical symmetry, and calculate the partial decay rates into partial waves, labelled by the angular momentum of daughter particles. We reveal the conditions that the I-ball decays exponentially, which
are found to depend on the mass and angular momentum ofdaughter particles and also be affected by the quantum uncertainty in the momentum of daughter particles.
• A new algorithm for calculating the curvature perturbations
in stochastic inflation
In collaboration with the members of ICRR and IPMU
We propose a new approach for calculating the curvature
perturbations produced during inflation in the stochastic formalism. In our formalism, the fluctuations of the e-foldings
are directly calculated without perturbatively expanding the
inflaton field and they are connected to the curvature perturbations by the δ N formalism. The result automatically includes
the contributions of the higher order perturbations because wesolve the equation of motion non-perturbatively. In this paper, we analytically prove that our result (the power spectrum
and the nonlinearity parameter) is consistent with the standard• Baryogenesis from the Gauge-mediation type Q ball and thedark matter New type Q ballIn collaboration with the members of ICRR and Kanagawa
University
We investigate that the two types of the Q balls explain
the baryon asymmetry and the dark matter of the universein the gauge-mediated supersymmetry breaking. The gaugemediation type Q balls of one flat direction produce baryon
asymmetry, while the new type Q balls of another flat direction become the dark matter. We show that the dark matternew type Q balls are free from the neutron star constraint.
n = 5 gauge mediation type and n = 6 new type Q balls are
displayed as an example, where the potential is lifted by thesuperpotential Φn . These dark matter Q balls may be detectedby future observations, such as in advanced IceCube-like observations [1].
• Axions as Hot and Cold Dark MatterIn collaboration with the members of ICRR, DESY and Tohoku University
The presence of a hot dark matter component has been
hinted at 3σ by a combination of the results from different
cosmological observations. We examine a possibility that pseudo
Nambu-Goldstone bosons account for both hot and cold dark
matter components. We show that the QCD axions can do
the job for the axion decay constant fa < O(1010 ) GeV, ifthey are produced by the saxion decay and the domain wallannihilation. We also investigate the cases of thermal QCD
axions, pseudo Nambu-Goldstone bosons coupled to the standard model sector through the Higgs portal, and axions produced by modulus decay [2].

70

• Baryon Asymmetry, Dark Matter, and Density Perturbationfrom PBH

3
T RH #

In collaboration with the members of ICRR and IPMU

1

Bibliography[1] S. Kasuya and M. Kawasaki, arXiv:1402.4546 [hep-ph].
[2] K. S. Jeong, M. Kawasaki and F. Takahashi, JCAP
1402, 046 (2014) [arXiv:1310.1774 [hep-ph],arXiv:1310.1774].
[3] T. Fujita, K. Harigaya and M. Kawasaki, Phys. Rev. D
88, 123519 (2013) [arXiv:1306.6437 [astro-ph.CO]].
[4] T. Fujita, M. Kawasaki, K. Harigaya and R. Matsuda, Phys. Rev. D 89, 103501 (2014) [arXiv:1401.1909[astro-ph.CO]].
[5] K. Harigaya, M. Kawasaki, K. Mukaida and M. Yamada,
Phys. Rev. D 89, 083532 (2014) [arXiv:1402.2846 [hepph]].

sca Mh"D

12

We estimate dark matter density for the Universe with areheating temperature smaller than the mass of dark matter,assuming dark matter to be a weakly interacting massive particle. During the reheating process, an inflaton decays and releases high-energy particles, which are scattered inelasticallyby the thermal plasma and emit many particles. Dark matters
are produced through these inelastic scattering processes andpair creation processes by high-energy particles. We properly
take account of the Landau-Pomeranchuk-Migdal effect on inelastic processes and show that the resultant energy density ofdark matter is much larger than that estimated in the literatureand can be consistent with that observed when the mass ofdark matter is larger than O(100) GeV (see Fig. 20).

.12

2 #0

0

0.

In collaboration with the members of ICRR, IPMU, and Tokyo
Univ.

2

2 0.1
th h #
M
"D

2 #
r h
di M

log10!TRH "GeV#2

TRH %&QCD

!1

!2

!3
2

• Dark Matter Production in Late Time Reheating

10"D

We investigate the consistency of a scenario in which thebaryon asymmetry, dark matters, as well as the cosmic density
perturbation are generated simultaneously through the evaporation of primordial black holes (PBHs). This scenario can
explain the coincidence of the dark matter and the baryon density of the universe, and is free from the isocurvature perturbation problem. We show that this scenario predicts the masses
of PBHs, right-handed neutrinos and dark matters, the Hubble
scale during inflation, the non-gaussianity and the running of
the spectral index. We also discuss the testability of the scenario by detecting high frequency gravitational waves from
PBHs [3, 4].

mDMmΦ %1015 GeV
Br!DMs#%0.02
3

4

5

6

7

8

log10!mDM"GeV#
Fig. 20. Exclusion plot in a scenario with low reheating temperature.
2
The abundance of DM produced from thermal production (ΩthDM h ),
dir2
sca
direct decay of inflaton (ΩDM h ), and inelastic scatterings (ΩDM h2 )is larger than that observed in the green, red, and blue shaded
regions, respectively. The striped regions are TRH > mDM /10, in
which DM is produced only thermally. The abundance of DM isless than that observed above the blue dashed line due to its annihilation. The red dotted lines represent the reheating temperature2
below which Ωsca
DM h is over-estimated.

Gravitational waves• On the estimation of gravitational wave spectrum from cosmic domain walls
In collaboration with the members of ICRR, Kyoto University
and Tokyo Institute of Technology
We revisit the production of gravitational waves from unstable domain walls analyzing their spectrum by the use of
field theoretic lattice simulations with grid size 10243, whichis larger than the previous study. We have recognized that thereexists an error in the code used in the previous study, andthe correction of the error leads to the suppression of the spectrum of gravitational waves at high frequencies. The peak of
the spectrum is located at the scale corresponding to the Hubble radius at the time of the decay of domain walls, and its
amplitude is consistent with the naive estimation based on thequadrupole formula. Using the numerical results, the magnitude and the peak frequency of gravitational waves at thepresent time are estimated. It is shown that for some choicesof parameters the signal of gravitational waves is strong enoughto be probed in the future gravitational wave experiments [1].
• Gravitational waves from a curvaton model with blue spectrum
In collaboration with the members of ICRR.
We investigate the gravitational wave background inducedby the first order scalar perturbations in the curvaton models.

71

We consider the quadratic and axion-like curvaton potential
which can generate the blue-tilted power spectrum of curvature perturbations on small scales and derive the maximal
amount of gravitational wave background today. We find thepower spectrum of the induced gravitational wave backgroundhas a characteristic peak at the frequency corresponding to thescale reentering the horizon at the curvaton decay, in the casewhere the curvaton does not dominate the energy density of
the Universe. We also find the enhancement of the amount of
the gravitational waves in the case where the curvaton dominates the energy density of the Universe. Such induced gravitational waves would be detectable by the future space-based
gravitational wave detectors or pulsar timing observations, as
shown in Fig. 21.
10-6

LISA

10-8

-10

ΩGW

10

10-12

SKA 10yr

-14

10

10-16
-18

DECIGO/BBO
ult-DECIGO

our result

10

10-20

10-10 10-8 10-6 10-4 10-2 100
frequency [Hz]

102

104

if the single slow-rolling inflation is responsible for the observed Pζ , the constraint from τnl is most stringent. We alsofind a general relationship between fnl and τnl generated in thismodel. Even if fnl ∼ O(1), a detectable τnl can be produced.
• CMB distortion anisotropies due to the decay of primordial
magnetic fields
In collaboration with the members of ICRR, Nagoya Univ.
and Arizona State Univ..
We investigate the power spectrum of the distortion of
Cosmic Microwave Background (CMB) due to the decay ofthe primordial magnetic fields. It is known that there are twotypes of the CMB distortions, so-called µ- and y-types andwe find that the signal of the y-type distortion becomes larger
than that of the µ-type one. We also discuss cross power
spectra between the CMB distortions and the CMB temperature anisotropy, which are naturally generated due to the existence of the primordial magnetic fields. We find that suchcross power spectra have small amplitudes compared with theauto-power spectra of the CMB distortions because of the Silk
damping effect of the temperature anisotropy. We also investigate the possibility of detecting such signal in the future CMB
experiments, including not only absolutely calibrated experiments such as PIXIE but also relatively calibrated experiments
such as LiteBIRD and CMBpol.
• Halo/Galaxy Bispectrum with Primordial non-Gaussianityfrom integrated Perturbation Theory (iPT)

Fig. 21. One example of the spectrum of the gravitational backgroundshown in Ref. [2]. The red thick line is the resultant spectrum
in Ref. [2]. We also show the sensitivity curves of LISA (dashedgreen), DECIGO/BBO (dotted blue), ultimate-DECIGO (small dotted magenta) and the pulsar timing observation by SKA (dash dotted cyan).

Bibliography[1] T. Hiramatsu, M. Kawasaki and K. ’i. Saikawa, JCAP
1402, 031 (2014) [arXiv:1309.5001 [astro-ph.CO]].
[2] M. Kawasaki, N. Kitajima and S. Yokoyama, JCAP
1308, 042 (2013) [arXiv:1305.4464 [astro-ph.CO]].

Primordial non-Gaussianity, Structure formation in the
Universe• Higher order statistics of curvature perturbations in IFF
model and its Planck constraints
In collaboration with the members of ICRR and Kavli IPMU.
We compute the power spectrum Pζ , and non-linear parameters fnl and τnl of the curvature perturbation induced during inflation by the electromagnetic fields in the kinetic coupling model (IFF model). By using the observational result ofPζ , fnl and τnl reported by the Planck collaboration, we study
the constraint on the model comprehensively. Interestingly,

In collaboration with the members of ICRR, Nagoya Univ.
and YITP.
We derive a formula for the halo/galaxy bispectrum on
the basis of the integrated Perturbation Theory (iPT). In addition to the gravity-induced non- Gaussianity, we consider
the non-Gaussianity of the primordial curvature perturbations,and investigate in detail the effect of such primordial nonGaussianity on the large-scale halo/galaxy bispectrum. In iPT,
the effects of primordial non-Gaussianity are wholly encapsulated in the linear (primordial) polyspectra, and we systematically calculate the contributions to the large-scale behaviorsarising from the three types of primordial bispectrum (local, equilateral-, and orthogonal-types), and primordial trispectrum of the local-type non-Gaussianity. We find that the equilateral- and orthogonal-type non-Gaussianities show distinct
scale-dependent behaviors which can dominate the gravityinduced non-Gaussianity at very large scales. For the localtype non-Gaussianity, higher-order loop corrections are foundto give a significantly large contribution to the halo/galaxy bispectrum of the squeezed shape, and eventually dominate over
the other contributions on large scales. A diagrammatic approach based on the iPT helps us to systematically investigate
an impact of such higher-order contributions to the large-scale
halo/galaxy bispectrum.
• Critical constraint on inflationary magnetogenesis
In collaboration with the members of ICRR and Kavli IPMU.

72

Recently, there are several reports that the cosmic magnetic fields on Mpc scale in void region is larger than 10−15 Gwith an uncertainty of a few orders from the current blazar
observations. On the other hand, in inflationary magnetogenesis models, additional primordial curvature perturbations areinevitably produced from iso-curvature perturbations due togenerated electromagnetic fields. We explore such induced
curvature perturbations in a model independent way and obtained a severe upper bound for the energy scale of inflationfrom the observed cosmic magnetic fields and the observed
1/4
amplitude of the curvature perturbation, as ρin f < 30GeV ×(Bobs /10−15 G)−1 where Bobs is the strength of the magnetic
field at present. Therefore, without a dedicated low energy inflation model or an additional amplification of magnetic fields
after inflation, inflationary magnetogenesis on Mpc scale isgenerally incompatible with CMB observations.
• Probing small-scale cosmological fluctuations with the 21
cm forest: effects of neutrino mass, running spectral index
and warm dark matterIn collaboration with the members of ICRR, Nagoya Univ.
and MPI.
Although the cosmological paradigm based on cold dark
matter and adiabatic, nearly scale-invariant primordial fluctuations is consistent with a wide variety of existing observations, it has yet to be sufficiently tested on scales smaller thanthose of massive galaxies, and various alternatives have been
proposed that differ significantly in the consequent small-scale
power spectrum (SSPS) of large-scale structure. Here we showthat a powerful probe of the SSPS at k & 10 Mpc−1 can beprovided by the 21 cm forest, that is, systems of narrow absorption lines due to intervening, cold neutral hydrogen in
the spectra of high-redshift background radio sources in thecosmic reionization epoch. Such features are expected to becaused predominantly by collapsed gas in starless minihalos,
whose mass function can be very sensitive to the SSPS. As
specific examples, we consider the effects of neutrino mass,
running spectral index (RSI) and warm dark matter (WDM)
on the SSPS, and evaluate the expected distribution in opticaldepth of 21 cm absorbers out to different redshifts. Within
the current constraints on quantities such as the sum of neutrino masses ∑ mν , running of the primordial spectral index
dns /d ln k and WDM particle mass mWDM , the statistics ofthe 21 cm forest manifest observationally significant differences that become larger at higher redshifts. In particular, it
may be possible to probe the range of mWDM & 10 keV that
may otherwise be inaccessible. Future observations of the 21
cm forest by the Square Kilometer Array may offer a uniqueand valuable probe of the SSPS, as long as radio sources suchas quasars or Population III gamma-ray bursts with sufficientbrightness and number exist at redshifts of z & 10 - 20, andthe astrophysical effects of reionization and heating can bediscriminated.

Bibliography[1] T. Fujita and S. Yokoyama, JCAP 1309, 009 (2013)[arXiv:1306.2992 [astro-ph.CO]].
[2] K. Miyamoto, T. Sekiguchi, H. Tashiro andS. Yokoyama, Physical Review D 89, 063508 (2014)
American Physical Society, [arXiv:1310.3886 [astroph.CO]].
[3] S. Yokoyama, T. Matsubara and A. Taruya, Phys. Rev. D
89, 043524 (2014) [arXiv:1310.4925 [astro-ph.CO]].
[4] T. Fujita and S. Yokoyama, JCAP 1403, 013 (2014)[Erratum-ibid. 1405, E02 (2014)] [arXiv:1402.0596[astro-ph.CO]].
[5] H. Shimabukuro, K. Ichiki, S. Inoue and S. Yokoyama,
arXiv:1403.1605 [astro-ph.CO].

73

OBSERVATORIES andA RESEARCH CENTER
Location of the Institute and the Observatories in Japan

Norikura Observatory
Location:
Telephone (Fax):
Telephone (satellite):Telephone (car):

Norikuradake, Nyukawa-cho, Takayama-shi, Gifu Prefecture 506-2100
N 36◦ 060 , E 137◦ 330 , 2770 m a.s.l.
+263-33-7456
090-7721-5674
090-7408-6224

Akeno Observatory
Location:
Telephone / Fax:

5259 Asao, Akeno-machi, Hokuto-shi, Yamanashi Prefecture 408-0201
N 35◦ 470 , E 138◦ 300 , 900 m a.s.l.
+551-25-2301 / +551-25-2303

Kamioka Observatory
Location:
Telephone / Fax:

456 Higashi-mozumi, Kamioka-cho, Hida-shi, Gifu Prefecture 506-1205
N 36◦ 250 2600 , E 137◦ 190 1100 , 357.5 m a.s.l.
+578-85-2116 / +578-85-2121

Research Center for Cosmic Neutrinos
Location:
Telephone / Fax:

5-1-5 Kashiwanoha, Kashiwa, Chiba Prefecture 277-8582+4-7136-3138 / +4-7136-3115

74

NORIKURA OBSERVATORY
Introduction
Norikura Observatory (36.10◦ N and 137.55◦ E) was founded in 1953 and attached to ICRR in 1976. It is located at
2770 m above sea level, and is the highest altitude mannedlaboratory in Japan. Experimental facilities of the laboratory
are made available to all the qualified scientists in the field ofcosmic ray research and associated subjects. The AC electric
power is generated by the dynamo and supplied throughout
the observatory. In 1996, two dynamos of 70 KVA each were
replaced with the new ones. The observatory can be accessedeasily by car and public bus in summer (July-September). The
50th anniversary of Norikura Observatory was celebrated in
2003.
Fig. 2. A dynamo of 115KV.

aerosol-related mechanism in the atmosphere, observation of
total ozone and UV solar radiation, for botanical study in thehigh-altitude environment, etc.

Cosmic Ray Physics

Fig. 1. Norikura Observatory.

The feasibility of the automatic operation of Norikura Observatory during winter period has been tested since winter2004 in order to study the possibilities to reduce maintenanceand labor costs without seriously damaging to the use of researches. A long-distance (∼40km) wireless LAN system(11M bps) was set up in 2003. Two new easy-to-handle andeasy-to-maintain dynamos of 115 KVA each were installed
in 2004 as well. The unmanned operation of Norikura Observatory has been mostly successful in winter, during which
the battery backed-up solar panels and/or wind power generators kept supplying the electricity to the wireless LAN andon-going cosmic-ray experiments. The 60th anniversary of
Norikura Observatory was celebrated in 2013.
Present major scientific interests of the laboratory is focused on the modulation of high energy cosmic rays in theinterplanetary space associated with the solar activity and thegeneration of energetic particles by the solar flares, both ofwhich require long-term monitoring. This research has been
carried out by the group of universities, where ICRR provides them with laboratory facility. A part of the facility has
been open for the environmental study at high altitude such as

A neutron monitor has been continuously operated to study
the correlation of solar activities and cosmic ray flux for along time. It is the only active one in Japan now. The neutron
monitor data are open to researchers worldwide as a world
observation network point (WDC). In addition, space weather
observation is actively made by a 25 m2 muon hodoscope at
Norikura Observatory[1], [2], [3], [4], [5], [6], [7], [8], [9].
The anisotropy observed with the global muon detector
network (GMDN) provides us with a unique information of
the spatial gradient of the GCR density which reflects thelarge-scale magnetic structure in the heliosphere. The solar
cycle variation of the gradient gives an important information on the GCR transport in the heliosphere, while the shortterm variation of the gradient enables us to deduce the largescale geometry of the magnetic flux rope and the interplanetary coronal mass ejection (ICME). Real-time monitoring of
the precursory anisotropy which has often been observed at
the Earth preceding the arrival of the ICME accompanied by astrong shock may provide us with useful tools for forecasting
the space weather with a long lead time. By using a selfsupporting power system utilizing the solar panels and batteries, we keep a 25 m2 muon hodoscope running at the Mt.
Norikura Cosmic Ray Observatory as an important component detector of the GMDN. The total power consumption ofthis detector has been suppressed as low as 36 Watt by replacing all amplifier boards with those using CMOS ICs and by introducing a new recording system using the FPGA. This new
system, in which the observation has been automatically carried out by a PC connected with the internet, also enabled us

75

to monitor the data on the real-time basis for the space weather
study.
The Sun is the nearest site to the Earth capable of accelerating particles up to high energies. When the Sun becomes
active, flares are frequently observed on its surface. The flareaccelerates the proton and ion to high energy and they are detected on the Earth soon after the flare. Among the particles
generated by the flare, high energy neutrons provide the mostdirect information about the acceleration mechanism as theycome straight from the flare position to the Earth without deflected by the magnetic field.
Observation of solar neutron has been conducted at the
Norikura Observatory since 1990. Neutron is used to clarify
the acceleration mechanism of high energy particles in association with solar flares, because the neutron is not reflectedby the interplanetary magnetic field. The 64m2 solar neutrontelescope was constructed in 1996, which is one of 7 solar
neutron telescopes deployed at different longitudes to makeup a network of 24 hour observation of solar neutrons. The
Norikura 64m2 solar neutron telescope has been operated bysolar batteries and windmills since 2004.
This collaborative work has started since fiscal 2007 succeeding to the previous project titled ‘Observation of solar
neutrons by using a new method.’ Although solar cycle 24
has started since 2008, the solar activity has continued to beinactive, and no new solar neutron event has been detectedby the network since 2006. The last solar neutron event wason September 7, 2005. This event is unique because it indicates ions were accelerated or trapped at the acceleration region longer than electrons. The summary of 11 solar neutron
events detected until 2005 shows that it may not be probablethat a very efficient acceleration such as the shock acceleration
works for ions at solar flares. This is given by deriving the energy spectrum of neutrons at the solar surface for each solar
neutron event with a power law. Power law indices obtained
span from 3 to 7. The energy spectrum of the original ions issofter than that of neutron. Therefore an efficient acceleration
has not been detected by the observation of solar neutrons so
far.This work continues in solar cycle 24 to accumulate more
events to obtain definite results related with particle acceleration at the solar surface.
Another effort aiming at observation of highest-energy solar cosmic rays started at the Norikura Observatory. The Sun
is an accelerator of protons and electrons in the universe. In
association with large solar flares, protons and electrons areaccelerated into high energies. It is known that protons areaccelerated over 50 GeV in the largest solar flares[24]. Thesehigh energy particles produce the Ground Level Enhancement(GLE).
In order to understand the acceleration mechanism of protons, we have prepared several solar neutron telescopes at thehigh altitude laboratories in the world. They are located at
Gornergrat (3,135m), Mt. Aragats in Armenia (3,200m), Tibet (4,200m), Mauna-Kea in Hawaii (4,200m), Mt. Chacaltaya in Bolivia (5,250m), and at Mt. Sierra Negra in Mexico(4,900m). We have constructed a solar neutron telescopes at

Mt. Norikura Cosmic Ray Observatory (2,770m) in 1990 andoperated it until 2004[21]. However due to the lack of power
supply during the winter time since 2005, the first solar neutron telescope (36 m2 ) has not been operated.
From 2008 to 2009, we have decided to make a new solar neutron telescope to utilize the large amount of the plastic
scintillator (0.5m3 ), as shown in Fig. 3, left at the observatory.

Fig. 3. 0.5-m2 plastic scintillation counter for a new neutron telescope.

The new solar neutron telescope with use of the recycledplastic scintillator consists of main target where neutrons areconverted into protons and of the anti-counters surrounding
the target. The signals of neutrons converted into protons areobserved by using one photomultiplier from bottom side to
reduce the electric power. Furthermore a lead plate with the
thickness of 1cm is located over the target and the lead plate is
sandwiched by two layers of the plastic scintillator to identify
gamma-rays from neutrons.
The new solar neutron telescope has a function to rejectcharged particles with an efficiency of 90%. Therefore the
new solar neutron telescope has capability of 1/3 of the 64m2
large solar neutron telescope located at the same place. We
are waiting large solar flares over our detectors.
In addition to the long-term cosmic-ray observations mentioned above, various kinds of short-dated experiments arecarried out every year taking an advantage of the high altitudeof the observatory.
High-energy radiations from thunderstorms have been observed by flight measurement, high-mountain observations andCount/30 sec

8500
8000
7500

4200
4000
3800
3600
3400

Counts (/MeV)

ground-based measurement. There are two types of those radiations associated with thunderstorms. One is short-duration
radiations with duration of 1 ms or less. The other is longduration emissions lasting for a few seconds to a few minutes,
or a few tens of minutes on rare occasions. It is believed thatboth emissions originate from electrons accelerated in strong
electric fields formed in lightning and thunderclouds. However, compared with the former, the latter has remained lessunderstood due to lack of a large sample of observations.
To investigate production mechanism of long-duration emissions and the relevant electron acceleration, we installed at
Norikura Cosmic-ray Observatory a radiation detection system and environmental sensors to measure light and electricfields during 2008−2010. The radiation system consists ofa spherical NaI scintillator and a thin plastic scintillator thatis placed just above the NaI counter. During the period, thesystem detected one long-duration bursts as well as five shortduration events.
Fig. 4 (top) shows the long-duration event observed during thunderstorms on 2008 September 20th [25]. The event
lasted for 90 sec. Fig. 4 (bottom) represents an observed photon spectrum extending from 10 keV to 10 MeV. This indicates that electrons can be accelerated to at least 10 MeV in aquasi-stable thundercloud electric field. In addition, we compared the observed spectrum with model ones, and concluded
that a gamma-ray source is located 60 m−130 m (at 90% confidence level) apart from our detector. Given these results, theobserved emission was found to consist of not only gamma
rays but also electrons. This was the first simultaneous observation of gamma rays and electrons in long-duration bursts

Count/30 sec

76

15:20

15:30

15:40

15:50

16:00

16:10
Time (UT)

104
103
102

50 m (21.5/16)
90 m (16.8/16)

10300 m (22.2/16)
1000 m (28.1/16)

10-1
1
10
Photon energy (MeV)
Fig. 4. (Top) Count rates per 30 sec observed by the >10 keV NaI
scintillator (upper) and > 100 keV plastic one (lower). (Bottom)
The photon spectrum observed by the NaI scintillator.

NSB [photons/(m2 sr ns nm)]

Observation of night sky background is carried out at Mt.
Norikura for basic study of ultra high energy cosmic-ray physics.
The JEM-EUSO mission is going on in order to study ultrahigh energy cosmic rays (UHECRs), especially above 1020 eV.
20
Norikura (2009/8/23-24JST)
A 2.5m telescope with 60◦ FoV will be attached to the Inter18
La Palma (S.Preuss+,NIMA 481 2002 229)
national Space Station in 2017 and detect fluorescence in near
16
Namibia (S.Preuss+,NIMA 481 2002 229)
UV band from extensive air showers induced by UHECRs.
14
Observation of UHECRs from a satellite orbit has not been12
done yet, so that the knowledge of background light intensity
10
is important to realize the observation. We have measured it
8from a balloon altitude, but the opportunity is limited. We
started the background measurement at Mt. Norikura.
6
Two 1 inch multi-anode photomultipliers (MAPMTs) devel4
oped for EUSO was used with UV filters. The center wave2
lengths of the filters were 337, 350, 358, 370, 380, 391, 400nm
0
300
320
340
360
380
400
420
440
with 10nm band width. In addition BG3 filter was used to deWavelength [nm]tect light in wider range from 330nm to 430nm. The MAPMTs
were collimated to 7◦ FoV. The data was taken with the photon Fig. 5. Spectrum of night sky background measured at Mt.Norikura
counting method.
compared with those at La Palma and Namibia.
We have observed several nights for three years. The intensity
at zenith was almost constant at 600-800 photons/ns∼sr m2
for BG3 filter. The spectral intensity was about 1.5-2 times Environmental Studylarger than those measured at La Palma and Namibia. The
One of the interesting topics is atmospheric environment
estimated portion of star light and zodiacal light was ∼30% especially relating with atmospheric aerosol particles and waand artificial light and nightglow at upper atmosphere may be ter soluble gases. The cosmic ray observatory at Mt. Norikura
the main components at Mt.Norikura.
provides us very unique opportunity for the observations ofatmosphere at free-tropospheric conditions with its high altitude, AC power supply at the site, accommodation facility,

77

and easy accessibility. From year 2000 to 2007, we conducted
continuous monitoring (mostly mid-May to mid-October) of
meteorological parameters, number-size distribution of aerosols, aerosol chemical composition, ozone and radon concentrations, and column amount of aerosols from sky radiometerand ceilometers. We also collected rain, fog, water-condensed
aerosol samples. These samples combined with other observed
parameters were used in publications in the following subjects[26, 27, 28]:
(1) Polluted air pumping effects over central Japanese Alpsin summer(2) Seasonal variation of aerosol chemistry in free troposphere(3) Vertical profiles of aerosols and clouds near the top of theatmospheric boundary layer.
Ceilometer (lidar with small output energy) was installed insummer 2002, and was operated in 6 summer seasons. The
aerosol and cloud profiles near the top of the atmosphericboundary layer have been observed. Some events of Asian
dust were detected.
Observations of total ozone and UV solar radiation with
Brewer spectrophotometer on the Norikura mountains are also
made[29, 30, 31].
Aerological Observatory started “ Observations of totalozone and UV solar radiation with Brewer spectrophotometer at Norikura mountains ” as a joint project with Institutefor Cosmic Ray Research (ICRR), University of Tokyo at the
Norikura Observatory of ICRR (Brewer site: 36.11 N, 137.56
E, 2,772 m a.s.l.), locating at the Northern Japanese Alps inevery summer seasons from 2009 (Ito et al.: 2011). Purposeof this study is based on the concept of developing Regional
Brewer Calibration Centre in Asia and study of total ozone, total sulfur oxide and global/diffuse UV included solar radiationon the high mountains. Observation results by using Brewer
spectrophotometers and other instruments for the observation
period of three summer seasons of recent three years between
2009 to 2011 are summarized as follows;(1) Daily means of ds O3 (total ozone) at Norikura for theobservation periods were approx. 280 to 290 m atm-cm andwere running on the lower values of approx. -3 to -6% compared to the value at Tsukuba (36.06 N, 140.13 E, 39 m a.s.l.)
at almost same latitude. Day-to-day variations at Norikura
were also small against Tsukuba. On the other hand, dailymean of ds SO2 (total sulfur oxide) values were not recognized at Norikura.
(2) Absolute calibration of Brewers for ds O3 and ds SO2
observations could be carried out within the range of air massfrom 7.928 (maximum) to 1.028 (minimum) at Norikura in theclear day. O3 and SO2 Extra-Terrestrial Coefficients (=ETC)
of Brewers could be produced as about 10 samples satisfying
the condition of ”R2 > 0.9997” by the calibrations. As an example of the calibration in 2011, the average of O3 ETC of
Brewers was identical within 1% to the currently used coefficient.
(3) In comparison to the data acquired at Tsukuba, the average of daily total GLUV (global UV, e.g. CIE) for the ob-servation periods indicated the intensities of approx. +23 %in 2009 to -6 % in 2011. The low intensity in 2011 was dueto the bad weather on the Norikura Mountain. In the case ofclear days, the GLUV at Norikura indicated high intensities ofapprox. +35 to +52 % against the values at Tsukuba. On theother hand, the GLUV increased in the short wavelength range
at Norikura against the average at Tsukuba. The altitudinal increasing rate of GLUV in the clear day indicated the calculated
amounts of approx. +13 to +18 % per 1,000 m.
This joint project had been clarifying the low total O3 ,high UV in clear day, low turbidity and etc. at Norikura against
the value at Tsukuba. Those environmental conditions areuseful for the intercomparison and the absolute calibrations
with Brewers. The continuous observations with Brewers andother instrument are very important for the clarification of theseasonal variation and the coefficient trends.

Botanical Study
Effects of snow cover on pine shrub Pinus pumila in the alpine
region of Mt. Norikura
High mountainous habit is one of the most severe habits
for plant life and sometimes dwarf shrubs cannot survive. In
the alpine regions of Japan, the dwarf shrub Pinus pumila(Japanese name : Haimatsu) forms communities together withsmall alpine plants, whereas dwarf shrubs occur only in thetransition zone between the alpine region and the subalpine
forest in Europe and North America. This characteristic ofalpine vegetation is considered to be owing to winter heavy
snow in the alpine regions of Japan. The purpose of this study
is to elucidate how snow cover protects Haimatsu from winterenvironmental stresses in the alpine region of Mt. Norikura.
Study site
Tree height of Haimatsu and snow depth differ greatly as aresult of slight difference in topography. Two site of the study
area were selected. (i) site P (wind-protected) and (ii) site E(wind-exposed). At site P, mean tree height was 1.1 m. There
was a lot of snow accumulation and Haimatsu was almost entirely covered with snow during the winter. Needle browningand death occurred rarely. At site E, mean tree height was 0.4
m. Snow accumulation was minimal, and Haimatsu was notentirely covered with snow. Needle browning and death wasobserved frequently.
Winter needle death in Haimatsu[32]At site E, the browning and death of needles of Haimatsu
occurred mainly in early spring at the point where the shootprotrudes from the snowpack. They are thought to be causedby excessive water loss due to mechanical damage to the cuticle and/or to a thinner cuticle. However, needle browningand death in Haimatsu were not related to mechanical damageof the cuticle but might be due to changes in the quality andstructure of the cuticle wax and resultant increase in water loss
from needle cells.
Photosynthetic capacity in Haimatsu[33]78

At site E, needles of Haimatsu had lower biomass, nitrogen, Rubisco (enzyme) and cell wall per unit area, and had
higher photosynthetic capacity and shorter needle life-span
than Haimatsu at site P. These results suggest that Haimatsu
at wind-exposed site produces needles at low cost with highproductivity to compensate for a short leaf life-span which
may be imposed by wind stress when needles appear above
the snow surface in winter.

Bibliography[1] K. Munakata, S. Yasue, C. Kato, J. Kota, M. Tokumaru, M. Kojima, A. A. Darwish, T. Kuwabara and J. W.
Bieber, “On the cross-field diffusion of galactic cosmic
rays into the magnetic flux rope of a CME”, Advances inGeosciences, 2, 115-124, eds. W. H. Ip and M. Duldig(World Scientific Publishing Co., USA), (2006).
[2] T. Kuwabara, J. W. Bieber, J. Clem, P. Evenson, R.
Pyle, K. Munakata, S. Yasue, C. Kato, S. Akahane,
M. Koyama, Z. Fujii, M. L. Duldig, J. E. Humble,
M. R. Silva, N. B. Trivedi, W. D. Gonzalez and N. J.
Schuch, “Real-time cosmic ray monitoring system forspace weather”, Space Weather, 4, S08001-1 10, (2006).
[3] M. R. Da Silva, A. Dal Lago, E. Echer, A. de Lucas, W.
D. Gonzalez, N. J. Schuch, K. Munakata, L. E. A. Vieira,and F. L. Guarnieri, “Muon and neutron observations inconnection with the corotating interaction regions”, Adv.
Space Res., 40, pp348-352, (2007).
[4] Y. Okazaki, A. Fushishita, T. Narumi, C. Kato, S. Yasue,
T. Kuwabara, J. W. Bieber, P. Evenson, M. R. Da Silva,
A. Dal Lago, N. J. Schuch, Z. Fujii, M. L. Duldig, J.
E. Humble, I. Sabbah, J. Kóta and K. Munakata, “Drifteffects and the cosmic ray density gradient in a solar rotation period: First observation with the Global Muon
Detector Network (GMDN)”, Astrophys. J., 681, 693707, (2008).
[5] T. Kuwabara, J. W. Bieber, P. Evenson, K. Munakata,
S. Yasue, C. Kato, A. Fushishita, M. Tokumaru, M. L.
Duldig, J. E. Humble, M. R. Silva, A. Dal Lago, andN. J. Schuch, “Determination of ICME Geometry andOrientation from Ground Based Observations of Galactic Cosmic Rays”, J. Geophys. Res., 114, A05109-1 10,
doi:10.1029/2008JA013717, (2009).
[6] A. Fushishita, T. Kuwabara, C. Kato, S. Yasue, J. W.
Bieber, P. Evenson, M. R. Da Silva, A. Dal Lago, N. J.
Schuch, M. Tokumaru, M. L. Duldig, J. E. Humble, I.
Sabbah, H. K. Al Jassar, M. M. Sharma, and K. Munakata, “Precursors of the Forbush Decrease on 2006
December 14 observed with the Global Muon Detector Network (GMDN)”, Astrophys. J., 715, 1239-1247,(2010).
[7] A. Fushishita, Y. Okazaki, T. Narumi, C. Kato, S. Yasue, T. Kuwabara, J. W. Bieber, P. Evenson, M. R. Da
Silva, A. Dal Lago, N. J. Schuch, M. Tokumaru, M. L.
Duldig, J. E. Humble, I. Sabbah, J. Kóta, and K. Munakata, “Drift effects and the average features of cosmic

ray density gradient in CIRs during successive two solar
minimum periods”, Advances in Geosciences, eds. W.
H. Ip and M. Duldig (World Scientific Publishing Co.,
USA), 21, 199-210, (2010).
[8] M. Tokumaru, M. Kojima, K. Fujiki, K. Munakata, T.
Kuwabara and K. Marubashi, “Relation between loopshaped interplanetary disturbances and the magnetic fluxrope”, Advances in Geosciences, eds. W. H. Ip and M.
Duldig (World Scientific Publishing Co., USA), 21, 2132, (2010).
[9] M. Rockenbach, A. Dal Lago, W. D. Gonzalez, K.
Munakata, C. Kato, T. Kuwabara, J. W. Bieber, N. J.
Schuch, M. L. Duldig, J. E. Humble, H. K. Al Jassar, M.
M. Sharma, and I. Sabbah, “Geomagnetic Storms Precursors Observed from 2001 to 2007 with the Global
Muon Detector Network GMDN”, Geophys. Res. Lett.,
38, L16108-1 4, doi:10.1029/2011GL048556, (2011).
[10] “Solar neutron events of October—November 2003”,
Watanabe, K. et al., Astrophys. J., 636, 1135–1144,
2006.
[11] “Solar neutron events in association with large solar
flares in November 2003”, Watanabe, K. et al., Adv.
Space Res., 38, 425–430, 2006.
[12] “Long-lived solar neutron emission in comparison withelectron-produced radiation in the 2005 September 7 solar flare”, Sako, T. et al., Astrophys. J., 651, L69–L72,
2006.
[13] “Highly significant detection of solar neutrons on 2005
September 7”, Watanabe, K. et al., Adv. Space Res., 39,
1462–1466, 2007.
[14] “A solar neutron telescope in Tibet and its capability examined by the 1998 November 28th event”, Muraki, Y.
et al., Astroparticle Phys., 28, 119–131, 2007.
[15] “Simultaneous detection of high-energy solar neutronsand protons at Chacaltaya observatory on April 15,
2001”, Muraki, Y. et al., in Proc. 30th Int. Cosmic Ray
Conf, Merida, 1, 25–28, 2007.
[16] “Search for solar neutrons associated with series of Xclass flares during the declining period of solar cycle
23”, Matsubara, Y. et al., in Proc. 30th Int. Cosmic Ray
Conf, Merida, 1, 29–32, 2007.
[17] “Ion acceleration and neutral emission mechanisms for2005 September 7 flare”, Watanabe, K. et al., in Proc.
30th Int. Cosmic Ray Conf, Merida, 1, 45–48, 2007.
[18] “Emission profile of solar neutrons obtained from theground-based observations for the 7 September 2005
event”, Sako, T. et al., in Proc. 30th Int. Cosmic Ray
Conf, Merida, 1, 53–56, 2007.
[19] “Energy spectrum for the solar neutron event of September 7 2005, derived from the SNT at Sierra Negra”, Gonzalez, L. X. et al., in Proc. 30th Int. Cosmic Ray Conf,
Merida, 1, 57–60, 2007.

79[20] “Status of the world-wide network of solar neutron telescopes in solar cycle 24”, Matsubara, Y. et al., in Proc.
31st Int. Cosmic Ray Conf, Lodz, 1, On Conference
homepage, 2009.
[21] “Detection of high-energy solar neutrons and protons byground level detectors on April 15, 2001”, Muraki, Y. etal., Astropart. Phys., 29, 229–242, 2008.
[22] “Solar neutron events as a tool to study particle acceleration at the Sun”, Valdes-Galicia, J. F. et al., Adv. SpaceRes., 43, 565–572, 2009.
[23] “Physics of ion acceleration in the solar flare on 2005
September 7 determines γ-ray and neutron production”,
Watanabe, K. et al., Adv. Space Res., 44, 789–793,
2009.
[24] “Observation of solar neutrons associated with the large
flare on 1991 June 4”, Muraki, Y. et al., ApJ, 400, L75L78 , 1992.
[25] “Observation of an energetic radiation burst frommountain-top thunderclouds”, H. Tsuchiya et al., Phys.
Rev. Lett. 102, 255003 (2009), Citation Index:13.
[26] Nishita, C., K. Osada, K. Matsunaga, Y.
Iwasaka, e, J. Geophys. Res., 113, D06202,
doi:10.1029/2007JD009302, 2008.
“Nucleation mode particles in up-slope valley winds
at Mt. Norikura, Japan: implications for the vertical extent of new particle formation events in thelower tropospher”, Nishita, C., K. Osada, K. Matsunaga, Y. Iwasaka, J. Geophys. Res., 113, D06202,
doi:10.1029/2007JD009302, 2008.
[27] “Temporal variation of water-soluble ions of free tropospheric aerosol particles over central Japan”, Osada, K.,
Kido, M., Nishita, C., Matsunaga, K., Iwasaka, Y., Nagatani, M., Nakada, H., Tellus, 59B, 742-754, 2007.

[28] “Number-size distributions of free tropospheric aerosol
particles at Mt. Norikura, Japan: effects of precipitation and air-mass transportation pathways”, Nishita, C.,
K. Osada, K. Matsunaga, Y. Iwasaka, J. Geophys. Res.,
112, doi:10.1029/2006JD007969, 2007.
[29] “Observations of total ozone and UV solar radiation with
Brewer spectrophotometers on the Norikura mountains
in 2009.”, Ito, M., M. Takano, H. Oguri, M. Takita, H.
Shimodaira and H. Ishitsuka, Jour. of the AerologicalObservatory, 69, 41-54 2011.
[30] “Observations of total ozone and UV solar radiation
with Brewer spectrophotometers on the Norikura mountains, Northern Japanese Alps, from 2009.”, Ito, M., S.
Shimizu, Y. Noto, T. Shimamura, M. Takano, M. Takita,
H. Shimodaira and H. Ishitsuka, The 13th WMO Biennial Brewer Workshop, Beijing, China in 2011, 2011.
[31] “Total ozone and UV solar radiation with Brewer spectrophotometers at Norikura of Northern Japanese Alps,in recent three years.”, Ito, M., S. Shimizu, Y. Noto, T.
Shimamura, M. Takita, H. Shimodaira and H. Ishitsuka,
Jour. of the Aerological Observatory, 70, in contribution.
[32] “Needle browning and death in Pinus pumila in thealpine region of central Japan were not related tomechanical damage of cuticle and cuticle thickness.”,Nakamoto A., Ikeda T., Maruta E., Can. J. For. Res. 42,
167-178 (2012).
[33] “Needle traits of an evergreen, coniferous shrub growing at wind-exposed and protected sites in a mountainregion: does Pinus pumila produce needles with greatermass per area under wind-stress conditions?”, Nagano
S., Nakano T., Hikosaka K and Maruta E., Plant Biology
11(Suppl.1), 94-100, (2009).

80

AKENO OBSERVATORY
Introduction
The Akeno Observatory is situated in Akeno of Hokutocity, 20 km northwest of Kofu and 130 km west of metropolitan Tokyo. The location is at the longitude of 138.5◦ E and thelatitude of 35.8◦ N. The altitude is ∼900 m above sea level.
It was established in 1977 as a research center for air showerstudies in the very high energy region, and it has been administered by the ICRR as a facility of joint-university-use.

Akeno Air Shower Experiments
The Akeno Air Shower Experiment started in 1979 withan array covering 1 km2 area (the 1 km2 array, see Fig.1).
The array was enlarged to 20 km2 in 1984 and was gradually
expanded to Akeno Giant Air Shower Array (AGASA) of approximately 100 km2 area by 1990. The AGASA was built

Fig. 2. One of the muon detector housings with concrete shielding.

AGASA

Fig. 1. Aerial View of Akeno Observatory and 1 km2 Array Area

to detect Ultra-High Energy Cosmic Rays (UHECRs) in theenergy range of 1020 eV.
One of the distinctive features of Akeno experiments isthat the measurements were made over five decades of energies well covering 1015 eV - 1020 eV by using both the surface detector for electromagnetic component, and the shielded
detector for muon component (Fig.2). The wide energy coverage was accomplished by the arrays of scintillation detectors of various inter-detector spacings from 3 m to 1 km andwith different triggering conditions. This feature of Akeno air
shower measurement is well demonstrated in Fig.3, in which
the spectra from Akeno 1 km2 array for 1014.5 eV - 1018.8 eV
7 and AGASA for 1018.5 eV - 1020.3 eV 8 are plotted.
*7 M. Nagano et al., J. Phys. G10, 1295 (1984); M. Nagano et al., J. Phys.
G18, 423 (1992).
*8 M. Takeda et al., Astropart. Phys. 19, 447 (2003).

The AGASA was composed of 111 surface detectors, eachwith plastic scintillator of 2.2 m2 area and 5 cm thickness.
The counters were deployed with ∼1 km spacing covering the
ground area of about 100 km2 in the suburban area of Akeno,
outside of the observatory campus. All counters were connected with optical fibers for the timing measurement and digital data transfer to the observatory. The AGASA served as thelargest air shower array in the world since its commissioning
in 1990 until it stopped data taking in January 2004, when theconstruction of the succeeding experiment, Telescope Array(TA), started in Utah. It was dismantled in 2007 together withother Akeno air shower arrays.
An exposure of 5.8 × 1016 m2 s sr above 1019 eV wasaccumulated by AGASA in 13 years of operation. Extensive
air showers with zenith angles smaller than 45◦ and with core
locations inside the array area were used for the analysis. The
AGASA reported an extension of the energy spectrum beyond
the predicted Greisen-Zatsepin-Kuzmin (GZK) cutoff in 1998
9 and a total of eleven UHECR events were observed above
1020 eV by 2003.

Measurement of UHECRs
Since the AGASA measurement in 1998, High Resolution
Fly’s Eye (HiRes) 10 , Pierre Auger Observatory (PAO) 11 , andTelescope Array (TA) 12 measured the energy spectra of UHECRs with higher statistics.
The HiRes observed the UHECR using the fluorescencetelescope. The PAO and TA measure the spectrum using thesurface array consisting of either water tanks (PAO) or plastic*9 M. Takeda et al., Phys. Rev. Lett. 81, 1163 (1998).
*10 R.U. Abbasi et al., Phys. Rev. Lett. 100, 101101 (2008).
*11 J. Abraham et al., Phys. Lett. B685, 239 (2010).
*12 T. Abu-Zayyad et al., arXiv:1205.5067v1 (2012).

log(FLUX * E3 in eV2m-2s-1sr-1)

81

26

25.5

25

24.5

24

23.5

23

14

15

16

17

18

19

20

21

log(ENERGY in eV)
Fig. 3. Akeno energy spectrum measurements for 1015 eV - 1020 eV.

scintillators (TA), but the energy scale of the array is determined by the fluorescence telescope using a subset of events
observed by the fluorescence telescope and surface array at
the same time. The adoption of the energy scale by the fluorescence telescopes is based on its small dependence on the
air shower simulation.
The energy spectra above 1018 eV by AGASA and otherexperiments are compiled and compared by the working grouprepresented by UHECR experiments in the UHECR-2012 symposium held at CERN for Feb. 13th - 16th, 2012 13 . The resultis plotted in Fig.4 with the energy scale of each experiment adjusted to a reference energy, which is set halfway between the
PAO and TA/HiRes.
Following factors were applied for the energy scale; ×1.10
for PAO, ×0.91 for TA and HiRes, ×0.65 for AGASA and×0.56 for Yakutsk.
As seen in Fig.4, the overall agreement between experiments is good, and a “dip” structure was seen around 1018.7
eV by all experiments. The HiRes, PAO and TA confirmed
a strong flux suppression above approximately 1019.7 eV. Although the AGASA spectrum does not demonstrate the cutoff*13 http://indico.cern.ch/conferenceDisplay.py?confId=152124

structure, the number of events above 1020 eV became only
two after the energy rescaling, making the claim of the extended spectrum statistically insignificant. The estimate ofsystematic uncertainty of the energy measurement is approximately 20% for all the experiments, and rescalings for the
TA/HiRes and PAO are within this limit. Rescaling of thesurface array energy, ×0.65 for AGASA and ×0.56 for Yaktsuk, indicates that there exist larger systematic uncertainties
than originally estimated by running the air shower simulation. This difference of energy scale obtained by the surface
array and by the fluorescence telescope remains as a basic
question in the understanding of the air shower phenomena.

Recent Research Activities
The study of UHECRs by AGASA in Akeno was succeeded by the Telescope Array (TA) experiment in Utah, USA
since 2008. After the cessation of AGASA, the Akeno observatory has been used for small scale cosmic ray experiments, astrophysical observations and as a test and maintenance facility of TA by the ICRR and university researchers.
Research activities in JFY 2013 (April 2013 - March 2014)
are described in the following.

82

J(E) × E3/1024 [eV2 m-2 s-1 sr-1]

10

1

10-1
18

TA

HiRes-I

PAO

HiRes-IIAGASA

Yakutsk18.5

19log (E/eV)

19.5

20

20.5

10

Fig. 4. Recent compilation of UHECR energy spectra. The energy scale of each experiment is adjusted as described in the text.

Research and development for the Telescope Arrayobservation in Utah by the TA collaboration
All the fluorescence imaging cameras and a part of the surface detectors of TA were assembled in the Akeno observatory by the TA collaboration team. The detectors were tested
in Akeno and shipped to the Utah observation site for the installation. All the unit mirrors of the TA fluorescence telescope were tested in Akeno and the atmospheric monitoring
lidar of TA using YAG laser was developed in Akeno. In JFY
2013, a certain number of scintillator counters were assembled for TA muon detectors and were sent to Utah. A part ofthe experimental hall was prepared for the test of the vibration control equipment and temporary storage of the KAGRA
gravitational antenna equipment.
Observation by the multi-color imager for transients,
survey and monstrous explosions (MITSuME) by N.
Kawai (Tokyo Institute of Technology) et al.
One of the three MITSuME robotic telescopes was installedin the Akeno observatory in 2003 on the roof of the unused
concrete muon house. The telescope has an aperture of 50
cm, an FOV of 28’ × 28’ and is equipped with a tricolor CCD
camera capable of g0 RC IC -bands photometry. It is operated
remotely from the Tokyo Tech using dedicated ADSL connections. Upon receiving a GRB alert from Swift or Fermi
satellite, it quickly directs the telescope (9◦ /s maneuverability) toward the GRB direction, and makes a prompt observation of the GRB and its afterglow. In JFY 2013, 46 GRBs
were observed, and 5 were identified as visible objects. Other
burst objects were also observed. The whole sky monitor was
installed 10 m away from the telescope dome, and this information is opened to the public via Internet. Since the air conditioning was controlled remotely, the focusing function was
improved during summer season.

Observation of galactic cosmic rays by large area
muon telescope by S. Shibata (Chubu University) etal.
Four layers of proportional counter telescopes, each with 25
m2 area, were installed in three muon houses in Akeno (Fig.2)
and have been continuously measuring the cosmic ray muonssince 2003. The mode energy of the primary cosmic rays isapproximately 2.5 GeV corresponding to 2m thick concrete
ceiling of the muon house and the latitude of Akeno observatory. The measurement in Akeno is combined with a simultaneous measurement in Ooty, India, and the modulation
effects of galactic cosmic rays by the solar activity such as
the Forbush decrease and its precursor have been continuously
monitored 14 . In JFY 2013, the network router was replaced
to improve the access from the outside, and the UPS was installed to operate the data server stably. And the observation
was continued.
Research and development for a small atmospheric
Cherenkov telescope in Akeno observatory by
T. Yoshikoshi, M. Ohishi (ICRR) et al.
A small alt-azimuth telescope is being setup in Akeno forprototype tests with atmospheric Cherenkov observations of
gamma rays 15 . The optical axis of segmented mirrors was adjusted. The system of reflectivity measurement and the systemof telescope position calibration were developed. The data acquisition system was installed to this telescope.

*14 T. Nonaka.et al, Proc. of the 29th ICRC, 1, 363-366 (2005).
*15 M. Ohishi et al., 33rd ICRC, (Rio deJaneiro), 9, in press (2013).

83

KAMIOKA OBSERVATORY
Kamioka observatory is located at 1000 m underground(2700 m water equivalent) in the Kamioka Mine, Gifu prefecture, about 200 km west of Tokyo. The observatory wasestablished in 1995 in order to operate Super-Kamiokande
experiment (SK). The underground laboratories are locatedunder Mt.Ikeno-yama and accessible to the experimental sitethrough a 1.7 km horizontal tunnel. The observatory also
has surface research buildings and a dormitory located at the
distance of 15 minutes drive from the entrance of the underground laboratories.
The Super-Kamiokande experiment had discovered neutrino oscillations through the observations of atmospheric andsolar neutrinos (see the section for Neutrino and Astroparticle Division). The atmospheric neutrino oscillation was confirmed by the long baseline neutrino oscillation experiment,
K2K, using accelerator neutrino beam, which was conducted
between 1999 and 2004. A new long baseline neutrino oscillation experiment (the T2K experiment) using a high intensity
beam, 50 times of the K2K neutrino beam, by the J-PARC
proton accelerator has started in 2009. In 2011, the experiment has observed 6 νe appearance events indicating non-zeroθ13 which was as yet determined the last neutrino oscillation
parameter. In 2012 and 2013, the collaboration accumulated
more electron neutrino appearance events and strengthen the
discovery of non-zero θ13 .

The low cosmic ray flux and low seismic noise environment in the underground site enables us to conduct various
researches. There is a 100 m long laser interferometer, which
is a proto-type of the 3 km gravitational wave antenna (seesection of Astrophysics Gravity Division) under construction.
Using the low radioactive background environment in the
Kamioka Mine, a dark matter experiment, called XMASS isoperated in Lab-C. The XMASS group constructed a 800kg
liquid xenon detector and started commissioning run in late
2010. In 2013, the detector was improved to remove backgrounds on the inner surface of the PMT plane. The R&D
study of a tracking type detector for dark matter detection leadby the Kobe University group (the NEWAGE experiment) has
also been performed in Lab-B. The commissioning run of the
CANDLE experiment in Lab-D (Osaka Univ.), a double beta
decay experiment is now conducted. The study to improve theneutrino detection sensitivity by adding gadolinium to SuperKamiokande is on going. A 200 ton test tank dedicated for
the R&D study of the gadolinium project was constructed in
Lab-E and a feasibility study has been performed. In orderto support those experiments and also related R&D works,
the Observatory is equipped with low background Germanium
detector in Lab-1 and Lab-A, ICP-MS and so on to measureextremely low radioactive backgrounds.

Fig. 1. Kamioka Underground Observatory.

84

RESEARCH CENTER FOR COSMIC NEUTRINOS
The Research Center for Cosmic Neutrinos (RCCN) wasestablished in April, 1999. The main objective of this center is to study neutrinos based on data from various observations and experiments. In order to promote studies of neutrino
physics, it is important to provide the occasion to discuss theoretical ideas and experimental results on neutrino physics.
Therefore, one of the most important tasks of this center isthe organization of neutrino-related meetings. On January
20, 2014, we hosted this year’s domestic neutrino workshop,
whose topic was on the measurement of absolute neutrino
masses by terrestrial experiments and cosological measurements. About 40 physicists participated in this meeting.
Members of this center have been involved in the SuperKamiokande and T2K experiments, carrying out researches inneutrino physics. (Please see the Super-Kamiokande and T2K
pages for the scientific results.) Atmospheric neutrino datafrom Super-Kamiokande give one of the most precise pieces
of information on neutrino oscillations. With increased data,
it is more important to have better predictions of the neutrino
flux. Therefore, in addition to data analysis of the above experiments, we work on the calculation of the atmospheric neutrino flux.

It is important to share our scientific achievements withthe general public. For this reason, we hold public lectures
every year. Since FY2009, ICRR and the Kavli Institute for
the Physics and Mathematics of the Universe (Kavli-IPMU)
have co-sponsored two public lectures each year. The public lecture held in Spring is co-organized by RCCN and the
Public Relation Office of ICRR. The Spring public lecture
in FY2013 was held on April 13, 2013. Two scientists lectured on the observations of the Universe and the physics ofthe Higgs particle.
RCCN, together with the computer committee of ICRR, isin charge of operating the central computer system in ICRR.
In FY 2013, the computer system was upgraded to a muchhigh performance one. Since then, the system has been operated without any serious problems. RCCN also supports theusers of the computer system, including physicists in the cosmic ray community in Japan.
Since 2004, RCCN has been acting as a body for accepting the ICRR inter-university programs related to the lowbackground underground facility in the Kashiwa campus. The
facility is currently equipped with 4 Ge detectors mainly forthe measurements of cosmic radioactive isotopes. The scientific activities related to this facility is described elsewhere.

85

APPENDICES

A. ICRR Workshops and Ceremonies
B. ICRR Seminars
C. List of Publications(a) Papers Published in Journals(b) Conference Papers(c) ICRR Report

D. Doctoral Theses
E. Public Relations(a) ICRR News(b) Public Lectures(c) Visitors

F. Inter-University Research Activities
G. List of Committee Members(a) Board of Councillors(b) Advisory Committee(c) User’s Committee

H. List of Personnel

86

A. ICRR Workshops and Ceremonies

4th Korea-Japan workshop on KAGRA
Date: June 10-11, 2013
Place: Osaka University, Japan
Outline: This workshop was the 4th Korea-Japan workshop on KAGRA, and was held at Osaka University. The
workshop was organized by the scientific advisory committee,
the scientific organizing committee chaired by Seiji Kawamura (ICRR), and the local organizing committee chaired by
Hideyuki Tagoshi (Osaka University).
The workshop consisted of several sessions: the opening,
plenary, instrument, data analysis, theory, detector characterization, data management, and discussion about the future collaboration sessions. After the opening talk given by Takaaki
Kajita (ICRR), in the plenary session Hyung Mok Lee (Seoul
National University) explained the activities of the Korean
gravitational wave group and Kazuaki Kuroda (ICRR) gave
a talk about the overview on the current KAGRA. In eachsession of subsystems, the past activities and the future plans
were presented and discussed, including a talk on the activitiesof the KAGRA data analysis subsystem by Hideyuki Tagoshi(Osaka University) and a talk on the status of KAGRA detector characterization by Kazuhiro Hayama (Osaka City University). In the instrument session Kyuman Cho (Sogang University) gave a talk about the precision tilt and radius curvature
sensor using a double-pass AOM, and indicated the possibilityof using it for KAGRA.
In the discussion session, first, some progress in the framework of the collaboration was reported, including the JSPS
core-to-core program KAGRA had obtained, the appointment
of Tai Hyun Yoon (Korea University) as an ICRR visiting professor, and the gravitational wave summer school that would
be held in August, 2013 at Pohang, Korea. Then we discussed
the future collaboration on each subsystem. For the instru-

ment, we agreed that we would investigate the possibility ofusing the tilt sensor for KAGRA, we would continue inviting
Korean researchers and students using the JSPS core-to-coreprogram, and we would keep the efforts of finding other Korean experimentalists interested in joining KAGRA. For thedetector characterization, we defined several projects for developing tools equipped to identify noise artifacts and to localize their sources, and decided to have a bi-weekly telecon in
the group. For the data analysis, we agreed that the bayesianparameter estimation was a good starting research to establish
closer collaboration. Finally we decided that the next workshop would be held on November 29 - 30, 2013 at Seoul National University, Seoul, Korea.
Participants: 34 participants.
Website: http://vega.ess.sci.osaka-u.ac.jp/korea-japan/

Fig. 1. 4th Korea-Japan workshop on KAGRA.

5th Japan-Korea workshop on KAGRA
Date: November 29-30, 2013
Place: Seoul National University, Seoul, Korea
Outline: This workshop was the 5th Japan-Korea workshop on KAGRA, and was held at Seoul National University,
Seoul, Korea. The workshop was organized by the scientific advisory committee, the scientific organizing committee
chaired by Hyung Mok Lee (Seoul National University) andSeiji Kawamura (ICRR), and the local organizing committee
chaired by Hyung Mok Lee (Seoul National University).
The workshop consisted of several sessions: the opening, plenary, detector characterization and data management,
instrument, optical follow-up, theory and data analysis, anddiscussion on the next steps sessions. After the opening
talk given by Hyung Mok Lee (Seoul National University),
Ho Jung Paik (University of Maryland) gave a talk about alow frequency gravitational wave detector with superconducting instrumentation, and Shinji Miyoki (ICRR) explained thepresent status of KAGRA. In each session of subsystems, thepast activities and the future plans were presented and discussed, including a talk on the status of KAGRA detector
characterization by Kazuhiro Hayama (Osaka City University), a talk on the current status of the KAGRA cryogenics by
Chihiro Tokoku (ICRR), and a talk on the status of the KAGRA data analysis subsystem by Hideyuki Tagoshi (Osaka
University). In the instrument session Tai Hyun Yoon (Korea
University) gave a talk about the high-finesse fiber ring cavity
for compact laser frequency stabilization system of KAGRA
and reported the progress he made during his visit to ICRR

87

an a visiting professor. In this workshop we decided to havethe optical follow-up session for the first time because of theimportance of the multi-messenger science, and Michitoshi
Yoshida (Hiroshima University) gave a talk about the opticalinfrared telescope network for follow-up observation of gravitational wave transients in Japan.
In the discussion session, for the instrument, we agreed
that we would investigate the possibility of using the fiber ringcavity which Tai Hyun Yoon (Korea University) developed for
KAGRA, and we would investigate the possibility of inviting
Tai Hyun Yoon (Korea University) and Kyuman Cho (Sogang
University) to ICRR as a visiting professor. For the detector characterization, we were discussing the KAGRA mockdata challenge and an EMD-based event-trigger-generation
development using CLIO data. For the data analysis, several
collaboration research projects were explained, and the groupplanned to have a monthly telecon. For the data management,
we had some discussion about the data transfer test, etc. Finally we decided that the next workshop would be held on
June 20 - 21, 2014 at National Astronomical Observatory ofJapan, and the workshop after next would be held in December, 2014 at Toyama University.
Participants: 36 participants.
Website: https://kgwg.nims.re.kr/kagra5th/kagra5th/Home.html

Fig. 2. 5th Japan-Korea workshop on KAGRA.

EliTES 2nd General Meeting
Date: Dec 4-5, 2013
Place:Deligation of the Eureopean Union to Japan & Sanjo Conference Hall, the University of Tokyo, Japan
Outline: The ELiTES program is initiated by partners;
European Gravitational Observatory sponsored by Italy andFrance, ICRR (Japan), Universit di Roma ”La Sapienza”(Italy), Friedrich-Schiller Universitaet, Jena (Germany), University of Glasgow (UK), FOM (Nitherland), MPG (Germany), Universit degli Studi del Sannio (Italy), Universityof West Scotland (UK). The acronym ELiTES stands for ET
LCGT(KAGRA, at present) interferometric Telescopes: Exchanges of Scientists. It is an initiative supported (2012-2016)
by the European Commission under FP7-people. In particular, ELiTES is supported as IRSES: International Research
Staff Exchange Scheme (RISE in H2020). ELiTES supports
the exchange of GW scientists between EU and Japan (andthe Japanese counterpart set-up a mirror initiative, consequent
to ELiTES). ELiTES idea born during the second ET general
meeting, focusing on the ET-KAGRA common aspects:• Cryogenics and Underground facilities• Very active and productive links are sustained throughELiTES consists of four working packages, WP1: Suspensions design and test, WP2: Suspensions materials andfibers, WP3: Infrastructures & Vacuum apparatuses and WP4:
organization. Under this ELiTES program, we have one technical workshop in Europe and one general meeting in Japan.
In this financial year, ICRR hosted the second general meeting in Tokyo as in the previous year. Since the program issponsored by EU, the first day was held in EU representative
house in Tokyo. First half of the beginning session of the firstday consisted of invited talks. First one was given by Dr. Barbara Rhode who is the Head of Science and Technology Sec-tion of the delegation of EU to Japan (EU house in Tokyo).
The second one was given by Mr. Shintaro Seto who is the
director for Scientific Research Coordination, Scientific Research Institutes Devision, Research Promotion Bureau, Ministry of Eduation, Culture, Sports, Science and Technology.
After this invited talks, KAGRA project by Raffaele Flaminio,
Advanced Virgo status by Fulvio Ricci, Advanced LIGO status by James Hough, and The Einstein Telescope Project byHarald Lueck were presented in the morning. The afternoon
was devoted to WP3-Infrasgtructures. Three talks focused on
KAGRA underground facility and one talk was for site studyof ET project.We had discussed about underground environmental sensors. Also correlated magnetic noise in Kamioka
was reported.
The second day, the meeting venue was moved to Sanjo
Hall in Hongo campus of UTokyo. WP1-WP2 joint activities
were presented and discussed. Modeling and testing of cryogenic sapphire suspensions is introduced and study of radiation shield vibration was reported by a KAGRA member. Also
the issues of vertical filters in crytogenic environment need tobe sorted out for both KAGRA and ET. Thermal noise relating to bulk material and optical coating was handled by pluralpresentations. Practically study of bonding sapphire fibers on
the main mirror was the most interested subject by KAGRA
suspension group. All presentations this year were satisfactory from the point of view of research development and letlisteners recognize steady advancement of the collaborative
work between Europe and Japan.
Participants: 46 people 6 countires on 4th, December 80
people 7 countries on 5th, December

88

CTA LST General Meeting
Date: January 14 2014 - Jaunuary 17 2014
Place: Kashiwa Library, the University of Tokyo, Japan
Outline: The CTA LST General meeting was held to discuss the science with the CTA large-sized telescopes and to
finalize the design of the CTA large-sized telescope, time schedule and to define the responsibilities, validation and verification
procedures for individual telescope elements.
Participants: 83 participants.

B. ICRR Seminars
1. April 4, 2013: Sadakazu Haino (National Central University), “Status of AMS-02”
2. June 25, 2013: Shigeki Aoki (Kobe University), “GRAINE project: Cosmic Gamma-ray Observation with BalloonBorne Emulsion Telescope”
3. July 5, 2013: Anne Verhamme (The Observatory of Geneva, Switzerland), “Lyman-alpha radiation transfer effects ingalaxies”
4. July 19, 2013: Shoei Nakayama (ICRR, the University of Tokyo), “The latest results from T2K”
5. July 24, 2013: Martin A. Lee (University of New Hampshire), “What is new in the outer heliosphere: Voyager and
IBEX?”
6. September 25, 2013: Rutger Van Haasteren (Jet Propulsion Laboratory), “Detecting gravitational-waves by observing
pulsars, nature’s most accurate natural clocks”
7. October 23, 2013: Eduardo de la Fuente Acosta (Departamento de Fisica, CUCEI, Universidad de Guadalajara), “The“High Altitude Water Cerenkov (HAWC)” Gamma Ray Observatory”
8. November 28, 2013: Kenneth Long (Imperial College London), “Neutrinos from stored muon beams”
9. February 18, 2014: Razmik Mirzoyan (Max-Planck-Institute for Physics, Munich, Germany), “Strong Boost of PMTand SiPM Parameters for Astro-Particle Physics Experiments”
10. March 11, 2014: Yoshinari Hayato (ICRR, the University of Tokyo), “The latest results from the T2K experiment”

C. List of Publications(a) Papers Published in Journals
1. “Calibration of the Super-Kamiokande Detector”, The Super-Kamiokande Collaboration, Nucl. Instr. & Meth, A 737C
(2014) [arXiv:1307.0162].
2. “First Indication of Terrestrial Matter Effects on Solar Neutrino Oscillation”, The Super-Kamiokande Collaboration,
Phys. Rev. Lett. 112, 091805(2014)[arXiv:1312.5176].
3. “Evidence for the Appearance of Atmospheric Tau Neutrinos in Super-Kamiokande”, The Super-Kamiokande Collaboration, Phys. Rev. Lett. 110, 181802 (2013).
4. “Future long-baseline neutrino facilities and detectors”, M. Diwan, R. Edgecock, T. Hasegawa, T. Patzak, M. Shiozawa,
and J. Strait, Advances in High Energy Physics Volume 2013 (2013), Article ID 460123.
5. “Search for inelastic WIMP nucleus scattering on 129Xe in data from the XMASS-I experiment, status and results”, U.
Uchida et al. (XMASS collaboration), Prog. Theor. Exp. Phys. 2014, 063C01.

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6. “Baryon Number Violation”, Baryon Number Violation Group. Report of the Community Summer Study (Snowmass2013), Intensity Frontier.
7. “Progress and open questions in the physics of neutrino cross sections”, L. Alvarez-Ruso, Y. Hayato, Invited review
article for New Journal of Physics.
8. “Monte-Carlo neutrino event generators”, H. Gallagher, Y. Hayato, Invited review article for Review of Particle Physics( 2014 ).
9. “The Development of a Hybrid Photo-Detector (HPD) for the Hyper-Kamiokande Project”, Seiko Hirota et al., Nucl.
Instrum. Meth. A 732 (2013) 303.
10. “XMASS detector”, The xmass Collaboration, Nucl. Instr. and Meth. in Phys.Res.A716 (2013) 78-85.
11. “Search for solar axions in XMASS, a large liquid-xenon detector”, The xmass Collaboration, Phys.Lett. B724 (2013)46-50.
12. “Observation of Electron Neutrino Appearance in a Muon Neutrino Beam”, The T2K Collaboration, Phys. Rev. Lett.
112, 061802 (2014).
13. “Measurement of Neutrino Oscillation Parameters from Muon Neutrino Disappearance with an Off-axis Beam”, The
T2K Collaboration, Phys. Rev. Lett. 111, 211803 (2013).
14. “Measurement of the Inclusive NuMu Charged Current Cross Section on Carbon in the Near Detector of the T2K
Experiment”, The T2K Collaboration, Phys. Rev. D 87, 092003 (2013).
15. “Evidence of Electron Neutrino Appearance in a Muon Neutrino Beam”, The T2K Collaboration, Phys. Rev. D 88,
032002 (2013).
16. “Search for Very-High-Energy Gamma Rays from the z = 0.896 Quasar 4C +55.17 with the MAGIC telescopes”, MAGIC
collaboration, Aleksić et al. MNRAS 440 (2014) 530.
17. “Optimized dark matter searches in deep observations of Segue 1 with MAGIC MAGIC collaboration”, Aleksić et al.
JCAP 02 (2014) .
18. “Discovery of very high energy gamma-ray emission from the blazar 1ES 1727+502 with the MAGIC Telescopes
MAGIC collaboration”, Aleksić et al. A&A 563 (2014).
19. “MAGIC upper limits on the GRB 090102 afterglow MAGIC collaboration”, Aleksić et al. MNRAS 437 (2014) 31033111.
20. “Multifrequency Studies of the Peculiar Quasar 4C+21.35 during the 2010 Flaring Activity MAGIC collaboration”,
Ackermann et al. ApJ 786 (2014) 157.
21. “Discovery of GeV Emission from the Circinus Galaxy with the Fermi Large Area Telescope”, M.Hayashida et al., ApJ
779 (2013) id131 (7pp).
22. “Introducing the CTA concept”, CTA Consortium, Astropart. Phys. 43 (2013) 3.
23. “Gamma-ray burst science in the era of the Cherenkov Telescope Array”, CTA Consortium, Astropart. Phys. 43 (2013)
252.
24. “Observations of the magnetars 4U 0142+61 and 1E 2259+586 with the MAGIC telescopes MAGIC collaboration”,
Aleksić et al. A&A 549 (2013) A23.
25. “The simultaneous low state spectral energy distribution of 1ES 2344+514 from radio to very high energies MAGIC
collaboration”, Aleksić et al. A&A 556 (2013) A67.
26. “Very high energy gamma-ray observation of the peculiar transient event Swift J1644+57 with the MAGIC telescopes
and AGILE MAGIC collaboration”, Aleksić et al. A&A 552 (2013) A11.
27. “Upper limit on the flux of photons with energies above 1019 eV using the Telescope Array surface detector”, T. AbuZayyada et al., Phys. Rev.D 88,112005 (2013).
28. “CORRELATIONS OF THE ARRIVAL DIRECTIONS OF ULTRA-HIGH ENERGY COSMIC RAYS WITH EXTRAGALACTIC OBJECTS AS OBSERVED BY THE TELESCOPE ARRAY EXPERIMENT”, T. Abu-Zayyada et al., Astrophys. J. 777, 88(8pp), 2013.

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29. “The energy spectrum of ultra-high-energy cosmic rays measured by the Telescope Array FADC fluorescence detectors
in monocular mode”, T. Abu-Zayyada et al., Astropart. Phys. 48(2013)16-24.
30. “THE COSMIC-RAY ENERGY SPECTRUM OBSERVED WITH THE SURFACE DETECTOR OF THE TELESCOPE ARRAY EXPERIMENT”, T. Abu-Zayyada et al., Astrophys. J. Lett., 768:L1 (5pp), 2013.
31. “Probe of the Solar Magnetic Field Using the vCosmic-Ray Shadowy” of the Sun”, M.Amenomori et al., PhysicalReview Letters, 111, 2013, 011101-1-5, [arXiv:1306.3009v2 [astro-ph.SR]].
32. “Wide-Band Spectra of Prompt Emission”, K. Asano, EAS Publications Series, Vol 61, 115-122 (2013).
33. “Photon and Neutrino Spectra of Time-Dependent Photospheric Models of Gamma-Ray Bursts”, K. Asano & P. Meszaros,
JCAP09(2013)008 [arXiv:1308.3563[astro-ph.HE]].
34. “Search for a correlation between giant radio pulses and hard X-ray emissions in the Crab pulsar”, Ryo Mikami, Toshio
Terasawa, Shota Kisaka, Hideaki Miyamoto, Katsuaki Asano, Nobuyuki Kawai, Yosuke Yamakoshi, Kumiko Nagata,
Ryuho Kataoka, Kazuhiro Takefuji, Mamoru Sekido, Hiroshi Takeuchi, Hirokazu Odaka, Tamotsu Sato, Yasuyuki T.
Tanaka, JPS Conf. Proc. , 015106 (2014) [arXiv:1309.165[astro-ph.HE]].
35. “Constraint on Pulsar Wind Properties from Induced Compton Scattering off Radio Pulses”, Shuta J. Tanaka, Fumio
Takahara, PTEP 2013 12, 123E01 [arXiv:1311.5337].
36. “Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A”, M. Ackermann, M. Ajello, K. Asano et al., ScienceVol. 343 no. 6166 pp. 42-47 (2014).
37. “Neutrino and Cosmic-Ray Release from Gamma-Ray Bursts: Time-Dependent Simulations”, Katsuaki Asano, Peter
Meszaros, ApJ 785 54 (2014) [arXiv:1402.6057[astro-ph.HE]].
38. “The Evolution of High Temperature Plasma in Magnetar Magnetospheres and its Implications for Giant Flares”, Makoto
Takamoto, Shota Kisaka, Takeru Suzuki, Toshio Terasawa, ApJ 787 84 (2014) [arXiv:1404.2766[astro-ph.HE]].
39. “The First Fermi LAT Gamma-Ray Burst Catalog”, M. Ackermann, M. Ajello, K. Asano et al., ApJS 209, 11(90pp)[arXiv:1303.2908[astro-ph.HE]].
40. “Spatially Resolved Spectroscopy of a Pulsar Wind Nebula in MSH 15-56”, Yoichi Yatsu, Katsuaki Asano, Nobuyuki
Kawai, Yuki Yano, and Takeshi Nakamori, ApJ, 773, 25(14 pp.), 2013.
41. “TARA:Forward-scattered radar detection of UHECR at the telescope array”, J. Belz, M. Abu Bakr Othman, C. Allen,
E. Barcikowski,D. Besson B. Farhang-Boroujeny, D. Ikeda, W. Hanlon, S. Kunwar, J.P. Lundquist, I. Kravchenko, S.
Larson, I.Myers, T. Nakamura, J.S. Rankin, H. Sagawa, P. Sokolsky, H. Takai, T. Terasawa and G.B. Thomson, theTARA Collaboratio, EPJ Web of Conferences 53 08012 (2013).
42. “Sapphire mirror for the KAGRA gravitational wave detector”, Eiichi Hirose, Dan Bajuk, GariLynn Billingsley, Takaaki
Kajita, Bob Kestner, Norikatsu Mio, Masatake Ohashi, Bill Reichman, Hiroaki Yamamoto, and Liyuan Zhang, Phys.
Rev. D 89 (2014) 062003.
43. “Evaluation of heat extraction through sapphire fibers for the GW observatory KAGRA”, A Khalaidovski, G Hofmann,
D Chen, J Komma, C Schwarz, C Tokoku, N Kimura, T Suzuki, A O Scheie, E Majorana, R Nawrodt and K Yamamoto,Class. Quantum Grav. 31 105004, 2014.
44. “Precise measurement of laser power using an optomechanical system”, Kazuhiro Agatsuma, Daniel Friedrich, Stefan
Ballmer, Giulia DeSalvo, Shihori Sakata, Erina Nishida, and Seiji Kawamura, Optics Express, 22 (2014) 2013-2030.
45. “Interferometer design of the KAGRA gravitational wave detector”, Yoichi Aso, Yuta Michimura, Kentaro Somiya,
Masaki Ando, Osamu Miyakawa, Takanori Sekiguchi, Daisuke Tatsumi, and Hiroaki Yamamoto (The KAGRA Collaboration), Phys. Rev.D, 88, 43007(2013).
46. “Cryogenics System for the Interferometric Cryogenics Gravitationak Wave Telescope, KAGRA -Design, Fabrication,
and Performance Test -,” C. Tokoku, N. Kimura, S. Koike, T. Kume, Y. Sakakibara, T. Suzuki, K. Yamamoto, S. Miyoki,
D. Chen, S. Goto, M. Tanaka, S. Ioka, K. Nakamoto, H. Nezuka, T. Uchiyama, M. Ohashi, and K. Kuroda, Adv. Cryog.
Eng. 59B (2014), pp.1254-1261.
47. “A Study of Cooling Time Reduction of Interferometric Cryogenic Gravitational Wave Detectors Using a High-Emissivity
Coating”, Y. Sakakibara, N. Kimura, T. Suzuki, K. Yamamoto, D. Chen, S. Koike, C. Tokoku, T. Uchiyama, M. Ohashi
and K. Kuroda, Adv. Cryog. Eng., AIP Publishing, AIP Conf. Proc. 1573 pp.1176-1183 (2014).

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48. “Calibrating [O II] star formation rates at z < 1 from dual Hα-[O II] imaging from HiZELS”, Hayashi, M., et al.,Monthly Notices Roy. Astron. Soc., 430, 1042-1050, 2013, [arXiv:1212.4905 [astro-ph.CO]].
49. “New Constraints on Cosmic Reionization from the 2012 Hubble Ultra Deep Field Campaign”, Robertson, B., et al.,Astrophys. J., 768, 71, 2013, [arXiv:1301.1228 [astro-ph.CO]].
50. “The UV Luminosity Function of Star-forming Galaxies via Dropout Selection at Redshifts z ∼ 7 and 8 from the 2012
Ultra Deep Field Campaign”, Schenker, M. A., et al., Astrophys. J., 768, 196, 2013, [arXiv:1212.4819 [astro-ph.CO]].
51. “First Spectroscopic Evidence for High Ionization State and Low Oxygen Abundance in Lyα Emitters”, Nakajima, K.,
Ouchi, M., et al., Astrophys. J., 769, 3, 2013, [arXiv:1208.3260 [astro-ph.CO]].
52. “SEDS: The Spitzer Extended Deep Survey. Survey Design, Photometry, and Deep IRAC Source Counts”, Ashby, M.
L. N., et al., Astrophys. J., 769, 80, 2013.
53. “A new multifield determination of the galaxy luminosity function at z = 7−9 incorporating the 2012 Hubble Ultra-Deep
Field imaging”, McLure, R. J., et al., Monthly Notices Roy. Astron. Soc., 432, 2696-2716, 2013, [arXiv:1212.5222[astro-ph.CO]].
54. “The UV continua and inferred stellar populations of galaxies at z ' 7 − 9 revealed by the Hubble Ultra-Deep Field
2012 campaign”, Dunlop, J. S., et al., Monthly Notices Roy. Astron. Soc., 432, 3520-3533, 2013, [arXiv:1212.0860[astro-ph.CO]].
55. “Evolution of star formation in the UKIDSS Ultra Deep Survey field - I. Luminosity functions and cosmic star formation
rate out to z = 1.6”, Drake, A. B., et al., Monthly Notices Roy. Astron. Soc., 433, 796-811, 2013, [arXiv:1305.1305[astro-ph.CO]].
56. “Star Formation on Subkiloparsec Scale Triggered by Non-linear Processes in Nearby Spiral Galaxies”, Momose, R., etal., Astrophys. J. (Letters), 772, L13, 2013, [arXiv:1306.5531 [astro-ph.CO]].
57. “Physical Properties of Spectroscopically Confirmed Galaxies at z ≥ 6. I. Basic Characteristics of the Rest-frame UVContinuum and Lyα Emission”, Jiang, L., et al., Astrophys. J., 772, 99, 2013, [arXiv:1303.0024 [astro-ph.CO]].
58. “Resolved Giant Molecular Clouds in Nearby Spiral Galaxies: Insights from the CANON CO (1–0) Survey”, Donovan
Meyer, J., et al., Astrophys. J., 772, 107, 2013, [arXiv:1305.5275 [astro-ph.GA]].
59. “Physical Properties of Spectroscopically Confirmed Galaxies at z ≥ 6. II. Morphology of the Rest-frame UV Continuumand Lyα Emission”, Jiang, L., et al., Astrophys. J., 773, 153, 2013, [arXiv:1303.0027 [astro-ph.CO]].
60. “The Galaxy Environment of a QSO at z ∼ 5.7”, Bañados, E., et al., Astrophys. J., 773, 178, 2013, [arXiv:1306.6642[astro-ph.CO]].
61. “On the evolution and environmental dependence of the star formation rate versus stellar mass relation since z ∼ 2”,
Koyama, Y., et al., Monthly Notices Roy. Astron. Soc., 434, 423-436, 2013, [arXiv:1302.5315 [astro-ph.CO]].
62. “Evolution of the Sizes of Galaxies over 7 < z < 12 Revealed by the 2012 Hubble Ultra Deep Field Campaign”, Ono,
Y., Ouchi, M., et al., Astrophys. J., 777, 155, 2013, [arXiv:1212.3869 [astro-ph.CO]].
63. “The 2012 Hubble Ultra Deep Field (UDF12): Observational Overview”, Koekemoer, A. M., et al., Astrophys. J. Suppl.,
209, 3, 2013, [arXiv:1212.1448 [astro-ph.CO]].
64. “An Intensely Star-forming Galaxy at z ∼ 7 with Low Dust and Metal Content Revealed by Deep ALMA and HST
Observations”, Ouchi, M., et al., Astrophys. J., 778, 102, 2013, [arXiv:1306.3572 [astro-ph.CO]].
65. “The Nature of Hα-selected Galaxies at z > 2. I. Main-sequence and Dusty Star-forming Galaxies”, Tadaki, K., et al.,Astrophys. J., 778, 114, 2013, [arXiv:1311.4259 [astro-ph.CO]].
66. “First Systematic Search for Oxygen-line Blobs at High Redshift: Uncovering AGN Feedback and Star Formation
Quenching”, Yuma, S., Ouchi, M., et al., Astrophys. J., 779, 53, 2013, [arXiv:1306.5246 [astro-ph.CO]].
67. “A fundamental metallicity relation for galaxies at z = 0.84 − 1.47 from HiZELS”, Stott, J. P., et al., Monthly Notices
Roy. Astron. Soc., 436, 1130-1141, 2013, [arXiv:1309.0506 [astro-ph.CO]].
68. “The Nature of Hα-selected Galaxies at z > 2. II. Clumpy Galaxies and Compact Star-forming Galaxies”, Tadaki, K., etal., Astrophys. J., 780, 77, 2014, [arXiv:1311.4260 [astro-ph.CO]].

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69. ““Direct” Gas-phase Metallicities, Stellar Properties, and Local Environments of Emission-line Galaxies at Redshifts
below 0.90”, Ly, C., et al., Astrophys. J., 780, 122, 2014, [arXiv:1307.7712 [astro-ph.CO]].
70. “Extragalactic science, cosmology, and Galactic archaeology with the Subaru Prime Focus Spectrograph”, Takada, M.,
et al., Publ. Astron. Soc. Japan, 66, 1, 2014, [arXiv:1206.0737 [astro-ph.CO]].
71. “The mass-metallicity relation at z ∼ 1.4 revealed with Subaru/FMOS”, Yabe, K., et al., Monthly Notices Roy. Astron.
Soc., 437, 3647-3663, 2014, [arXiv:1311.2624 [astro-ph.CO]].
72. “Mapping the large-scale structure around a z = 1.46 galaxy cluster in 3D using two adjacent narrow-band filters”,
Hayashi, M., et al., to be published in Monthly Notices Roy. Astron. Soc., 2014, [arXiv:1401.3919 [astro-ph.CO]].
73. “What is the Physical Origin of Strong Lyα Emission? I. Demographics of Lyα Emitter Structures”, Shibuya, T., Ouchi,M., et al., to be published in Astrophys. J., 2014, [arXiv:1401.1209 [astro-ph.CO]].
74. “Dark Matter Production in Late Time Reheating”, K. Harigaya, M. Kawasaki, K. Mukaida and M. Yamada, Phys. Rev.
D 89, 083532 (2014) [arXiv:1402.2846 [hep-ph]].
75. “Critical constraint on inflationary magnetogenesis”, T. Fujita and S. Yokoyama, JCAP 1403, 013 (2014) [Erratum-ibid.
1405, E02 (2014)] [arXiv:1402.0596 [astro-ph.CO]].
76. “Baryon Asymmetry, Dark Matter, and Density Perturbation from PBH”, T. Fujita, M. Kawasaki, K. Harigaya and
R. Matsuda, Phys. Rev. D 89, 103501 (2014) [arXiv:1401.1909 [astro-ph.CO]].
77. “Flat Higgs Potential from Planck Scale Supersymmetry Breaking”, M. Ibe, S. Matsumoto and T. T. Yanagida, Phys.
Lett. B 732, 214 (2014) [arXiv:1312.7108 [hep-ph]].
78. “One-loop anomaly mediated scalar masses and (g − 2)m u in pure gravity mediation”, J. L. Evans, M. Ibe, K. A. Oliveand T. T. Yanagida, Eur. Phys. J. C 74, 2775 (2014) [arXiv:1312.1984 [hep-ph]].
79. “Lower Bound on the Garvitino Mass m3/2 > O(100) TeV in R-Symmetry Breaking New Inflation”, K. Harigaya, M. Ibe
and T. T. Yanagida, Phys. Rev. D 89, 055014 (2014) [arXiv:1311.1898 [hep-ph]].
80. “Decay rates of Gaussian-type I-balls and Bose-enhancement effects in 3+1 dimensions”, M. Kawasaki and M. Yamada,
JCAP 1402, 001 (2014) [arXiv:1311.0985 [hep-ph]].
81. “Hypercharged Dark Matter and Direct Detection as a Probe of Reheatingff, B. Feldstein, M. Ibe and T. T. Yanagida,
Phys.ReV.Lett. 112, 101301 (2013) [ arXiv:1310.7495 [hep-ph]] .
82. “Halo/Galaxy Bispectrum with Primordial non-Gaussianity from integrated Perturbation Theory (iPT)”, S. Yokoyama,
T. Matsubara and A. Taruya, Phys. Rev. D 89, 043524 (2014) [arXiv:1310.4925 [astro-ph.CO]].
83. “Axions as Hot and Cold Dark Matter”, K. S. Jeong, M. Kawasaki and F. Takahashi, JCAP 1402, 046 (2014) [arXiv:1310.1774[hep-ph]].
84. “A Closer Look at Gaugino Masses in Pure Gravity Mediation Model/Minimal Split SUSY Model”, K. Harigaya, M. Ibe
and T. T. Yanagida, JHEP 1312, 016 (2013) [arXiv:1310.0643 [hep-ph]].
85. “On the estimation of gravitational wave spectrum from cosmic domain walls”, T. Hiramatsu, M. Kawasaki and K. ’i. Saikawa,
JCAP 1402, 031 (2014) [arXiv:1309.5001 [astro-ph.CO]].
86. “A new algorithm for calculating the curvature perturbations in stochastic inflation”, T. Fujita, M. Kawasaki, Y. Tada and
T. Takesako, JCAP 1312, 036 (2013) [arXiv:1308.4754 [astro-ph.CO]].
87. “Peccei-Quinn symmetry from a gauged discrete R symmetry”, K. Harigaya, M. Ibe, K. Schmitz and T. T. Yanagida,
Phys. Rev. D 88, 075022 (2013) [arXiv:1308.1227 [hep-ph]].
88. “Large Scale Cosmic Perturbation from Evaporation of Primordial Black Holes”, T. Fujita, K. Harigaya and M. Kawasaki,
Phys. Rev. D 88, 123519 (2013) [arXiv:1306.6437 [astro-ph.CO]].
89. “Higher order statistics of curvature perturbations in IFF model and its Planck constraints”, T. Fujita and S. Yokoyama,
JCAP 1309, 009 (2013) [arXiv:1306.2992 [astro-ph.CO]].
90. “Non-Universalities in Pure Gravity Mediation”, J. L. Evans, K. A. Olive, M. Ibe and T. T. Yanagida, Eur. Phys. J. C 73,
2611 (2013) [arXiv:1305.7461 [hep-ph]].

9391. “Domain wall and isocurvature perturbation problems in axion models”, M. Kawasaki, T. T. Yanagida and K. Yoshino,
JCAP 1311, 030 (2013) [arXiv:1305.5338 [hep-ph]].
92. “Gravitational waves from a curvaton model with blue spectrum”, M. Kawasaki, N. Kitajima and S. Yokoyama, JCAP
1308, 042 (2013) [arXiv:1305.4464 [astro-ph.CO]].
93. “AMS-02 Positrons from Decaying Wino in the Pure Gravity Mediation Model”, M. Ibe, S. Matsumoto, S. Shirai and
T. T. Yanagida, JHEP 1307, 063 (2013) [arXiv:1305.0084 [hep-ph]].
94. “Recent Result of the AMS-02 Experiment and Decaying Gravitino Dark Matter in Gauge Mediation”, M. Ibe, S. Iwamoto,
S. Matsumoto, T. Moroi and N. Yokozaki, JHEP 1308, 029 (2013) [arXiv:1304.1483 [hep-ph]].
95. “Muon g-2 and 125 GeV Higgs in Split-Family Supersymmetry”, M. Ibe, T. T. Yanagida and N. Yokozaki, JHEP 1308,
067 (2013) [arXiv:1303.6995 [hep-ph]].
96. “Implications of Planck results for models with local type non-Gaussianity”, T. Suyama, T. Takahashi, M. Yamaguchi
and S. Yokoyama, JCAP 1306, 012 (2013) [arXiv:1303.5374 [astro-ph.CO]].
97. “Focus point gauge mediation in product group unification”, F. Brümmer, M. Ibe and T. T. Yanagida, Phys. Lett. B 726,
364 (2013) [arXiv:1303.1622 [hep-ph]].
98. “Statistics of general functions of a Gaussian field-application to non-Gaussianity from preheating”, T. Suyama andS. Yokoyama, JCAP 1306, 018 (2013) [arXiv:1303.1254 [astro-ph.CO]].
99. “Universality in Pure Gravity Mediation”, J. L. Evans, M. Ibe, K. A. Olive and T. T. Yanagida, Eur. Phys. J. C 73, 2468
(2013) [arXiv:1302.5346 [hep-ph]].
100. “Heavy gravitino in hybrid inflation”, M. Kawasaki, N. Kitajima, K. Nakayama and T. T. Yanagida, JCAP 1306, 037(2013) [arXiv:1301.6281, arXiv:1301.6281 [hep-ph]].
101. “A Simple Solution to the Polonyi Problem in Gravity Mediation”, K. Harigaya, M. Ibe, K. Schmitz and T. T. Yanagida,
Phys. Lett. B 721, 86 (2013) [arXiv:1301.3685 [hep-ph]].
102. “Natural supersymmetryfs last hope: R-parity violation via UDD operators”, B. Bhattacherjee, J. L. Evans, M. Ibe,
S. Matsumoto and T. T. Yanagida, Phys. Rev. D 87, 115002 (2013) [arXiv:1301.2336 [hep-ph]].
103. “Axions: Theory and Cosmological Role”, M. Kawasaki and K. Nakayama, Ann. Rev. Nucl. Part. Sci. 63, 69 (2013)[arXiv:1301.1123 [hep-ph]].
104. “Revisiting the Cosmological Coherent Oscillation”, M. Kawasaki, N. Kitajima and K. Nakayama, Phys. Rev. D 87,
023513 (2013) [arXiv:1112.2818 [hep-ph]].

(b) Conference Papers
1. “Future of Super-Kamiokande and Hyper-Kamiokande”, M. Nakahata, Proceedings of the 13th International Conferenceon Topics in Astroparticle and Underground Physics(TAUP2013), Asilomar, California USA, September 8-13, 2013.
2. “XMASS experiment”, K. Abe, Proceedings of Dark Matter 2014, February, 2014.
3. “Status of the XMASS experiment”, S. Moriyama, Proceedings of TAUP2013, September, 2013.
4. “Design of low-energy calibration sources for liquid xenon dark matter detectors”, K. Hosokawa, Proceedings of TAUP2013,
September, 2013.
5. “Low background techniques from XMASS”, H. Ogawa, Proceedings of LRT2013, April, 2013.
6. “Neutrino Physics (rapporteur talk)”, M. Nakahata, Proceedings of the 33rd International Cosmic Ray Conference(ICRC2013), to be published, Rio de Janeiro, Brazil, July 2-9, 2013.
7. “Solar neutrino analysis of Super-Kamiokande”, H. Sekiya, Proceeding of 33rd International Cosmic Ray Conference(ICRC 2013), Jul, 2013.
8. “Recent results from XMASS”, K. Hiraide, Proceedings of 48th Rencontres de Moriond on Very High Energy Phenomena in the Universe.

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9. “The Hyper-Kamiokande project”, M. Shiozawa, Proceeding of Neutrino Oscillation Workshop (NOW 2012), September, 2012, published in Nuclear Physics B Proceedings Supplement.
10. “Super-Kamiokande Atmospheric Neutrino Oscillation Analysis”, R. Wendell, Proceeding of Neutrino Oscillation Workshop (NOW 2012), September, 2012, published in Nuclear Physics B Proceedings Supplement.
11. “Super-Kamiokande Low Energy Results”, H. Sekiya, Proceeding of Neutrino Oscillation Workshop (NOW 2012),
September, 2012, published in Nuclear Physics B Proceedings Supplement.
12. “Atmospheric neutrino oscillation and mass hierarchy determination in Super-Kamiokande”, K. Okumura, Proceedingsof TAUP2013, September, 2013.
13. “Detection of the Atmospheric Showers with Telescope Array (TA) Experiment”, H. Sagawa for the TA collaboration,
Proceedings of the Conference on Calorimetry for the High Energy Frontier (CHEF2013), April 22-25, 2013, Paris.
14. “Highlights from the Telescope Array Experiment”, H. Sagawa for the TA collaboration, Proceedings of the 33rd International Cosmic Ray Conference (ICRC2013), July 2-9, 2013, Rio de Janeiro.
15. “The Plan of the Telescope Array Experiment for the Next Five Years”, H. Sagawa for the TA collaboration, Proceedingsof ICRC2013, Rio de Janeiro.
16. “SD energy spectrum of TA and its fitting with the energy loss model of UHECR protons”, E. Kido for the TA collaboration, Proceedings of the ICRC2013, Rio de Janeiro.
17. “Search for Ultra-High Energy Photons and Neutrinos using the Telescope Array Scintillator Array Data”, G. I. Rubtsov
for the TA collaboration, Proceedings of the ICRC2013, Rio de Janeiro.
18. “Telescope Array Measurements of the UHECR Energy Spectrum”, D. Bergman for the TA collaboration, Proceedingsof the ICRC2013, Rio de Janeiro.
19. “Study on Mass Composition of Ultra-High Energy Cosmic Rays by Telescope Array”, Y. Tsunesada for the TA collaboration, Proceedings of the ICRC2013, Rio de Janeiro.
20. “TA anisotropy summary”, P. Tinyakov for the TA collaboration, Proceedings of the ICRC2013, Rio de Janeiro.
21. “Composition Analysis of a Multispecies UHECR Spectrum Compatible with Auger Data via Telescope Array Hybrid
Reconstruction”, W. F. Hanlon for the TA collaboration, Proceedings of the ICRC2013, Rio de Janeiro.
22. “Measuring Large-Scale Anisotropy in the Arrival Directions of Cosmic Rays Detected at the Telescope Array and
the Pierre Auger Observatory above 1019 eV”, O. Deligny for the Telescope Array and Pierre Auger Collaborations,
Proceedings of the ICRC2013, Rio de Janeiro.
23. “Absolute energy calibration of the Telescope Array Fluorescence detector with an Electron Linear Accelerator”, T.
Shibata for the TA collaboration, Proceedings of the ICRC2013, Rio de Janeiro.
24. “The Telescope Array Low Energy Extension”, S. Ogio for the TA collaboration, Proceedings of the ICRC2013, Rio deJaneiro.
25. “The mass composition of ultra-high energy cosmic rays measured by new fluorescence detectors in the Telescope
Array experiment”, T. Fujii for the TA collaboration, the 13th International Conference on Topics in Astroparticle andUnderground Physics (TAUP2013), Sept. 8-13, 2013, Asilomar.
26. “Recent results from Telescope Array”, T. Okuda for the TA collaboration, Symposium on Cosmology and Particle
Astrophysics (CosPA2013), Nov. 12-15, 2013, Honolulu.
27. ““Cosmic-ray shadow” of the Sun at 3 TeV observed by the Tibet Air Shower Array”, M. Amenomori et al., Proceedingsof The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013, ID=0340.
28. “A Northern Sky Survey for TeV gamma-ray steady point sources using the Tibet-III air shower array”, M. Amenomori
et al., Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013,
ID=0498.
29. “Average mass of primary cosmic rays in the knee energy region inferred from Tibet experiment”, M. Amenomori et al.,Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013, ID=0525.

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30. “Observation of Multi-TeV Gamma Rays from MGRO J2019+37 and MGRO J2031+41 with the Tibet Air Shower
Array”, M. Amenomori et al., Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil,
July 2 - July 9, 2013, ID=0513.
31. “Observation of thundercloud-related charged particles in Tibet”, M. Amenomori et al., Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013, ID=0505.
32. “The TIBET AS+MD Project; progress report 2013”, M. Amenomori et al., Proceedings of The 33rd International
Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013, ID=0508.
33. “A Monte Carlo study to measure heavy-component spectra of the primary cosmic-rays at the knee by a new hybrid
experiment (YAC-II+Tibet-III+MD)”, L.M. Zhai et al., Proceedings of The 33rd International Cosmic Ray Conference,
Rio de Janeiro, Brazil, July 2 - July 9, 2013, ID=1049.
34. “Hadronic interaction and EAS muon investigated with the (YAC + Tibet-III + MD) hybrid experiment”, M. Amenomori
et al., Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013,
ID=1051.
35. “Observation of the large-scale sidereal anisotropy of the galactic cosmic ray at 300 TeV with the Tibet Air shower
Array”, M. Amenomori et al., Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil,
July 2 - July 9, 2013, ID=0256.
36. “Primary proton and helium spectra at energy range from 50 TeV to 1015 eV observed with (YAC+Tibet-III ) hybrid
experiment”, M. Amenomori et al., Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro,
Brazil, July 2 - July 9, 2013, ID=1047.
37. “Progress Report on the MD-A under TIBET III array”, M. Amenomori et al., Proceedings of The 33rd International
Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013, ID=1018.
38. “Study on the primary mass sensitivity of muon multiplicity measured with (YAC-II +Tibet-III + MD) experiment”, J.S.
Liu et al., Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013,
ID=1057.
39. “Test of the hadronic interaction model EPOS-LHC and QGSJETII-04 with Tibet EAS core data”, M. Amenomori et al.,Proceedings of The 33rd International Cosmic Ray Conference, Rio de Janeiro, Brazil, July 2 - July 9, 2013, ID=1056.
40. “Progress report on the TIBET AS+MD Project”, M. Amenomori et al., Proceedings of the 12th Asia Pacific Physics
Conference, Makuhari Messe, Chiba, Japan, July 14 - July 19, 2013, JPS Conf. Proc. 1, 2014, 013124-1-4.
41. “Wide-Band Spectra of Prompt Emission”, K. Asano, Proceedings of Gamma-ray Bursts: 15 Years of GRB Afterglows.
42. “Broadband Emission Structure of Pulsar Wind Nebulae”, S. J. Tanaka, Proceedings of the 33rd International Cosmic
Ray Conference 2013.
43. “High Energy Emission from Spherically Symmetric Pulsar Wind Nebulae”, S. J. Tanaka, Proceedings of SUZAKUMAXI 2014.
44. “Synchrotron Emission from Old Pulsars”, S. J. Tanaka and S. Kisaka, Proceedings of SUZAKU-MAXI 2014.
45. “Electric field screening at the pulsar polar cap”, S. Kisaka and T. Terasawa Proceedings of SKA Science Workshop in
East Asia.
46. “Axisymmetric and stationary magnetic field structures in neutron star crusts under various boundary conditions”, K.
Fujisawa and S. Kisaka Proceedings of IAU Symposium 302, Magnetic fields throughout stellar evolution, 2013.
47. “Hard X-ray observations with Suzaku HXD at the time of giant radio pulses from the Crab pulsar”, R. Mikami, T.
Terasawa, S. Kisaka, K. Asano, S. J. Tanaka, M. Sekido, K. Takefuji, H. Takeuchi, H. Odaka, T. Sato, Y. T. Tanaka and
N. Kawai, Proceedings of SUZAKU-MAXI 2014.
48. “CALET observational performance expected by CERN beam test”, Y. Akaike for the CALET collaboration, Proceedings of the 33rd International Cosmic Ray Conference 2013.
49. “The CALET Structure and Thermal Model used for beam test at CERN”, Y. Ueyama, S. Torii, K. Kasahara, S. Ozawa,T. Niita, M. Nakamura, S. Kaneko, R. Katahira, A. Murata, T. Tamura, Y. Katayose, Y. Akaike, Y. Shimizu, Proceedingsof the 33rd International Cosmic Ray Conference 2013.

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50. “CALET Calibration on ISS Orbit Using Cosmic Rays”, T. Niita and the CALET collaboration, Proceedings of the 33rd
International Cosmic Ray Conference 2013.
51. “The Calorimetric Electron Telescope (CALET) for High Energy Astroparticle Phsycis on the International Space Station”, S. Torii for the CALET collaboration, Proceedings of the 33rd International Cosmic Ray Conference 2013.
52. “Expected Performance of CALET as a High Energy Gamma Ray Observatory”, M. Mori for the CALET collaboration,
Proceedings of the 33rd International Cosmic Ray Conference 2013.
53. “Dark Matter Search with CALET”, K. Yoshida for the CALET collaboration, Proceedings of the 33rd International
Cosmic Ray Conference 2013.
54. “CALET perspectives in high-energy gamma-ray observations”, A. Moiseev for the CALET collaboration, Proceedingsof the 33rd International Cosmic Ray Conference 2013.
55. “Particle Beam Tests of the Calorimetric Electron Telescope”, T. Tamura for the CALET collaboration, Proceedings ofthe 33rd International Cosmic Ray Conference 2013.
56. “CALET measurements with cosmic nuclei and performance of the charge detectors”, P. S. Marrocchesi for the CALET
collaboration, Proceedings of the 33rd International Cosmic Ray Conference 2013.
57. “CALET Positron/Electron Measurements Using the Geomagnetic Field”, B. Rauch for the CALET collaboration, Proceedings of the 33rd International Cosmic Ray Conference 2013.
58. “CALET Measurement of Ultra-Heavy Cosmic Rays”, B. Rauch for the CALET collaborationP. S. Marrocchesi for the
CALET collaboration, Proceedings of the 33rd International Cosmic Ray Conference 2013.
59. “The CALorimetric Electron Telescope (CALET) ground data handling and processing system”, T. Guzik for the CALET
collaboration, Proceedings of the 33rd International Cosmic Ray Conference 2013.
60. “CALET Gamma-ray Burst Monitor (CGBM)”, K. Yamaoka for the CALET collaboration, Proceedings of the 33rd
International Cosmic Ray Conference 2013.
61. “Search for PeV-EeV Tau Neutrinos and Optical Transients from Violent Objects with Ashra-1”, M.Sasaki, Proceedingsof 14th ICATPP Conference on Astroparticle, Particle, Space Physics and Detectors for Physics Applications, 2013.
62. “Ashra NTA: Towards Survey of Astronomical Tau Neutrino Sources”, Y. Aita, T. Aoki,Y.Asaoka, H.M Motz, M. Sasaki,
C. Abiko, C.Kanokohata, S.Ogawa ,H. Shibuya, T. Takada, T. Kimura, J. G. learned, S.Matsuno, S. Kuze, P. Chang,*G.W-S. Hou, Y.B. Hsiung, J-G. Shu, K. Ueno, M. Wang, P. M. Binder, J. Goldman, N. Sugiyama, Y. Watanabe, C-C.
Hsu (Ashra NTA Collaboration), Proceedings of the 12th Asia Pacific Physics Conference of AAPPS ASEPS3 The third
Asia-Europe Physics Summit, 2013.
63. “Trigger and readout system for the Ashra-1 detector”, Aita, T. Aoki,Y.Asaoka, Y.Moromoto, H.M Motz, M. Sasaki, C.
Abiko, C. Kanokohata, *S.Ogawa, H. Shibuya, T. Takada, T. Kimura, J. G. learned, S.Matsuno, S. Kuze, P. M. Binder, J.
Goldman, N. Sugiyama, Y. Watanabe (Ashra-1 Collaboration), Proceedings of the 12th Asia Pacific Physics Conferenceof AAPPS ASEPS3 The third Asia-Europe Physics Summit, 2013.
64. “Search for PeV-EeV Tau Neutrinos and Optical Transients from Violent Objects with Ashra-1”, Y. Aita, T. Aoki,
Y.Asaoka, H.M Motz,*M. Sasaki, C. Abiko, C.Kanokohata, S.Ogawa, H. Shibuya, T. Takada, T. Kimura, J. G. learned,
S.Matsuno, S. Kuze, P. M. Binder,J. Goldman, N. Sugiyama, Y. Watanabe (Ashra-1 Collaboration), Proceedings of 33th
Intl. Cosmic Ray Conf. (Rio), 2013.
65. “Ashra NTA: Towards Survey of Astronomical Tau Neutrino Sources”, Y. Aita, T. Aoki, Y.Asaoka, H.M Motz, M.
Sasaki, C. Abiko, C.Kanokohata,S.Ogawa, H. Shibuya, T. Takada, T. Kimura, J. G. learned, S.Matsuno, S. Kuze, P.
Chang, *G.W-S. Hou, Y.B. Hsiung, J-G. Shu, K. Ueno, M. Wang, P. M. Binder, J. Goldman, N. Sugiyama, Y. Watanabe,
C-C. Hsu (Ashra NTA Collaboration), Proceedings of 33th Intl. Cosmic Ray Conf. (Rio), 2013.
66. “Neutrino Telescope Array (NTA)”, G. W.-S. Hou on behalf of the NTA Collaboration, The 7th International Workshop
on Very High Energy Particle Astronomy - Next Generation Explorer for Cosmic Ray Origin - (Kashiwa), 2014.
67. “Real Time Control for KAGRA 3km Cryogenic Gravitational Wave Detector”, Osamu Miyakawa and KAGRA collaboration, ICALEPCS 2013, 2013/10/5-10/11, San Francisco U.S.A, Proceedings of the 14th International Conference on
Accelerator & Large Experimental Physics Control Systems, 23-26, 2013.
68. “Mahalo-Subaru: Mapping Star Formation at the Peak Epoch of Massive Galaxy Formation”, Kodama, T., Hayashi, M.,
et al., Proceedings of the International Astronomical Union, 295, 74-77, 2013.

97

69. “From Mahalo-Subaru to Gracias-ALMA: Resolving Galaxy Formation at Its Peak Epoch”, Kodama, T., Tanaka, I.,
Hayashi, M., et al., ASP Conference Series, 476, 37, 2013.
70. “Axino dark matter and baryon number from Q-ball decay”, S. Kasuya, E. Kawakami and M. Kawasaki, J. Phys. Conf.
Ser. 485, 012025 (2014).

(c) ICRR Reports
1. ICRR-Report-652-2013-1“AMS-02 Positrons from Decaying Wino in the Pure Gravity Mediation Model”
Masahiro Ibe, Shigeki Matsumoto, Satoshi Shirai, Tsutomu T. Yanagida.
2. ICRR-Report-653-2013-2“Domain wall and isocurvature perturbation problems in axion models”
Masahiro Kawasaki, Tsutomu T. Yanagida, Kazuyoshi Yoshino.
3. ICRR-Report-654-2013-3“Implications of Planck results for models with local type non-Gaussianity”
Teruaki Suyama, Tomo Takahashi, Masahide Yamaguchi, Shuichiro Yokoyama.
4. ICRR-Report-655-2013-4“Higher order statistics of curvature perturbations in IFF model and its Planck constraints”
Tomohiro Fujita, Shuichiro Yokoyama.
5. ICRR-Report-656-2013-5“Large Scale Cosmic Perturbation from Evaporation of Primordial Black Holes”
Tomohiro Fujita, Keisuke Harigaya, and Masahiro Kawasaki.
6. ICRR-Report-657-2013-6“The Peccei-Quinn Symmetry from a Gauged Discrete R Symmetry”
Keisuke Harigaya, Masahiro Ibe, Kai Schmitz, Tsutomu T. Yanagida.
7. ICRR-Report-658-2013-7“A new algorithm for calculating the curvature perturbations in stochastic inflation”
Tomohiro Fujita, Masahiro Kawasaki, Yuichiro Tada, Tomohiro Takesako.
8. ICRR-Report-659-2013-8“On the estimation of gravitational wave spectrum from cosmic domain walls”
Takashi Hiramatsu, Masahiro Kawasaki, Ken’ichi Saikawa.
9. ICRR-Report-660-2013-9“A Closer Look at Gaugino Masses in Pure Gravity Mediation Model/Minimal Split SUSY Model”
Keisuke Harigaya, Masahiro Ibe, Tsutomu T. Yanagida.
10. ICRR-Report-661-2013-10“Axions as Hot and Cold Dark Matter”
Kwang Sik Jeong, Masahiro Kawasaki, Fuminobu Takahashi.
11. ICRR-Report-662-2013-11“I-ball formation with logarithmic potential”
Masahiro Kawasaki, Naoyuki Takeda.
12. ICRR-Report-663-2013-12“Halo/Galaxy Bispectrum with Primordial non-Gaussianity from integrated Perturbation Theory (iPT)”
Shuichiro Yokoyama, Takahiko Matsubara, Atsushi Taruya.
13. ICRR-Report-664-2013-13“Hypercharged Dark Matter and Direct Detection as a Probe of Reheating”
Brian Feldstein, Masahiro Ibe, Tsutomu T. Yanagida.
14. ICRR-Report-665-2013-14“Lower Bound on the Garvitino Mass m3/2 > O(100) TeV in R-Symmetry Breaking New Inflation”
Keisuke Harigaya, Masahiro Ibe, Tsutomu T. Yanagida.

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15. ICRR-Report-666-2013-15“Mixed (Cold+Warm) Dark Matter in the Bino-Wino co-annihilation scenario”
Masahiro Ibe, Ayuki Kamada, Shigeki Matsumoto.
16. ICRR-Report-667-2013-16“Decay rates of Gaussian-type I-balls and Bose-enhancement effects in 3+1 dimensions”
Masahiro Kawasaki, Masaki Yamada.
17. ICRR-Report-668-2013-17“Baryon Asymmetry, Dark Matter, and Density Perturbation from PBH”
Tomohiro Fujita, Keisuke Harigaya, Masahiro Kawasaki, Ryo Matsuda.
18. ICRR-Report-669-2013-18“Critical constraint on inflationary magnetogenesis”
Tomohiro Fujita, Shuichiro Yokoyama.
19. ICRR-Report-670-2013-19“Probing small-scale cosmological fluctuations with the 21 cm forest: effects of neutrino mass, running spectral index
and warm dark matter”
Hayato Shimabukuro, Kiyotomo Ichiki, Susumu Inoue, and Shuichiro Yokoyama.
20. ICRR-Report-671-2013-20“Dark Matter Production in Late Time Reheating”
Keisuke Harigaya, Masahiro Kawasaki, Kyohei Mukaida, Masaki Yamada.
21. ICRR-Report-672-2013-21“Baryogenesis from the Gauge-mediation type Q ball and the dark matter New type Q ball”
Shinta Kasuya, Masahiro Kawasaki.
22. ICRR-Report-673-2013-22“Neutrino masses, leptogenesis, and sterile neutrino dark matter”
Takanao Tsuyuki.
23. ICRR-Report-674-2013-23“Compensation for large tensor modes with iso-curvature perturbations in CMB anisotropies”
Masahiro Kawasaki, Shuichiro Yokoyama.

D. Doctoral Theses
1. “Cosmological implications from supersymmetric axion models– origin of matter and its fluctuations”,
E. Kawakami,
Ph.D Thesis, Mar. 2013.
2. “Primordial blackhole formation and gravitational wave production in a curvaton model”,
N. Kitajima,
Ph.D Thesis, Mar. 2013.
3. “The Effective Masses of Scalar Fields in the Radiation Dominated Universe”,
T. Takesako,
Ph.D Thesis, Mar. 2013.

E. Public Relations(a) ICRR NewsICRR News is a quarterly publication written in Japanese about scientific and educational activities at ICRR. It includes :1. reports on scientific activities of ICRR staff members and those conducted at one or more of its facilities,

99

2. reports of international conferences on topics relevant to ICRR’s research activities,
3. reports on topics discussed at ICRR’s Committees,
4. list of publications published by ICRR [ICRR-Report],
5. list of seminars held at ICRR,
6. announcements, and7. other items of relevance.

Below lists the main topics in the issues published in FY 2013:
No.85 (June 30, 2013)• Report of ICRR Spring School 2013, Masahiro Teshima.
• TA Low energy Extention (TALE) Experiment, Shoichi Ogio & Toshiyuki Nonaka.
• Staff reassignment.
• ICRR-Seminar.
• ICRR-Report.
No.86 (September 30, 2013)• AMS-02 positron flux anomaly and possibilities for dark matter in supersymmetric models, Masahiro Ibe.
• Probing the coronal magnetic field via the Sun’s Shadow, Kazumasa Kawata & Masato Takita.
• The current status of the T2K Experiment -search for the electron neutrino appearance-, Yoshinari Hayato.
• Staff reassignment.
• ICRR-Seminar.
• ICRR-Report.
No.87 (December 27, 2013)• Report of the speech and the ceremony commemorating the 60th anniversary of Norikura Observatory, Masato Takita.
• KAGRA’s Y-arm tunnel is now complete, Misato Hayashida.
• Report of 2013 Kashiwa Open Campus, Misato Hayashida.
• Staff reassignment.
• ICRR-Seminar.
• ICRR-Report.
No.88 (March 31, 2014)• Precision measurement of neutrino oscillation parameters in T2K experiment, Yasuhiro Nishimura.
• Report of the 3rd ICRR Graduate Students Workshop, Misato Hayashida.
• Staff reassignment.
• ICRR-Seminar.
• ICRR-Report.

100(b) Public Lectures• ”Gallery talk”, Apr. 7, 2013, Toyama Science Museum, Toyama-city, Toyama, Masaki Yamashita & Jun kameda (ICRR,
the University of Tokyo).
• ”SSH The Shizuoka-kita High School”, Apr. 25, 2013, Kamioka-cho, Hida-city, Gifu, Atsushi Takeda (ICRR, theUniversity of Tokyo).
• ”Hirameki Tokimeki Science”, Apr. 7, 2013, Kamioka-cho, Hida-city, Gifu, Atsushi Takeda & Jun kameda (ICRR, theUniversity of Tokyo).
• ”GSA Science seminar”, July. 29, 2013, Kamioka-cho, Hida-city, Gifu, Yoichiro Suzuki (ICRR, the University ofTokyo).
• “SSH The Kyoto Prefectural Momoyama Senior High School”, July. 29, 2013, Kamioka-cho, Hida-city, Gifu, Makoto
Shiozawa (ICRR, the University of Tokyo).
• “SSH The Tochigi Ashikaga High School”, July. 30, 2013, Kamioka-cho, Hida-city, Gifu, Jun Kameda (ICRR, theUniversity of Tokyo).
• “SSH The Fujishima Senior High School”, Aug. 7, 2013, Kamioka-cho, Hida-city, Gifu, Yoichiro Suzuki (ICRR, theUniversity of Tokyo).
• “Yumenotamago-Jyuku”, Aug. 9, 2013, Kamioka-cho, Hida-city, Gifu, Hiroyuki Sekiya (ICRR, the University ofTokyo).
• “SSH The Yamanashi Eiwa Junior & Senior High School”, Aug. 19, 2013, Kamioka-cho, Hida-city, Gifu, Jun Kameda(ICRR, the University of Tokyo).
• “Yume Challenge”, Aug. 20, 2013, Kashiwa, Chiba, Shigetaka Moriyama (ICRR, the University of Tokyo).
• “SSH The Senior High School Attached to Kyoto University of Education”, Aug. 21, 2013, Kamioka-cho, Hida-city,
Gifu, Makoto Miura (ICRR, the University of Tokyo).
• “School of Engineering The University of Tokyo”, Aug. 27, 2013, Kamioka-cho, Hida-city, Gifu, Shigetaka Moriyama(ICRR, the University of Tokyo).
• “School of Engineering The University of Tokyo”, Aug. 27, 2013, Kamioka-cho, Hida-city, Gifu, Yoshinari Hayato(ICRR, the University of Tokyo).
• “SSH The kaisei Academy (The kaisei Junior and Senior High Schools)”, Aug. 28, 2013, Kamioka-cho, Hida-city, Gifu,
Shigetaka Moriyama (ICRR, the University of Tokyo).
• “Science cafe”, Sep. 23, 2013, Nigata-city, Nigata, katsuki Hiraide (ICRR, the University of Tokyo).
• “SSH The Nanao High School”, Oct. 2, 2013, Kamioka-cho, Hida-city, Gifu, Ko Abe (ICRR, the University of Tokyo).
• “SSH The Senri Senior High School”, Oct. 10, 2013, Kamioka-cho, Hida-city, Gifu, Roger Wendell (ICRR, the University of Tokyo).
• “Science cafe at Astronomical Observatory of Toyama”, Oct. 19, 2013, Toyama-city, Toyama, Yoichiro Suzuki (ICRR,
the University of Tokyo).
• “Lecture”, Oct. 26, 2013, Toyama Science Museum, Toyama-city, Toyama, Yoichiro Suzuki (ICRR, the University ofTokyo).
• “Science cafe”, Dec. 21, 2013, Gifu-sinbunsya, Gifu-city, Gifu, Yoichiro Suzuki (ICRR, the University of Tokyo).
• “The University of Twente, Oranda”, Feb. 25, 2014, Gifu-sinbunsya, Gifu-city, Gifu, Yasuhiro Kishimoto (ICRR, theUniversity of Tokyo).
• “Detecting Cosmic Rays in Desert”, May 11, 2013, The University of Tokyo, Tokyo, T. Nonaka (ICRR, the Universityof Tokyo).
• “Mt. Katakake-Mozumi Ginzan to Kamioka mine–Towards KAGRA Project”, Forth Saturdays of Apr. through Sep.,
2013, Inotani-Sekisho-Kan, Toyama, S. Miyoki, O. Miyakawa, T. Ohashi, and S. Kawamura (ICRR, the University ofTokyo).

101• “KAGRA’s detection method: Michelson Interferometer”, September 8, 2013, Inotani-Sekisho-Kan, Toyama, S. Miyoki,
O. Miyakawa (ICRR, the University of Tokyo).
• “Introduction to Gravitational Wave Detector KAGRA - Hands-on Michelson Interferometer -”, September 28-29, 2013,
Toyama University, Toyama, O. Miyakawa (ICRR, the University of Tokyo).
• “Gravitational Waves: The melody of the universe predicted by Einstein”, November 23, 2013, Osawano Center for
Lifelong Lerning, Toyama, O. Miyakawa (ICRR, the University of Tokyo).
• “Detection Physics and Technology of Gravitational Waves”, July 30-August10, 2013, Numerical Relativity & Gravitational waves School in Pohang 2013, Korea, K. Kuroda (ICRR, the University of Tokyo).
• “The new ear of the 21st century to hear the universe - Gravitational Waves”, October 26, 2013, Sawayaka Plaza, Chiba,
S. Miyoki (ICRR, the University of Tokyo).
• “Physics and Gravitational Waves, Study and Research in Germany and Japan”, October 18, 2013, Inotani-Sekisho-Kan,
Toyama, S. Miyoki & Alexander Khalaidovski (ICRR, the University of Tokyo).
• “Cryogenic system for the interferometric cryogenic gravitational wave telescope, KAGRA”, July 12, 2013, Wroclaw
University of Technology, Poland, N. Kimura (KEK).
• “Cosmic History Probed by the Deepest Observations”, April 13, 2013, Amuser Kashiwa, Chiba, M. Ouchi (ICRR, theUniversity of Tokyo).
• “From Bangkok to the Early Universe”, July 27, 2013, Kofu Higashi High School, Yamanashi, S. Yuma (ICRR, theUniversity of Tokyo).
• “Cosmic History Studied with the Large Telescopes”, October 25, 2013, ICRR, Chiba, M. Ouchi (ICRR, the Universityof Tokyo).
• “Galaxy formation and evolution revealed by resent observations”, October 25, 2013, ICRR, Chiba, M. Hayashi (ICRR,
the University of Tokyo).
• “Cosmic History Studied with the Large Telescopes”, November 20, 2013, Tokyo Metropolitan Musashi High School,
Tokyo, M. Ouchi (ICRR, the University of Tokyo).
• “Galaxies in the Universe”, March 15, 2013, Kavli IPMU, Chiba, R. Momose (ICRR, the University of Tokyo).
• “The Standard Model and Higgs particle”, December 1, 2013, the University of Tokyo. Tokyo, M. Ibe (ICRR, theUniversity of Tokyo).

(c) Visitors
KASHIWA Campus(Total: 11 groups, 328 peoples)• Higashi-Katsushika High School• RKU Kashiwa High School

KAMIOKA Observatory(Total: 159 groups, 3,024 peoples)• Yumeno Tamago Jyuku (Hida Academy for HighSchool Students)• Miyazaki Nishi High School• MEXT Super Science High School (SSH) project: total
14 schools• Others: 8 groups• Schools and Universities: total 13 groups• Researchers: total 13 groups• Others: 118 groups

102

F.

Inter-University Research Activities

Numbers of Researchers
Number ofApplications

Number of
Adoptions

Number of
Researchers

Facility Usage
Kamioka Observatory
Akeno Observatory
Norikura Observatory
Low-Level Radioisotope Measurement Facility
Cryogenic Laser Interferometer in Kashiwa
Laboratorial Facility in Kashiwa
Computer Facility in Kashiwa
Conference Facility in Kashiwa
Over Sea Facilities
Annual Sums

34
4
9
5
21
9
17
7
12
118

33
4
9
5
21
9
17
7
12
117

1,030
47
86
33
423
246
287
292
146
2,590

Joint Research
Neutrino and Astroparticle ResearchHigh Energy Cosmic Ray Research
Astrophysics and Gravity Research
Research Center for Cosmic neutrinos
Annual Sums

35
49
23
11
118

34
49
23
11
117

1,035
952
470
133
2,590

Research Project Titles
1. Precise measurement of Day/Night effect for B8 solar neutrinos
2. Energy spectrum measurement of solar neutrinos in Super-Kamiokande
3. Study of Solar Neutrino Flux
4. Study of simulation for atmospheric neutrino
5. Study of atmospheric neutrino flux and neutrino oscillations
6. Study of three flavor oscillation in atmospheric neutrinos
7. Study of flavor identification of atmospheric and beam neutrinos
8. Study for Supernova monitor
9. Study of Supernova Relic Neutrinos
10. Study of proton decay p → νK +11. Search for proton decay via e+ π 0 mode
12. Study in upward-going muons and high energy neutrinos
13. Sidereal daily variation of ∼10TeV galactic cosmic ray intensity observed by the Super-Kamiokande
14. Tokai to Kamioka Long Baseline Experiment T2K
15. Neutrino interaction study using accelerator data
16. Study for the electron neutrino appearance search in the T2K experiment
17. Energy calibration for Super-Kamiokande

103

18. Development of low concentration radon detection system
19. R&D of a Mton water Cherenkov Hyper-Kamiokande
20. Development of the Hybrid Photo Detector
21. Neutrino workshop
22. Direction-sensitive dark matter search experiment
23. Strain, tilt, seismic measurement in Kamioka-mine
24. Study for double beta decay of 48Ca
25. Studies on steady removal of noble gas impurities using laser resonance ionization
26. Integration of crustal activity observation around the Atotsugawa fault
27. Microdetermination of impurity gas in Xe
28. Development of radon detector for purified gases
29. Calibration study of liquid xenon detector
30. A study on infrared emission of liquid xenon scintillator
31. Study for upgrade of XMASS detector
32. A Search for Dark Matter using Liquid Xenon Detector
33. Study of annual modulation for dark matter search
34. Study for lowering backgrounds of radioisotopes in large volume detectors
35. R&D for a Small Atmospheric Cherenkov Telescope in Akeno Observatory
36. Reconstruction of the optical system of a small Cherenkov telescope at the Akeno Observatory
37. Multi-Color Imager for Transients, Survey and Monstrous Explosions
38. Observation of Galactic Cosmic Ray Intensities using Large Area Muon Telescopes
39. Observation of solar neutrons in solar cycle 24
40. Space weather observation using muon hodoscope at Mt. Norikura
41. Evaluation of altitude dependent doses of secondary cosmic neutrons
42. Observation of cosmogenic nuclides concentrations with temporal variability at Mt. Norikura
43. Alpine vegetation study on Mt. Norikura
44. Observations of total ozone and UV solar radiation with Brewer spectrophotometer on the Norikura mountains
45. In-Situ Conservation - Establishment of handling method of chicks for one month after hatching by cage captivity
46. Dynamics of Abies mariesii forests of forest line of Mt. Norikura
47. Evaluation of Response to the Gamma-ray of the Emulsion Telescope
48. Experimental Study of High-energy Cosmic Rays in the Tibet AS γ Experiment
49. Sidereal daily variation of ∼10TeV galactic cosmic ray intensity observed by the Tibet air shower array
50. Cosmic ray interactions in the knee and the highest energy regions
51. Study of High Energetic Radiation from Thundercloud in Tibet
52. Study of the composition of cosmic-rays at the Knee
53. A study on variation of interplanetary magnetic field with the cosmic-ray shadow by the sun

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54. BASJE (Bolivian Air Shower Joint Experiment)
55. Towards the imaging of the massive black hole in SgrA*
56. Observation with the All-sky Survey High Resolution Air-shower detector (Ahsra)
57. Test and installation of image pipeline for Ashra observation
58. Automatization of Ashra observation
59. Test of the sensor to detect cosmic rays for Ashra observation
60. Integration of the optical fiber trigger system for Ashra
61. Study of Extremely-high Energy Cosmic Rays by Telescope Array
62. Development of new surface detector for observation of ultra high energy cosmic ray at Telescope Array site
63. Study of radio detection of highest energy cosmic rays
64. Development of the steering system on CLF at the Telescope Array Experiment
65. Calibration for TA FD with RC helicopter
66. Study of absolute energy calibration of air shower by a compact electron linac
67. Improvementof low-energy sensitivity of the TA surface detector (TALE project) and study of the cosmic-ray anisotropy
68. Calibration of TA-EUSO 64ch multi-anode PMT and comparison with CRAYS
69. Observation of airshower fluorescence light at the TA FD site by using an Imaging UV telescope
70. Research and development of detectors for MBR microwave radiations
71. CTA Project R&D
72. Development of the readout system for the CTA large-size telescopes
73. Development of Foal Plane Instruments for the CTA Large Scale Telescope
74. Development of camera for CTA small-sized telescopes
75. Development of advanced photon counter for the future IACT
76. CTA-Japan Physics Research
77. CTA Monte Carlo Simulation
78. The extreme Universe viewed in very high energy gamma-rays 2013
79. Study of High Energy Gamma-ray Objects with the MAGIC telescopes
80. Development of a high-sensitivity cosmic gamma-ray detector exploring 0.5-30 MeV
81. Study on High Energy Cosmic Ray Sources by Observations in Space
82. Observational study of particle acceleration in the Crab nebula/pulsar
83. Comparative study of astrophysical particle acceleration phenomena
84. Research and Development for the ultra high sensitivity quantum interferometer in KAGRA
85. Data analysis using CLIO data (IV)
86. Real time control for interferometer using computers (II)87. Gravitational Wave Detector in Kamioka (XII)
88. Development of optical cavities for ultranarrow stable lasers
89. Development of the output mode-cleaner for KAGRA

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90. Numerical simulation of Electric-Magnetic Wave Propagation in Gravitational wave Detector
91. Application of geophysical observations in the Kamioka mine to the dynamics of snow and water
92. Research on ultra-low frequency anti-vibration system for KAGRA
93. Development of beam position minitoring and controling systems for KAGRA
94. Development of Sapphire Mirror Suspension for KAGRA(LCGT) (X)
95. Study for KAGRA data analysis and Research for its System (III)96. Development of precision profiler for mirrors of LCGT interferometer 3
97. Development of Very Low Vibration Cryo-Cooler System
98. Research on cryogenic payload for KAGRA
99. Research of Large-scale Gravitational wave Telescope (III)100. The development of a super sensitive shadow sensor for a gravitational antenna101. Gravitational Wave Detection using Non-Harmonic Analysis
102. Characterization of Sapphire mirror for KAGRA using electron spin resonance103. Development of a stabilization system for the KAGRA laser source
104. R&D for the intensity stabilization of the laser system in KAGRA
105. Cosmic Reionization Probed with Large Optical Near-Infrared Telescopes
106. Evolution of the universe and particle physics
107. Frontier of the planetary material science
108. Nondestructive characterization of planetary materials using Imaging Plates
109. Detection of time variations for cosmogenic Be-7
110. Observation of global air-mass motion measuring radionuclides of Cs in the air
111. Study on solar and cosmic-ray effects on climate variations
112. Continuous Environment Measurement of the Kashiwa Underground Laboratory
113. Evaluation of the erupted radioactivities into the environment.
114. Precise calculation of the atmospheric neutrino flux
115. Simulation study for the IceCube Neutrino Observatory
116. CRC workshop for future plans in cosmic ray research
117. The 7th International Workshop on Very High Energy Particle Astronomy (VHEPA2014) - Next Generation Explorer
for Cosmic Ray Origin -106

G. List of Committee Members(a) Board of Councillors
KAJITA, Takaaki
FUKUSHIMA, Masaki
KAWASAKI, Masahiro
NAKAHATA, Masayuki
AIHARA, Hiroaki
MATSUMOTO, Yoichiro
YAMAUCHI, Masanori
SASAKI, Misao
HAYASHI, Masahiko
YUDA, Toshinori
MURAKI, Yasushi
MASAIKE, Akira
MAKINO, Fumiyoshi
SUGIYAMA, Naoshi
KOMAMIYA, Yukio

ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo
The University of Tokyo
The University of Tokyo
KEK
YITP, Kyoto University
National Astronomical Observatory of JapanThe University of Tokyo
Nagoya University
Kyoto University
Institute of Space and Astronautical Science
Nagoya University
ICEPP, the University of Tokyo(b) Advisory Committee
KAJITA, Takaaki
HISANO, Junji
SUGIYAMA, Naoshi
HAZUMI, Masashi
KISHIMOTO, Tadafumi
YOKOYAMA, Masashi
KANDA, Nobuyuki
ITOW, Yoshitaka
NISHIJIMA, Kyoshi
OGIO, Shoichi
SUZUKI, Yoichiro
KURODA, Kazuaki
NAKAHATA, Masayuki
KAWASAKI, Masahiro
TERASAWA, Toshio
TESHIMA, Masahiro

ICRR, the University of Tokyo
Nagoya University
Nagoya University
KEK
Osaka University
The University of Tokyo
Osaka City University
Nagoya University
Tokai University
Osaka City University
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, University of Tokyo(c) Inter-University Research Advisory Committee
NISHIJIMA, Kyoshi
MUNAKATA, Kazuoki
TAJIMA, Hiroyasu
MASUDA, Kimiaki
YAMAMOTO, Tokonatsu
ANDO, Masaki
TSUNESADA, Yoshiki
KUBO, Hidetoshi
TERASAWA, Toshio
TAKITA, Masato
SAGAWA, Hiroyuki
OHASHI, Masatake
KISHIMOTO, Yasuhiro

Tokai University
Shinshu University
Nagoya University
Nagoya University
Konan University
The University of Tokyo
Tokyo Institute of Technology
Kyoto University
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo
ICRR, the University of Tokyo

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H. List of Personnel

Director

KAJITA, Takaaki,

Vice-Director

TERASAWA, Toshio,

Kamioka Observatory (Neutrino and Astroparticle Division)
Scientific Staff
ABE, Ko,
HAYATO, Yoshinari,
ICHIMURA, Koichi,
IKEDA, Motoyasu,
KISHIMOTO, Yasuhiro,
KOBAYASHI, Kazuyoshi,
MORIYAMA, Shigetaka,
NAKAHATA, Msayuki,
OGAWA, Hiroshi,
SEKIYA, Hiroyuki,
SUZUKI, Yoichiro,
TAKEDA, Atsushi,
TOMURA, Tomonobu,
YAMASHITA, Masaki,
WENDELL, Roger Alexandre,
Administrative Staff
OIDA, Yoshihito,
TANAKA, Masahiro,
Technical Staff
NOZAWA, Noriyuki,
ONOUE, Tatsuya,
Research Fellow
BAI, Lili,
WILKING, Michael Joseph,
Secretary
OKURA, Yoko,
TANIMURA, Naoko,

Research Center for Cosmic Neutrinos (Neutrino and Astroparticle Division)
Scientific Staff
KAJITA, Takaaki,
MASUDA, Kimiaki,
OKUMURA, Kimihiro,
Technical Staff
SHINOHARA, Masanobu,
Secretary
KITSUGI, Atsuko,
WATANABE, Keiko,High Energy Cosmic Ray Division
Scientific Staff
ASANO, Katsuaki,
HAYASHIDA, Masaaki,
MIRZOYAN, Razmik,
TAKEDA, Masahiro,
TESHIMA, Masahiro,
SASAKI, Makoto,Technical Staff
AOKI, Toshifumi,
OOKI, Kaoru,
Research Fellow
AITA, Yuichi,
FUJII, Toshihiro,
KIDO, Eiji,
MIYAMOTO, Hideaki,
TANAKA, Syuta,
Secretary
KOKUBUN, Yayoi,

HIRAIDE, Katsuki,
KAMEDA, Jun,
MIURA, Makoto,
NAKAYAMA, Shoei,
SHIOZAWA, Masato,
TANAKA, Hidekazu,
YANG, Byeongsu,

TAMORI, Yukio,
YONEZAWA, Keiko,

NISHIMURA, Yasuhiro,

ENOMOTO, Ryoji,
IKEDA, Daisuke,
NONAKA, Toshiyuki,
TAKITA, Masato,
OHNISHI, Munehiro,
SHIBATA, Tatsunobu,
KOBAYASHI, Takahide,SUZUKI, Masao,
AKAIKE, Yosui,
HANABATA, Yoshitaka,
KISAKA, Shota,
SAITO, Koji,

FUKUSHIMA, Masaki,
KAWATA, Kazumasa,
NAKAJIMA, Daisuke,
TERASAWA, Toshio,
OHISHI, Michiko,
YOSHIKOSHI, Takanori,
NIWA, Hiroki,

OKAMURA, Takako,

SUGAHARA, Midori,

INOUE, Susumu,
KUMAR, Rahul,
SAKO, Takashi,

Akeno Observatory (High Energy Cosmic Ray Division)
Scientific Staff
SAGAWA, Hiroyuki,
Tecnical Staff
OHOKA, Hideyuki,
SHIMIZU, Kanetoshi,

Norikura Observatory (High Energy Cosmic Ray Division)
Technical Staff
AGEMATSU, Yoshiaki,
ISHITSUKA, Hideki,
SHIMODAIRA, Hideaki,
TOKOKU, Chihiro,

OKAZAKI, Nao,
USHIMARU, Tsukasa,

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Astrophysics and Gravity Division
Scientific Staff
HIROSE, Eiichi,
KAWASAKI, Masahiro,
MIYAKAWA, Osamu,
OHISHI, Naoko,
SAITO, Yoshio,
UCHIYAMA, Takashi,
Administrative Staff
TAKAYAMA, Kyouichi,
Technical Staff
FURUTA, Kiyoshi,
SAKATA, Shihori,
Research Fellow
FRIEDRICH, Daniel Dieter,
KHALAIDOVSKI, Alexander ,SHIBUYA, Takatoshi,
YOKOYAMA, Shuichiro,
Secretary
KAWAKAMI, Akiko,
OKINAKA, Mihoko,

Graduate Students
DoctorMaster

CHEN, Dan,KAWAKAMI, Etsuko,
NAKANO, Yuuki,
SAKAKIBARA, Yusuke,
TAKEDA, Naoyuki,
YAMADA, Masaki,
AIZAWA, Tasuku,
HIGUCHI, Chika,
ISHIO, Kazuma,
KOJIMA, Takumi,
NAITO, Yoshiaki,
NAKANO, Masayuki,
OKA, Naoya,
SASAKI, Kento,
TAMAZAWA, Hiroko,
TSUYUKI, Takanao,

Administrative Division
Administrative Staff
AKIYAMA, Makiko,
IRIMAJIRI, Aki,
MORITSUBO, Shigeru,
SAITO, Akiko,Research Administrator
SATO, Ritsuko,
Outreach Staff
HAYASHIDA, Misato

IBE, Masahiro,
KIMURA, Nobuhiro,
MIYOKI, Shinji,
ONO, Yoshiaki,
SUZUKI, Toshikazu,
YAMAMOTO, Kazuhiro,

KAWAMURA, Seiji,
KURODA, Kazuaki,
OHASHI, Masatake,
OUCHI, Masami,
TAKAHASHI, Ryutaro,
YOON Tai Hyun,IWASAKI, Utako,

KAMIIZUMI, Masahiro,

HARIKANE, Yuichi,
MOMOSE, Rieko,
SHIOMI, Sachie,
YUMA, Suraphong,
KIKUCHI, Rie,

HAYASHI, Masao,
NISHIDA, Erina,
YAMANAKA, Yuji,

IRVINE, Tristan James,
KITAJIMA, Naoya,
OBI, Yoshio,
SEKIGUCHI, Takanori,
TAKEISHI, Ryuji,
YOSHINO, Kazuyoshi,
HAGA, Yuto,
HONG, Jeong Pyong,
KAMETANI, Isao,
KONISHO, Shiori,
NAKAGAWA, Katsuma,
NISHIMURA, Tsubasa,
ONO, Kenji,
SHIN, Heungsu,
TEJIMA, Koudai,
WATANABE, Atsushi,

ASAKA, Sadako,
ISHII, Yoshikazu,
NAKAMURA, Saori,
WATANABE, Wataru,

MASHIMA, Chieko,

IYOGI, Kazuki,
MIKAMI, Ryo,
RICHARD, Euan Neil,
TAKACHIO, Osamu,
TAKESAKO, Tomohiro,
HAYAKAWA, Taku,
ISHIGAKI, Masaufumi,
KOBAYASHI, Masatoshi,
KONNO, Akira,
NAKAJIMA, Tateo,
OGINO, Momoko,
ORII, Asato,
TAKAHASHI, Mitsunari,
TO, Sho,

FUJIE, Tamiko,
MARUMORI, Yasuko,
OCHI, Masashi,
YAMAGUCHI, Akiko,