INSTITUTEFORCOSMIC RAY RESEARCH
UNIVERSITY OF TOKYOANNUAL REPORT(APRIL 2010 – MARCH 2011)

Editorial Board
YOSHIKOSHI, Takanori
OHASHI, Masatake
OBAYASHI, Yoshihisa
BAI, Lili
TAKENAGA, Yumiko
ITOH, Hideoc Institute for Cosmic Ray Research, 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

15

Astrophysics and Gravity Division40.........................................................................

Observatories and a Research Center

58

Norikura Observatory

59

Akeno Observatory

64

Kamioka Observatory

65

Research Center for Cosmic Neutrinos

66.............................................................

68..............................................................................

68..........................................................................

69

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.............................................................................

75

Appendix E.

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

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

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

78

Appendix G.

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

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

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

83

PREFACE
This report summarizes the scientific activities of the Institute for Cosmic Ray Research(ICRR) of the University of Tokyo in the Japanese FY 2010.
ICRR is an inter-university research institute for studies of cosmic rays. The headquarters of ICRR is located 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, and Astrophysics 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 3 major experimental facilities outside of Japan. They are located in Utah in USA, Yangbajing in Tibet, China, and Woomera in Australia.
More than 300 researchers from various Japanese institutions are involved in the research programs of ICRR. It should be noted that most of the scientific outputs from thisinstitute are the results of the collaborative efforts by many institutions. In order to produce outstanding results, it is very important to carry out an experiment by an international
collaboration composed of top-level researchers all over the world. Hence, most of the experimental collaborations that ICRR is involved are international ones. For example, thenumber of collaborators in the Super-Kamiokande experiment is about 130; among them 60
are from abroad (USA, Korea, China, Poland and Spain).
Many exciting scientific activities of ICRR are described in this report. One of thehighlights is the initial results from the T2K long-baseline neutrino oscillation experiment,
which studies neutrino oscillations in detail including the third mixing angle θ13 . Anotherhighlight is the start of the construction of Large-scale Cryogenic Gravitational wave Telescope (LCGT), which intends to detect gravitational waves for the first time and open a new
field of ”gravitational wave astronomy”.
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 thisresearch field, the University of Tokyo and the Japanese Ministry of Education, Culture,
Sports, Science and Technology. They are indispensable for the 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.

The system of four imaging atmospheric Cherenkov telescopesof 10m diameter of CANGAROO
project for detection of very highenergy gamma-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 suspension system for Large Scale Cryogenic
Gravitational Wave Telescope.

Wide-view telescope of 2.5 m diameter (left telescope) in Arizona,
USA for the Sloan Digital Sky Survey project.

A public lecture held by ResearchCenter for Cosmic Neutrinos.

Organization

Number of Staff Members (As of April 1, 2010)
Scientific
Staff

Technical
Staff

Research
Fellows

22
15
10
1
48

5
14
0
0
19

4
4
3
0
11

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

Administrators
andSecretaries
14
5
1
11
31

Total

45
38
14
12
109

FY 2005–2010 Budget
Personnel
expenses
Nonpersonnel
expenses
Total

2005

2006

2007

2008

2009

2010

465 000

566 000

624 000

632 000

590 000

576 000

1 822 000

812 000

1 253 000

1 121 000

1 292 000

1 048 000

2 287 000

1 378 000

1 877 000

1 753 000

1 882 000

1 624 000
(in 1 000 yen)

1

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

Astrophysics and Gravity Division
Overview
Gravitational Wave GroupLCGT Project
CLIO Project

Sloan Digital Sky Survey
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 innerdetector and 1,885 20 cm-diameter PMTs for its outer detector. The data taking of SK started in April 1996. The mostimportant physics results are the discovery of neutrino oscillation in atmospheric neutrinos in 1998 and thereby demonstrating that neutrinos have a finite mass, and the accurate
measurement of the solar neutrino flux from the decay of 8 B
which served to confirm the long-conjectured neutrino oscillation hypothesis in solar neutrinos beyond doubt. The search
for nucleon decay at SK gives the current best limit whichstrongly constrains the grand unification scenario of particle interactions. SK has been monitoring for neutrinos fromsupernova bursts. If a supernova burst occurs at a distancefrom the center of our galaxy, SK will be able to detect about
8,000 neutrino events. A high intensity neutrino beam experiment using the J-PARC accelerator (T2K) was started in 2009.
The T2K experiment uses the SK detector as the far detector.
The third oscillation pattern (the effect of the mixing angleθ13 ) and the high precision measurement of oscillation parameters are main physics subjects in T2K. In 2010, the first results of the T2K experiment were released as described below.
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
which is dedicated for the dark matter search was finished in2010 and the commissioning of the detector was started.
Recent progress of research activities in the Neutrino andAstroparticle division is presented here.

Super-Kamiokande experiment
Supernova neutrinos
Kamiokande and IMB observed the neutrino burst fromsupernova 1987a. This observation confirmed that the energy
released by neutrinos is about several×1053ergs. However,
the observed number of events were only 11 by Kamiokande
and 8 by IMB, respectively. Super-Kamiokande would be
able to detect several thousand neutrino events if a supernova
happened near the center of our galaxy. Such an observation
would enable us to investigate in detail the mechanics of thesupernova explosion. Galactic supernovae are searched foralmost in real time at SK. The online data acquisition system running in the mine sends data to the offline computer
system in the surface building of Kamioka observatory. As

soon as a block of data (usually a block corresponds to several minutes) is transferred to the offline system, a program
called SNWATCH searches for time clustered events. Current
criteria of SNWATCH are (1) more than or equal to 7 events
within 0.5sec, (2) more than or equal to 8 events within 2sec,
and (3) more than or equal to 13 events within 10sec. Whenat least one of these criteria are met, SNWATCH reconstructs
vertex position and energy of the events together with neighboring cosmic ray muons. In most cases, these clusters are
due to spallation products whose vertex positions are alignedwith their parent cosmic ray muon. If SNWATCH finds anevent cluster whose vertex spread is larger than a given criterion, an alarm signal is sent to experts by an e-mail. Then, theexperts check whether it is a real supernova signal or not bylooking at various plots which are uploaded to a secured site
accessible from the Internet (including i-mode keitai). Suchalarms happen almost once per month. They are usually due
to the accidental coincidence of two cosmic ray induced clusters. We have a supernova drill at least once per year. So far,no real supernova neutrino burst signal has been observed at
Super-Kamiokande.
In the drill, the SNWATCH conveners and the executive
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 every month. SK shift members are notified by a dummy alarmthat SNWATCH makes when the LED is illuminated. The
shift members then call to the SNWATCH experts and give areport. The SK collaborators will be ready for the real supernovae through the drill and the training.
We also search for neutrinos from old supernovae, which
are called Supernova Relic Neutrinos (SRNs). The SRN signal is the diffuse supernova neutrino background from all thesupernovae in the past. This signal has never been detected,
but it is expected to be detectable in the 16-30 MeV energy region, which is the gap between the energy ranges of solar neutrinos and atmospheric neutrinos. We have applied carefully
tuned data selection to enhance the SRN candidates, improving the efficiency of our search by over 20% compared to the2003 SK-I study, which currently provides the world’s best
limit on SRN flux. Our improved data selection also allows us
to now search the 16-18 MeV positron energy region, which
was previously unusable due to spallation background. Our
updated search utilizes SK-II and SK-III data as well as SKI, considers two new background channels, and performs a
sophisticated maximum likelihood search in multiple regionsof the Cherenkov angle distribution to extract the most accurate flux limit possible(Fig.1). Multiple systematic errors are
considered. A flux limit of between 2.7 and 3.0 ν̄ cm−2 s−1(positron energy > 16 MeV) is our new result, with the exact value depending on the shape of the neutrino spectrum

Number of events

3

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)53

SN νe Energy in 10 erg

Fig. 1. 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.

3

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

Fig. 3. In the new cavern the Gd pre-mixing and pre-treatment 15 tontank (front left), the selective filtration system (front right) and the
200 ton tank (rear of the hall) have been installed.

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

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. 2. 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.

assumed. This new result will replace the 2003 study to be
the most accurate measure of the SRN signal ever performed.
Furthermore, a new method of presenting the SRN flux limit
is also ready which is of great use to theorists and does nodepend on any particular model (Fig.2).

Super-Kamiokande R&D gadolinium project
As mentioned above, although at SK a few SRN events ayear are expected, SRNs have not been detected yet because
the large backgrounds constrain our search. The main goalof our research is to reduce these backgrounds and be able todetect SRNs. The observation of SRNs in general or neutrinos from distant supernovae in particular, would give us some
information about the universe, for example the core collapse
rate from SRNs, and the neutrino itself too, for example about(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 µ sec). 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 and since then a new hallnear the SK detector has been excavated and a 200 ton tankwith its ancillary equipment has been installed, see Fig.3. The
idea is to mimic the conditions at SK inside the 200 ton tank. It
has been equipped with a selective water filtration system, thatwill filter out water impurities while keeping Gd in the water,a Gd pre-mixing and pre-treatment 15 ton tank and a device
to measure the water attenuation length (UDEAL). Since themiddle of January, the 200 ton tank has been filled with purewater. The water system, which has been running stably since
the beginning of February has proven to keep a high water
quality, see Fig.4. Soon we will test adding gadolinium sulfate
to the pre-mixing 15 ton tank and circulate the water throughthe water system. The next step will be to add gadolinium
sulfate to the 200 ton tank and by the end of 2011 we expect
to mount 240 50-cm photomultipliers, thus entering in the lastphase of this exciting project.

4Fig. 5. Solar angle distribution of the SK-III final sample. The livetime
is 298 days for the energy range from 5 to 6.5 MeV and 548 days
for the energy range from 6.5 to 20 MeV. Data points are fittedusing the 8 B spectrum calculated by Winter et al.. The best fit
curve is indicated by the solid curve.
Fig. 4. Water attenuation length for pure water from the 200 ton tankfor three wave lengths: 337nm, 375nm and 405nm. The water
attenuation length decreases first and then increases as soon as
the water filtration system ran continuously.

SourceEnergy scale
Energy resolution
Theoretical uncertainty of 8 B spectrum
Trigger efficiency
Angular resolution
Vertex shift
Event quality cuts
Spallation
External event cut
Small cluster hits cut
Background shape
Signal extraction method
Livetime
Cross section
Total

Total flux
±1.4
±0.2
±0.2(+1.1−1.0 )±0.5±0.67(±1.2)±0.54(±1.3)±0.65(+2.1−1.6 )
±0.2
±0.25
±0.5
±0.1
±0.7
±0.1
±0.5
±2.1(+3.5−3.2 )

Table 1. Systematic uncertainty summary for the total flux in %. SK-I
values are also shown in parentheses for the largely improved systematic sources in the current SK-III analysis.

Solar neutrinos
SK detects solar neutrinos through elastic neutrinoelectron scattering, ν + e → ν + e, where the energy, direction and time of the recoil electron are measured. Due to its
large fiducial mass of 22.5 kiloton, SK gives the most precise
measurement of the solar neutrinos’ flux with accurate information of the energy spectrum and time variations. To achieve
this high precision, precise calibrations are performed for theenergy scale, energy resolution, angular resolution and thevertex position resolution using a LINAC and 16 N radioisotope generated by a DT neutron generator.
This year, the SK-III data analysis was finalized with alivetime of 298 days for the total electron energy range between 5 MeV and 6.5 MeV, and 548 days for the range between 6.5 MeV and 20 MeV [1]. The SK-III data have alower background level in the low energy region than the SK-

Fig. 6. Energy spectrum of solar neutrino flux in SK-III data from 5
MeV to 20 MeV. Each point shows the ratio of the data and the
expected flux calculated from the SSM. The line indicates the averaged value of the SK-III data.

I data because the amount of the Rn contamination within
the fiducial volume has been reduced by changing the water flow inside the tank and keeping the water with relatively
rich radioactivity from entering into the fiducial volume. Also
because pure water was supplied through a RO (reverse osmosis) system which seems to have removed radium content
in water. Detector simulation and event reconstruction tools
have been improved in this analysis, which give lower systematic uncertainties (See Table 1). Among the improvements inthe detector simulation, the position dependence of the watertransparency in the tank was newly implemented and the reflectivity of the sheet, optically separating the inner detector
from the outer detector, was carefully measured and updated.
An example of refinement in the reconstruction tools is the
improvement in the direction fitter, which yields a 10 % better angular resolution. With all those improvements, the systematic uncertainties for total flux of the SK-III data becomes±2.1%, which is reduced from +3.5
−3.2 % of the SK-I data [2].
Fig. 5 shows the result of the solar angle distribution for
the SK-III final sample. After subtracting background and fitting with the 8 B energy spectrum by Winter et al. [3], we obtained the 8 B flux value of 2.32 ± 0.04(stat.) ± 0.05(sys.) ×
106 cm−2 s−1 , which is consistent with the previous SK-I andII results. The energy spectrum of the solar neutrino flux for

5Fig. 7. Allowed region for neutrino oscillation parameters, ∆m2 andtan2 θ from solar analysis. The left figure shows the results fromthe SK-I, II and III combined analysis with the 8 B flux constrainedby SNO NC measurement. The right figure presents the resultof global analysis including SK and other solar experiments(SNO,
Borexino, Homestake, GALLEX-GNO and SAGE).

the SK-III data is shown in Fig. 6. The energy range used forthe analysis is from 5 to 20 MeV. As shown in the figure, theratio of the data and the expected flux from the Standard Solar
Model (SSM) [4] scatters almost flat at 0.4, and the energy
spectrum distortion which is expected from the LMA solution
is not observed yet.
Oscillation analysis has also been done including the SKIII solar neutrino data. The two flavor analysis for the determination of the solar oscillation parameters, θ12 and ∆m212
was done with the combined SK-I, II and III data. In theanalysis, the total 8 B flux is constrained by the SNO NC
measurement[5][6]. The result is shown in Fig.7. As shownin the left figure, the LOW solution is excluded and the LMA
solution is only allowed to explain the solar neutrino oscillation. Note that this result was obtained using SK results only
(not global analysis) with the 8 B flux constraint.
We have also done the same analysis using
the data from SK and other solar experiments, i.e.
SNO[5][6][7][8], Borexino[9], and radiochemical experiments (Homestake[10], SAGE[11] and GALLEX-GNO[12]).
The allowed region from the global analysis is shown in
Fig.7(right). The best-fit parameters are tan 2 θ12 = 0.44 ± 0.33
and ∆m221 = (7.6 ± 0.2) × 10−5eV2 .
In addition to the two flavor analysis, three flavor analysis was also done. We used three oscillation parameters,∆m212 , θ12 and θ13 as free parameters and set a fixed value of
2.4×10−3eV2 for ∆m223 . Fig.8 shows the allowed region forsin2 θ13 and tan2 θ12 from the three flavor analysis of SK andother solar experiments together with the KamLAND threeflavor analysis[13]. The allowed region for the combined
analysis from the solar global and KamLAND analyses is also
indicated. The limit of sin2 θ13 is 0.060 at 95% C.L. for thesolar global analysis. After combination with the KamLAND
result, the best fit value of sin2 θ13 is found to be 0.025+0.018−0.016and upper bound is obtained as sin2 θ13 < 0.059 at 95% C.L.
These results will be published soon.
Since SK-IV was started with new electronics and online
system in October 2008, we continue taking the solar neutrino data without large unscheduled downtime. By the endof March 2011, data of about 754.1 days livetime were col-Fig. 8. Allowed region for sin2 θ13 and tan2 θ12 from the three flavor
analysis. The thick lines and the star mark show the allowed regions and the best fit point of the global solar analysis. The thinlines and the square mark show the allowed regions and the best
fit point of our KamLAND analysis. The filled areas and the filled
circle mark show the allowed regions and the best fit point of the
combined analysis. For all regions, the innermost area (red), themiddle area (green) and the outermost area (blue) show 68.3, 95,
99.7 % C.L. respectively.

Fig. 9. Solar angle distributions of 754.1 days SK-IV data sample forsolar neutrino with energy between 4.0-4.5 MeV (left) and 4.5-5.0
MeV (right).

lected. In SK-IV period, we have introduced a precise temperature control system for the inlet water to avoid water convection which causes Rn rich water to enter the fiducial volume. In Fig.9, the solar angle distribution in the 4.5-5.0 MeV
energy region and that in the 4.0-4.5 MeV energy region are
shown. They show that the solar neutrinos even below 5 MeV
are clearly observed in SK-IV. High quality 8 B solar neutrino
data are being accumulated and the SK-IV data analysis is
now ongoing.

Atmospheric neutrinos
Cosmic ray interactions in the atmosphere produce neutrinos. The prediction of the absolute flux has an uncertainty
of at least ±20 %. However, the flavor ratio of the atmospheric neutrino flux, (νµ + ν̄µ )/(νe + ν̄e ), has been calculated to an accuracy of better than 5 %. Another importantfeature of atmospheric neutrinos is that the fluxes of upwardand downward going neutrinos are expected to be nearly equalfor Eν >(a few GeV) where the effect of the geomagnetic field
on primary cosmic rays is negligible. The livetime and ob-6served number of atmospheric neutrino events during the fourSK run periods are summarized in Table 2. Fully contained(FC) events deposit all of their Cherenkov light in the innerdetector, while partially contained (PC) events have exiting
tracks which deposit some Cherenkov light in the outer detector. The neutrino interaction vertex is required to be reconstructed within a 22.5 kiloton fiducial volume, defined to be> 2 m from the PMT wall.
The FC events are classified into “sub-GeV” (Evis <1330 MeV) and “multi-GeV” (Evis > 1330 MeV). These
events are further separated into sub-samples based on thenumber of observed Cherenkov rings. Single- and multi-ring
are then divided into electron-like (e-like) or muon-like ( µ like) samples depending on pattern identification of the mostenergetic Cherenkov ring. The sub-GeV samples are additionally divided based on their number of decay-electrons andtheir likelihood of being a π 0 .
The PC events are separated into ”OD stopping” and ”OD
through-going” categories based on the amount of light deposit by the exiting particle in the OD.
Energetic atmospheric νµ ’s passing through the Earth interact with rock surrounding the detector and produce muons
via charged current interactions. These neutrino events areobserved as upward going muons. Upward going muons
are classified into two types. One is “upward through-going
muons” which have passed through the detector, and theother is “upward stopping muons” which come into and stop
inside the detector. The upward through-going muons are
subdivided into ”showering” and ”non-showering” based onwhether their Cherenkov pattern is consistent with light emitted from an electro-magnetic shower produced by a very highenergy muon.
The livetime and number of observed events for the first
three SK periods are summarized in Table 3.
Table 2. Atmospheric neutrino livetimes and the number of observed
FC and PC events for each SK run period. (*)Numbers for SK-IV
are preliminary since data taking is still ongoing.

SK-I
SK-II
SK-III
SK-IV∗

Livetime(days)
1,489
799
518
763

FC
12,232
6,584
4,356
6,187

PC
896
429
343
485

Table 3. Atmospheric neutrino induced upward-going muon livetimeand the number of observed events for the first three SK run periods. (*)Numbers for SK-IV are preliminary since data taking is stillongoing.

SK-I
SK-II
SK-III
SK-IV∗

Livetime(days)
1,646
828
636
763

through-going
1,856
889
735
924

stopping
458
228
210
223

The zenith angle and lepton momentum distributions foreach of the above samples compared with the atmospheric
neutrino Monte Carlo predictions are shown in Fig. 10. The

200

Sub-GeV e-like 1-dcy e

Sub-GeV µ -like 0-dcy e

Sub-GeV e-like 0-dcy e

Sub-Gev µ -like 1-dcy e
500

500

200

0

0

100

0

Sub-GeV π -like 1-R00-1Multi-GeV µ -like

Multi-GeV e-like

0

1

Up Stop µ
200

100

200
200

50

100

100

0

0

Sub-GeV µ -like 2-dcy e

0

200

0

Multi-Ring µ -like

Multi-Ring e-like

100

Non-showering µ

200
500
100

50

100

0

0

Sub-GeV π0-like M-R

0

PC Stop

0

Showering µ

PC Through

400
100

50

200

200

0

50

500

1000

lepton momentum (MeV)

0
-1

0

cos zenith

1

0
-1

0

cos zenith

1

0
-1

-0.5

0

cos zenith

Fig. 10. The zenith angle and lepton momentum distributions for eachdata sample. cos Θ =1 indicates downward-going particles. The
blue histograms show the MC prediction without neutrino oscillation and the red histograms show the MC prediction for νµ ↔ ντ
oscillations with sin2 2θ = 1.0 and ∆m2 = 2.1 × 10−3 eV2 .

prediction is based on the recent precise measurements of primary cosmic rays by BESS, AMS and a three dimensional
calculation of the neutrino flux by Honda et al. The µ -likedata from SK exhibit a strong up-down asymmetry in theirzenith angle (Θ) distribution while no significant asymmetry
was observed in the e-like data. The data were compared with
the Monte Carlo expectation without neutrino oscillations andthe best-fit expectation for νµ ↔ ντ oscillations. The oscillated Monte Carlo reproduces the zenith angle distributions of
the data well.
We carried out νµ → ντ 2-flavor oscillation analysis using
the entire SK-I, II and III atmospheric neutrino data set. Red
contours in Figure 11 show the allowed neutrino oscillation
parameter regions for νµ ↔ ντ oscillations. The best fit oscillation parameters are sin 2 2θ = 1.0 and ∆m2 = 2.2 × 10−3eV2 .
The allowed oscillation parameter range is sin 2 2θ > 0.96 and∆m2 = (1.8 − 2.6) × 10−3eV2 at 90 % C.L.
The atmospheric neutrino data are well described by neutrino oscillations. The survival probability of a νµ is given
by a sinusoidal function of L/E, where L is the distance traveled by the neutrino and E is the neutrino energy. We also
performed an oscillation analysis binning the data in the combined variable L/E. Low energy or horizontal-going events
are rejected in this analysis since they have either large scattering angles or large dL/dΘzenith . This creates a sample withgood resolution in the L/E variable that is used to search forthe maximum in the oscillation probability sinusoid. The obtained allowed oscillation parameter regions are shown in Figure 11. This result is consistent with that of the oscillation
analysis using the zenith angle binning. The observed L/E

480

478

478

476

476

3

χ

2

2

4

χ

∆ m2 [10−3eV2]

7
480

474

474

472

472

470

470

0

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7

sin θ132

sin θ23
2

SK(zenith) 90%C.L.
SK(zenith) 68%C.L.

2

Fig. 13. χ 2 distribution as a function of (left:)sin2 θ13 and (right:)sin2 θ23 .
The normal hierarchy and inverted hierarchy cases are plotted with
red and black lines, respectively.

SK(L/E) 90%C.L.
MINOS 90%C.L.
K2K 90%C.L.

0.5

0.6

0.7

0.8

0.9

1

sin22θ

Fig. 11. Allowed region of νµ → ντ neutrino oscillation parameters obtained by SK using contained atmospheric neutrino events and upward-going muon events. Solid and dashed contours correspondto 90 and 68% C.L. respectively. Red contours are obtained by
the zenith angle analysis and blue contours are obtained by the
L/E analysis (see text). Allowed regions by long-baseline neutrino
oscillation experiment K2K and MINOS are shown in black andgreen contours, respectively.

distribution gives the first direct evidence that the neutrino
survival probability obeys the sinusoidal function predictedby neutrino flavor oscillations.
0.4

0.00350.00350.35

130.0025

0.002

0.002

0.00150.00150.00350.0035

sin 2

m223

m223

0.3

0.003

0.003

0.0025

SK atmospheric neutrino samples.
We have performed an extended oscillation analysis including all the mixing parameters and the CP violating term.
The matter effect in the Earth is also considered in this calculation and both the normal and inverted mass hierarchies
are tested. Figure 12 shows the allowed regions for (∆m2 ,sin2 2θ23 ), (∆m2 , sin2 θ13 ), and (sin2 θ13 , δcp ) for the normal
and inverted mass hierarchies. A comparison of χ 2 between
normal and inverted hierarchy case is shown in Figure 13.
The best fit parameter sets are (∆m223 , sin2 θ23 , sin2 θ13 , δCP )=(2.11·10−3eV 2 , 0.525, 0.006, 220◦ ) for the normal hierarchyand (2.51·10−3eV 2 , 0.575, 0.044, 220◦ ) for the inverted hierarchy case. All fits are consistent with the two flavor oscillation results and CHOOZ experiment’s upper limit on θ13 . No
indication for either mass hierarchy is seen in the data. [14].

0.25

0.01

0.2
0.15
0.1
0.05

0.008

0.40

0.3

0.002

0.25

0.006

0.2
0.15
0.1

2

0.002

0.0025sin 20.0025

13

0.003

m223

m223

0.003

0.05
0.00150.84 0.86 0.88 0.9 0.92 0.94 0.96 0.98
sin 2 2 23

0.001510

0.05

0.1 0.15

0.2
2

sin

0.25
13

0.3

0.35

0.4

0
0

∆ m23 (eV2)

0.35

50

100

150

200

250

300

cp

Fig. 12. The allowed regions for (∆m2 , sin2 2θ23 ); left, (∆m2 , sin2 θ13 );middle, and (sin2 θ13 , δcp ); right for the normal (upper figure) andinverted (lower figure) hierarchy. The blue, red, and green contours correspond to 68, 90 and 99% C.L. allowed regions obtainedby this analysis, respectively. The shaded regions corresponds tothe area excluded at 90% C.L. by the CHOOZ experiment.

Two flavor neutrino oscillations which assume that θ13 =0
and ∆m212 ≪ ∆m223 successfully describe the SK atmospheric
neutrino data with maximum mixing angle (θ23 =π /4). However, nonzero θ13 may be observable in the excess of multiGeV electron neutrino events, and to a lesser extent in theoscillations of multi-GeV muon neutrinos. Additionally, theeffects of the solar oscillation parameters and non-maximal
mixing are observable as a sub-leading oscillation effect on
the event rate of the Sub-GeV electron-like samples. If theCP violating term δcp is also considered, there are additional
sub-dominant oscillation effects predicted across many of the

0.004

0.002

0
0.5

0.6

0.7

0.8

0.9

1

sin2 2 θ23
Fig. 14. Allowed regions for the anti-neutrino mixing parameters. The
blue, red and green contours correspond to the 68%, 90%, and
99% C.L. allowed regions respectively. Shaded region shows theallowed regions by MINOS experiment [15].

Recently MINOS experiment reported the indication of
the larger ∆m2 in anti-neutrino (ν¯µ ) oscillation [15]. We
also performed a CPT violation test of the atmospheric neutrino data using separated two-neutrino disappearance model,
which allows neutrino and anti-neutrino to oscillate with different parameter sets of (∆m2 , θ ) and (∆m̄2 , θ̄ ), respectively.

8

According to the fitting result, the allowed region for antineutrino mixing parameters is shown in Figure 14, and thebest fit parameters are ( ∆m2 , ∆m̄2 , sin2 2θ , sin2 2θ̄ ) = (2.1 × 10−3 eV2 , 2.0 × 10−3 eV2 , 1.0, 1.0 ). The atmosphericmixing parameters for anti-neutrino oscillations are consistent
with those for neutrinos and therefore no evidence for CPT violation is found.

Fig. 15. Zenith angle distribution of tau-selected events by neural network method. SK-I, II, III dataset is used. Zenith angle cos(θ )=-1
(1) indicates upward-going (downward-going) direction. The data
(dot with error bar) and the best-fit MC including tau signal (shaded
region) and background from atmospheric neutrinos (νe and νµ )are shown.

Tau events, which are produced via ντ charge current (CC)interactions oscillated from νµ , are expected to be observedin SK. It would bring the direct evidence of νµ → ντ oscillation, however, the detection of ντ CC events in SK is challenging; the interaction rate of ντ charged current events is
low since the neutrino energy threshold is 3.5 GeV and theatmospheric neutrino flux above this energy is relatively low.
Also tau events are difficult to be identified individually because they tend to produce multiple particles. Tau analysis isperformed employing neural network technique to discriminate tau events of hadronic decay from backgrounds of atmospheric νe and νµ events. Figure 15 shows the zenith angle
distribution of tau-selected events. Tau events are expected
to appear in the upward-going events because they originatesνµ → ντ oscillation. The zenith angle shape of data is fittedwith the MC expectation including tau signal and backgroundwith their normalizations free. According to the fitting result,the signal excess is estimated to 213.6 ± 45 (stat) +13.2−29.75 (syst)
events, and the detection significance correspond to 3.8 σ .
We have observed 763 days of atmospheric neutrinos datawith SK-IV. The quality of the observed data are consistent
with the previous SK-I, II, III results. Due to the electronics
upgrade, several performance are expected to be improved,

such as the performance of Michel electrons tagging, the energy resolution in multi-GeV electron sample, etc. The further
analysis including SK-IV data are going on.

Search for nucleon decay
Proton decays and bound neutron decays (nucleon decays
in general) is the most dramatic prediction of Grand Unified
Theories 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 andit has accumulated data of 91.7 kt·yrs (SK-I), 49.2 kt·yrs (SKII), 31.9 kt·yrs (SK-III), and 32.9 kt·yrs (SK-IV), resulting in
206 kt·yrs data in total. Various nucleon decay modes havebeen looked for in the period from SK-I to SK-IV data but wehave found no significant signal excess so far.
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 and discovery of the signal would give us the information of the massof the gauge mesons. To discriminate the signal from the atmospheric neutrino background, we reconstruct the numberof particles (Cherenkov rings) and reconstruct the total visible energy corresponding to parent proton mass and total momentum corresponding to the proton’s Fermi momentum. The
signal efficiency of SK-IV is estimated to be 45.0 % and thebackground induced by the atmospheric neutrino interactions
is estimated to be 0.05. The BG rate was confirmed by an
artificial neutrino beam by using 1-kton water Cherenkov detector [16]. There are no candidate events in data from SK-I to
SK-IV, on the other hand, expected background in total (fromSK-I to SK-IV) is 0.42. Then we obtained a lower limit on thepartial lifetime of the proton; τ /B p→e+ π 0 > 1.2 × 1034 years
at 90% confidence level.
In addition, we looked for SUSY favored decay modes
which include K mesons in the final state, p → ν̄ K + , n →ν̄ K 0 , p → µ + K 0 , and p → e+ K 0 . In p → ν̄ K + search, wehave analyzed data until SK-IV. In this mode, we tag the signal by decay products from K + . The momentum of K + is below the Cherenkov threshold, and is stopped in the water anddecay into µ + ν or π + π 0 with monochromatic momenta. On
the other hand, the residual nucleus after proton decay emits
γ ray ( 40% probability) and it is also useful to tag the proton
decay signal. In SK-IV, SK electronics has been replaced andall of hits information are recorded by DAQ. As a result, thedecay electron tagging efficiency is improved and the selection efficiencies of p → ν̄ K + are improved. The efficiency ofthe prompt γ tagging method is increased from 7.2 % (SK-I)
to 8.2 % (SK-IV), and the efficiency of the π + π 0 method isincreased from 6.5 % to 7.9 %.
Figure 16 shows one analysis method in which we search
for muon with the monochromatic momentum 236 MeV/c. It
shows the comparison of the muon momentum distributions
for single-ring µ -like events between data, atmospheric ν MC,
and proton decay MC, and there are no significant excess indata. We have analyzed the data from SK-I to SK-IV, there areno candidates in the prompt γ method and the π + π 0 method.
Therefore we conclude that there is no evidence of nucleon
decays and we calculated partial lifetime limits taking into ac-Number of Events

9[8] S.N.Ahmed et al., “Electron Energy Spectra, Fluxes, and
Day-Night Asymmetries of 8 B Solar Neutrinos from the391-Day Salt Phase SNO Data Set”, Phys. Rev. C 72
(2005) 055502.

8070[9] C.Arpesella et al., “Direct Measurement of the 7 Be Solar
Neutrino Flux with 192 Days of Borexino Data”, Phys.
Rev. Lett. 101 (2008) 091302.

60
50
40

[10] B.T.Cleveland et al., “Measurement of the Solar Electron Neutrino Flux with the Homestake Chlorine Detector Bruce T. Cleveland”, Astrophys. J. 496 (1998) 505.

30
20[11] J.N.Abdurashitov et al., “Measurement of the solar neutrino capture rate with gallium metal”, Phys. Rev. C 60
(1999) 055801.

10
0

200

225

250

275

300

Pµ(MeV/c)[12] M.Altmann et al., “GNO solar neutrino observations: results for GNO I”, Phys. Lett. B 490 (2000) 16.

Fig. 16. The comparison between data and fitting results of themuon momentum distribution for single-ring µ -like events. The
filled circles show data with statistical errors. The solid line showsp → ν̄ K + MC. The dashed line shows the best fitted atmospheric
neutrino MC with free normalization.

[13] S. Abe et al., “Precise Measurement of Neutrino Oscillation Parameters with KamLAND”, Phys. Rev. Lett. 100(2008) 221803.

count systematic uncertainties. Obtained limit is 3.9 × 1033
years at 90% confidence level for p → ν̄ K + .
Moreover, we have performed extensive study for events;p → µ K 0 using decay products from KL0 , in which we haveincluded KS0 decays in the previous paper. Now just SK-I data
has been analyzed and the results of all SK data will be coming up soon.

Bibliography[1] Super-Kamiokande Collaboration, “Solar neutrino results in Super-Kamiokande-III”, Phys. Rev. D 83 (2011)052010.

[14] R. Wendell, C. Ishihara et al. [Super-Kamiokande Collaboration], “Atmospheric neutrino oscillation analysis
with subleading effects in Super-Kamiokande I, II, andIII”, Phys. Rev. D 81 (2010) 092004.
[15] P. Adamson et al. [MINOS collaboration], “First direct observation of muon antineutrino disappearance,”
arXiv:1104.0344 [hep-ex].
[16] S. Mine et al. [K2K Collaboration], “Experimental studyof the atmospheric neutrino backgrounds for proton
decay to positron and neutral pion searches in water
Cherenkov detectors,” Phys. Rev. D 77, 032003 (2008)[arXiv:0801.0182 [hep-ex]].

[2] Super-Kamiokande Collaboration, “Solar neutrino measurements in Super-Kamiokande-I”, Phys. Rev. D 73
(2006) 112001.

[17] H. Nishino et al. [Super-Kamiokande Collaboration],“Search for Proton Decay via p → e+ π 0 and p → µ + π 0
in a Large Water Cherenkov Detector,” Phys. Rev. Lett.
102, 141801 (2009) [arXiv:0903.0676 [hep-ex]].

[3] W. T. Winter et al., “The 8 B neutrino spectrum”, Phys.
Rev. C 73 (2006) 025503.

Hyper-Kamiokande[4] J.N.Bahcall and M.H.Pinsonneault, “What Do We (Not)Know Theoretically about Solar Neutrino Fluxes?”,
Phys. Rev. Lett. 92 (2004) 121301.
[5] B. Aharmim et al., “Independent Measurement of the
Total Active 8 B Solar Neutrino Flux Using an Array of
3 He Proportional Counters at the Sudbury Neutrino Observatory”, Phys. Rev. Lett. 101 (2008) 011301.
[6] B. Aharmim et al., “Low Energy Threshold Analysis of
the Phase I and Phase II Data Sets of the Sudbury Neutrino Observatory” Phys. Rev. C 81 (2010) 055504.
[7] B. Aharmim et al., “Determination of the νe and Total 8 B
Solar Neutrino Fluxes with the Sudbury Neutrino Observatory Phase I Data Set”, Phys. Rev. C 75 (2007) 045502.

Feasibility study has been performed for the next generation nucleon decay and neutrino detector Hyper-Kamiokandethat aims to explore unification of elementary particles andfull picture of neutrino masses and mixings. The water
Cherenkov detector with the dimension of 1 million tones hascapability of exploring nucleon lifetimes about 10 times aslong as the limits set by the Super-Kamiokande. For example, the sensitivity for the decay mode p → e+ π 0 is expected
to be beyond 1 × 1035 years [1]. The detector also aims tostudy neutrino properties such as Dirac CP phase, mass hierarchy, octant of θ23 , and so on by using a high power accelerator based neutrino beam and atmospheric neutrinos. Figure
1 shows the expected significance to exclude CP conservationsin δCP = 0, for the parameter space of θ13 and δCP by using
upgraded JPARC neutrino beam with the power of 1.66 MW

101tion of Electron Neutrino Appearance from an
Accelerator-produced Off-axis Muon Neutrino Beam,”
arXiv:1106.2822 [hep-ex].

δ [π]

5σ
3σ

0

Hyper-K (540kt FV)
1.5yrs ν + 3.5yrs ν
1.66MW

T2K Experiment

Normal hierarchy

-1 -3
10

10-2

10-1

sin22θ13

Fig. 1. The expected significance to exclude leptonic CP conservationin θ13 and δ parameter space by using upgraded JPARC ν beamand the Hyper-Kamiokande.

Fig. 2. The preliminary design of the Hyper-Kamiokande water tank.

×5years and the Hyper-Kamiokande detector with the fiducial
volume of 0.54 Megaton [1].
If the indication of electron neutrino appearance in theT2K experiment [2] is the result of nonzero θ13 , we are opening possibility of exploring these remaining neutrino parameters, i.e. CP phase and mass hierarchy. The suggested large
size of θ13 is really encouraging and it will boost the activities
toward realization of the future detector. Conceptual design(Fig.2), scheduling, and costing of the detector have been already started.

Bibliography[1] M. Shiozawa, “Large Underground Water Cherenkov
Detectors”, Proceeding of the XXIV International Conference on Neutrino Physics and Astrophysics (Neutrino2010), June, 2010. to be published in Nuclear
Physics B Proceedings Supplement.
[2] K.

Abe

et

al.

[T2K

Collaboration],“Indica-

The T2K (Tokai-to-Kamioka) experiment [1] is a long
baseline neutrino oscillation experiment. Its main goal is
to measure the last unknown lepton sector mixing angle θ13
by observing νe appearance in a νµ beam. It also aims to
make a precision measurement of the known neutrino oscillation parameters with precision of δ (∆m223 ) ∼ 10−4 eV2 andδ (sin2 2θ23 ) ∼ 0.01 via νµ disappearance studies. In addition
to neutrino oscillation studies, the T2K neutrino beam (withEν ∼ 1GeV) will enable a rich fixed-target physics program ofneutrino interaction studies at energies covering the transition
between the resonance production and deep inelastic scattering regimes.
T2K adopts the off-axis method [2] to generate thenarrow-band neutrino beam using the new MW-class proton
synchrotron at J-PARC. In this method the neutrino beamis purposely directed at an angle with respect to the baseline connecting the proton target and the far detector, SuperKamiokande. The off-axis angle is set at 2.5◦ so that thenarrow-band muon neutrino beam generated toward the far
detector has a peak energy at ∼ 0.6 GeV, which maximizes
the effect of the neutrino oscillation at 295 km and minimizes
the background to electron-neutrino appearance detection.
Details of the T2K experimental setup are described elsewhere [3]. The J-PARC Main Ring (MR) accelerator [4] provides 30 GeV protons with a cycle of 0.3 Hz. Beam bunches
are single-turn extracted in 5 µ s and transported an extraction
line arc defined by superconducting combined-function magnets to the production target. The target is a graphite rod witha diameter of 2.6 cm and a length of 90 cm (corresponding to
1.9 interaction length). Charged particles exiting the target aresign selected and focused into the 96 m long decay tunnel by
three magnetic horns pulsed at 250 kA.
The near detector site at ∼ 280 m from the production
target houses two detector systems. The on-axis Interactive Neutrino GRID (INGRID), composed of an array ofiron/scintillator sandwiches, measures the neutrino beam intensity, direction and profile. The off-axis detector measuresthe muon neutrino flux and energy spectrum, and intrinsic
electron neutrino contamination in the beam in the direction of the far detector, along with measuring rates for exclusive neutrino reactions. These measurements are essential
in order to characterize signals and backgrounds that are observed in the Super-Kamiokande far detector. The off-axis
detector consists of three large volume time projection chambers (TPCs) [5] interleaved with two fine-grained detectors(FGDs), a π 0 -optimized detector and a surrounding electromagnetic calorimeter. The whole off-axis detector is placedin a 0.2 T magnetic field provided by the recycled UA1 magnet, which also serves as part of a side muon range detector.
The far detector, Super-Kamiokande [6], is a 50 kton water Cherenkov detector located in the Kamioka Observatory.
In 2008, the Super-Kamiokande collaboration completed an

11Fig. 1. Accumulated number of protons on target (green/blue lines)
and protons per pulse (red/purple dots) during the T2K’s first two
physics runs.

upgrade to the detector’s readout electronics [7]. The newelectronics includes a new front-end capable of a higher dataprocessing rate and also improves upon the triggering method.
In the new system, the arrival time and charge of each PMT
hit is sent to a cluster of PCs that organizes the hit data andsearches for event candidates based on programmable software triggers. For the T2K experiment, the DAQ system triggers in time with the beam spills produced by the J-PARC
accelerator. Each beam spill is given a GPS timestamp that is
immediately sent to the online Super-Kamiokande PCs. Eachtimestamp is used to define an additional software trigger thatrecords all the PMT hits within ±500 µ s of the expected beam
arrival time (taking a neutrino time-of-flight into account).
These spill events are then collected and written to disk. Laterthe events are fed into offline processing which applies theusual Super-Kamiokande software triggers used to search forneutrino events, and any candidate events found are extracted
for further T2K data analysis.
The T2K experiment began accumulating neutrino beamdata for physics analysis in January 2010. Figure 1 shows
accumulated number of protons on target (p.o.t.), along withnumber of protons per pulse. The first two physics runs aredefined as Run 1 (January–June 2010) and Run 2 (November
2010–March 2011). During this time period, the MR proton
beam power was continuously increased and reached 145 kW
with 9 × 1013 protons per pulse. The number of bunches
was six during Run 1 and eight during Run 2. By the endof Run 2, a total of 2,474,419 spills were retained for analysis after beam and Super-Kamiokande quality cuts, yielding
1.43 × 1020 p.o.t.. The proportion of Super-Kamiokande good
spills to the total number of spills selected by beam conditions
was 99 %. In FY2010, neutrino oscillation studies were performed by using the whole Run 1 data, which correspond to
3.23 × 1019 p.o.t..
The neutrino flux is predicted by a Monte Carlo (MC) simulation based on experimental data. Pion production is basedon the data by the NA61/SHINE experiment [8], which measured hadron production by 30 GeV protons on a graphite target. Other hadronic interactions inside the target are simulatedby FLUKA. GEANT3/GCALOR handles particle propagation through the magnetic horns, target hall, decay volume andbeam dump. The predicted neutrino flux is predominantly νµwith < 1 %νe contamination. Pion and kaon production uncertainties dominate the neutrino flux prediction uncertainty.

The NEUT MC event generator [9], which has been tuned
with recent neutrino interaction data in an energy region compatible with T2K, is used to simulate neutrino interactionsin the near and far detectors. An energy-dependent error on
charged-current quasi-elastic interactions (CCQE) is assigned
to account for the uncertainty in the low energy cross-section,
especially for the different target materials between the nearand far detectors.
An inclusive νµ charged-current (CC) measurement in
the off-axis near detector is used to constrain the expected
event rate at the far detector. Neutrino interactions in the
FGDs with tracks entering the downstream TPC are selected.
A dE/dx of the most energetic negative track in the TPC
is require to be compatible with a muon. To reduce background from interactions outside the FGDs, there must be
no track in the upstream TPC. The analysis selects 1529
events. The measured data/MC ratio is 1.061 ± 0.028(stat.)+0.044−0.038 (det.syst.)±0.039(phys.syst.). The detector systematic
errors mainly come from tracking and particle identification
efficiencies, and physics uncertainties are related to the interaction modeling.
At Super-Kamiokande, a fully-contained fiducial volume(FCFV) sample is extracted by requiring no event activity ineither the OD or in the 100 µ s before the event trigger time, atleast 30 MeV electron-equivalent energy deposited in the ID(defined as visible energy Evis ), and the reconstructed vertex
in the 22.5 kton fiducial region. The Run 1 data have 23 such
FCFV events. All of them are within the time range from -2 to
10 µ s around the beam trigger time. The accidental contamination from non-beam related events (predominantly from atmospheric neutrino interactions) is estimated to be less than
10−2 events.
The electron neutrino appearance analysis produces a
Super-Kamiokande event sample enhanced in νe CCQE interactions arising from νµ → νe oscillations. The main background are intrinsic νe contamination in the beam and neutralcurrent (NC) interactions with a misidentified π 0 . The selection criteria for this analysis were fixed from MC studies
before the data were collected, optimized for the initial running conditions. The analysis relies on the well-establishedSuper-Kamiokande reconstruction techniques developed forother data samples [10]. Among 23 FCFV events, ten events
are reconstructed with a single ring, and two of those areelectron-like (e-like). Both events satisfy a visible energy
cut Evis > 100 MeV, but one of these has a delayed-electron
signal and is rejected. To suppress misidentified π 0 mesons,the reconstruction of two rings is forced by comparison of theobserved and expected light patterns calculated under the assumption of two showers [11] , and a cut on the two-ring invariant mass Minv < 105 MeV/c2 is imposed. The remaining
one event is not rejected. Finally, the neutrino energy Eνrecis computed using the reconstructed momentum and direction of the ring, by assuming quasi-elastic kinematics and neglecting Fermi motion. The event is remained after requiring
Eνrec < 1250 MeV, aimed at suppressing events from the intrinsic νe component arising primarily from kaon decays. The νeappearance signal efficiency is estimated from MC to be 68 %while rejection for νµ and intrinsic νe are > 99 % and 79 %,respectively. Figure 2 shows a display of the event satisfies all12πSuper-Kamiokande IV
T2K Beam Run 33 Spill 822275
Run 66778 Sub 585 Event 134229437
10-05-12:21:03:22
T2K beam dt =1902.2 ns

Inner: 1600 hits, 3681 pe
Outer: 2 hits, 2 pe
Trigger: 0x80000007
D_wall: 614.4 cm

π/2e-like, p = 381.8 MeV/c

Charge(pe)

δCP

>26.7
23.3-26.7
20.2-23.3
17.3-20.2
14.7-17.3
12.2-14.7
10.0-12.2
8.0-10.0
6.2- 8.0
4.7- 6.2
3.3- 4.7
2.2- 3.3
1.3- 2.2
0.7- 1.3
0.2- 0.7
< 0.2

0

260
0 mu-edecays

208

-π/2

156
104
52
0
0

500

1000

1500

2000

Times (ns)-π00.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
sin22θ13

1

Fig. 2. A display of the observed νe candidate event.

Table 1. Contributions from various sources and the total relative
uncertainty for sin2 2θ13 = 0 and 0.1

Sourceneutrino flux
near detector
near det. statistics
cross section
far detector
exp
exp
Total δ NSK/NSK

sin2 2θ13 = 0± 8.9 %
+5.6
−5.2 %± 2.7 %
± 14.3 %± 15.8 %+23.9−23.8 %

sin2 2θ13 = 0.1± 11.9 %+5.6−5.2 %± 2.7 %
± 10.6 %± 9.5 %
+19.5
−19.4 %the νe selection criteria.
The expected number of events at Super-Kamiokande
exp(NSK) is calculated by using the near detector νµ CC interaction rate measurement as normalization, and the ratio of expected events in the near and far detectors, wherecommon systematic errors cancel. The oscillation parameters other than sin2 2θ13 are fixed at ∆m212 = 7.6 × 10−5 eV2 ,∆m223 = 2.4 × 10−3eV2 , sin2 2θ12 = 0.8704, sin2 2θ23 = 1.0,
exp
and δCP = 0 unless otherwise noted. The computed NSK
are 0.34(1.20) events for sin2 2θ13 = 0(0.1), which consistof 0.14(0.14) νµ + ν µ , 0.18(0.16) intrinsic νe , and 0.02(0.9)νµ → νe oscillation events. As shown in Table 1, the total sysexp
depends on θ13 . The errors fromtematic uncertainty on NSK
cross-section modeling are dominated by uncertainties in intranuclear final state interactions (FSI) and by the knowledgeof the σ (νe )/σ (νµ ) ratio. estimated to ±6 %. The systematic uncertainties due to event selection in Super-Kamiokande
were studied with cosmic-ray muons, electrons from muon
decays, and atmospheric neutrino events. Main contribution
exp
exp
/NSK
for e.g. sin2 2θ13 = 0.1 is 5.0 % from ringto δ NSK
counting, 4.9 % from particle identification, and 6.0 % from
the Minv cut.
The oscillation analysis is based entirely on comparing
the number of νe candidate events with predictions, varying
sin2 2θ1 3 for each δCP value. At each oscillation parameter
point, a probability distribution for the expected number of
events is constructed, incorporating systematic errors, which

Fig. 3. The 90 % C.L. upper limit (red) and sensitivity (purple) on
sin2 2θ13 for each value of δCP assuming normal mass hierarchy.

is used to make the confidence interval, following the unified
ordering prescription of Feldman and Cousins [12]. Figure 3
shows the upper limit and sensitivity on sin2 2θ13 at 90 % confidence level (C.L.) for normal mass hierarchy. Though theconstraint on θ13 obtained from the first T2K data was not as
stringent as those set by CHOOZ [13] and MINOS [14] due totheir low statistics, our strategy in a νe appearance search including high background suppression by the off-axis neutrino
beam technique and a nice e/π 0 separation, near/far error cancellation, etc., was verified.
In the νµ disappearance study, a νµ CCQE enriched sample is selected by applying the following additional cuts on
the FCFV sample : (1) single ring, (2) muon-like ( µ -like),(3) number of delayed-electron signals is 0 or 1, and (4) reconstructed muon momentum > 200 MeV/c. Eight events remained in the whole Run 1 data, while the expected number of events with a normalization by the near detector νµ
CC interaction rate measurement is 22.81 ± 3.19(syst.) in
the null oscillation case and 6.34 ± 1.04(syst.) in the twoflavor νµ → ντ oscillation case with ∆m223 = 2.4 × 10−3 eV2and sin2 2θ23 = 1.0. Significance from the null oscillation hypothesis is 2.6σ . Figure 4 shows the reconstructed neutrinoenergy distribution of the selected events.
By the end of Run 2, we have already accumulated about
5 times as much as the data obtained during Run 1. The result of the νe appearance search using these new data with
reduced systematic errors will be reported in FY2011, as wellas the first result of the T2K νµ disappearance analysis. The
T2K beam production has been suspended since the Tohoku
Earthquake occurred on March 11, 2011. Recovery works
on the damaged accelerator and beamline components are in
progress in order to resume the neutrino beam data-taking by
December, 2011.

Bibliography[1] Letter of intent: Neutrino oscillation experiment at JHF,
2003. http://neutrino.kek.jp/jhfnu/loi/loi JHFcor.pdf.

Cross−section [cm2] (normalised to nucleon)

13

5

Events/100MeV/3.23E19 POT

Null oscillation4νµ - ντ oscillation
22(sin 2θ,∆m )=(1.0, 0.0024)

3

Data

2

−42

10

CDMSIIXENON100

−43

10

−44

10

XMASS 1yr

−45

10

−46

10

1

10

2

10

3

10

WIMP Mass [GeV/c2]

Fig. 1. XMASS sensitivity compared to other experiments.
http://dmtools.berkeley.edu/

10Spin independent
−41

10

0

0.5

1
1.5
2
Reconstructed Eν

2.5

3
GeV

Fig. 4. Reconstructed neutrino energy of the events selected in theνµ disappearance analysis.

[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] K. Abe et al. (T2K Collaboration), accepted for publication in Nucl. Instrum. Methods, article in press (2011),
doi: 10.1016/j.nima.2011.06.067,
arXiv:1106.1238 [physics.ins-det].
[4] Y. Yamazaki et al., KEK Report 2002-13 and JAERITech 2003-44 and J-PARC-03-01 (2003).
[5] N. Abgrall et al., Nucl. Instrum. Meth. A637, 25 (2011),
arXiv:1012.0865 [physics.ins-det].
[6] Y. Fukuda et al. (Super-Kamiokande Collaboration),
Nucl. Instrum. Meth. A501, 418 (2003).
[7] S. Yamada et al. (Super-Kamiokande Collaboration),
IEEE Trans. Nucl. Sci. 57, 428 (2010).
[8] N. Abgrall et al. (NA61/SHINE Collaboration), submitted to Phys. Rev. C (2011), arXiv:1102.0983 [hep-ex].
[9] Y. Hayato, Nucl. Phys. (Proc. Suppl.) B112, 171 (2002).
[10] Y. Ashie et al. (Super-Kamiokande Collaboration),
Phys. Rev. D71, 112005 (2005), hep-ex/0501064.
[11] T. Barszczak, (2005), Ph.D. Thesis (University of California, Irvine), UMI-31-71221.
[12] G. J. Feldman and R. D. Cousins, Phys. Rev. D57, 3873
(1998).
[13] M. Apollonio et al. (Chooz Collaboration), Eur. Phys. J.
C27, 331 (2003), hep-ex/0301017.
[14] P. Adamson et al. (MINOS Collaboration), Phys. Rev.
D82, 051102 (2010), arXiv:1006.0996 [hep-ex].

See

XMASS experiment
The XMASS experiment aims to detect 7 Be/pp solar
neutrinos, neutrino-less double beta decay, and dark mattersearches using ultra-pure liquid xenon. The first stage of
XMASS experiment is concentrated on dark matter searches
using 800 kg liquid xenon detector. The 800 kg detector construction in the Kamioka mine was funded and started in April
2007. Construction work was completed in September 2010
and commissioning run has been started since October 2010.
Several astronomical observations indicate that the universe contains a large amount of nonbaryonic dark matter.
One of the most plausible candidates for the nonbaryonicdark matter is a weakly interacting massive particle (WIMP)
provided by the supersymmetry in the form of the lightest
supersymmetric particle. WIMPs can be directly detected
through their elastic scattering off target nuclei in a detector. XMASS searches for the WIMP-xenon nucleus interaction in liquid xenon. Liquid xenon has the several advantages
for dark matter searches. Large amount of scintillation light(42,000 photons/MeV), which is as good as NaI(Tl) scintillator enables us to detect small energy signals such as dark
matter recoil. Owing to the high atomic number of xenon(Z = 54) and the high density of liquid xenon (∼ 2.9 g/cm3),
target volume can be small and external background gammarays can be absorbed within a short distance from the detector
wall. With 20 cm self-shielding, gamma-rays from 238 U contamination is expected to be reduced more than 3 orders ofmagnitude in the 5-50 keV electron recoil energy range fromthe simulation study. Figure 1 shows the expected sensitivityof the XMASS experiment. Our goal is to reach 10 −45 cm2 .
Most of the XMASS facilities are located at Hall-C in the
Kamioka mine 1,000m underneath the top of Mt. Ikenoyama.
The XMASS detector consists of the cylindrical water tankwith 72 50cm PMTs (outer detector: OD) and spherical liquid
xenon detector with 642 2inch PMTs (inner detector: ID) as
shown in figure 2. The spherical liquid xenon detector is contained in a double wall vessel. The vessel consisting of innerand outer vacuum chamber (IVC and OVC) is made from oxygen free high conductivity (OFHC) copper. The gap between
IVC and OVC is kept vacuum for thermal isolation. The inner surface of IVC was polished with electro-chemical buffing(ECB) to reduce emanation of hydrogen and radon from copper.

14Electronics
hut

Water tank

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

~1.2m

72 50cm PMTs (veto)Fig. 2. Schematic view of the water tank and the liquid xenon vessel.

Fig. 4. Photo of liquid xenon vessel inside the water tank as of
September 2010.

Calibration system

Electronics hut

Refrigerator
water tank

Clean boothat the entrance

Fig. 3. Photo of IVC (left). The inner surface of upper part (right, top)
and lower part (right, bottom).

In July 2010, the vessel was delivered at Kamioka mine,and detector assembling work was started inside the watertank. We made a clean booth inside the water tank and assembling work was done there while the IVC was opened.
The radon concentration in the water tank was kept about 200
mBq/m3 which is 1/100 of that in the atmosphere, and the dustlevel was less than 1000 particles/ft3 (Particle size > 0.5µ m)
during the assembling work. All the ID PMTs had been already mounted in the OFHC copper holder in February 2010
as reported in the last annual report. They were put inside theIVC, and PMT signal and high-voltage cables are connectedto the electronics system at the top of the water tank throughthe vertical pipe and feed-through. The xenon supplying andcirculation lines were also connected between the side of vessel and outside of the water tank. The refrigerators, circulation
pump, filters, and liquid xenon reservoir were put outside thewater tank, and connected each other. The 72 50-cm diameter
PMTs were also put on the inner wall of the water tank to tag
the incoming cosmic ray muons. All the detector assembling
work was completed in September 2010 (figure 4). A calibration system was also mounted inside the IVC. This systemenables us to drive a radio active source inside the IVC along
one axis with < ±1 mm accuracy.
Internal background needs to be removed before and also
the data taking. 85 Kr in xenon is a potential source of the internal contamination. Therefore, we processed one ton xenon
with our distillation system [2] to reduce the 85 Kr for ten daysin September 2010. After distillation, xenon was introduced
into the IVC. The gas xenon was passed through SAES get-LXe reservoir

Distillation
tower

GXe buffer tank
10m3 x 2, < 10bar

GXe compressor

Fig. 5. Photo of Hall-C. All the facilities of XMASS 800 kg detector
have been completed.

ter at the 30 L/min of flow rate and liquefied with two 200 W
pulse tube refrigerators.
After 1st filling of xenon, we collected liquid xenon fromthe detector to the reservoir through the stainless particle filter(10µ m mesh) to remove dust. The liquid xenon was evaporated, passed through SAES getter, liquefied with refrigerators, and introduced into the detector again. We purified xenon
by the above method two times.
After xenon purification, we have started commissioning
run since October 2010. We put several kind of radio active
sources at several positions inside the IVC by using calibration system and observed scintillation photons. About 16%
improvement of light yield was observed with 57 Co source
owing to xenon cleaning. Vertex reconstruction study andevaluation of internal contamination (radon, krypton, etc.)
have been carried out.

Bibliography[1] Y. Suzuki et al., “Low energy solar neutrino detection byusing liquid xenon”, Aug. 2000, hep-ph/0008296.
[2] K. Abe et al. (the XMASS collaboration), ”Distillationof Liquid Xenon to Remove Krypton”, Astroparticle
Physics, 31 (2009) 290.
[3] S. Moriyama, “Status of XMASS Experiment”, proceedings of identification of dark matter 2010 (IDM2010),
July 2010.

15

HIGH ENERGY COSMIC RAY DIVISION
Overview
There are three major experimental research activities inthe High Energy Cosmic Ray Division, the study of high energy gamma rays and the design study of the next generation
telescopes by the Cherenkov Cosmic Gamma Ray group, thestudy of extremely high energy cosmic rays by the Telescope
Array (TA) group, and the study of very high energy cosmic
rays and gamma rays by the Tibet AS gamma group. Other
activities, such as experiments utilizing the Akeno observatory, the Norikura observatory, the Mt. Chacaltaya observatory (jointly operated with Bolivia), and the emulsion-pouring
facilities are closely related to inter-university joint research
programs. Also an all-sky high resolution air-shower detector(Ashra) has been installed on the Hawaii island. The HighEnergy Astrophysics Group created in the fiscal year 2009
aims to explore various high energy astrophysical phenomena,
through theoretical and observational approaches.
The Cherenkov Cosmic Gamma Ray group operates the
CANGAROO telescope system, a set of large imaging atmospheric Cherenkov telescopes, to make observations of highenergy air showers originated by TeV gamma rays. The CANGAROO project started as a single telescope with a relatively
small mirror (3.8 m in diameter) in 1992. In 1999 a new telescope with a 7 m reflector has been built, and now it has a
10 m reflector with a fine pixel camera. An array of four 10 m
telescopes was completed in March 2004 so that more sensitive observations of gamma rays are realized with its stereoscopic imaging capability of Cherenkov light. For further development of Very High Energy Gamma Ray Astronomy, theCherenkov Cosmic Gamma Ray Group is also working on thedesign study and development of the next generation international ground-based gamma ray observatory CTA.
At the Akeno observatory, a series of air shower arrays of
increasing geometrical sizes were constructed and operated toobserve extremely high energy cosmic rays (EHECRs). The
Akeno Giant Air Shower Array (AGASA) was operated from1991 to January 2004 and covered the ground area of 100 km 2
as the world largest air shower array. In 13 years of operation, AGASA observed a handful of cosmic rays exceeding
the theoretical energy end point of the extra-galactic cosmic
rays (GZK cutoff) at 1020 eV. The Telescope Array (TA), alarge plastic scintillator array with air fluorescence telescopes,
has been constructed in Utah, USA, which succeeds AGASA
and measures the EHECRs with an order of magnitude larger
aperture than that of AGASA to unveil the origin of superGZK cosmic rays discovered by AGASA. The full-scale TA
has started taking data as the largest array viewing the northern sky.
An air shower experiment aiming to search for celestial
gamma-ray point sources started in 1990 with Chinese physicists at Yangbajing (Tibet, 4,300 m a.s.l.) and has been successful. This international collaboration is called the Tibet
ASγ Collaboration. An extension of the air shower array wascompleted in 1995 and an emulsion chamber has been combined with this air shower array since 1996 to study the primary cosmic rays around the knee energy region. After successive extensions carried out in 1999, 2002 and 2003, thetotal area of the air shower array amounts to 37,000 m 2 . The
sun’s shadow in cosmic rays affected by the solar magnetic
field was observed for the first time in 1992, utilizing its goodangular resolution at multi-TeV energy region. From this experiment with better statistics, we expect new information to
be obtained on the large-scale structure of the solar and interplanetary magnetic field and its time variation due to the
11-year-period solar activities.
A new type of detector, called Ashra (all-sky survey highresolution air-shower detector), was developed. The firstphase stations were installed near the Mauna Loa summit in
the Hawaii Island and high-efficiency observation is continuing. It monitors optical and particle radiation from highenergy transient objects with a wide field-of-view.
The High Energy Astrophysics group is conducting theoretical researches on fundamental processes responsible fornonthermal particle acceleration in various astrophysical environments, including first-order diffusive shock acceleration,
second order stochastic acceleration in shock downstream regions, modification of shock structure by pick-up interstellar
neutrals, as well as injection processes of suprathermal particles. In addition to these theoretical works, R/D studies forradio observations of pulsars and cosmic ray air showers arealso being made.

CANGAROO and TeV Gamma-Ray Projects
CANGAROO-III[Spokespersons: R.W. Clay, R. Enomoto, and T. Tanimori]
Collaboration list:
Institute for Cosmic Ray Research, University of Tokyo,
Chiba, Japan; School of Chemistry and Physics, Universityof Adelaide, Australia; Mt Stromlo and Siding Spring Observatories, Australian National University, Australia; Australia Telescope National Facility, CSIRO, Australia; Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, Ibaraki, Japan; Faculty of Science,
Ibaraki University, Ibaraki, Japan; Department of Physics, Konan University, Hyogo, Japan; Department of Physics, Kyoto University, Kyoto, Japan; Solar-Terrestrial Environment
Laboratory, Nagoya University, Aichi, Japan; National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Tokyo, Japan; Department of Physics, Tokai
University, Kanagawa, Japan; Department of Physics, Yamagata University, Yamagata, Japan; Faculty of Management Information, Yamanashi Gakuin University, Yamanashi, Japan;
Faculty of Medical Engineering and Technology, Kitasato

16
Table 1. Summary of CANGAROO-III observations carried out in thefiscal year 2010 (April 2010 to March 2011).

Observation
Term
April 2010
June 2010
September 2010
November 2010
December 2010
March 2011

Observation
TargetHESS J1507−622
HESS J1507−622
RX J1713.7−3946
Crab Nebula
Crab Nebula
Vela X

Observation
Time (hr)
23.5
20.2
2.7
5.1
8.2
6.7

University, Kanagawa, Japan; Department of Physics, Hiroshima University, Hiroshima, Japan; Department of Basic
Physics, Tokyo Institute of Technology, Tokyo, Japan; Department of Physics, College of Science and Engineering, Ritsumeikan University; Institute of Particle and Nuclear Studies, High Energy Accelerator Research Organization (KEK),
Ibaraki, Japan [1].

Status of the Project
CANGAROO is the acronym for the Collaboration ofAustralia and Nippon (Japan) for a GAmma Ray Observatory in the Outback. The collaboration started in 1992 with asingle Imaging Atmospheric Cherenkov Telescope (IACT) of
3.8 m diameter called CANGAROO-I in the desert area near
Woomera, South Australia (136◦47′ E, 31◦ 06′ S, 160 m a.s.l.).
As its third-generation experimental setup, the CANGAROOIII stereoscopic IACT system has been in operation since
March 2004 with four IACTs of 10 m diameter. Stereoscopic observations of atmospheric Cherenkov light images
produced by particle showers caused by high-energy particles
bombarding the earth allow effective discrimination of gamma
rays from charged cosmic rays which are the overwhelming
backgrounds. Two of the four telescopes (called T3 and T4 in
the order of construction) have been used in observations, as
the first and second telescopes have degraded. A stereoscopic
triggering system was installed at the beginning of 2005 andhas been working properly, rejecting most single muon events,
which are the major background component at low energies.
We are continuing observations of various candidates of celestial gamma-ray emitters on moonless, clear nights.

CANGAROO-III Observations
We have carried out six observation shifts in the fiscal year
2010, which are summarized in Table 1. Relatively strong
TeV gamma-ray sources with hard spectra have been selected
as observation targets considering deteriorated performanceof the CANGAROO-III system. A preliminary analysis of thedata taken in April and June 2010 from the H.E.S.S. unidentified gamma-ray source HESS J1507−622 [2] has been performed and no statistically significant gamma-ray signal has
been found. We therefore estimated preliminary upper limit
to the gamma-ray flux from HESS J1507−622, which areconsistent with the fluxes detected by H.E.S.S. The results
were presented in the Japan Physical Society Meeting held in

Fig. 1. Preliminary 2σ upper limits to the TeV gamma-ray flux from 30
Doradus in LMC obtained by CANGAROO-III. The red line represents the result of the standard analysis, whereas the green line isthat of the analysis with software padding, in which artificial noiseis added to pixels offline in order to equalize noise levels between
on- and off-source data [4]. The gray points represent the fluxes
detected by Fermi LAT [3].

September 2010. The presentation also included preliminary
results for the data previously taken from 30 Doradus, which
is a starburst region in the Large Magellanic Cloud (LMC)from which an extended GeV gamma-ray signal has been detected by Fermi LAT [3], and the Sculptor dSph galaxy, which
is a dwarf spheroidal galaxy in the vicinity of the Milky Way
Galaxy and possibly causes gamma-ray emission due to dark
matter annihilations because of its mass concentration. However, no statistically significant TeV gamma-ray signals havebeen detected from these objects and flux upper limits havebeen presented. Figure 1 shows the upper limits to the flux
from 30 Doradus in comparison with the Fermi GeV spectrum.

Bibliography[1] Collaboration website:
u-tokyo.ac.jp/.

http://vesper.icrr.

[2] F. Acero et al., Astron. Astrophys., 525, A45 (2011).
[3] A. A. Abdo et al., Astron. Astrophys., 512, A7 (2010).
[4] M. F. Cawley, Proc. Towards a Major Atmospheric
Cherenkov Detector II, ed. R. C. Lamb (Calgary), 172(1993).

CTA Project (Cherenkov Telescope Array)[CTA-Japan Spokespersons: T. Totani and M. Teshima]
Collaboration list:
Institute for Cosmic Ray Research, University of Tokyo,
Chiba, Japan; Department of Physics, Yamagata University,
Yamagata, Japan; Faculty of Science, Ibaraki University,
Ibaraki, Japan; Institute of Particle and Nuclear Studies, HighEnergy Accelerator Research Organization (KEK), Ibaraki,
Japan; Department of Physics, Tokyo University of Science, Chiba, Japan Department of Physics, The University of17Tokyo, Tokyo, Japan; Interactive Research Center of Science,
Tokyo Institute of Technology, Tokyo, Japan; Department of
Physics, Aoyama Gakuin University, Tokyo, Japan; Faculty of
Science and Engineering, Waseda University, Tokyo, 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 Medical Engineeringand Technology, Kitasato University, Kanagawa, Japan; Faculty of Management Information, Yamanashi Gakuin University, Yamanashi, Japan; Department of Physics, Nagoya University, Aichi, Japan; Solar-Terrestrial Environment Laboratory, Nagoya University, Aichi, Japan; Kobayashi-Maskawa
Institute, Nagoya University, Aichi, Japan; Department of
Astronomy, Kyoto University, Kyoto, Japan; Department of
Physics, Kyoto University, Kyoto, Japan; Yukawa Institute for
Theoretical Physics, Kyoto University, Kyoto, Japan; Department of Earth and Space Science, Osaka University, Japan;
Department of Physics, Kinki University, Osaka, Japan; Department of Physics, Konan University, Hyogo, Japan; Department of Physics, Hiroshima University, Hiroshima, Japan;
Hiroshima Astrophysical Science Center, Hiroshima University, Hiroshima, Japan; Faculty of Integrated Arts and Sciences, The University of Tokushima; Department of Applied
Physics, University of Miyazaki, Miyazaki, Japan; Graduate
School of Science and Technology, Kumamoto University,
Kumamoto, Japan; Center for Cosmology and Astroparticle
Physics, Ohio State University, Ohio, USA; Technical University of Dortmund, Dortmund, Germany [1].

CTA Project
During the past few 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 observed with ground-based IACTs. The history of VHE gamma
ray astronomy began with the discovery of VHE gamma raysfrom the 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.

Fig. 2. Artist view of the CTA observatory. CTA consists of three typesof telescopes, Large Size Telescopes (23m diameter), Mid Size
Telescopes (12m) and Small Size Telescopes (6m), and covers
the broad energy band from 20GeV to 100TeV.

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 ∼ 10−14erg 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
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 re-

18

Fig. 4. 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 400of these clusters, cooling plates and camera housing.

Fig. 3. 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.

quire 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 two current observatories; one is MAGIC [4] on La Palma,
Canary Islands, in the Northern hemisphere, and the otheris CANGAROO [5] at Woomera, Australia, in the Southernhemisphere. These two facilities are used not only for scientific observations but also for technological development toward the future observatory CTA.

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, (2010), available atarXiv1008.3703.
[3] Status of Very High Energy Gamma Ray Astronomy
and Future Prospects, M. Teshima, The Astronomical

Fig. 5. Prototype of the high precision segmented mirror 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 will beapplied to enhance the reflectivity and to elongate the lifetime.

Herald, 104 (2011) 333-342.
[4] MAGIC Collaboration website:
mppmu.mpg.de/ .

http://magic.

[5] CANGAROO Collaboration website://vesper.icrr.u-tokyo.ac.jp/.

http:Other Activities
As a test bench of domestic R & D activities for future ground-based gamma-ray observatory projects, a used
Cherenkov telescope of a 3 m diameter has been obtained
and repaired. We have placed it at the Akeno observatory
in November 2010, as shown in Figure 6. Some prototype
imaging cameras and electronics systems are planned to be19construction of the TA was performed mainly by the Grantsin-Aid for Scientific Research (Kakenhi) of Priority Areas“The Origin of Highest Energy Cosmic Rays” (JFY2003JFY2008) and the US National Science Foundation (NSF).
All the three fluorescence stations started the observation in
November 2007. Major construction of the surface detector
array was completed in February 2007, and the array of thesurface detectors started the full operation in March 2008.
The TA is operated by the international collaboration of researchers from US, Russia, Korea and Japan. The main fund
for the TA operation is the Grants-in-Aid for Scientific Research (Kakenhi) of Specially Promoted Research “Extreme
Phenomena in the Universe Explored by Highest Energy Cosmic Rays” (JFY2009-JFY2013).

Fig. 6. 3 m Cherenkov telescope installed at the Akeno observatory
as a test bench for future ground-based gamma-ray observatories.

installed to this telescope, and test observations will be carried out in the near future.

TA: Telescope Array Experiment
Spokespersons:
M. Fukushima / ICRR, University of Tokyo
P. Sokolsky / Dept. of Physics, University of Utah
Collaborating Institutions:
Chiba Univ., Chiba, Japan; Chungnam Nat. Univ., Daejeon, Korea; 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. ofTokyo, Kashiwa, Japan; Kanagawa Univ., Yokohama, Japan;
KEK/IPNS, Tsukuba, Japan; Kinki Univ., Higashi-Osaka,
Japan; Kochi Univ., Kochi, Japan; Nat. Inst. of Rad. Sci.,
Chiba, Japan; Osaka City Univ., Osaka, 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; Univ. of Utah, Salt Lake City, UT, USA; Univ. of
Yamanashi, Kofu, Japan; Waseda Univ., Tokyo, Japan; Yonsei
Univ., Seoul, Korea

Overview and Status of TA
The TA [1] is the detector that consists of the surface arrayof plastic scintillator detectors (a la AGASA) and fluorescence
detectors (a la HiRes). The aim of the TA is to explore theorigin of extremely-high energy (EHE) cosmic rays by measuring energy, arrival direction and mass composition. It is
located in the West Desert of Utah, 140 miles south of Salt
Lake City (lat. 39.3◦N, long. 112.9◦W, alt. ∼1400 m). The

Surface Detector Array
The surface detector (SD) array consists of 507 plastic
scintillators on a grid of 1.2 km spacing. It covers the groundarea of about 700 km2 .
The counter is composed of two layers of plastic scintillator overlaid on top of each other. One layer of scintillatoris 1.2 cm thick and 3 m2 in area. Light from each layer iscollected by 104 wave length shifter fibers 5 m long, which
are installed in grooves on the surface. Both ends of the fibers
are bundled and optically connected to one photomultiplier foreach layer. Power of each SD is supplied by a solar panel andbattery. The communication between SDs and the host at thecommunication tower is performed by wireless LAN.
Fluorescence Telescope
The TA has three fluorescence detector (FD) stations. The
fluorescence station in the southeast is located at the Black
Rock Mesa (BRM) site. The southwestern station is locatedat the Long Ridge (LR) site and the station in the north islocated at the Middle Drum (MD) site.
Twelve reflecting telescopes were newly constructed andinstalled at each of the BRM and LR stations and cover the skyof 3◦ -34◦ in elevation and 108◦ in azimuth looking toward thecenter of the surface detector array.
The MD station was constructed using refurbished equipment from the old HiRes-1 observatory. Fourteen reflecting
telescopes cover the sky of 3◦ -31◦ in elevation and 114◦ inazimuth.
We also built a laser shooting facility (Central Laser Facility: CLF), which is located at an equal-distance (20.85 km)
from three fluorescence stations for atmospheric monitor. The
Rayleigh scattering at high altitude can be considered as “standard candle” observable at all the stations.
A LIDAR (LIght Detection And Ranging) system locatedat the BRM station is used for the atmospheric monitoring. It
consists of a pulsed Nd:YAG laser and a telescope attached toan alto-azimuth. The back-scattered light is received by thetelescope to analyze the extinction coefficient along the pathof the laser.
For monitoring the cloud in the night sky, we installed an
infra-red CCD camera at the BRM station, and take data of
the night sky every hour during FD observation.
In order to confirm absolute energy scale of the fluorescence detector in situ, we installed a compact electron linear

20

accelerator (Electron Light Source: ELS) [2] at the BRM FD
site. A beam of 109 electrons with energy of 40 MeV and a
duration of 1 µ s well simulates a shower energy depositionof ∼4×1016 eV 100 m away from the station, which corresponds to a shower of ∼4×1020 eV 10 km away. The calibration is performed by comparing the observed fluorescencesignal with the expected energy deposition calculated by the
GEANT simulation [3]. We began to start up the ELS in June
2010, and we shot electron beam vertically up into the atmosphere from the ELS for the first time and took the images
with FD on September 3rd, 2010. Fig. 1 shows the imageof the pseudo shower by the electron beam together with theimage by Geant MC simulation.
Fig. 3. Observation hours per night and integrated observation hours
for the BRM (upper) and LR (lower) fluorescence detector sites
from November 2007 through February 2011. The horizontal axes
represent modified Julius day (MJD).

Energy spectrum
The Auger group and the HiRes group published the results of energy spectrum, which are consistent with GZK cutoff with their energy scales determined by the method of fluorescence telescope [4, 5]. We present energy spectra using
three different methods: the MD monocular FD analysis, hybrid analysis, and SD analysis.
Fig. 1. The image of the pseudo shower by the electron beam thatwas shot from the ELS at the BRM FD site for the first time on
September 3rd, 2010 (upper). The image by Geant MC simulation(lower).

100

100

90

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70

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60

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30

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20

20

10

10

0
Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar May Jul Sep Nov Jan Mar

trigger/104(%)

Status of TA Observation
Fig. 2 shows the rate of operation of the surface detectors
from May 2008 through March 2011. There were periods forwhich the fraction of operation decreased because of maintenance and bad weather. The average rate of operation is close
to 100%.
Fig. 3 shows the observation hours for the BRM and LR
fluorescence detectors from November 2007 through February 2011. We observe during moonless night, and the observation time per night in winter is longer than that in summer.

0

Date

Fig. 2. The rate of operation of the surface detectors in red and theintegrated number of triggered air shower events in green fromMarch 2008 through March 2011.

Energy spectrum by the MD monocular FD analysis
The analysis of monocular FD data at the MD station
provides a direct comparison between the TA and HiRes energy spectra. The MD spectrum uses the data collected overa three-year period between December 2007 and September
2010. The MD spectrum is based on the monocular observation technique and is analyzed using the profile-constrained
geometry reconstruction technique developed by the HiRes-1.
The preliminary monocular energy spectrum from the MD fluorescence detector is shown in Fig. 4. The TA MD monocularenergy spectrum is in good agreement with the HiRes spectra.
The details of the analysis of the MD FD data is described in[6].
Energy spectrum by hybrid analysis
The hybrid events which are detected both by FD and SD
are useful to compare the reconstructed results from FD and
SD. In addition, we improve the reconstruction of FD events
more precisely by using information both of FD and SD forhybrid events than FD monocular analysis alone. Here we use
timing information from one SD. When we use only data of
the fluorescence detectors, the aperture depends on energy ofprimary cosmic rays, but hybrid analysis has the merit that theaperture is kept constant above 1019 eV by the size of the surface detector array and the systematic error of the aperture becomes smaller. The hybrid event candidates were searched forby the condition that the trigger time difference between FD
and SD is less than 200 µ s from May 2008 through September
2009. We found 1978 hybrid events. The effective aperture
after the quality cuts is obtained from the Monte Carlo simulation code COSMOS [7] with QGSJET-II model for pure pro-

21

1024
HiRes-1
HiRes-2

3

2

2

E J(E) [eV /m /s/str]

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TA FD: MD

1023 17
10

18

10

19

10
Energy [eV]20

10Fig. 4. The preliminary monocular energy spectrum from the TA MD
fluorescence detector (black circles). Green triangles and purple
downward triangles represent those for the HiRes-1 and HiRes-2
detectors, respectively.

There are two types of fits in SD event reconstruction: thefit to determine the geometry of the shower and the fit to determine the lateral density distribution. Monte Carlo data weregenerated by CORSIKA air shower simulation program [9]with QGSJET-II proton model. The detector simulation withfront-end electronics and trigger was constructed with Geant4
simulation. The fit result of the Monte Carlo data by the parameters tuned by the observed data is also good in the same
way as that of the observed data.
The basic idea of the energy reconstruction is to use thecharge density at a distance of 800 m from shower core (S 800 )as an energy estimator. The correlation of S 800 and zenith
angle with primary energy from Monte Carlo study is used
for the first estimation of the primary energy of the data.
We compare the energy scales of FD and SD using hybrid
events. The scatter plot of the energies of well-reconstructed
331 events is shown in Fig. 6. It shows that the energy of SD
is 27% larger than that of FD. We choose the energy scale ofFD, and the SD energy is rescaled by 27%.

ton including calibration factors for the whole period. The exposure of the hybrid analysis is approximately 4×1015 m2 sr s
above 1019 eV. After the reconstruction procedure, 124 events
remain above 1018.65 eV. The total systematic uncertainties
are 19% in energy measurement, and 10% in flux from cloudmonitoring. The preliminary energy spectrum from the hybrid
analysis is shown in Fig. 5. The energy spectrum by this analysis is consistent with the other TA results. The details of thehybrid analysis are described in [8].

TA FD: Hybrid

1025

TA FD: MD

2

E J(E) [eV /m /s/str]

TA SD

2

Fig. 6. The preliminary result of the comparison of the energies between FD and SD. The red line corresponds to ESD = EFD . The
blue line corresponds to ESD = 1.27×EFD .

3

1024

1018

1019
Energy [eV]1020

Fig. 5. The preliminary TA energy spectra measured by three different methods. Green downward triangles denote the spectrum byhybrid analysis. Black squares denote the spectrum by the MD
monocular FD analysis. Red circles denote the spectrum by thedata of the surface detectors with “energy scaled to FD energy”.

Energy spectrum by using the data of the surface detectors
We measure the energy spectrum by using the SD datafrom May 2008 through February 2010. The exposure is approximately 1500 km2 sr yr which is equivalent to the total
exposure of the AGASA.

After the reconstruction procedure, 6264 events withzenith angles below 45◦ remain. We obtain the energy spectrum from the number of events in each energy bin by using the effective aperture obtained from the Monte Carlo data.
The preliminary energy spectrum is shown in Fig. 5. An excess of UHECRs exceeding the prediction by GZK, which had
been observed by AGASA in 1998, was not confirmed. We
performed a fit using power laws in three regions, and foundthe two breaks at logE (E in eV) of 19.75 and 18.71, whichcorrespond to the GZK suppression [10, 11] and the ankle,
respectively. We observed five events above the break point
at 1019.75 eV while the expected number of events along thecontinuous spectrum is 18.4. This result provides evidence forthe flux suppression with the significance of 3.5σ . The detailsof the SD analysis are described in [12].
The obtained preliminary energy spectra by three different methods from the TA experiment are shown together withother experiments in Fig. 7.

2230
P QGSJETFe QGSJET
Data

TA FD: Hybrid

HiRes-1

TA FD: MD

HiRes-2

TA SD

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20

Auger (ICRC31)
15

2

2

E J(E) [eV /m /s/str]

1025

AGASA

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Fig. 7. The preliminary spectra from the Telescope Array together
with the spectra from other experiments. The green closed downward triangles represent the TA hybrid spectrum, the black closed
squares the monocular FD spectrum from the MD station, and thered closed circles the TA SD spectrum. The light-blue closed triangles represent the AGASA spectrum, the blue open squares the
HiRes-1 spectrum, the blue open circles the HiRes-2 spectrum,and the purple open triangles the PAO spectrum. The light-blue
dotted bars are 90% C.L. upper limits for the AGASA.

Measurement of mass composition by shower
maximum depth (Xmax )The basic idea to determine the mass composition of
UHECRs is to use the dependence of the atmospheric depthof shower maximum on the primary energy and mass composition.
For composition in EHE region, the Auger data suggests
a change to a heavier composition [13] while the HiRes datais consistent with constant elongation rate which stays with
proton [14].
The data set from November 2007 through September
2010 is used in this analysis. The events observed simultaneously at two new FD stations are analyzed for the showergeometry by stereo technique and for the longitudinal development in the same way as hybrid technique to measure theatmospheric depth of shower maximum (Xmax ).
The Monte Carlo data are generated by CORSIKA withthe particle types of proton and iron, and the interaction models of QGSJET-01 and SIBYLL. The resolution of energy is
8% and that of Xmax is 23 g/cm2 at energy around 1019.0 eV
from QGSJET-01 proton Monte Carlo simulation. We noticethat the measured Xmax has a bias from the limit of the fieldof view. Since this bias also depends on the model, the reconstructed Xmax from the observed data and Monte Carlo data arecompared by applying the same analysis procedure. An example of the distribution of Xmax for the TA stereo data alongwith QGSJET-01 Monte Carlo data is shown in Fig. 8. The
distribution of Xmax of the observed data is in good agreementwith that of the Monte Carlo data for protons.
The evolution of the average Xmax with energy was measured and compared with the Monte Carlo data in the energy
range from 1018.2 to 1020.0 eV as shown in Fig. 9. The observed TA data are in good agreement with the QGSJET-01
pure proton prediction. The details of the mass composition

Fig. 8. The preliminary reconstructed Xmax distribution for the TA
stereo data (points) along with QGSJET-01 Monte Carlo data inthe energy region from 1018.8 to 1019.0 eV. The red and blue histograms are the proton and iron predictions, respectively.
900
Preliminary
850

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1019
Energy [eV]

<Xmax> [g/cm ]

1018

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700
P-QGSJET01
Fe-QGSJET01
P-SIBYLL
Fe-SIBYLL
data

650

600
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18.5

19
log(E/eV)

19.5

20

Fig. 9. The preliminary result of the average reconstructed Xmax as
a function of energy. The black points are the TA stereo data.
The upper set of red lines are predictions for pure protons with theinteraction models of QGSJET-01 (solid line) and SIBYLL (dashedline). The lower set of blue lines are under the assumption of iron.

study are described in [15].

Search for UHE photons
Several models were proposed for the interpretation of theorigin of highest energy cosmic rays. There is a possibility that cosmic rays were generated and accelerated in very
active region up to highest energy cosmic rays (bottom-up
model), and were observed at the earth through GZK process. If highest energy cosmic rays are generated and accelerated at the sources such as AGN, there is a possibility that
UHE photons with energy around 1019 eV are generated byresonant π 0 production in GZK-type process. It is also expected that large amount of UHE photons with energy above
1019 eV could be generated by non-accelerated model (topdown model) such as unknown super-heavy particles. It is expected that UHE photons with energy above 1019 eV interact
in deeper atmosphere than UHE hadrons. Then the curvatureof air shower front of photons around the ground is larger thanthat of hadrons.
Fig. 10 shows the curvature of air shower front for thedata of the surface detectors taken from May 2008 throughOctober 2009. We obtained the limit on the integral flux of23photons with energy above 1019 eV to be
3.4 × 10−2 km−2 sr−1 yr−1
at 95% confidence level as shown in Fig. 11 [16].

Fig. 10. The preliminary result of the distribution of the curvature of
shower front of UHE cosmic rays (Linsley curvature parameter)for zenith angle from 45◦ to 60◦ . Black points denote the distribution of curvature of the TA data. The histogram corresponds tothe expected distribution of the curvatures for the photons that are
generated by the spectrum with power index of -2.

We use the 2MASS Galaxy Redshift Catalog (XSCz) [19]that is derived from the 2MASS Extended Source Catalog(XSC) with redshifts that have either been derived from the
2MASS photometric measurements or measured spectroscopically. We use the galaxies at distances from 5 to 250 Mpc
and with Ks magnitudes less than 12.5. This catalog provides
the most accurate information about three-dimensional galaxy
distribution. We assume that UHECRs are protons. We also
assume that the effects of the Galactic and extragalactic magnetic fields are approximated by a Gaussian smearing angle.
The flux map calculated with these assumptions at the energy
threshold of 57 EeV is shown in Fig. 12. The rectangularregion around the Galactic center (|b| < 10◦ and |l| < 90◦ ) is
excluded from the analysis because the underlying galaxy catalog is incomplete. We choose an a priori confidence level of
95%, which means that the two distributions are incompatible
at the 95% C.L. if the KS-test probability (p-value) is smaller
than 0.05. The data both above 40 EeV and 57 EeV are compatible with LSS model. For isotropic model, the data above
40 EeV are compatible while the data above 57 EeV are incompatible at the 95% C.L. [20, 21]

Fig. 12. The sky map of expected flux from LSS model together withobserved arrival directions of UHECRs with energies above 57
EeV (green points) in the Galactic coordinates. Darker gray region
indicates larger flux and each band contains 1/5 of the total flux.
The region |b| < 10◦ and |l| < 90◦ is excluded from the analysis.
The smearing angle is 6◦ .

Fig. 11. Upper limits on the integral flux of UHE photons for different
experiments: the latest preliminary TA result (TA) in red, TA at
ICRC09 (TA ICRC) in gray, AGASA (A), Auger (PA), and Yakutsk(Y).

Arrival directions of UHE cosmic rays
We present the analysis of UHECRs for correlations withthe large-scale structure (LSS), correlations with AGN andsmall-scale anisotropy. The analysis is based on the SD datacollected for zenith angles less than 45◦ from March 2008
through September 2010.
Correlations with LSS
At large angular scales, the anisotropy in the PAO data
was claimed [17], and that in the HiRes data was not confirmed [18].

Correlations with AGN
The Pierre Auger Collaboration reported correlations between the arrival directions of UHECRs with energies above
57 EeV and positions of nearby AGN [22]. The probability
that the correlations for angular separations less than 3.1 ◦ has
occurred by chance is 1.7×10−3. However, the HiRes groupreported that no correlations have been found [23]. To test
AGN hypothesis, we use nearby AGN from Véron 2006 catalog [24], with the cut on redshift 0<z≤0.018. As is seen from
Fig. 13 [20], the preliminary TA result is compatible both withisotropic distribution and the AGN hypothesis.
Small-scale anisotropy
The small-scale clusters of UHECR arrival directions
were observed by the AGASA experiment at the angular scaleof 2.5◦ [25, 26]. On the other hand, the result of smallscale anisotropy by the HiRes experiment is consistent with
an isotropic distribution [27]. Following the analysis of the
AGASA, we used the events with energies above 10 EeV and
40 EeV. Fig. 14 shows the distribution of separation angles for

24
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expectation

N_corr

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data

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background

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Fig. 13. The preliminary result of the correlations with AGN. The horizontal axis is the number of observed events and the vertical axis
is the number of correlated events with AGN. The red crosses are
the TA data. The turquoise shaded area shows 1σ region and thelight-blue shaded area shows 2σ region. The black solid line is theprediction from isotropic distribution and the blue solid line is theprediction from the result of the Pierre Auger Observatory [22].

any two cosmic rays with energies above 40 EeV normalizedby solid angle. Then we count the number of pairs separated
by less than 2.5◦ . For the events with energies above 10 EeV,
we find 311 pairs while 323 are expected for the isotropic
model. For the events with energies above 40 EeV, we find
one pair while 0.8 are expected for the isotropic model. No
significant autocorrelations (clustering) at small scales were
found in the data sets [20, 28].

In the near future, we plan to determine energies of air
showers within total uncertainty of about 10% and measure
the spectrum of UHE cosmic rays precisely by using endto-end absolute energy calibration of fluorescence telescopeswith the ELS.
Towards large-scale UHECR observatory, wide attention
has been raised to the detection of UHECR with radio techniques, either passive and active, in addition to the extension
with the surface detectors and/or fluorescence detectors. An
R/D study of the detection of radar echoes from extensive air
showers (EAS) has started by installing a transmitter and receivers at the TA site. The R/D studies of the detection ofbremsstrahlung from EAS are being discussed first by using
the ELS.
A construction of TALE, a Low Energy extension of TAwith the energy range down to 1017 eV is proposed to investigate the modulation of cosmic ray composition and spectrum
expected by the galactic to extra-galactic transition of cosmic
ray origins including “second knee” in the 1017 eV decade. By
the TA+TALE project, comprehensive studies on UHE cosmic rays will be possible for wide energy range from 10 16.5 to1020 eV or above.

Bibliography[1] H. Kawai et al. (Telescope Array Collaboration), Nucl.
Phys. B Proc. Suppl., 2008, 175-176, 221-226; H. Kawai
et al. (Telescope Array Collaboration), J. Phys. Soc. Jpn.
Suppl. A 79 (2009), 108; H. Sagawa for the Telescope
Array Collaboration, Proc. 31st ICRC, Lodz, Poland(2009).
[2] T. Shibata et al., Nucl. Instr. and Meth. A 597 (2008)
61-66.
[3] S. Agostinelli et al., Nucl. Instr.and Meth. A 506 (2003)
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[4] R.U. Abbasi et al. (HiRes Collaboration), Phys. Rev.
Lett. 100 (2008) 101101.
[5] J. Abraham et al. (Pierre Auger Collaboration), Phys.
Rev. Lett. 101 (2008) 061101.
[6] D. Rodriguez, Ph.D. thesis, University of Utah (2011).

Fig. 14. The preliminary distribution of separation angles for any two
cosmic rays with energies above 40 EeV normalized by solid angle. The points are the observed data and the blue line is theisotropic model. Error bars represent the Poisson upper and lower
limits at 68% C.L.

[7] K. Kasahara and F. Cohen, Proc. 30th ICRC, Merida,
Mexico 4 (2008) 581.
[8] D. Ikeda, Ph.D. thesis, University of Tokyo (2010).
[9] Heck, D. et al., Report FZKA (1998) 6019.

Prospects[10] K. Greisen, Phys. Rev. Lett. 16, 748 (1966).

We will analyze the increasing TA data and measure energy spectrum, particle composition including UHE photons
and UHE neutrinos, anisotropy of arrival directions more indetail and explore the origin of UHE cosmic rays and understand the extreme phenomena of the universe by using
the characteristic features of the TA detector, the sampling ofelectromagnetic shower energy, the unique calibration of fluorescence generation, usage of HiRes-1 telescopes in the TA
site, and the measurement in the northern hemisphere.

[11] G.T. Zatsepin and V.A. Kuz’min, JETP Lett. 4, 78 (1966)[Pis’ma Zh. Eksp. Teor. Fiz. 4, 114 (1966)].
[12] B. Stokes et al. (Telescope Array Collaboration), Proceedings of the International Symposium on the Recent
Progress of Ultra-high Energy Cosmic Ray Observation(UHECR2010), 10-12 Dec 2010.
[13] J. Abraham et al (Pierre Auger Collaboration), Phys.
Rev. Lett. 104 (2010) 09110.

25[14] R.U. Abbasi et al, (HiRes Collaboration), Phys. Rev.
Lett. 104 (2010) 161101.
[15] Y. Tameda, Ph.D. thesis, Tokyo Institute of Technology,
2010; Y. Tameda et al., Proceedings of UHECR2010,10-12 Dec 2010.
[16] G. Rubtsov et al. (Telescope Array Collaboration), Proceeding of UHECR2010 10-12 Dec. 2010.
[17] T. Kashti and E. Waxman, JCAP 05 (2008) 006.
[18] R.U. Abbasi et al. (HiRes Collaboration), Astrophys. J.
Lett. 71B (2010) 64.
[19] T. Jarrett, arXiv:astro-ph/0405069.
[20] P. Tinyakov et al. (Telescope Array Collaboration), Proceedings of UHECR2010, 10-12 Dec 2010.
[21] E. Kido et al. (Telescope Array Collaboration), Proceedings of UHECR2010, 10-12 Dec 2010.
[22] J. Abraham et al. (Pierre Auger Collaboration), Science
318 (2007) 939; J. Abraham et al. (Pierre Auger Collaboration), Astropart. Phys. 29 (2008).
[23] R.U. Abbasi et al. (HiRes Collaboration), Astropart.
Phys. 30 (2008) 175-179.
[24] M.P. Véron-Cetty, P. Véron, and Astron. Astrophys. 455(2006) 773.
[25] N. Hayashida et al., Phys. Rev. Lett. 77 (1996) 78.
[26] M. Takeda et al., J. Phys. Soc. Jpn (Suppl.) B 70 (2001)15.
[27] R.U. Abbasi et al., Astrophys. J., 610 (2004) 73.
[28] T. Okuda et al. (Telescope Array Collaboration), Proceedings of UHECR2010, 10-12 Dec 2010.

Tibet ASγ Project
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 northern 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 m 2 , 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-diameterphotomultiplier tube (FT-PMT), and 52 out of 185 FT counters are also equipped with a wide dynamic range 1.5-inchdiameter PMT (D-PMT) by which we measure up to 500 particles which saturates FT-PMT output, and all the D-countersFig. 1. Schematic view of the Tibet III array.

have a D-PMT. A 0.5 cm thick lead plate is put on the topof each counter in order to increase the counter sensitivity by
converting gamma rays into electron-positron pairs in an electromagnetic shower. The mode energy of the triggered eventsin 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 wascovered by the high-density array by adding 200 FT-countersmore. Finally we set up 56 FT-counters around the 36,900 m 2high 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. 1.
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 ◦ .011,
by displacement of the shadow’s center from the apparent center in the north-south direction, as the east-west component of
the geomagnetic field is very small at the experimental site.
On the other hand, the shadow center displacement in the eastwest direction due to the geomagnetic field enables us to spectroscopically estimate the energy scale uncertainty less than
±12 %.
Thanks to high statistics, the Tibet air shower experimentintroduces a new method for energy scale calibration otherthan the conventional estimation by the difference between

26

the measured cosmic-ray flux by an air shower experiment andthe higher-energy extrapolation of cosmic-ray flux measured
by direct measurements by balloon-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 [3],(3) Cosmic-ray anisotropy in the multi-TeV region with highprecision[4],(4) Global 3-dimensional structure of the solar and interplanetary magnetic fields by observing the Sun’s shadow incosmic rays.
We will introduce a part of the results obtained in this fiscal year.
The first topic is on the knee-physics-related one.
We use the air shower array to measure the energy andarrival direction of each air shower. The primary energy ofeach event is determined by the shower size Ne , which is calculated by fitting the lateral particle density distribution to themodified NKG structure function. The energy resolution isless than 20% for the knee energy range. The arrival direction of an air shower is determined as follows. The direction
cosine of the shower axis is determined using a least square
method where the difference is minimized between the arrival
time signals of each FT counter and the expected values on
the assumed cone with a given direction cosine. This procedure determines the arrival angle with an accuracy smaller
than 0.2◦ at energies above 1014 eV. The core detector was
designed to detect the high-energy particles at the AS core by
converting them into electromagnetic cascade showers (burst)
using lead absorber of 160 cm × 50 cm in area and 7 cm (inPhase I) or 3.5 cm (in Phase II) in thickness. The burst size
under the lead plate was measured by scintillation countersof the same size as the lead plate in area and 2 cm in thickness. Four photo-diodes were mounted to the each corner ofthe scintillator whose attenuation length for the scintillation
light was calibrated with electron beam. From the 4 photodiode signals, we can estimate the burst size and the positionof the burst center with spatial resolution of 10 cm. One hundred core detectors were used (total area is 80 m 2 ) to detectburst size greater than 5 × 104 . The study of the primary masscomposition was made in two experimental phases. In the firstphase, 6 layers of X-ray films were placed between lead plateswith 1 cm depth interval to register the development of shower
spots induced by high-energy γ and electrons (hereafter abbreviated as γ -rays) over a few TeV which are incident upon thedetector, and detailed analysis on the structure of the high energy core has been made with use of image scanner in 2004
to obtain proton and helium spectra in 2006. The energy de-termination of the individual γ -rays was made by comparing
the transition curve of the optical density of the shower spots
with electromagnetic shower theory. Such procedure of theenergy determination using X-ray films was calibrated using
200 GeV electron beam at FNAL. A bundle of high energy γ rays from successive nuclear interactions of the primary cosmic rays in the atmosphere is called γ -family, which can bedetected by spatial reconstruction of the shower spots registered on X-ray films with angular resolution of 2.5 ◦ . They
are reconstructed as groups of parallel tracks with typical lateral spread of at most several cm among uncorrelated single
tracks, which are dropped off as background. The assignmentof a γ family to an accompanied AS was made through the positional correlation between the X-ray film and the scintillator,
and the correlation between the burst and air shower was madeby their time stamps. The arrival directions obtained from air
shower and the reconstruction of the shower spots were also
used to uniquely determine the air shower candidate.
Such γ -family events are more efficiently generated bylight primaries than the case of heavy primaries because of
the penetrating nature in the atmosphere. Therefore, the AS
core detectors can select the air showers of light primary origin naturally. The contamination of the events of heavy nuclei
origin was estimated using Artificial Neural Network (ANN)based on extensive Monte Carlo simulation of air showers(MC) assuming interaction models and primary models using CORSIKA code. Two interaction models of QGSJET and
SIBYLL are used in estimating the efficiency of the γ family
generation, and also two mass composition models of proton
dominant (PD) and heavy dominant (HD) are used to appreciate the contamination rate of heavy primaries. The efficiencyof the family generation for various primary nuclei and its energy dependence is calculated by MC and used for obtaining
the primary proton and helium fluxes. For example, the efficiencies by protons at the knee energy 4 PeV in phase I experiment are about 7 % and 10 % by QGSJET model and SIBYLL
model, respectively. ANN is also used in procedures to obtainproton and helium spectra. Phase I experiment selected 177
γ family events with core energy ∑ Eγ > 20 TeV and AS size
Ne > 2 × 105.
In the second phase experiment, X-ray films were not usedand proton+helium (P+He) spectrum was studied without separating them but with higher statistics than that of phase I. The
core detector was tuned to decrease the detection threshold energy of the AS core to have several times higher efficiency.
The energy spectrum of all particles was obtained asshown in Fig. 2 together with other data. The uncertainty of
the absolute intensity due to the interaction models used in
the analysis is shown by QGSJET and SIBYLL (10 % difference at most). The uncertainty due to the assumed primary
mass composition is also shown by HD and PD. Although thecomposition is fairly different between HD and PD models atenergies above 1015 eV, the difference of the absolute intensity
is 20% at most between the two models and it decreases withincreasing primary energy. Note that the shapes of the spectrafrom different models are almost the same and the position of
the knee is clearly found at the energy around 4 PeV.
From the second phase experiment of air shower core observation, the energy spectrum of P+He was obtained with

27
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Akeno array1
Akeno array20
Tibet3-QGSJET+HD
Tibet3-QGSJET+PD
Tibet3-SIBYLL+HD

E

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Primary Energy [GeV/particle]

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Fig. 2. All particle spectrum obtained by Tibet III. The results fromthree models of QGSJET+HD, QGSJET+PD, and SIBYLL+HD
adopted in the analysis are shown.
5

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Primary Energy [eV/particle]

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Fig. 4. Model A:Sharp knee is attributed to extra component (dashedline) from nearby source. Solid red line represents sum of the
global component and the extra component.

10

QGSJETdJ[GeV1.5/m2 sec sr]
dE

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Fig. 3. P+He spectrum obtained by AS core observation (black closed
circle).

high statistics and in good agreement with phase I as shownin Fig. 3, in which QGSJET model was used for the analysis. Use of SIBYLL model results in about 30 % lower intensity than that of the QGSJET analysis There is a problem of
discrepancy between Tibet and KASCADE data as shown in
Fig.3, e.g., the flux of the light nuclei by KASCADE is higher
than Tibet by more than a factor of 2. However, if SIBYLL
model is used in the analysis of KASCADE, the difference between two data is much reduced. This fact does not necessarily mean that SIBYLL model is more preferable to explain thedata at this energy range. KASCADE reported that QGSJET
model explains high energy data better than SIBYLL, on theother hand, SIBYLL model is better at lower energies. This
problem is related to the interaction model dependence of MC
calculations and also to the different experimental methods
used in two experiments. The Tibet experiment observes highenergy part of the air showers, namely, the most forward region of the center of mass system (CMS) of interacting particles, while KASCADE experiment observes Ne − Nµ correlation, in which the muon component is sensitive to the central
region of the CMS. The model dependence in forward region
is about 30 % as studied by Tibet, but that of central region
seems to be as large as a factor of 2.
Remarkable features of the energy spectrum of light com-ponent around 1015 eV are; (1) The power index is steeper
than that of all-particle spectrum before the knee, suggestingthat the light component has the break point at lower energy
than the knee. (2) The fraction of the light component to the
all-particles is less than 30 % which tells that the main component responsible for the knee structure is heavier than helium.
The features of the energy spectrum and primary mass composition obtained by Tibet experiment can be interpreted by
two scenarios of the origin of cosmic rays.
Model A : Sharp knee is caused by extra component fromnearby source(s) as first pointed out by single source model.
Figure 4 shows that the sharp knee of the all-particle spectrum
can be reproduced by adding extra component around the kneeover the global component which can be calculated as diffusive cosmic rays originating from multiple sources. The energy spectrum of the extra component can be approximated by∝ E −2 exp(−E/4PeV), which is close to the source spectrum
expected from diffusive shock acceleration (DSA) mechanismof cosmic rays. A possible explanation of such extra component together with the knee composition is to assume nearby
source(s) dominated by heavy elements such as type Ia SNRsor pulsars.
Model B : The knee is due to the characteristics of the DSA
mechanism in which nonlinear effect plays an important role
resulting in hard source spectrum of cosmic rays near acceleration limit energy. Figure 5 shows the primary mass composition calculated by nonlinear model in which it is assumed
that heavy elements are more efficiently accelerated than lightelements
This model predicts the rigidity-dependent hardening of
the energy spectrum before the knee and heavy elements dominate at the knee and beyond. Recent direct observations of
ATIC and CREAM reported hardening of the energy spectrumin 1012 − 1014 eV region and model B seems to be favorable toaccount for these data. It is also possible that both of models
A and B contribute to the structure of the knee.
The second topic is related to cosmic-ray anisotropy.
Past cosmic-ray experiments that observed cosmic-ray
anisotropy in the sidereal time frame consistently reported that

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1018

Fig. 5. Model B:Nonlinear effect in the DSA mechanism can explain the structure of the knee when high acceleration efficiency
for heavy elements is assumed.

in the anisotropy there are two distinct broad structures with
an amplitude of ∼0.1%; one is a deficit in the cosmic-ray flux
called “loss-cone”, distributed around 150◦ to 240◦ in Right
Ascension, and the other an excess called “tail-in”, distributed
around 40◦ to 90◦ in Right Ascension. Recent undergroundmuon and air-shower experiments are studying the anisotropy
in great detail at multi-TeV energies. It is considered that theanisotropy of galactic cosmic rays at TeV energies reflects the
structure of the local interstellar magnetic field surrounding
the heliosphere, since the trajectories of charged cosmic rays
are deflected and disturbed by the local interstellar magnetic
field while they are traveling through the interstellar medium.
The air-shower events collected during the period from
November 1999 through December 2008 (1916 live days)
are used for analysis. After our standard data selections,
4.5×1010 events are left with a modal energy of 7 TeV.
The main systematic error to be accounted for is the amplitude of the anisotropy observed in the anti-sidereal time frame(364.2422 cycles/yr), because a possible seasonal change ofthe solar daily variation due to solar activities might produce a spurious variation in the sidereal time frame, which
can be estimated by the daily variation observed in the antisidereal time frame. The root mean square of the anti-sidereal
anisotropy in each declination band is calculated and added
to the statistical error for the sidereal anisotropy in the corresponding declination band. Shown in Fig.1(a) is the relative
intensity map obtained in 5◦ × 5◦ pixels, which we model interms of two components as:
GA
MAIn,m = In,m
+ In,m,(2)

GA and I MA , respectively, denote the intensities of thewhere In,mn,mGlobal Anisotropy (GA) and the Midscale Anisotropy (MA)of the (n, m) pixel in the equatorial coordinate system. The
GA is written as the combination of a uniGA component In,mdirectional flow (UDF) and a bi-directional flow (BDF):
GA
In,m= a1⊥ cos χ1 (n, m : α1 , δ1 )+a1k cos χ2 (n, m : α2 , δ2 )+ a2k cos2 χ2 (n, m : α2 , δ2 ).

(3)

In Eq.(3), the orientation (α2 , δ2 ) denotes the reference axisof the BDF, and a2k the amplitude of the BDF. The UDF is
decomposed into two; one that is parallel to the BDF and has
an amplitude of a1k , and the other that is perpendicular to the
BDF, parallel to the axis (α1 , δ1 ), and has an amplitude of a1⊥ .
The χ1 denotes the angular distance of the center of the (n, m)
pixel measured from the reference axis ( α1 , δ1 ), and the χ2
denotes that measured from the axis (α2 , δ2 ). Fig.6(b) shows
the anisotropy map reproduced by attempting to fit Fig.6(a)GA alone. Although Fig.6(b) successfully reproduces
with In,m
the global “tail-in” and “loss-cone” structures, there remains
MA ,the midscale anisotropy as can be seen in Fig.6(c). The In,mincorporated to model the residual midscale anisotropy, is expressed as:(!
(φn,m − Φ)2MAIn,m = b1 exp −
+
2σφ2
!)
!
2
θn,m
(φn,m + Φ)2
exp − 2 ,(4)b2 exp −2σφ22σθwhere b1 and b2 denote the amplitudes of the two excesses
along the best-fit plane with the heliotail direction on it, bothof which are symmetrically centered away from the heliotail
direction by an angle Φ along the plane. The σφ and σθ denote the widths of the excesses parallel and perpendicular tothe best-fit plane, respectively. The φn,m and θn,m denote the“longitude” of the center of the (n, m) pixel measured from theheliotail direction and its “latitude” measured from the bestfit plane, respectively. Fig.6(e) and (f) show the reproduced
anisotropy and the residual anisotropy when we fit Fig.6(a)GA + I MA . The I MA extracted from Fig.6(e) is shown inwith In,mn,mn,mFig.6(d). Note that the obtained best-fit plane along which the
MA is assumed is fairly consistent with the Hydrogen Deflection Plane (HDP) suggested by Gurnett et al. which contains
the directions of the interstellar wind velocity and the interstellar magnetic field upstream the helionose; the angle difference between the direction normal to our best-fit plane andthat to Gurnett’s HDP is only 2.1◦ . The best-fit parameters inEq.(3) and Eq.(4) are listed in Table 1.
The GA can be interpreted as follows (for details. The
local interstellar space of scale ∼2 pc surrounding the heliosphere would be responsible for the GA. The BDF is produced by cosmic rays drifting parallel to the Local Interstellar
Magnetic Field (LISMF) line into the heliosphere from outside the Local Interstellar Cloud surrounding the heliosphere.
The UDF, perpendicular to the LISMF (a1⊥ ≫ a1k ) with anamplitude comparable to that of the BDF (a1⊥ ≃ a2k ), can beproduced by a diamagnetic drift arising from a spatial density
gradient (∇n/n) of galactic cosmic rays in the LISMF.
A sketch of a possible mechanism for the MA is shown in
Fig.7(a). During the period of the data we analyzed, the orientation of the magnetic field in the heliotail Bhelio is directed
toward (away from) the Sun in the northern (southern) hemisphere. Suppose, for simplicity, that the Bhelio surrounding
the solar system is uniform within the spatial scale L toward
the heliotail direction. Then the uniform Bhelio bends the trajectories of cosmic rays propagating along the HDP from theheliotail direction, leading them to the solar system. A simple

29

geometrical consideration gives the following relation:
L [AU](5)

where RL is the Larmor radius of cosmic rays with energy
E in Bhelio . This equation implies that sin Φ ∝ 1/E if L isindependent of energy. The observed energy dependence ofsin Φ, shown in Fig.7(b), gives the following function:sin Φ = (0.68 ± 0.04) (E/10 [TeV])−0.20±0.08,(6)suggesting L ∝ E 0.8 . This energy dependence of L might result
from actual complex spatial structures of Bhelio . These structures could be identified in the future by studies on the cosmicray transport in Bhelio by means of Magneto-Hydrodynamic
simulations. Substituting Eq.(6) into Eq.(5) and assuming
Bhelio = 10µ G, the following equation holds:
L [AU] = (140 ± 8) (E/10 [TeV])0.80±0.08,

heliotail(a)= RL [AU] sin Φ= 206(E [TeV]/Bhelio [µ G]) sin Φ,

Galactic Plane

Galactic Plane(7)

Eq.(7) implies that in the energy range of 4−30 TeV Bhelio
within ∼70 AU to ∼340 AU from the Sun is responsible for
the MA. The MA being placed along the HDP suggests thatit possibly originates from the modulation of galactic cosmic
rays in Bhelio . Another candidate for the heliospheric signature could be the excess region first reported as the “hot-spot”
by the Milagro experiment. This region corresponds to the
pixel in Fig.6(a) centered at (72.5◦, 17.5◦), close to the heliotail, observed with the highest significance 9.06σ among all
the pixels. The excess region is so collimated that it is difficult to construe it as a cosmic-ray inflow along the neutral
sheet that separates Bhelio between the northern and southernhemispheres. The Milagro experiment reported that the “hotspot” has a localized spatial extension with a half-width of
2.6◦ ± 0.3◦ and a half-length of 7.6◦ ± 1.1◦. It should be noted
here that the size of such a small-scale structure is greatly
susceptible to the size and shape of the analysis window forbackground estimation to subtract the large-scale anisotropy
superposed on the structure.

Other Activities
This group has developed and completed several automatic measuring systems that are powerful for analyzing cosmic ray tracks or air shower spots, that is, automatic microdensitometers, precise coordinate-measuring systems andimage scanners controlled by a computer. Enormous data
recorded on nuclear emulsion plates or X-ray films are rapidly
and precisely measured by the use of these measuring systems.
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 µ m thickness each. In this way, these facilities are open to
all the qualified scientists who want to carry out joint research
program successfully.

F B

H

(b)

F B

H

F B

H

F B

H

(d)

(e)
Lallement’s HDP

F BHGurnett’s HDP

(c)

(f)

Fig. 6. Two-dimensional anisotropy maps of galactic cosmic rays observed and reproduced at the modal energy of 7 TeV. Each panel
shows the relative intensity map or the significance map in 5◦ × 5◦
pixels in the equatorial coordinate system.
obs ), (b): the best-fit Global(a): the observed cosmic-ray intensity (In,mGA ), (c): the significance map of theAnisotropy (GA) component (In,mGA from I obs , (d): the best–
residual anisotropy after subtracting In,mn,mMA ), (e): the best-fit
fit Midscale Anisotropy (MA) component (In,m
GA + I MA ), and (f): the significance map of
GA+MA components (In,mn,mGA + I MA from I obs .
the residual anisotropy after subtracting In,mn,mn,mThe solid black curves represent the galactic plane. The dashedblack curves represent the Hydrogen Deflection Plane reported by
Gurnett et al. and Lallement et al. The heliotail direction (α , δ )= (75.9◦ , 17.4◦ ) is indicated by the black filled circle. The open
cross and the inverted star with the attached characters “F” and“H” represent the orientation of the local interstellar magnetic field(LISMF) by Frisch and by Heerikhuisen et al., respectively. The
open triangle with “B” indicates the orientation of the best-fit bi-directional cosmic-ray flow (BDF) obtained in this analysis.

Future Plans(1) Gamma-ray astronomy in the 100 TeV region
We have a plan 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. 8, has the world-best
sensitivity in the 100 TeV region, superior to HESS above 1020 TeV and to CTA above 30-40 TeV.
Then, how many unknown/known sources do we expect
to detect by Tibet AS + MD, assuming the energy spectraof the gamma-ray sources extend up to the 100 TeV region?
Eleven of the HESS new 14 sources discovered by the galactic plane survey in the southern sky would be detected by Tibet AS + MD, if it were located at the HESS site. As no extensive search has been done by an apparatus with sensitivity
comparable to HESS (1 % in unit of RX J1713.7-3946/50hour observation) in the northern sky, we expect to discoversome 10 new gamma-ray sources in the northern sky. In ad-

30
Table 1. Best-fit parameters in Eq.(3) and Eq.(4) for the 2D galactic-cosmic-ray anisotropy map observed at 7 TeV.

a1⊥ (%)
0.139 ± 0.002

a1k (%)
0.007 ± 0.002
b1 (%)
0.154 ± 0.018

Global Anisotropy (GA)a2k (%)
α1 (◦ )
δ1 (◦ )
0.131 ± 0.004 33.3 ± 1.1 38.4 ± 1.2
Midscale Anisotropy (MA)b2 (%)
σφ (◦ )σθ (◦ )
0.092 ± 0.006 24.5 ± 1.1 10.7 ± 0.8

α2 (◦ )
279.9 ± 0.9

δ2 (◦ )
−26.7± 2.0

Φ (◦ )
49.2 ±1.4(b)(a)
Fig. 7. (a): a possible mechanism for the Midscale Anisotropy. (b): the observed energy dependence of sinΦ.

dition to unknown point-like sources, we expect to detect established sources in the 100 TeV region: TeV J2032+4130,
HESS J1837-069, Crab, some new Milagro sources, Mrk421,
Mrk501 are sufficiently detectable and Cas A, HESS J1834087,LS I+63 303, IC443 and M87 are marginal.
Furthermore, our integral flux sensitivity to diffuse
gamma rays will be the world-best as well. The diffuse
gamma rays from the Cygnus region reported by the Milagrogroup and also diffuse gamma-rays from the galactic plane
will be clearly detected. Diffuse gamma-rays of extragalactic
origin may be an interesting target as well.
In fall, 2007, a prototype underground muon detector,
composed of two 52m2 water pools, was successfully constructed in Tibet to demonstrate the technical feasibility, costestimate, validity of our Monte Carlo simulation. Preliminary
analysis indicates that our MC simulation reproduces real dataquite reasonably.
In 2010, construction of roughly one-third of the full-scale
MD started and the concrete-based water pools were successfully completed, as in Fig. 9. The data-taking of the Tibet III
and the partial MD will is scheduled in 2011.
(2) Chemical composition of primary cosmic rays making the knee in the all-particle energy spectrum
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 nuclei

Fig. 8. Tibet AS + MD (red curve) integral flux sensitivity (5σ or 10
events/1yr) for a point source.

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 air shower core detector array(1000 to 5000 m2 in area) around the center of Tibet III to distinguish the heavy component making the knee by measuring
the difference in lateral distribution of energetic air shower
cores. This will be the first experiment to selectively measure
the energy spectrum of the heavy component in the knee en-31Japan; Max-Planck Institute foer Physik, Munich, Germany;
Shonan Inst. of Technology, Fujisawa, Japan; RIKEN, Wako,
Japan; School of General Education, Shinshu Univ. Matsumoto, Japan; Nihon University, Narashino, Japan; Institute of Disaster Prevention Science and Technology, Yanjiao,
China.

Bibliography
Papers in refereed journals[1] “Observation of TeV Gamma Rays from the Fermi
Bright Galactic Sources with the Tibet Air Shower Array”, M. Amenomori et al., ApJ 709 L6–L10, (2010).
Fig. 9. Construction scene of underground muon detectors in 2010.

[2] “On Temporal Variations of the Multi-TeV Cosmic Ray
Anisotropy Using the Tibet III Air Shower Array”, M.
Amenomori et al., ApJ, 711 119–124, (2010).
[3] “Cosmic-ray energy spectrum around the knee observedwith the Tibet air-shower experiment”, M. Amenomori
et al., Astrophysics and Space Sciences Transactions, 7
15–20, (2011).
Papers in conference proceedings[4] “Heliospheric signatures seen in the sidereal anisotropyof high-energy galactic cosmic ray intensity”, M.
Amenomori et al., AIP Conf. Proc., 1302 285–290,(2010).

Fig. 10. Expected cosmic-ray iron energy spectra with Tibet AS +YAC.

ergy region and will demonstrate that the knee of the all particle energy spectrum is really composed of heavy nuclei. Figure 10 shows the expected energy spectra of cosmic-ray ironnuclei depending on theoretical models. Tibet AS + YAC has
a strong model discrimination power. Sixteen YAC detectors
were set up at Yangbajing in 2009 and preliminary analysis isunder way.

Tibet ASγ collaboration
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of:Hirosaki Univ., Hirosaki, Japan; Saitama Univ., Urawa, Japan;
IHEP, Beijing, China; Yokohama National Univ., Yokohama,Japan; Hebei Normal Univ., Shijiazhuang, China; Tibet Univ.,
Lhasa, China; Shandong Univ., Jinan, China; South West Jiaotong Univ. Chengdu, China; Yunnan Univ., Kunming, China;
Kanagawa Univ., Yokohama, Japan; Faculty of Education, Utsunomiya Univ., Utsunomiya, Japan; ICRR, Univ. of Tokyo,
Kashiwa, Japan; Konan Univ., Kobe, Japan; Department of
Physics, Shinshu Univ., Matsumoto, Japan; Center of Space
Science and Application Research, Beijing, China; Tsinghua
Univ., Beijing, China; Waseda Univ., Tokyo, Japan; NII,
Tokyo, Japan; Sakushin Kakuin Univ., Utsunomiya, Japan;
Tokyo Metropolitan Coll. of Industrial Technology, Tokyo,

The Ashra Project[Spokesperson: Makoto Sasaki]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of:
ICRR, University of Tokyo, Kashiwa, Japan; Toho University, Funabashi, Japan; University of Hawaii at Manoa, Honolulu, USA; University of Hawaii at Hilo, Hilo, USA; Nagoya
University, Nagoya, Japan; Kanagawa University, Yokohama,Japan
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 [5] and CMOS technology. The project primarily aims to observe Cherenkov and fluorescence lights fromthe lateral and longitudinal developments of very-high-energy(VHE) cosmic-ray air showers in the atmosphere. It can also
be used to monitor optical transients in the wide field of sky.
The observatory will firstly consist 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 was constructed on
Mauna Loa (3,300 m) on Hawaii Island in 2007.
We started observation of optical transients and commissioning observation of VHE tau neutrinos with some of

32

the light collectors in 2008. By analyzing the accumulated
data from optical observations, we have already searched forearly optical emissions in the field of GRB081203A [6] andGRB100906A [7] around the Swift/BAT-triggered GRB time.
Furthermore, we reported [8] the first observational search for
tau neutrinos (ντ ) from gamma-ray bursts (GRBs) using thelight collector facing Mauna Kea. The earth-skimming ντtechnique of imaging Cherenkov τ showers was applied as adetection method in this search. We set stringent upper limits
on the ντ fluence in PeV–EeV region for 3780 s (between 2.83
and 1.78 hr before) and another 3780 s (between 21.2 and 22.2
hr after) surrounding the Swift trigger time of GRB081203A.
This first search for PeV–EeV ντ complements other experiments in energy range and detection method, and implies theprologue of “multi-particle astronomy” [9] with a precise determination of time and location.
Project
The observatory will firstly consist 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 features of the system werestudied with a prototype detector unit located on Haleakala.
The main station was constructed on Mauna Loa (3,300 m) in
2007.
The key technical feature of the Ashra detector rests on
the use of electrostatic lenses to generate convergent beams
rather than optical lens systems. This enables us to realize ahigh resolution over a wide field of view. This electron optics
requires:

EeV cosmic rays; For fluorescence lights from VHE cosmic
rays the effective light gathering efficiency is comparablewith that of the High Resolution Fly’s Eye detector (HiRes).
The arcmin pixel resolution of Ashra provides finer imagesof longitudinal development profiles of EeV cosmic ray(EeV-CR) air showers. The resolution of arrival direction
with the stereo reconstruction is thus significantly improved
and it is better than one arcmin for the primary energy of EeV
and higher [10]. This is useful to investigate events clusteredaround the galactic and/or extragalactic sources. This in turnwould give us information as to the strength and coherence
properties of the magnetic field.
PeV-EeV neutrinos; Ashra may detect Cherenkov and/or
fluorescence signals generated from tau-particle induced
air-showers that is generated from interactions of tau neutrinos with the mountain and/or the earth. This is identified
by peculiar geometry of the air-shower axis. The 1-year
detection sensitivity with the full configuration of Ashra
is 5 and 2 times larger than the Waxman-Bahcall limit for
mountain-produced event (Cherenkov) and earth-skimming
event (fluorescence), respectively. The most sensitive energyof around 100 PeV is suitable for the GZK neutrino detection.
The expected performance for each observational object
is summarized in Table 1. An example of a 42-degree FOV
image taken by the Ashra light collector is shown in Figure 1.

• image pipeline; the image transportation from imaging
tube (image intensifier) to a trigger device and image
sensors of fine pixels (CCD+CMOS), with high gain
and resolution, and• parallel self-trigger: the systems that trigger separately
for atmospheric Cherenkov and fluorescence lights.
Observational Objectives
optical transients; Ashra will acquire optical image every 6s after 4-s exposure. 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 B ≃ 13
mag, for which we expect 3-σ signals. The unique advantage
is the on-time detection of the events without resorting tousual satellite alerts. 10∼20 events per year are expected incoincidence with the Swift gamma-ray events. The field ofview that is wider than satellite instruments allows to detect
more optical transients, including an interesting possibility
for an optical flash, not visible with gamma rays.
TeV gamma rays; Atmospheric Cherenkov radiation will be
imaged by Ashra. Requiring the signal-to-noise ratio (SNR)>5, the system will allow to explore VHE gamma-ray sources
with the energy threshold of several TeV at the limiting flux
sensitivity of 5% Crab for 1-year observation.

Fig. 1. Example of a 42-degree FOV image taken by the Ashra lightcollector. The solid lines are drawn to indicate constellations.

Site Preparation
After finishing the grading work for the area of 2,419 m 2
at the Mauna Loa site at the end of July 2005, installationof electrical power lines and transformers was performed until the beginning of September. We started the constructionof the detector in October 2005 after receiving materials from

33

Opt. Transients
B-UV
λ =300∼420nm
15 mag./4s @3σ
2 arcmin

TeV-γ
Cherenkov
several TeV
5% Crab/1yr@5σ
6 arcminMountain-νCherenkov
a few 100 TeV
5 WB-limit/1yr
unknown

Earth-skimming-ν
Fluorescencea few 10 PeV
2 WB-limit/1yr
3 arcmin @ 100 PeV

EeV-CR
Fluorescencea few 100 PeV
1600/1yr >10 EeV
1 arcmin @ 10 EeV

Table 1. Summary of performance with the full configuration (Ashra-2) of three Ashra sites. Detected light, energy threshold, sensitivity limit,
and angular resolution are listed from top down for each objective. For EeV-CRs, trigger requirement is two or more stations. Waxman
and Bahcall have calculated a neutrino flux upper limit from astrophysical transparent source, here referred to as the WB-limit. For theobservation time for objectives other than optical transients, the realistic detection efficiency is taken into account.

The civil engineering construction of light collectors inshelters at the Mauna Loa site was completed in August 2007.
Figure 2 shows a picture of the constructed Mauna Loa stations. In this Ashra-1 experiment, we are performing device
installation and specific observation in a step-by-step way toenhance the scientific impacts.

We have accumulated more than 3500 hours of observation
time in two years of observation. Good weather rate of 94%
shows the superiority of our site and operation efficiency of
99% demonstrates the stability of our operation, where good
weather rate is defined by observable time divided by maximum observation time and operation efficiency is defined byobserved time divided by observable time.
Ashra Observation
Accumulated Observation Time [hr]Japan. By the middle of December 2005, the first shelters having motorized rolling doors, acrylic plate windows to maintain
air-tightness, and heat-insulating walls and floors have been
constructed and positioned on eight construction piers of concrete blocks at the Mauna Loa site. In the shelters, the opticalelements of the light collectors have been already installed.
The optical performance were checked and adjusted to be optimum with star light images from the pilot observation.
In December 2005, we evaluated the night sky background flux on Mauna Loa using the Ashra light collector
installed and aligned in a shelter. The result is fairly consistent
with the background in La Palma and Namibia by the HESS
group From the star light observations, our understanding of
the light correction efficiency to be accurate within 5% level.

4500

Duty Factor 19.2% (in total 765 days)

4000
3500
3000
2500
2000

S012
S011
S010
S009
S008
S007
1000
S006
S005
S004
500
S003
S002
S001

S025
S024
S023
S022
S021
S020
S019
S018
S017
S016
S015
S014
S013

1500

Maximum Observable Time 3766.2 hr
Observable Time3546.0 hr ( 94.2%)

Observed Time

3526.5 hr ( 99.5%)0080702 081001 090101 090402 090702 091002 100101 100402 100702 101002

Date [yymmdd]

Fig. 3. Summary of Ashra optical transient observation time.

Fig. 2. The Ashra main and sub stations at the Mauna Loa site.

Observation
As a first step, we have started the observation of optical transients. During observation, Optical images were constantly collected every 6 s after 4-s exposure. Figure 3 summarizes our observation statistics up to now. Maximum observable time is defined by the following condition:• Sun condition; the altitude of the sun must be lower than
−18 degree.
• Moon condition; the altitude of the moon is lower than
0 degree, or the moon fraction is less than 0.2.

GRB100906A: Ashra-1 observation of early opticalemission [7]Our wide field observation covered the Swift-BAT error
circle at the time of GRB100906A. We searched for optical emission in the field of GRB100906A around the BATtriggered GRB time (T0) with one of the light collector units
in the Ashra-1 detector. The Ashra-1 light collector unit usedin this analysis has the achieved resolution of a few arcmin,viewing 42 degree circle region of which center is located at
Alt = 60 deg, Azi = 0 deg.
We quickly analyzed 200 images covering the field of
GRB100906A every 6s with 4s exposure time respectively
during the observation between T0-600s and T0+600s. We
detected no new optical object within the PSF resolution
around the GRB100906A determined by Swift-UVOT. As aresult of our preliminary analysis, the 3-sigma limiting magnitudes were estimated in comparison with stars in Tycho2 Catalog to be distributed between 12.0 and 12.2. Figureof limiting optical magnitudes vs time comparing with othermeasurements is shown in Fig.4.

34with other experiments using photomultiplier arrays at the focal surface. Figure 5 shows a photograph of a 20-inch PLI.
The design and performance of the 20-in. PLI in Ref. [5].

Fig. 4. Summarized lightcurve for GRB100906A around the trigger
time. 3-sigma limiting magnitudes of our observation (labeled as
Ashra-1) and other observations are compared as a function oftime since GRB. The horizontal axis is in linear scale to show thelimiting magnitudes in the precursor phase.

Performance of a 20-in. photoelectric lens image intensifier tube [5]Fig. 5. A photograph of a 20-inch photoelectric lens image intensifiertube (PLI) [5].

We have evaluated a 20-in. photoelectric lens image intensifier tube (PLI) to be mounted on the spherical focal surfaceof the Ashra light collectors. The PLI, the worlds largest image intensifier, has a very large effective photocathode area of
20-in. diameter and reduces an image size to less than 1-in.
diameter using the electric lens effect. This enables us to use
a solid-state imager to take focal surface images in the Ashra
light collector. Thus, PLI is a key technology for the Ashra
experiment to realize a much lower pixel cost in comparison

Observational search for PeV–EeV tau neutrino from
GRB081203A [8]First physics publication [8] from the Ashra-1 experiment was achieved by PeV–EeV tau neutrino search from
GRB081203A. Here, we summarized our first published result.
The GRB standard model [11], which is based on internal/external shock acceleration, has been used to describe thegeneral features of a GRB and the observed multi-wavelength
afterglow. However, the standard model cannot well reproduce the complicated time evolution of GRBs and the highenergy components in the prompt emission [12, 13, 14]. Although many authors have proposed theoretical models to reproduce these features, none of them are conclusive [15]. To
better understand the ambiguous mechanisms of GRBs, observational probes of the optically thick region of the electromagnetic components, as well as hadron acceleration processes
throughout the precursor, prompt, and afterglow phases are
required. VHE ν s can be used as direct observational probes,
which are effective even in optically thick regions. A monitor
search with sufficient time and spatial resolution and survey
capability for VHEν s associated with GRBs is plausible.
The earth-skimming tau neutrino (ντ ) technique [16],which detects extensive air showers, has the advantage of alarge target mass, since it uses air showers produced by decay particles of tau leptons (τ s) in the atmosphere as the observed signals. τ s emerge out of the side of the mountainor the ground facing the detector; they are the product ofinteractions between VHE ντ and the earth matter they traverse. No air Cherenkov observation was made to date basedon the earth-skimming ντ technique with air showers inducedby τ decays (hereafter referred to as the Cherenkov τ shower
method). However, it can achieve sufficient detection sensitivity in the PeV–EeV region to be useful in the search for ν soriginating from hadrons accelerated to EeV at astronomical
objects. 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 ν s in the PeV–EeV energy range.
As shown in Fig. 6, one of the Ashra light collectors built
on Mauna Loa has two geometrical advantages: (1) it faces
Mauna Kea, allowing it to encompass the large target massof Mauna Kea in the observational FOV, (2) it has an appropriate distance of ∼30 km from Mauna Kea, yielding good
observational efficiency when imaging air-shower Cherenkov
lights which are directional with respect to the air-shower axis.
Using the advanced features, we performed commissioning
search for Cherenkov τ showers for 197.1 hr between Octoberand December of 2008. We served limited 62 channels of photomultiplier tubes (PMTs) as trigger sensors prepared for thecommissioning runs to cover the view of the surface area of
Mauna Kea, maximizing the trigger efficiency for Cherenkov
τ showers from Monte Carlo (MC) study. Adjacent-two logic
was adopted to trigger the fine imaging, by judging discrim-

35

Fig. 6. Conceptual drawing of Cherenkov τ shower method. The right
mountain is Mauna Kea and the left is Mauna Loa.

inated waveform signals from each pixel of the multi-PMT
trigger sensor. During the search period, ∼2 hr before thetrigger of GRB081203A. GRB counterpart (R.A. 15:32:07.58,
decl. +63:31:14.9) passed behind Mauna Kea, as viewed fromthe Ashra-1 observatory.
To investigate the features, selection criteria, detection efficiency, and background rate for the observation of
Cherenkov τ shower images, intensive Monte Carlo (MC)studies were performed by utilizing CORSIKA, TAUOLA,
and other relevant MC packages. The photometric and trigger
sensitivity calibration of the Ashra light collector was basedon a very stable YAP-light pulser. Non-uniformity in the detector gain due to the input light position was relatively corrected by mounting a spherical plate uniformly covered withluminous paint on the input window. To correct for the time
variation of the photometric and trigger sensitivity becauseof variations in atmospheric optical thickness, we performed
careful cross-calibration to compare the instrumental photoelectric response with the photometry of standard stars suchas BD+75D325 of B-magnitude 9.2, for which the detected
images passed through the same optical and photoelectric instruments except for the final trigger-controlled readout device.
To confirm the detection sensitivity and gain calibration
for the Cherenkov τ shower, we detected and analyzed 140
events of normal cosmic-ray air-shower Cherenkov images fora total of 44.4 hr in 2008 December using the same instruments used in neutrino observation, but after rearranging thetrigger pixel layout to view the sky field above Mauna Kea. In
the cosmic-ray observation, the trigger pixel layout is centeredat zenith angle of ∼65◦. The observed and MC cosmic-ray
flux spectra are shown in Fig. 7, in which the MC predictionused the typically observed cosmic-ray flux in the knee region [17, 18]. Since the primary cosmic-ray components areobservationally undefined, we present the MC prediction ofcosmic-ray flux spectra, assuming either only protons or irons
as the primary cosmic rays in Fig. 7. Note that the same reconstruction procedure was applied to both of the observedand MC data to extract the observed energy. In both cases,
the observed data and the MC prediction agreed well on thenormalization and the shape of the distribution within the expected errors. The estimation of the detection sensitivity of
the Ashra light collector and the validity of the reconstruction
procedure were well demonstrated.
For the ντ search, we used image data acquired using
the trigger for 197.1 hr in only case of the data status defined as good out of the total observation time of 215.8 hr.
Detailed data analysis yielded a null ντ candidate [8]. Ef-

fective areas for Cherenkov τ showers induced by ντ s fromthe GRB081203A counterpart with changing ντ energy (Eντ )were obtained from an MC study that assumed seven original positions on the GRB counterpart trajectory. On the basisof the above null result and the estimated effective areas, weplaced 90% confidence level (CL) upper limits on the ντ fluence of precursor and afterglow emissions in the PeV–EeV
region, for two 3780 s periods, the first between 2.83 and1.78 hr before GRB081203A and the second between 21.2
and 22.2 hr after it, as shown in Fig. 8. As sources of systematic uncertainty in the MC estimates of the effective detection
areas, we considered the ντ charged current interaction crosssection, the energy loss by τ in the earth and the mountain,
the geological model around the observation site, and the gain
calibration of the light collector, which were evaluated to be
50%, 50%, 10%, and 30%, respectively. The conservatively
combined systematic sensitivity error was obtained from thesquare sum of the above uncertainties as 77%, which affects
the result of the 90% CL upper limit shown in Fig. 8, where
we assumed a typical Eν−2 flux to ensure unbiased constraints
on observationally undefined physical mechanisms of a GRB.
For comparison, Fig. 8 shows other observational limits
on the ν fluence from point sources [19, 20]. Our results
are the most stringent in the PeV–EeV region and complementary to the IceCube results for the sub-PeV energy region, and indicate the advanced instantaneous sensitivity ofthe system even during this commissioning phase. Full-scale
Ashra observations are expected to have 100 times better sensitivity, since the trigger pixel size is halved (1/4 the pixelarea) and the trigger sensor will cover the entire FOV of thelight collector. With this higher sensitivity, contamination of
0.55 clusters of air-shower secondary particles is expected in
one year of observation data. The advanced angular determination of Ashra for Cherenkov τ showers to within 0◦.1 willallow perfect rejection against contamination from air-shower
secondary particles, and will provide a viable search method
for earth-skimming ντ events, fully utilizing the zero background conditions. Our first search for PeV–EeV ντ reported
in Ref. [8] complements other experiments in energy range
and detection method, and implies the prologue of “multiparticle astronomy” [9] with a precise determination of timeand location.

Bibliography[1] http://www.icrr.u-tokyo.ac.jp/∼ashra[2] M. Sasaki, J. Phys. Soc. Japan 77SB, 83 (2008).
[3] Y. Aita et al., in Proc. of 30th ICRC (Mexico, 2007),Vol. 3, p. 1405 (2008).
[4] M. Sasaki et al., in Proc. of 30th ICRC (Mexico, 2007),Vol. 3, p. 1559 (2008).
[5] Y. Asaoka and M. Sasaki, Nucl. Instrum. Methods Phys.
Res. A 647, 34 (2011).
[6] Y. Aita et al., GCN Circ., 8632 (2008).
[7] Y. Asaoka et al., GCN Circ., 11291 (2010).

Number of Events

36
2

10

Data
Proton MC
Iron MC

10

1

-1

10

1

3

2

10

10

4

10

10

Observed Energy [PeV]
Observed
Energy [PeV]11

10

Ashra limit on ν τ from GRB081203A
IceCube limit on prompt ν µ
IceCube limit on precursor ν µ

10

10

9

10

107
6

10

Rice limit on prompt ν e
Rice limit on afterglow ν e

8

10

5

10

104

7

10

3

10
6

10

102

E2 × flux [GeV m-2 s-1 ]E2 × fluence [GeV m-2 ]Fig. 7. Observed cosmic-ray flux spectrum (filled box) with bars indicating statistical and systematic errors and the MC predictions for proton
primary (hatched band) and iron primary (shaded band) assumptions [8]. The width of the bands shows the evaluated systematic error of
30% of the MC prediction.

5

10

10
104
1
3

10

10-2

10-1
10-1

1

10

102

3

10

104

Eν [PeV]Fig. 8. Ashra 90% CL limit (thick continuous line (red)) on ντ fluence of precursor and afterglow emissions from the GRB081203A counterpart
in the PeV–EeV region [8]. For comparison, IceCube limits [19] in the prompt (long dashed dotted (gray)) and precursor (long dashed dotted(blue)) phases and RICE limits [20] in the prompt (dashed (green)) and afterglow (dashed dotted (magenta)) phases are shown. The energy
ranges were defined as containing 90%, 90%, and 80% of the expected signals from assumed spectrum for Ashra, IceCube, and RICE,
respectively.

[8] Y. Aita et al., ApJL 736, L12 (2011).

[16] D. Fargion, ApJ 570, 909 (2002).

[9] M. Sasaki, in Proc. ICRR2000 Satellite Symposium:
Workshop of Comprehensive Study of the High Energy
Universe, p. 110 (2000).

[17] T. Antoni et al., Astropart. Phys. 24, 1 (2005).

[10] M. Sasaki, A. Kusaka and Y. Asaoka, Nucl. Instrum.
Methods Phys. Res. A 492, 49 (2002).
[11] P. Mésźaros, Rep. Prog. Phys. 69, 2259 (2006), and references therein.
[12] J. A. Nousek et al., ApJ 642, 389 (2006).
[13] A. A. Abdo et al., ApJ 706, L138 (2009).
[14] M. De Pasquale et al., ApJL 709, L146 (2010).
[15] M. Ackermann et al., ApJ 716, 1178 (2010).

[18] M. Amenomori et al., ApJ 678, 1165 (2008).
[19] R. Abbasi et al., ApJ 710, 346 (2010).
[20] D. Besson, S. Razzaque, J. Adams, and P. Harris, Astropart. Phys. 26, 367 (2007).

High Energy Astrophysics Group[Spokesperson: T. Terasawa]
ICRR, Univ. of Tokyo, Kashiwa, 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

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Fig. 1. Particle acceleration in a sheared flow, Vz (y) = 0.3ctanh Ly(c: the velocity of light) with superposed time-dependent perturbations. The magnetic field is in the x direction. (a) An example ofthe particle trajectories in the y-z plane, where the spatial scale isnormalized by a characteristic gyro radius, c/Ωc (Ωc : the non-relativistic cyclotron frequency). (b) An example of the energy historyof accelerated particles.

nonthermal cosmic ray particles are being accelerated. Targets of the group’s study include high energy astrophysicalobjects such as supernova explosions/pulsar magnetospheres,
giant flares and repeating bursts of magnetars, jets from active
galactic nuclei (AGN), star-burst galaxies, mysterious gamma
ray bursts (GRB), as well as galaxy clusters. Research works
on the origin of ultra high energy cosmic rays (UHECRs) arealso within the coverage of the group.
In addition, studies have been made also for nonthermal
phenomena within the heliosphere [5,11], such as interplanetary shocks and the earth’s bow shock, magnetic reconnection, the interaction processes between the solar wind andthe moon. While these heliospheric phenomena are limitedin their energy coverage, their studies have proved to give atheoretical basis to interpret distant astrophysical high energy
phenomena.
Research topics: 1. Reevaluation of acceleration processes
While the diffusive shock acceleration process has been
accepted as the standard model of astrophysical particle acceleration, interests are being renewed on other processes suchas second-order stochastic acceleration in relativistic turbulences. We have presented new results on the stochastic acceleration in time-dependent velocity-shear turbulence [6] (Figure 1) expected in relativistic jets in AGNs and GRBs.
Research topics: 2. Magnetars and pulsars
The magnetosphere around neutron stars are candidate
sites for efficient particle acceleration. Magnetars, slowlyrotating neutron stars with strong magnetic field of 10 13−15
G, occasionally show giant-flare (GF) activities with peakgamma-ray luminosities reaching to 1047 erg s−1 [1], which
are as strong as the luminosities of AGNs. In addition to giant flares, magnetars also show burst activities, much weaker
than GFs but repeating many times. Recently we have discovered ionospheric disturbances caused by repeating bursts ofthe magnetar SGR J1550-5418 in January 2009. Such iono-

(e)

(f)

Fig. 2. (a) VLF (very low frequency) wave propagation path from the
NPM transmitter in Hawaii to the ATI observing station in Brazil.
The gray-shaded hemisphere indicates the nightside part of the
Earth at 6:48 UT on 22 January 2009, when the largest burst occurred. The part of the Earth illuminated by gamma rays fromthe magnetar SGR J1550-5418 is shaded by lines. (b) Amplitude
and phase variations of a VLF signal from the NPM transmitter(21.4kHz) observed at ATI from 5:15 UT to 5:20 UT, when repeated
SGR bursts were detected at 05:17:51.7 UT and 05:18:39.5 UT.
(c) The same as (b) but from 06:40 UT to 06:50 UT when repeated SGR bursts were detected at 06:41:02.1 UT, 06:44:36.4
UT, 06:45:13.9 UT, 06:47:57.1 UT, and 06:48:04.3 UT. (d) The
same as (b) but from 08:15 UT to 08:25 UT when a repeated
SGR burst was detected at 08:17:29.4 UT. (e) Relation between
observed amplitude changes of VLF signals (NPM-ATI) and gamma-ray fluences (25 keV to 2 MeV) measured by the INTEGRAL
satellite. (f) Same as (e) but for observed phase changes of the
VLF signals.

spheric disturbance can be used as a new monitoring method
for magnetars [4,10] (Figure 2).
Crab pulsar, the remnant of the supernova explosion in
1054 A.D., is one of the well-known neutron stars. Whileits physical properties have been studied for more than 40
years since its discovery, there remains an enigma about theorigin of giant radio pulses (GRPs). While for a long time
the GRPs had been regarded as a phenomenon limited to theradio frequency pulsar emission, a 3% enhancement of the
optical emission at the GRP timing was discovered recently(Shearer et al., Science, 2003). Since only a very loose upper limit (<250%) was obtained for the enhancement, if any,of the hard X-ray emission at the GRP timing (Lundgren etal., 1995), we have started a correlational study between theradio and hard X-ray observations collaborating with radio
and X-ray astronomers at National Institute of Information
and Communications Technology, Tokyo Institute of Technol-38Superposed epoch analysis
Radio
Intensity(arbitraryunit)

1 pulse before
GRPs

GRPs

1 pulse after
GRPs

Numberof X-ray
photons

Phase angle (0deg = peak of radio frequency main pulses)

Fig. 3. (a) upper panel: Superposed intensity profile of the radio signal from the Crab pulsar in the interval of ±1 pulse from the arrivalof the GRPs. (b) lower panel: A blue curve shows the averaged
X-ray intensity profile (SUZAKU/HXD, 15-75 keV) when the intensity of the radio pulses are normal (repeated 3 cycles). The redhistogram shows the superposed X-ray intensity profile in the interval of ±1 pulse from the arrival of the GRPs.

ogy, and Institute of Space and Astronautical Science in Japan
Aerospace Exploration Agency.
Figure 3 [7] shows the preliminary result of our analysis: The average photon count rates around the main-pulse
GRP peaks was 21.9±3.5 s−1 bin−1 while the average photon count rates at the same timing of normal radio pulses was
18.0±0.4 s−1 bin−1 . Therefore while a weak enhancement of
the photon count rates at the GRP peaks is seen, this is notstatistically significant. We are continuing this correlational
study to improve the photon statistics.
Research topics: 3. 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). Parallel tothe above R/D study, we have also joined a radar research
project for extraterrestrial grains (meteors) collaborating withradar physicists and planetary physicists at National Institutefor Polar Research, Research Institute for Sustainable Humanosphere in Kyoto University, and Department of Earth
Planetary Sciences in the University of Tokyo. Despite morethan three orders of magnitude difference in the echo duration between UHECR echoes (<∼ µ s, expected but not yet
identified) and meteor echoes (several - several tens of ms,
observed), the know-how developed in the latter project provides a technical basis for the former (Figure 4, Yoshida et al.,in preparation).

Fig. 4. A multi-static forward scattering radar system for the detection of extraterrestrial grains (meteors) was set over the Honshu
island of Japan during the July-August season in 2007. Threeamateur-radio beacon transmitters were at Sabae, Ikeda, andToyoshina (blue dots), while a receiver array consisting of six stations (red dots) was deployed around the Tokyo bay. The impact
geometry of an interplanetary grain at 19:04:50.5 JST (10:04:50.5
UT) on 31 July 2007 was successfully determined: It is found that
this meteor had a radiant point (RA, DEC)=(22.2 hour, -14.7 deg)with the input velocity=33.5 km/s, and impacted against the atmosphere at the point (138.7o E, 35.8o N) (a black arrow in the centerof the figure). Black-blue-yellow-red contours show the residual
errors in the least-square fitting procedure for the impact pointsearch. A blue hyperbola on the lower-right corner of the figure
shows the footprint of the meteor radio echo at the timing of its
first ground detection.

Research topics: 4. Interaction process between supersonic flow and solid objects
It is expected that the interactions between supersonicplasma flows and surfaces of solid bodies play important roles
in many astrophysical environments.
The nearest example found recently is in the solar-windmoon interaction [2,3,8,9], where detailed studies of kinetic
properties of plasmas can be made. Figure 5 [2, 9] shows
the time series data from SELENE, the Japanese lunar orbiter,
between 12:00 and 18:00 UT on 4 April 2008, showing quiet(# 1) and active (# 3) conditions of the wake in the near-Moon
space. From these observations, a new model of the nearMoon wake environment is proposed ([2], Figure 6), where
the electromagnetic acceleration of the solar wind particles
and the kinetic plasma instability (two stream instability) areplaying the dominant role.

Bibliography
Papers in refereed journals
1. Masada, Y., S. Nagataki, K. Shibata, and T. Terasawa,“Solar-type magnetic reconnection model for magnetar
giant flares”, Pub. Astron. Soc. Japan, 104, 1093-1102,
2010.
2. Nishino, M. N., M. Fujimoto, Y. Saito, S. Yokota, Y.
Kasahara, Y. Omura, Y. Goto, K. Hashimoto, A. Ku-

39Fig. 6. A new model of the near-Moon wake environment where theprotons of the solar wind origin scattered at the sunlit region of theMoon and accelerated by the -V×B electric field are penetrating
deeply into the middle of the wake region and forming the proton
governed region (PGR) [2]. Vectors in the figure, SW, E, and IMF,
show directions of the solar wind flow, the ambipolar electric field,
and the interplanetary magnetic field, respectively.

ThesisFig. 5. Energy-time spectra of (a) protons and (b) electrons, (c) magnetic field in the SSE (Selenocentric Solar Ecliptic) coordinate, (d)frequency-time spectrogram of the plasma wave detector, and (eand f) spacecraft locations in the SSE coordinates and solar zenith
angle (SZA) are shown [2]. Intervals of sunlit/shadow regions areindicated by orange/blue bars at the top of the figure, where thewake was observed within the shadow region.

mamoto, T. Ono, H. Tsunakawa, M. Matsushima, F.
Takahashi, H. Shibuya, H. Shimizu, and T. Terasawa,“Effect of the solar wind proton entry into the deepest lunar wake”, Geophys. Res. Lett., 37, L12106.1-4,
2010.
3. Saito, Y., S. Yokota, K. Asamura, T. Tanaka, M. N.
Nishino, T. Yamamoto, Y. Terasawa, M. Fujimoto, H.
Hasegawa, H. Hayakawa, M. Hirahara, T. Mukai, T.
Nagai, T. Nagatsuma, T. Nakagawa, M. Nakamura, K.I.
Oyama, E. Sagawa, S. Sasaki, K. Seki, I. Shinohara, T.
Terasawa, H. Tsunakawa, H. Shibuya, M. Matsushima,
H. Shimizu, F. Takahashi, “In-flight performance andinitial results of plasma energy angle and composition
experiment (PACE) on SELENE (Kaguya)”, Space Sci.
Rev., 154, 265-303, 2010.
4. Tanaka, Y. T., J.-P. Raulin, F. C. P. Bertoni, P. R. Fagundes, J. Chau, N. J. Schuch, M. Hayakawa, Y. Hobara, T.
Terasawa, and T. Takahashi, “First very low frequency
detection of short repeated bursts from magnetar SGR
J1550-5418”, Astrophys. J., 721, L24-L27, 2010.
Books
5. Terasawa, T., “Shocks in the heliosphere”, Chapter 12,
IAGA Special Sopron Book Series vol. 4, “The Sun, theSolar Wind, and the Heliosphere”, ed. by M. P. Miralles
and J. S. Almeida, Springer, 2011.

6. Fujinuma, A., “Acceleration of UHECR in relativistic
jets with velocity shear” (in Japanese), Master thesis,
Department of Physics, Tokyo Institute of Technology,
March 2011.
7. Nagata, K., “Study of giant radio pulses from the Crabpulsar” (in Japanese), Master thesis, Department of
Physics, Tokyo Institute of Technology, March 2011.
Conference papers
8. Nishino, M. N., X. Wang, M. Fujimoto, H. Tsunakawa,
Y. Saito, S. Yokota, W. Bian, C. Li, H. Shibuya, M. Matsushima, H. Shimizu, F. Takahashi, and T. Terasawa,“Anomalous deformation of the Earth’s bow shockin the lunar wake: Joint observations by Chang’E-1
and SELENE”, Proceedings of American GeophysicalUnion Fall meeting, Paper P54B-07, 2010.
9. Nishino, M. N., M. Fujimoto, Y. Saito, K. Yokota, Y.
Kasahara, Y. Omura, Y. Goto, K. Hashimoto, A. Kumamoto, T. Ono, H. Tsunakawa, M. Matsushima, F.
Takahashi, H. Shibuya, H. Shimizu, and T. Terasawa,“Effect of the solar-wind proton entry into the deepest
lunar wake”, Proceedings of EGU General Assembly,
vol. 5, EPSC2010-473, 2010.
10. Tanaka, Y, M. Hayakawa, T. Terasawa, T. Takahashi,“VLF detection of ionospheric disturbance caused by amagnetar giant gamma-ray flare”, Proceedings of 38th
COSPAR Scientific Assembly, C11-0172-10, 2010.
11. Terasawa, T., “Collisionless shock and particle acceleration” in the IAU symposium 274, “Advances in
Plasma Astrophysics”, 2010.

40

ASTROPHYSICS and GRAVITY DIVISION
Overview

LCGT Project

Astrophysics and Gravity Division consists of Gravitational Wave Group, The Sloan Digital Sky Survey Group,
Theory Group and Primary Cosmic Ray Group. The Gravitational Wave Group conducts experimental research of gravitational wave with researchers of gravitational wave experimentand theory in Japan. The main items are the construction of
the large scale cryogenic interferometer(LCGT) at Kamioka
underground and the operation of CLIO. The Sloan Digital
Sky Survey Group has completed the planned imaging andspectroscopy observations, and it continues publishing papers in collaboration with worldwide researchers. This grouphas started a new optical deep survey project with the widefield imager of Hyper Suprime-Cam mounted on the Subaru
telescope. Theory Group conducts both theoretical study of
the Universe and astroparticle physics.Primary Cosmic RayGroup reconstructs past cosmic ray changes and studies theirimpacts on climate change.

ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of:Gravitational Wave Group
Introduction
A gravitational wave is a physical entity in space-time predicted by Einstein’s theory of general relativity. Its existence
was proven by the observation of PSR1913+16 by Taylor and
Hulse 1 , who won the Nobel prize in 1993. However, nobody
has succeeded to directly detect gravitational waves. The theory of gravitation can be tested by the detection of gravitational waves. A gravitational wave detector is the last toolof mankind to inspect the universe. In order to directly observe gravitational waves, we have started to construct theLarge scale Cryogenic Gravitational wave Telescope (LCGT).
In prior to the construction of LCGT, we developed a 300 mbaseline interferometric gravitational wave detector, TAMA,at the Mitaka campus of the National Astronomical Observatory of Japan (NAOJ) and nine observation runs had been
conducted. TAMA project started in April, 1995, as a fiveyear project and it was extended by two years after 1999. We
acquired the interferometer technology and knowledge for thelarge scale interferometer by the experience of TAMA project,which was organized by researchers belonging to universities
and national laboratories. We conducted the development ofSeismic Attenuation System (SAS) installed for four main
mirrors and tried to enhance the interferometer sensitivity.
In regard with CLIO project, the construction of which wasstarted in 2003 and ended in March, 2007, we have succeeded
to break the room temperature limit by cryogenic mirror system that is operated at cryogenic temperature at first in theworld.
*1 J. H. Taylor and J. M. Weisberg, Astrophysical J., 345 (1989) 434.

LCGT collaboration; National Astronomical Observatory(NAOJ), High Energy Accelerator Research Organization(KEK), Department of Physics (University of Tokyo, abbreviated as UT hereafter), Research Center for the Early Universe (UT), Institute for Laser Science (University of ElectroCommunications), Photonic Innovation Center (University ofElectro-Communications), Department of Advanced Materials Science (UT), Earthquake Research Institute (UT), Department of Astronomy (UT), Department of Physics (Osaka
City University), Faculty of Engineering (Hosei University),
Metrology and Measurement Science (National Institute of
AIST), Space-Time Standards Group (National Institute of Information and Communication Technology), Department ofEarth and Space Science (Osaka University), Department of
Physics (Kyoto University), Yukawa Institute for Theoretical
Physics (Kyoto University), Graduate School of Humanities
and Sciences (Ochanomizu University), Advanced ResearchInstitute for the Sciences and Humanities (Nihon University), Department of Advanced Physics (Hirosaki University),
Astronomical Institute (Tohoku University), Department of
Physics (Niigata University), Department of Physics (Rikkyo
University), Department of Physics (Waseda University), College of Industrial Technology (Nihon University), Department of Humanities (Yamanashi Eiwa College), Departmentof Physical Science (Hiroshima University), Faculty of Science (University of the Ryukyu), Max Planck Institute forGravitational physics (AEI), California Institute of Technology, Department of Physics (University of Western Australia),
Department of Physics (Louisiana State University), Centerfor Computational Relativity and Gravitation (Rochester Institute of Technology), Department of Physics (Glasgow University), Columbia Astrophysics Laboratory (Columbia University in the city of New York), Department of Physics (Birmingham University), Department of Astronomy (Beijing Normal University), Inter University Center for Astronomy &Astrophysics (Pune University), Sternberg State Astronomical Institute (Moscow University), LATMOS (CNRS), Center
for Astrophysics (University of Science and Technology ofChina), Center for Astrophysics (Tsinghua University), Institute of High Energy Physics (Chinese Academy of Sciences),
Shanghai United Center for Astrophysics (Shanghai Normal
University) , Center for Measurement Standards (Industrial
Technology Research Institute), Physics Department (Maryland University)
Objective of LCGT
After the discovery of the highly relativistic binary neutron star system 2 , a new young binary pulsar was detected*2 M. Burgay, et al., Nature, 426 (2003) 531.

41
3 . The former discovery increased the coalescence rate from10−6 to 10−5 a year in a galaxy as big as our Galaxy 4 andthe latter pushed up by another factor of six. Although it wasgood news for the detection of gravitational waves, we stillneed to wait for long time to detect by the presently existing
detectors. This is the reason why we need to construct LCGT
(Large-scale Cryogenic Gravitational wave Telescope). The
objective of LCGT is to detect a few events of gravitational
wave in a year. Since there are many other possible gravitational wave sources in the universe other than the coalescenceof binary neutron stars, those sources are possible targets of
LCGT project.
Status of LCGT Project
In order to fulfill the objective of LCGT, we designed thesensitivity of LCGT so as to observe binary neutron star coalescence events occurring at 250 Mpc with S/N=8 in its optimum configuration[1]. This is ten-times more sensitive thanthat of the LIGO (I), and by two orders more than that of
TAMA at their most sensitive frequencies. This is achievedby the laser interferometer located underground, using threekilometer length baseline, cooling mirrors at cryogenic temperature, and a high-power laser source employing 180 W
output. The optical configuration is a power recycled FabryPerot-Michelson interferometer with the resonant-sidebandextraction (RSE) scheme (in Fig. 1). The detailed design ofthe control system was tested for the resonant sideband extraction scheme.[2] Table 1 lists the important parameters of
LCGT. You may trace the history of the evolution of LCGT
by references. [3] Ultimate sensitivity of a laser interferometer is determined by seismic noise at low frequencies (1030 Hz) (which is reduced by improving the vibration isolation
system), and it is limited by photon shot noise at higher frequencies (more than 300 Hz), which can be improved only
by increasing the light power in the main cavities. The sensitivity of middle frequencies (30-300 Hz) is limited by thefluctuation of the photon recoil force noise. This requires that
thermal noise is reduced both by decreasing the temperatureand by decreasing the internal mechanical loss (i.e., increasing
the mechanical Q of vibration modes). The source of thermal
noise comes from both mirror internal vibration, mechanicalloss of the optical coating and swing noise of the pendulum
suspending the mirror. The reduction of thermal noise is attained by cooling both the mirror, itself, and the suspension
system that suspends the mirror.
Figure 2 compares the sensitivity curve of LCGT withthose of TAMA, CLIO (a 100 m prototype cryogenic interferometer placed underground of Kamioka mine), LIGO (initial
LIGO) and the design of TAMA. The sensitivity at low frequencies of LCGT is attained by SAS, which will be provenby the current SAS in TAMA. That of higher frequencies is attained by higher laser power, which has been basically shown
by TAMA. The mid-frequency region is improved by cryogenic mirror and suspension system, which has been provenby CLIO (described in the next section*). The sensitivity improvement of two orders of magnitude at low frequencies iscertainly realized by the completion of LCGT interferometer.
*3 D.R. Lorimer, et al., Astrophysical J. 640(2006) 428.
*4 C. Kim, V. Kalogera and D. R. Lorimer, Astrophysical J. 584 (2003) 985.

Table 1. LCGT design parameters to detect binary neutron-star coalescence events in 250 Mpc.

Item
Baseline LengthInterferometer

Optical PowerBeam radius
Main Mirror

Suspension
Pendulum
VacuumParameter
3 km
One setPower recycled Fabry-Perot-Michelson with RSE
Laser:180 W; Finesse:1550
Input power at BS: 825 W
Cavity power 780 kW
3.4 cm(ITM)/4.5 cm(ETM)
Sapphire 30 kg, 20 K
Diameter 25 cm
Mechanical Q:108
Frequency: 1 Hz;
Q:5 × 108
16 K
≤ 10−7 Pa

Fig. 2. LCGT design sensitivity compared with those of TAMA (redline), CLIO (a 100m prototype cryogenic interferometer placed underground of Kamioka mine, blue line), LIGO (initial LIGO, yellowline) and the CLIO limit at room temperature (red broken line). The
horizontal axis is frequency [Hz] and the vertical√ axis represents
sensitivity spectrum for gravitational waves [1/ Hz].

Cryogenic Mirror development
The design of the cryogenic mirror system is shown in
Fig. 3. The mirror is suspended by two loops of sapphirefibers connected to an auxiliary mirror that is a part of suspension point interferometer. This mirror is also suspended
from an alignment control platform that is suspended with aninsulator rod connected through the center holes of the radiation shields to an isolation table suspended by a low-frequency
vibration isolator, which is placed at room temperature. The
auxiliary mirror has a heat link to the platform and anotherheat link connects the platform and a heat anchor point (4 K)
inside the vacuum located just above the platform. Both thecryogenic system and the vibration isolator are put inside acommon high-vacuum chamber.

42

Fig. 1. Optical design of LCGT. The optical configuration is a power recycled Fabry-Perot-Michelson interferometer with the resonant-sideband-extraction (RSE) scheme.

To realize this concept, the following research subjects
were conducted and reported:
1. Removal of heat produced by high-power laser illumination (annual report 1997-1998 and also in references[4])
2. Holding the high Qs of the mirror internal modes andsuspension pendulum [5]3. Reducing the contamination of mirror surfaces (annual
report 2000-2001 and also in [6])4. Estimating heat production by optical loss in the mirror[7]
5. Alignment control of mirrors in a cryogenic environment [8]6. Low mechanical loss of the optical coating (annual report 2003-2004 and also in reference [9])Fig. 3. Schematic design of the cryogenic suspension system. The
mirror is suspended by sapphire fibers connected to an auxiliary
mirror, which is suspended by metal wires from a platform that hasa heat link to a 4 K heat anchor inside the vacuum. The platform isalso suspended with an insulator rod connected through the holesof radiation shields to an isolation table suspended by a seismic
attenuation system placed at room temperature in the common
high vacuum.

As for item 5, we confirmed that a superconducting film
could be used for the receptor of the magnetic force in placeof permanent bar magnets that are normally used in the existing detectors. The film can be easily sputtered on the mirror surface without harmfully degrading the mechanical Q of
the mirror. With respect to the last item, we reported on ameasurement of the bulk substrate of the mirror at cryogenic
temperature in the annual report (2003–2004). We could correctly estimate the thermal vibration noise of the optical coating while considering the inhomogeneous loss that had been
neglected at an early stage of interferometer development.
The substrate of the cryogenic mirror is sapphire, which has a43large thermo-elastic thermal noise at room temperature. However, since the thermal-expansion ratio of sapphire at cryogenic temperature goes down to nearly 0 and the heat conductivity becomes greater, the thermo-elastic noise drastically reduces at the cryogenic temperature. Thermal noise estimatedfrom the Q of the coating is well below the design sensitivityof LCGT, which means that this coating noise does not limit
the sensitivity, whereas, the sensitivity of a room-temperature
mirror is limited by this effect. Also thermal lens effect disappears at cryogenic temperature in the LCGT design. These
are the significant merits of the cryogenic mirror system.
Study on the Bandwidth Optimization of LCGT
A broad band RSE (resonant-sideband extraction) configuration was selected as a default LCGT optical design since2004. With recent progresses in technology, it appears that wehave a chance to enhance the sensitivity of LCGT by selecting
more suitable optical parameters. We obtained a recommendation by a working group to discuss and optimize the optical configuration including a possibility of the detuned RSE
which has a narrower bandwidth but a better sensitivity in total (annual report 2009-2010). The purpose of this working
group was to investigate and to make recommendations on
the interferometer optical configuration design of LCGT and
its observation band for gravitational waves.
6
5)zHtr/1( ytivitisnes TGCL

4

3

2

averaged).5.

The BRSE configuration (red curve) has wider
observation band to cover various sources, and moderate observable range of 114 Mpc for neutron-star inspirals. The blueand sky-blue curves are for the VRSE configuration with a detuned mode VRSE (D) and with a broadband mode VRSE (B),respectively. They have slightly narrower and wider observation bands than the BRSE (red curve) configuration, respectively.
Scientific outcomes obtained from GW observation highly
depend on the sensitivity and observation band of a detector.
We surveyed possible GW sources which would be targets of
LCGT, and discussed advantages and disadvantages of eachcandidate interferometer configurations.
The most important criteria in the comparison is to increase the possibility to achieve the minimum success of
LCGT: detect at least a few GW events within one year operation. The primary target of LCGT is coalescences of neutronstar binaries. We estimated the observable range, expected
event rates, required observation period for the first detection, and measurement accuracy of binary mass parameters forthese sources. Figure 5 shows the expected detection rate asa function of sky average detection range. Then we surveyed
scientific outcomes from the other GW sources: black-hole binaries, black-hole ringdown, supernovae with stellar-core collapses, pulsars. We also compare the candidate configurations
from a viewpoint of international observation network. Here,
we show Table 3 summarizing the range for black-hole binaries, etc.
The working group concluded the following interferometer design and observation strategy as a part of new default
LCGT design.

-23

10

SQL
7
6

fixed BRSE

5

fixed DRSE

4

v-RSE (B)v-RSE (D)

3

2

3

4

5

6

7

8

9

2

3

100

4

5

6

7

8

9

2

1000

Frequency (Hz)Fig. 4. Sensitivity curves of the candidate configurations: BRSE (redcurve), DRSE (green curve), and VRSE (B/D) with sky-blue/blue
curves.

It is possible to optimize and tune the observation frequency band for target gravitational-wave sources, by choosing suitable optical parameters. So as to determine the opticalparameters, we define three candidate parameter sets: broadband RSE (BRSE), detuned RSE (DRSE), and variable RSE(VRSE) configurations. VRSE is designed to have good sensitivity both with tuned and detuned operation, and to switchobservation bands depending on the observation purposes andtargets. The detector sensitivity curves are estimated with thecurrent best-estimated boundary conditions of LCGT: an input
laser power, suspension and mirror thermal noises, seismic
noise, and optical readout noises. The estimated sensitivity
curves are shown in Fig. 4. and Table 2 shows brief summaryof optical parameters.
The DRSE configuration (green curve) has the best floorlevel sensitivity at around 100 Hz, and the best observable distance of 132 Mpc for neutron-star inspiral events (SNR=8, sky• The optical configuration of LCGT should be VRSE:
a RSE (resonant-sideband extraction) with variable observation band.
• In the first observation phase, LCGT interferometershould be operated with a detuned mode, VRSE (D),for earlier detection of gravitational-wave signals. Afterthe first detections, the variable configuration provides
the option to change the observation band to broadband,
VRSE (B), so as to obtain more scientific information.
Construction of LCGT
Organization
In order to conduct the construction of LCGT according
to the budget under the program of the leading edge researchfacilities, the LCGT collaboration was reinforced by nominating the director of ICRR as the project integrator of LCGT and
creating an executive committee controlling each sub-working
group that was chaired by chief leader. The origin of each subworking group was based on the team that functioned to establish the design of LCGT. The structure of the organizationis represented in Fig.6.
*5 Here, observable distance is defined as the range within which events aredetected with higher signal-to-noise ratio than 8. Detector antenna pattern and wave polarizations are all-sky-averaged. Whereas, the horizon
distance is the most remote distance under optimum configurations of
the interferometer and the orbit.

44
Table 2. Setup parameters, inspiral range (IR), and strain sensitivity at 1 kHz of each configuration. The first number in each IR column is withthe assumption that wave come from the optimal direction for LCGT, and each number in parenthesis is with the average over whole sky.

Ts

0.004 (1550)
0.009 (690)0.004 (1550)
0.004 (1550)

0.23
0.08
0.15
0.15

φ
[deg]
90
74.6
90
86.5

ζ
[deg]
127.6
103.8
121.8
134.7

1 event / year1

0.1

sky average range of
BRSE
DRSE
VRSE(B)
VRSE(D)

0.01
05. 107

1. 108

1.5 108

2. 108

detection range pc$(S/N>8, whole sky average)

10

IR
[Mpc]
259 (114)
299 (132)
255 (112)281 (123)

Sensitivity[Hz−1/2 ]1.4 × 10−23
2.1 × 10−22
1.1 × 10−23
1.5 × 10−23

Binary coalescences
BRSE
DRSE
VRSE(B)
2
VRSE(D)BH quasi-normal mode
BRSE
DRSE
VRSE(B)
VRSE(D)

5
4
3

100

Average Detection Range [pc]Expected number of detection within 1 year

BRSE
DRSE
VRSE (B)
VRSE (D)T (Finesse)

10

9
7
6
5
4
3
2

10

8
7
6
5
4
3

10

0

10

1

2

10
10
mass of star [Msolar]

3

10

4

Fig. 5. Left: Solid thick black line is Expected event rate as a function of sky average detection range, and gray shaded zone is a confidence bandof 95%. Solid thin lines show the range for binary coalescence. Colors are corresponding to the IFO configurations. Right: Sky-averaged
detection ranges as a function of total mass of the source. Solid lines show the range for binary coalescence. Dashed lines show the range
for ringdown GW from black-hole quasi-normal mode. Colors are corresponding to the IFO configurations.

Schedule
The funding was available for manufacturing the laser interferometer including its vacuum system for three years since
FY 2010 and the excavation of the underground would start in
FY 2011 for the period of two years. We planned to take themost efficient and most reliable way under these constrains.
The present schedule is shown in Fig. 7. We note that thedetail of the schedule would be flexibly changed due to thefunding status in future.
Special working groups
We have established 14 sub-working groups under the executive committee. These groups shared the role of construction of LCGT. Along with activities of these groups we established several special working groups for solving on-goingproblems. They were
• Installation of two story floors for seismic attenuation
system• Cope with inclination of tunnel from horizontal levelfor drain water• Shift to low frequency band
• Study of bandwidth design• Roadmap to objective
The idea of two story floors came from the effective usage ofrock structure of the underground, which guarantees the stable footing of the seismic attenuation system with lower costof excavation of the tunnel. The problem of the undergroundwater forced us to design the inclined base floor of the tunnel, the effect of which was the increase of cross coupling
between vertical vibration to horizontal. Without this inclination, we need to introduce drain water pumping system along
the beam tubes, which might produce unexpected result on
the seismic noise in low frequency. One of the recommendations by the review B (see the following sub-section*) was tolower the observational bandwidth from the present design of
LCGT, which might reduce the laser power and ease the loadof the heat extraction in the input test mass made of relatively
higher optical absorption. We decided not to adopt this recommendation by fearing lose of objective range of observation.
Both the results of last two items; study of the bandwidth androadmap, will be presented in the report of the next year.
Topical R&Ds
Although we have confirmed the performances of new instruments applied to the interferometer of LCGT, some parts
require the practical tests using the real models of those instruments. For example, the SAS (seismic attenuation system)
was applied to TAMA interferometer and produced expected
result. However, we have to technically know the difference
between TAMA300 and LCGT with 3 km baseline. In prior
to the installation of the real system, we plan to test the realmodel of SAS using TAMA interferometer at Mitaka campus.
In respect with the cryogenic system, its prototype had been
already applied to CLIO interferometer. However, the sizeand power of the refrigerator were increased and the cryo-45
Table 3. BH observations. In this estimation, we assume the amplitude of ringdown GW corresponding to 3% of mass.

BRSE
Binary coalescences NS-BH (1.4-10M⊙)
Detection range davg [Mpc]
Expected event rate [events/yr]
Binary coalescences BH-BH (10-10M⊙)
Detection range davg [Mpc]
Expected event rate [events/yr]
Quasi-normal mode :Detection range davg [Gpc] for 200 M⊙
Survey mass region at 1 Gpc [M⊙ ]IFO configurations
VRSE (B) VRSE (D)

240

235

570

557

261
0.006 − 6

278

615

677

2.3
100 - 490

3.0
100 - 450

0.07 − 7
2.1
110 - 910

2.0
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㩿㪬㪫㪃㩷㪘㪤㪪㪀㪫㪼㫃㪸㪻㪸
㩿㪘㪠㪪㪫㪀

㪤㫀㫆㩿㪬㪫㪃㩷㪘㪤㪪㪀㪙㪸㫊㪼㫃㫀㫅㪼
㪠㫅㫋㪼㫉㪽㪼㫉㫆㫄㪼㫋㪼㫉㩿㪬㪫㪃㩷㪜㪩㪠㪀㪛㪸㫋㪸㪸㫅㪸㫃㫐㫊㫀㫊㪃㫄㪼㫋㪿㫆㪻㪃
㪸㫅㪸㫃㫐㫊㫀㫊㪃㪻㪸㫋㪸㩷㪺㫆㫅㫋㫉㫆㫃㪛㪼㫊㫀㪾㫅㪃
㪚㫆㫅㫊㫋㫉㫌㪺㫋㫀㫆㫅㪃㪪㪸㪽㪼㫋㫐
㫄㪸㫅㪸㪾㪼㫄㪼㫅㫋㪃㪣㫆㪺㪸㫃㩷㫃㫀㪸㫀㫊㫆㫅㪚㫃㪼㪸㫅㪼㫅㫍㫀㫉㫆㫅㫄㪼㫅㫋㪃㪧㫆㫎㪼㫉㫃㫀㫅㪼㪃㪤㪼㪺㪿㪸㫅㫀㪺㪸㫃㫊㫆㫌㫅㪻㩷㫅㫆㫀㫊㪼㪃㫀㫅㫋㪼㫉㫅㪼㫋

㪪㫇㪼㪺㫀㪽㫐㪃
㪦㫉㪻㪼㫉㫀㫅㪾㪃㪧㫉㫆㪺㫌㫉㪼㪃
㪘㫊㫊㪼㫄㪹㫃㫀㫀㫅㪾㪃㪭㪸㪺㫌㫌㫄㩷㫋㪼㫊㫋㪃㪠㫅㫊㫋㪸㫃㫃㪸㫋㫀㫆㫅㪛㪼㫊㫀㪾㫅㪃
㪦㫉㪻㪼㫉㫀㫅㪾㪃㪧㫉㫆㪺㫌㫉㪼㪃
㪠㫅㫊㫋㪸㫃㫃㪸㫋㫀㫆㫅㪛㪼㫊㫀㪾㫅㪃
㪦㫉㪻㪼㫉㫀㫅㪾㪃㪧㫉㫆㪺㫌㫉㪼㪃
㪠㫅㫊㫋㪸㫃㫃㪸㫋㫀㫆㫅㪛㪼㫊㫀㪾㫅㩷㩿㫉㫆㫆㫄㫋㪼㫄㫇㪼㫉㪸㫋㫌㫉㪼㪀㪃㪦㫉㪻㪼㫉㫀㫅㪾㪃㪧㫉㫆㪺㫌㫉㪼㪃
㪪㫌㪹㫊㫋㫉㪸㫋㪼㩷㪽㫆㫉㪺㫉㫐㫆㪾㪼㫅㫀㪺㫄㫀㫉㫉㫆㫉

㪠㫅㫋㪼㫉㪽㪼㫉㫆㫄㪼㫋 㪠㫅㫋㪼㫉㪽㪼㫉㫆㫄㪼㫋㪼㪼㫉㩷㪻㪼㫊㫀㪾㫅㪃㪛㪼㫊㫀㪾㫅㩷㫆㪽㫉㩷㪺㫆㫅㫋㫉㫆㫃㫊㫇㪼㪺㫀㪽㫀㪺㪸㫋㫀㫆㫅㪻㫀㪾㫀㫋㪸㫃㩷㫊㫐㫊㫋㪼㫄㪃㩿㫃㪼㫅㪾㫋㪿㪃
㫄㪸㫅㫌㪽㪸㪺㫋㫌㫉㫀㫅㪾㪃㪸㫃㫀㪾㫅㫄㪼㫅㫋㫊㪃㫊㩷㫋㫆㩷㫊㫌㪹㪄㪸㪻㫁㫌㫊㫋㫄㪼㫅㫋
㫃㫆㪺㫂
㪮㪞㫊㪃
㫇㫉㫆㪺㪼㪻㫌㫉㪼㪀㫊㪺㪿㪼㪻㫌㫃㪼

㪛㪼㫊㫀㪾㫅㪃
㪤㪸㫅㫌㪽㪸㪺㫋㫌㫉㫀㫅㪾㪃㪘㪻㫁㫌㫊㫋㫄㪼㫅㫋㪛㪼㫊㫀㪾㫅㪃
㪤㪸㫅㫌㪽㪸㪺㫋㫌㫉㪼㪃㪠㫅㫊㫋㪸㫃㫃㪸㫋㫀㫆㫅㩿㪣㪸㫊㪼㫉㩷㪄
㪧㪩㪤㪀㪛㪼㫍㪼㫃㫆㫇㫄㪼㫅㫋㪃㪤㪸㫅㫌㪽㪸㪺㫋㫌㫉㪼㪃㪠㫅㫊㫋㪸㫃㫃㪸㫋㫀㫆㫅㪚㫆㫄㫇㪼㫅㫊㪸㫋㫀㫆㫅㫆㪽㩷㪹㪸㪸㫊㪼㫃㫀㫅㪼㫃㪼㫅㪾㫋㪿㩷㪺㪿㪸㫅㪾㪼㪘㫉㪸㫐㪸

Fig. 6. LCGT organization for construction in the end of FY 2010.

genic payload completely changed from the prototype. It isnatural to test in prior to the practical installation to LCGT.
The test was planned to conduct in the next fiscal year.
Reviews
After finishing the design detail by sub-working groups,
we conducted peer review on each sub-working group repeatedly since the November of 2010 and ended in January 2011.
Summarizing these results, we organized the external review
committee consisting of overseas specialists chaired by Dr.
Mike Zucker in MIT (LIGO MIT), which was held for one
week in the end of February and the beginning of March.
The committee scrutinized the detailed design of LCGT except the facility and geophysical interferometer sub-working
group. The report with recommendation was presented in
March and we coped with the problems for solution. These
series of reviews will be summarized by the review of the program advisory board in the next fiscal year.
Academic Agreements with overseas projects
In order to exchange technical information and support
from overseas projects, we exchanged academic agreementswith gravitational wave research projects in abroad. First, wemade an attachment of collaborative research agreement be-

tween LIGO laboratory in Caltech and ICRR. The agreement
was exchanged in prior fiscal year for introducing digital control system from LIGO to CLIO. Second, we exchanged theacademic agreement of collaboration of gravity wave research
between EGO/Virgo and ICRR. Third, the research agreement
between Shanghai United Center of Astrophysics in Shanghai Normal University and ICRR was exchanged to promote
R&D of LCGT and data analysis. Preparation of exchange ofacademic agreements was ongoing with GEO, Sannio University, and so on.
Public Relations
The nickname of LCGT was being searched by the naming
committee chaired by Writer, Yoko Ogawa. The announcement of the recommendation of the committee was postponedto the next fiscal year due to the Eastern Japan disaster.
The current activity of LCGT was uploaded in the webpage: http://gwcenter.icrr.u-tokyo.ac.jp/en/

Bibliography[1] K. Kuroda et.al., “Status of LCGT”, Class. Quantum
Grav. 27 (2010) 084004.

46

Fig. 7. Tentative schedule of LCGT for construction being discussed in the roadmap meeting.

[2] F. Kawazoe et al., J. Phys.: Conference Series 122(2008) 012017.
[3] K. Kuroda et.al., Int. J. Mod. Phys. D 8 (1999) 557; K.
Kuroda,et al., Class. Quantum Grav. 19 (2002) 1237;
T. Uchiyama, et al., Class. Quantum Grav. 21 (2004)
S1161.
[4] T. Uchiyama, et.al., Phys. Lett. A 242 (1998) 211.
[5] T. Uchiyama, et.al., Phys. Lett. A 261 (1999) 5;ibid
A273(2000)310.
[6] S. Miyoki, et al., Cryogenics 40 (2000) 61: ibid 41(2001) 415.
Fig. 9. Overview of the CLIO interferometer.

[7] T. Tomaru, et al., Phys. Lett. A 283 (2001) 80.
[8] N. Sato, et al., Cryogenics 43 (2003) 425.
[9] K. Yamamoto, et al., Class. Quantum Grav. 21 (2004)
S1075.

CLIO Project[Spokesperson : Masatake Ohashi]
ICRR, 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 LCGT (3 km cryogenic interferometer at Kamioka).
The site of CLIO, near the Super-Kamiokande neutrino detector, is shown in Fig. 8. The tunnel was dug in 2002, anda strain 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]. 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 shownin 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 −4Pa 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 con-

47

Fig. 8. Location of the CLIO interferometer.

sistent with the estimation of mirror thermal noise reduction
due to cooling.

100
servo onservo off

R&D: Local Suspension Point Interferometer
Local Suspension Point Interferometer (LSPI) is an active
control system for a cryogenic mirror suspension system of
CLIO. One set of LSPI has been installed in a cryostat of
CLIO since 2010 and we successfully observed the damping
effect in the room temperature as shown in Fig. 10. We found
low effectiveness of a conventional magnet damping system
for a cryogenic mirror suspension system, when the mirrors
were at cryogenic temperature. Purpose of a damping system
is to reduce amplitude of mirror motion. Without the damping system, it is impossible to keep a Fabry-Perot cavity on
resonance. Thus, we have developed LSPI as a new damping system that is possible to use at cryogenic temperature.
LSPI consists of a motion sensor using an interferometer anda feedback control system. The interferometer senses motionof a mass of the mirror suspension system. Feedback signal
generated by the control system is converted to damping force
by coil magnet actuators on the mass. Figure 10 shows transfer function of the mirror suspension system with and without
LSPI in the room temperature. High Q factor resonances of
0.48Hz and 1.18Hz in the curve of without LSPI were clearly
damped by LSPI.
Digital system in CLIO
The next generation interferometer for gravitational wave
detection will have a very complicated control topology
as called RSE (resonant sideband extraction) which has

Arbitrary Unit

10
1
0.1
0.01
0.001
0.1

2

3

4 5 672

1Frequency [Hz]3

4 5 67

10

Fig. 10. Comparison with transfer function of a mirror suspension
system with and without LSPI. There are two high Q resonances
at 0.48Hz and 1.18Hz in the curve of without LSPI (servo off).
Those resonances are damped by LSPI.

5 degrees of freedom for length control, ∼40 degrees of freedom for alignment control, and ∼100 degrees of freedom for
local controls of damping suspensions. It is really important
to implement a digital control system to deal with such a complicated interferometer since the digital system provides us avery flexible human interface. The flexibility leads a drastic
reduction of time for noise hunting.
We developed a digital controls system for the gravitational wave detector by an international collaboration with
LIGO group in the U.S and installed it into CLIO. This firstsystem is a very simple standalone model to check the perfor-

48

Fig. 11. A sapphire mirror and cryogenic suspension system" '!

3:!!A3*/1*)2)B)2@
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3:!!A30)==D=32F/=0-,31D)*/3
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3C=@DE/1).30)==D=32F/=0-,31D)*/
33G<=D1238!A3J3K1L3:!!AI" &!

These noises have been effectively reduced using the whitening/dewhitening fileters. Finally we have shown the performance that the ADC and DAC noises are at least 10times
lower than the best sensitivity of CLIO (See Fig. 13). Actually, the noise floor can be 10 times smaller if we use stronger
whitening/dewhitening filters because we still can afford the
dynamic range of whitening/dewhitening filters. We believethat this CLIO digital system showed an enough performanceeven for the km class interferometer like LCGT.
This digital control system has many number of input andoutput channels, so it can be used for many purposes, not only
for the main arm length control. For example in CLIO, we
implemented Mode Cleaner auto alignment, laser power controller injected into photo detector, local control system for
LSPI which is used for the damping of mirror suspension, andso on. Currently we are planning to have an engineering observation run using this system to develop a data analysis environment including analysis software and data pipe line inthis fiscal year.
This study at CLIO is a very good test bench for LCGT
and it will lead not only a smooth installation of a full digitalsystem into LCGT but also a smooth commissioning work forwhole LCGT project.

85

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

CLIO sensitivity

" %

!

10-11

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!

" #

!

8

:

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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.

mance of digital system for noise, feasibility, flexibility and soon. This system consists of a computer, an I/O extension box,
ADCs, DACs, and the related analog circuits like anti aliasing/imaging filters, whitening/dewhitening filters. The ADC
has 32 differential channels and the DAC has 16 differential
channels.
With this system we have established the lock acquisition of the single test mass control loop. The error signal of this arm motion is always monitored and calibrated
into the sensitivity for gravitational waves. Using this ordinary sensitivity monitor, noise hunting has been performed
very smoothly. It is known that the noise of ADC and DAC
is typically 1000 times higher than general analog circuits.

Displacement noise (m/rHz)

ADC noise

10-12

DAC noise

10-13

20K Analog best (2010/03/20)

Digital best (2010/08/19)

-14

10

10-15
10-16
10-17
10-18
10-19
10-20
10-21

10

*T0=08/09/2010 01:16:38

102
Frequency (Hz)
*Avg=17/Bin=4L

103*BW=0.187493

Fig. 13. Noise contribution of ADC and DAC noises. Green: DAC
noise, blue: ADC noise, red: best sensitivity using digital servo,
gray: best sensitivity of CLIO using analog servo. ADC and DAC
noise is at least 10 times lower than CLIO best sensitivity.

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] R. W. P. Drever, et al., Appl. Phys. B 31 (1983) 97-105.

49

Sloan Digital Sky Survey
Observational Cosmology[Spokesperson : Masami Ouchi]

Statistics of 207 Lyα Emitters at a Redshift
Near 7: Constraints on Reionization andGalaxy Formation Models
In collaboration with the members of Observatories of theCarnegie Institution of Washington, University of Tokyo, National Astronomical Observatory, IPMU, Tohoku University,
ICRR, and Okayama Astrophysical Observatory
We have investigated Lyα luminosity function (LF), clustering, and Lyα line profiles based on the largest sample,
to date, of 207 Lyα emitters (LAEs) at z = 6.6 on the 1deg2 sky of Subaru/XMM-Newton Deep Survey (SXDS) field(Fig. 1). Our z = 6.6 Lyα LF including cosmic varianceestimates yields the best-fit Schechter parameters of φ ∗ =+0.6
42−1 with−4−3 and L∗
8.5+3.0
Lyα = 4.4−0.6 × 10 erg s−2.2 × 10 Mpc
a fixed α = −1.5, and indicates a decrease from z = 5.7 at the& 90% confidence level (Fig. 2). However, this decrease is
not large, only ≃ 30% in Lyα luminosity, which is too small
to be identified in the previous studies. A clustering signal ofz = 6.6 LAEs is detected for the first time. We obtain the correlation length of r0 = 2 − 5 h−1
100 Mpc and bias of b = 3 − 6,and find no significant boost of clustering amplitude by reionization at z = 6.6. The average hosting dark halo mass inferredfrom clustering is 1010 − 1011M⊙ , and duty cycle of LAE population is roughly ∼ 1% albeit with large uncertainties. The
average of our high-quality Keck/DEIMOS spectra shows an
FWHM velocity width of 251 ± 16km s−1 . We find no large
evolution of Lyα line profile from z = 5.7 to 6.6, and no anticorrelation between Lyα luminosity and line width at z = 6.6.
The combination of various reionization models and our observational results about the LF, clustering, and line profile indicates that there would exist a small decrease of IGM’s Lyαtransmission owing to reionization, but that the hydrogen IGM
is not highly neutral at z = 6.6 (Fig. 3). Our neutral-hydrogen
fraction constraint implies that the major reionization process
took place at z & 7.

Bibliography[1] Ouchi, M., et al. 2010, Astrophys. J., 723, 869[2] Ouchi, M., et al. 2008, Astrophysical Journal Supplement, 176, 301

The Subaru Lyα blob survey: A sample of
100 kpc Lyα blobs at z = 3
In collaboration with the members of Durham University, Tohoku University, Carnegie Institution of Washington, University of Tokyo, and University of Tsukuba.
We have conducted a survey for giant Lyα nebulae(LABs) at z = 3 with Subaru/Suprime-Cam. We obtained Lyα
imaging at z = 3.09 ± 0.03 around the SSA22 protocluster andFig. 1. Spectra and snapshots of some of our z = 6.6 LAEs confirmedwith Keck/DEIMOS. Each object has a spectrum in the right panel
and snapshots of B, V , R, i′ , z′ , and NB921 images in the left panels. Each snapshot is presented in a 6′′ × 6′′ box. The right bottom
panel shows a typical DEIMOS spectrum of the sky backgroundthat is obtained in the process of sky subtraction. This figure is
reproduced by permission of the AAS.

in several blank fields. The total survey area is 2.1 square
degrees, corresponding to a comoving volume of 1.6 × 106
Mpc3 . Using a uniform detection threshold of 1.4 × 10−18 erg
s−1 cm−2 arcsec−2 for the Lyα images, we construct a sample of 14 LAB candidates with major-axis diameters larger
than 100 kpc, including five previously known blobs and two
known quasars. This survey triples the number of known
LABs over 100 kpc. The giant LAB sample shows a possible ”morphology-density relation”: filamentary LABs reside
in average density environments as derived from compact Ly αemitters, while circular LABs reside in both average density
and overdense environments. Although it is hard to examine the formation mechanisms of LABs only from the Lyαmorphologies, more filamentary LABs may relate to cold gas
accretion from the surrounding inter-galactic medium (IGM)
and more circular LABs may relate to large-scale gas outflows, which are driven by intense starbursts and/or by AGN
activities. Our survey highlights the potential usefulness ofgiant LABs to investigate the interactions between galaxies
and the surrounding IGM from the field to overdense environments at high-redshift.

50

Fig. 2. Error ellipses of our Schechter parameters, L∗Lyα and φ ∗ . Red
contours represent the fit of z = 6.6 LF with the fixed slope of
α = −1.5 based on SXDS and SDF data. The inner and outer contours indicate 68% and 90% confidence levels, respectively, which
include cosmic variance errors. Blue contours denote z = 5.7 LFs
given by [2], which are similarly derived with cosmic variance errors. For a fair comparison with our z = 6.6 LF, we show error ellipses of the z = 5.7 LF derived by the classical method (see moredetails in [2]). The error ellipses of the z = 5.7 LF are larger thanthose of our z = 6.6 LF. This is because the data of z = 5.7 LF havemore uncertainties of cosmic variance. Black solid and dotted lines
indicate 1, 2, and 3 sigma confidence levels of z = 6.6 and z = 5.7
LFs with no cosmic variance errors previously derived solely withthe smaller data of SDF. This figure is reproduced by permissionof the AAS.

Bibliography[1] Matsuda, Y., et al. 2011, Monthly Notices of the Royal
Astronomical Society, 410, L13

Keck Spectroscopy of Faint 3 < z < 7 Lyman
Break Galaxies:- II. A High Fraction of Line
Emitters at Redshift Six
In collaboration with the members of University of Cambridge
and California Institute of Technology.
As Lyman α photons are scattered by neutral hydrogen, achange with redshift in the Lyα equivalent width distributionof distant galaxies offers a promising probe of the degree ofionization in the intergalactic medium and hence when cosmic reionization ended. This simple test is complicated by thefact that Lyα emission can also be affected by the evolving
astrophysical details of the host galaxies. In the first paperin this series, we demonstrated both a luminosity and redshiftdependent trend in the fraction of Lyα emitters seen withincolor-selected ‘Lyman-break’ galaxies (LBGs) over the range
3 < z < 6; lower luminosity galaxies and those at higher redshift show an increased likelihood of strong emission. We
have studied the results from much deeper 12.5 hour exposures with the Keck DEIMOS spectrograph focused primarily
on LBGs at z ≃ 6 which enable us to confirm the redshift de-

Fig. 3. Neutral hydrogen fraction, xHI , of IGM as a function of redshift. Top and bottom panels are the same, but with a vertical axisof linear and log scales, respectively. Filled square and circle are
the upper limits of xHI that we obtain from the evolution of Lyα LF
and clustering, respectively. Open symbols denote the upper limits
from Lyα LF and Lyα damping wing of GRB given by the previous
studies. Filled hexagon and pentagons indicate constraints given
by GRB spectra and QSO dark gap statistics, respectively. Filled
diamonds represent the measurements from GP optical depth of
SDSS QSOs. Triangle plots the 1σ lower-limit of redshift of a neutral universe given by WMAP7 in the case of instantaneous reionization. Avoiding overlapping symbols, we give a small offset along
redshift to the positions of the filled circle and the open diamond.
Dotted, dashed, and solid lines show the evolution of xHI for minihalo, small, and large halo cases, respectively, predicted by thesemi-analytic models. Gray solid line presents the prediction in the
double reionization scenario suggested by the theoretical model.
This figure is reproduced by permission of the AAS.

pendence of line emission more robustly and to higher redshift
than was hitherto possible. We find 54 ± 11% of faint z ≃ 6
Lyman break galaxies show strong (WLyα ,0 > 25 Å) emission,
an increase of 1.6× from a similar sample observed at z ≃ 4(Fig. 4). With a total sample of 74 z ≃ 6 LBGs, we determine
the luminosity-dependent Lyα equivalent width distribution.
Assuming continuity in these trends to the new population ofz ≃ 7 sources located with the Hubble WFC3/IR camera, wepredict that unless the neutral fraction rises in the intervening 200 Myr, the success rate for spectroscopic confirmation
using Lyα emission should be high.

Bibliography[1] Stark, D. P., Ellis, R. S., & Ouchi, M. 2011, Astrophys.
J., 728, L2

51
2.1
0.8

1.8

1.5

WLyα,0>25 Å

Cosmic Time (Gyr)1.1 1.0 0.90 0.81 0.73 0.67 0.61

−20.25<MUV<−18.75

WLyα,0>55 Å

0.6

XLyα

1.3

0.4

0.2

rate, resulting in little evolution of the rest-frame UV LF fromz = 6 to 3. The rest-frame UV LF of both LAEs and LBGs
at z = 3 & 6 can be described well by the stochastic scenario
provided the extinction is moderate, E(B−V ) ≈ 0.15, for both
populations, although our simulation might be overpredicting
the number of bright LBGs at z = 6. We also discuss the correlation function and bias of LAEs. The Lyα LFs at z = 6 ina field-of-view of 0.2 deg2 show a significantly larger scatterowing to cosmic variance relative to that in a 1 deg2 field, andthe scatter seen in the current observational estimates of the
Lyα LF can be accounted for by cosmic variance.

0.0

WLyα,0>25 Å
WLyα,0>55 Å

0.4−21.75<MUV<−20.25

Bibliography[1] Nagamine, K., Ouchi, M., Springel, V., & Hernquist, L.
2010, Publications of the Astronomical Society of Japan, 62, 1455

XLyα

0.3

0.2

Primary Cosmic Ray Group[Spokesperson : H. Miyahara]

0.1

ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
0.0
3

4

5
6
Redshift (z)78Fig. 4. Evolution in the overall fraction of Lyα emitters (XLyα ) in the
LBG population over 4 < z < 6. Luminous LBGs are consideredin the bottom panel, and less luminous systems in the top panel.
In each panel, we derive the Lyα fraction of LBGs with Lyα EWs
larger than 25 Å (circles) and 55 Å (squares). Assuming a linear
relationship between XLyα and z, we extrapolate these trends toz ≃ 7 (triangles with dashed-line error bars). This figure is reproduced by permission of the AAS.

Lyman-α Emitters and Lyman-break Galaxies at z = 3 − 6 in Cosmological SPH Simulations
In collaboration with the members of IPMU, University of
Nevada Las Vegas, Observatories of the Carnegie Institution of Washington, Max-Planck-Institut für Astrophysik, andHarvard University.
We study the properties of Lyman-α emitters (LAEs) andLyman-break galaxies (LBGs) at z = 3 − 6 using cosmological SPH simulations. We investigate two simple scenarios for
explaining the observed Lyα and rest-frame UV luminosity
functions (LFs) of LAEs: (i) the “escape fraction” scenario, in
which the effective escape fraction (including the IGM attenuation) of Lyα photons is fLyα ≈ 0.1 (0.15) at z = 3 (6), and (ii)the “stochastic” scenario, in which the fraction of LAEs thatare turned on at z = 3 (6) is Cstoc ≈ 0.07 (0.2) after correcting
for the IGM attenuation. Our comparisons with a number ofdifferent observations suggest that the stochastic scenario ispreferred over the escape fraction scenario. We find that themean values of stellar mass, metallicity and black hole mass
hosted by LAEs are all smaller in the stochastic scenario thanin the escape fraction scenario. In our simulations, the galaxy
stellar mass function evolves rapidly, as expected in hierarchical structure formation. However, its evolution is largely compensated by a beginning decline in the specific star formation

Reconstruction of solar cycles at the grandsolar minima
In collaboration with the members of Univ. of Tokyo, Yamagata Univ. Hirosaki Univ. and Australian National Univ.
Our group has been conducting the reconstruction of solar cycles during the prolonged sunspot absence such as theMaunder Minimum and the transitional periods, by measuring the cosmogenic nuclide in tree rings with annual resolution using the Accelerator Mass Spectrometer. It will provide
a clue for understanding the mechanism of long-term changes
in solar activity and constructing a methodology of forecasting near future solar activity. For this study, trees from Yaku
Island, Nara prefecture, Aomori prefecture and Shizuoka Prefecture have been used. We use the Accelerator Mass Spectrometers at the University of Tokyo, Yamagata University
and The Australian National University. We have detected thedeviations of solar cycle lengths from 11 years around the two
preceding cycles of grand solar minima, although the characteristics may be different by the duration of event (Miyahara
et al., 2010).

Bibliography[1] H. Miyahara, K. Kitazawa, K. Nagaya, Y. Yokoyama,
H. Matsuzaki, K. Masuda, T. Nakamura, and Y. Muraki,
Journal of Cosmology, 8 (2010) 1970.

Long-term changes in solar modulation ofgalactic cosmic rays in the heliosphere andtheir influence on climate change
In collaboration with the members of Univ. of Tokyo, Nagoya
Univ. Hirosaki Univ. and National Institute of Polar Research.
We have investigated solar modulation of galactic cosmic
rays around the Maunder Minimum based on beryllium-10

52
positive

negative

positive

Solar activity

Cosmic ray flux

negativet
solar cycle
positive

negative

positive

Solar activity

Cosmic ray flux

negativet
solar cycle

Fig. 1. Model of cosmic ray variations at present (above) and at
the Maunder Minimum (below) (Miyahara et al., 2009) estimatedbased on the results of numerical simulation of solar modulation
by Kota and Jokipii (2001). For the Maunder Minimum, the rangeof the tilt angle is assumed to be 0-75 degrees. For this case, thevariability of cosmic rays at negative solar polarity get anomalously
increased, resulting in the amplification of the 22-year cosmic-ray
cycles.

records from ice cores. Variation of beryllium-10 content
provides the information on the state of solar modulation ofcosmic rays at sunspot absence, and thus the state of solar
magnetic field and the heliosphere. We find that the variationof cosmic rays associated with solar polarity reversals wereunique at the Maunder Minimum. About 30-50

Bibliography[1] H. Miyahara, Y. Yokoyama, and Y. T. Yamaguchi, Proceedings of the IAU symposium No. 264, (2009) 427.
[2] Y. T. Yamaguchi, Y. Yokoyama, H. Miyahara, K. Sho
and T. Nakatsuka, Synchronized Northern Hemisphere Climate Change and Solar Magnetic Cycles during the Maunder Minimum, Proceedings of
the National Academy of Sciences, (2010) doi:
10.1073/pnas.1000113107.

Fig. 2. Comparison of cosmic rays and reconstructed climate aroundthe Maudner Minimum (Yamaguchi et al., 2010). (a) Reconstructed relative humidity in Japan around June. (b) Reconstructed temperature based on oxygen-18/oxygen-16 ratio in theGreenland ice core by Vinther et al. (2003). (c) Beryllium-10 record
from Greenland ice core by Berggren et al. (2009). The blue
shaded areas correspond to the solar cycle minima of polarity negative determined by carbon-14 record.

Influence of solar rotation on the tropicalconvective clouds
In collaboration with the members of Univ. of Tokyo and
Hokkaido Univ.
We have examined the influence of the 27-day rotation of
the Sun on cloud formation. Total solar Irradiance (TSI), solar ultraviolet (UV), and galactic cosmic rays change in association with the 27-day rotation of the Sun. The variabilityof solar-related parameters at a range of 27-day period tends
to be larger at solar maximal periods. We have found thatthe 27-day solar rotational period affect cloud activity around
the Western Pacific Warm Pool (WPWP) and Indian Ocean.
The generation of 30-60 day period in cloud activity called as
Madden-Julian Oscillation (MJO) in tropics has not been wellunderstood. We suggest that its rhythm is under the control of
periodic variation of solar related parameters. Our study alsosuggests that the areas 27-day variations are detected are influenced by the two phases of Quasi-Biennial Oscillation (QBO)
in the stratosphere (Fig. 3).

Bibliography[1] Y. Takahashi, Y. Okazaki, M. Sato, H. Miyahara,
K. Sakanoi, and P. K. Hong, Atmospheric Chemistry andPhysics 10 (2010), 290.

53

Fig. 3. Power of the 27-day periodicity in cloud activity for solar maxima/solar minima and for QBO easterly/westerly phases.

[2] P. K. Hong, H. Miyahara, Y. Yokoyama, Y. Takahashi,
M, Sato, Implications for the low latitude cloud formations from solar activity and the Quasi-Biennial Oscillation, Journal of Atmospheric and Solar-Terrestrial
Physics (2011), doi:10.1016/j.jastp.2010.11.026.

reliable short-term record of variations since 1978. However,this instrumental record has not yet led to a consensus result
for solar variations on multi-decadal and longer timescales. It
is important to clarify the actual variability of TSI in terms of
distinguishing the contribution of change in TSI to the Little
Ice Age. We have conducted the re-analysis of thermal properties of lunar regolith obtained by the Apollo Heat Flow Experiments, and conducted numerical simulations of heat flowin the regolith. We have shown that the historical changes in
Total Solar Irradiance can be distinguished by small but potentially detectable differences in temperature, on the order of
0.01 K and larger depending on latitude, within 10 m depth of
the Moon’s surface (Fig. 5). In order to accomplish this experiment, we are now conducting discussions on the possible
future missions. We are now discussing the potential preliminary mission for shallower depth at the next Japanese lunar
landing mission.

Bibliography[1] H. Miyahara, G. Web, and R. F. Cahalan, GeophysicalResearch Letters 35 (2008), L02716.

Reconstruction of climate change based onstable isotopes in tree rings
In collaboration with the members of Univ. of Tokyo, Nagoya
Univ. and Tokyo Institute of Technology.
We are now conducting the measurements of multiple stable isotopes in tree rings from Japan in order to reconstruct
the climate changes during the past two millenia in Japan. We
have mainly conducting measurements using the 1850-year
old cedar tree from Yakushima (Fig. 4) as well as the recent
150-year trees from the same area for the calibration.

Fig. 5. Temperature anomalies in lunar regolith as response to 2
W/m2 difference in total solar irradiance at the Maunder Minimum,at the equator, mid-latitude (40S) and near the south pole (80S)(Miyahara et al., 2008).

Theory Group
Fig. 4. Japanese cedar tree used in this study. The tree has beenobtained from the Yaku Island.

Deriving Historical Total Solar Irradiancefrom Lunar Borehole Temperatures
In collaboration with the members ofNASA/Goddard Space Flight Center.

JAXA

and

As the Moon lacks atmosphere as well as any influenceof human activities, lunar borehole temperatures are primarily
driven by changes in solar irradiance. Variations of total solar irradiance (TSI), directly measured by radiometers flown
onboard several satellites in recent decades, have provided a

We have studied particle physics (mainly particle physics
phenomenology) and astroparticle physics (mainly particle
cosmology).
The supersymmetric (SUSY) extension of the standard
model (SM) in the particle physics is considered to be oneof the most promising models beyond the standard model. It
solves the naturalness problem for the Higgs boson mass termin the standard model, and it is also compatible with the grandunified theories (GUTs). Our group has been studying phenomenological and cosmological aspects of the SUSY models.
Recent cosmological observations determine precisely themean densities of matter and baryon in the Universe, and existence of non-baryonic dark matter is established. Weaklyinteracting massive particles (WIMPs) are considered to be54

good candidates of the dark matter. They act as the cold
dark matter in the structure formation of the universe. Ourgroup has been studying model building for dark matter anddetectability 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
BBN, which leads to constraints on the new particles and theparticle physics models.
The grand unified theories (GUT) predict that our universe
undergoes several vacuum phase transitions. In the courseof phase transitions topological defects (monopoles, cosmic
strings and domain walls) are generally produced dependingon symmetries of the vacua. Our group has studied evolutionof various topological defects.

Particle Phenomenology[Spokesperson : J. Hisano]

Gluon contribution to dark matter direct detection

tion is smaller than the previous results by more than an orderof magnitude, while the cross section of the first Kaluza-Klein
photon dark matter turns out to be larger by up to a factor often.

Bibliography[1] J. Hisano, K. Ishiwata and N. Nagata, Phys. Rev. D 82
(2010) 115007 [arXiv:1007.2601 [hep-ph]].
[2] J. Hisano, K. Ishiwata and N. Nagata, Phys. Lett. B 690(2010) 311 [arXiv:1004.4090 [hep-ph]].
[3] J. Hisano, K. Ishiwata, N. Nagata and M. Yamanaka,
arXiv:1012.5455 [hep-ph].

Direct Detection of Electroweak-Interacting
Dark MatterIn collaboration with the members of ICRR .
Assuming that the lightest neutral component in anSU(2)L gauge multiplet is the main ingredient of dark matter in the universe, we calculate the elastic scattering crosssection of the dark matter with nucleon, which is an important
quantity for the direct detection experiments. When the dark
matter is a real scalar or a Majorana fermion which has only
electroweak gauge interactions, the scattering with quarks
and gluon are induced through one- and two-loop quantum
processes, respectively, and both of them give rise to comparable contributions to the elastic scattering cross section.
We evaluate all of the contributions at the leading order andfind that there is an accidental cancellation among them. As
a result, the spin-independent cross section is found to beO(10−(46−48)) cm2 , which is far below the current experimental bounds.

Bibliography

In collaboration with the members of ICRR, Nagoya University, IPMU, California Institute of Technology, University ofTokyo, and MISC .

[1] J. Hisano, K. Ishiwata, N. Nagata, T. Takesako,[arXiv:1104.0228 [hep-ph]].

We calculate the nucleon-dark matter elastic scatteringcross section at the leading order of the strong coupling constant αs , which is relevant to the dark matter direct detection
experiments. Our approach based on the effective field theory
reveals that the interaction of dark matter with gluon as well as
quarks yields sizable contribution to the scattering cross section, though the gluon contribution is induced at loop level.
In the evaluation of the contribution, we treat separately theloop diagrams whose typical loop momentum scales are themasses of quarks and other heavier particles. Then, we haveproperly taken into account each contribution and completed
formulae for the cross section. As an application of our formulae, we study the direct detection of pure bino[1] and wino
dark matter[1, 2] in the supersymmetric model, and the first
Kaluza-Klein photon dark matter in the minimal universal extra dimension model[3]. It is found that there is a substantial
difference between all of the results and those in the previous
works. In the wino dark matter scenario we find the cross sec-

Astrophysics and Cosmology[Spokesperson : M. Kawasaki]

Kahler moduli double inflation
In collaboration with the members of ICRR.
We show that double inflation is naturally realized inKähler moduli inflation, which is caused by moduli associatedwith string compactification. We find that there is a small coupling between the two inflatons which leads to amplificationof perturbations through parametric resonance in the intermediate stage of double inflation. This results in the appearanceof a peak in the power spectrum of the primordial curvature
perturbation. We numerically calculate the power spectrum
and show that the power spectrum can have a peak on observationally interesting scales. We also compute the TT-spectrumof CMB based on the power spectrum with a peak and see thatit better fits WMAP 7-years data.

55

Bibliography[1] M. Kawasaki and K. Miyamoto, JCAP 1102, 004 (2011)[arXiv:1010.3095 [astro-ph.CO]].

Inflation from a Supersymmetric Axion
Model
In collaboration with the members of ICRR and Tohoku Univ.
We show that a supersymmetric axion model naturally induces a hybrid inflation with the waterfall field identified asa Peccei-Quinn scalar. The Peccei-Quinn scale is predicted
to be around 1015 GeV for reproducing the large-scale density perturbation of the Universe. After the built-in late-time
entropy-production process, the axion becomes a dark mattercandidate. Several cosmological implications are discussed.

Bibliography[1] M. Kawasaki, N. Kitajima and K. Nakayama, Phys. Rev.
D 82, 123531 (2010) [arXiv:1008.5013 [hep-ph]].

Prospects for Direct Detection of Inflationary Gravitational Waves by Next Generation
Interferometric Detectors
In collaboration with the member of ICRR, Nihon Univ. andNagoya Univ.

inflation model on the reheating temperature which influences
the amplitude and shape of the spectrum, and find that thegravitational waves could be detected for chaotic/natural inflation models with high reheating temperature. From the detection of the gravitational waves, a lower bound on the reheating
temperature could be obtained. The implications of this lower
bound on the reheating temperature for particle physics arealso discussed.

Bibliography[1] S. Kuroyanagi, T. Chiba and N. Sugiyama, Phys. Rev. D
83, 043514 (2011) [arXiv:1010.5246 [astro-ph.CO]].

Effects of Light Fields During Inflation
In collaboration with the member of IPMU.
In the inflationary universe, there can be light fields otherthan the inflaton. We explore a possibility that such light fields
source the primordial perturbations, while minimally affecting
the inflaton dynamics. We show that during inflation, fluctuations of the light fields can be converted to adiabatic curvature perturbations, which accumulate and become significant
by the end of the inflationary era. An additional goal of thiswork is to distinguish between light fields which can/cannot
be ignored during inflation. Such criteria become useful for
examining cosmological scenarios with multiple fields. As
concrete examples, our results are applied to D-brane inflation models. We consider effects from KK modes (oscillation
modes) of wrapped branes in monodromy-driven large-fieldmodels, and angular directions of throat geometries in warped
D-brane inflation.

Bibliography[1] T. Kobayashi and S. Mukohyama, Phys. Rev. D 81,
103504 (2010) [arXiv:1003.0076 [astro-ph.CO]].

Non-Gaussianity from Lifshitz Scalar
In collaboration with the members of IPMU.

Fig. 1.
Spectra of the gravitational wave background for different inflation models and different reheating temperatures
TRH = 106 ,107 ,108 GeV, shown with the sensitivity curves of DECIGO (dotted) and BBO (solid).

We study the potential impact of detecting the inflationary gravitational wave background by the future space-based
gravitational wave detectors, such as DECIGO and BBO.
The signal-to-noise ratio of each experiment is calculated forchaotic/natural/hybrid inflation models by using the precise
predictions of the gravitational wave spectrum based on numerical calculations. We investigate the dependence of each

A Lifshitz scalar with the dynamical critical exponent z= 3 obtains scale-invariant, super-horizon field fluctuations
without the need of an inflationary era. Since this mechanism
is due to the special scaling of the Lifshitz scalar and persistsin the presence of unsuppressed self-couplings, the resulting
fluctuation spectrum can deviate from a Gaussian distribution.
We study the non-Gaussian nature of the Lifshitz scalar’s intrinsic field fluctuations, and show that primordial curvature
perturbations sourced from such field fluctuations can havelarge non-Gaussianity of order fN L = O(100), which will be
detected by upcoming CMB observations. We compute thebispectrum and trispectrum of the fluctuations, and discuss
their configurations in momentum space. In particular, the bispectrum is found to take various shapes, including the local,
equilateral, and orthogonal shapes. Intriguingly, all integrals
in the in-in formalism can be performed analytically.

56

Bibliography

Quantum Statistical Corrections to Astro[1] K. Izumi, T. Kobayashi and S. Mukohyama, JCAP 1010, physical Photodisintegration Rates
031 (2010) [arXiv:1008.1406 [hep-th]].

Running Spectral Index from Inflation with
Modulations
In collaboration with the member of IPMU.
We argue that a large negative running spectral index, if
confirmed, might suggest that there are abundant structures in
the inflaton potential, which result in a fairly large (both positive and negative) running of the spectral index at all scales.
It is shown that the center value of the running spectral index
suggested by the recent CMB data can be easily explained byan inflaton potential with superimposed periodic oscillations.
In contrast to cases with constant running, the perturbation
spectrum is enhanced at small scales, due to the repeated modulations. We mention that such features at small scales may
be seen by 21 cm observations in the future.

Bibliography[1] T. Kobayashi and F. Takahashi, JCAP 1101, 026 (2011)[arXiv:1011.3988 [astro-ph.CO]].

In collaboration with the members of Univ. Notre Dame, Mimar Sinan Fine Arts Univ. Besiktas, NAOJ, Univ. Tokyo,
Univ. Wisconsin, Madison and ICRR.
Tabulated rates for astrophysical photodisintegration reactions make use of Boltzmann statistics for the photons involved as well as the interacting nuclei. We derive analytic
corrections for the Planck-spectrum quantum statistics of thephoton energy distribution. We show that these corrections
affect not only the photodisintegration rates but also modify
the conditions of nuclear statistical equilibrium as represented
in the Saha equation. We deduce new analytic corrections tothe classical Maxwell-Boltzmann statistics which can easily
be added to the reverse reaction rates of existing reaction network tabulations. We show that the effects of quantum statistics, though generally quite small, always tend to speed up
photodisintegration rates and are largest for nuclei and environments for which Q/kT 1. As an illustration, we examine
possible effects of these corrections on the r-process, the rpprocess, explosive silicon burning, the -process, and big bang
nucleosynthesis. We find that in most cases one is quite justified in neglecting these corrections. The correction is largest
for reactions near the drip line for an r-process with very highneutron density, or an rp-process at high temperature.

Destruction of 7 Be in big bang nucleosynthesis via long-lived sub-strongly interacting massive particles as a solution to the Li
Bibliography
problem
In collaboration with the members of ICRR.
We identify reactions which destroy Be7 and Li7 during
big bang nucleosynthesis (BBN) in the scenario of BBN catalyzed by a long-lived sub-strongly-interacting massive particle (sub-SIMP or X particle). The destruction associated withnonradiative X captures of the nuclei can be realized only if
the interaction strength between an X particle and a nucleon
is properly weaker than that between two nucleons to a degree
depending on the mass of X. Binding energies of nuclei to an
X particle are estimated taking the mass and the interaction
strength to nuclei of the X as input parameters. Nuclear reaction rates associated with the X are estimated naively andadopted in calculating evolutions of nuclear abundances. We
suggest that the Li7 problem, which might be associated withas-yet-unrecognized particle processes operating during BBN,
can be solved if the X particle interacts with nuclei strongly
enough to drive Be7 destruction but not strongly enough toform a bound state with He4 of relative angular momentum
L=1. Justifications of this scenario by rigorous calculations ofreaction rates using quantum mechanical many-body models
are highly desirable since this result involves many significant
uncertainties.

Bibliography[1] M. Kawasaki and M. Kusakabe, Phys. Rev. D 83,
055011 (2011) [arXiv:1012.0435 [hep-ph]].

[1] G. J. Mathews, Y. Pehlivan, T. Kajino, A. B. Balantekin and M. Kusakabe, Astrophys. J. 727, 10 (2011)[arXiv:1012.0519 [astro-ph.SR]].

Cosmological constraints on dark mattermodels with velocity-dependent annihilation cross section
In collaboration with the member of ICRR, Nagoya Univ.
KEK, and Tokyo Univ.
We derive cosmological constraints on the annihilation
cross section of dark matter with velocity-dependent structure, motivated by annihilating dark matter models throughSommerfeld or Breit-Wigner enhancement mechanisms. Inmodels with annihilation cross section increasing with decreasing dark matter velocity, big-bang nucleosynthesis andcosmic microwave background give stringent constraints.

Bibliography[1] J. Hisano, M. Kawasaki, K. Kohri, T. Moroi,
K. Nakayama and T. Sekiguchi, Phys. Rev. D 83, 123511(2011) [arXiv:1102.4658 [hep-ph]].

Improved estimation of radiated axions
from cosmological axionic strings
In collaboration with the member of ICRR, Kyoto Univ.
Tokyo Inst. Tech. and Tokyo Univ.

57

differential spectrum

103
102
101
100
10-1
10-2
0

50
100
150
comoving wavenumber kτcrit200

Fig. 2. Differential energy spectrum of radiated axions. Green (red)bars correspond to statistical errors alone (statistical and systematic errors). τcrit is the conformal time at the phase transition. The
scale in y-axis is arbitrary.

Cosmological evolution of axionic string network is analyzed in terms of field-theoretic simulations in a box of 5123
grids, which are the largest ever, using a new and more efficient identification scheme of global strings. The scaling parameter is found to be ξ = 0.87 + −0.14 in agreement withprevious results. The energy spectrum is calculated precisely
using a pseudo power spectrum estimator which significantly
reduces the error in the mean reciprocal comoving momentum. The resultant constraint on the axion decay constantleads to fa <= 3 ∗ 101 1 GeV. We also discuss implications
for the early Universe.

Bibliography[1] T. Hiramatsu, M. Kawasaki, T. Sekiguchi, M. Yamaguchi and J. Yokoyama, arXiv:1012.5502 [hep-ph].

Fig. 3. The distribution of the potential energy and the phase of the
PQ field.

Study of gravitational radiation from cosmic domain walls
In collaboration with the members of ICRR and Tohoku Univ.

Bibliography

In this work, following the previous study, we evaluate
the spectrum of gravitational wave background generated bydomain walls which are produced if some discrete symmetryis spontaneously broken in the early universe. We apply two
methods to calculate the gravitational wave spectrum: One is
to calculate the gravitational wave spectrum directly from numerical simulations, and another is to calculate it indirectly by
estimating the unequal time anisotropic stress power spectrumof the scalar field. Both analysises indicate that the slope ofthe spectrum changes at two characteristic frequencies corresponding to the Hubble radius at the decay of domain walls
and the width of domain walls, and that the spectrum between
these two characteristic frequencies becomes flat or slightly
red tilted. The second method enables us to evaluate the GW
spectrum for the frequencies which can not be resolved in thefinite box lattice simulations, but relies on the assumptions forthe unequal time correlations of the source.

[1] T. Hiramatsu, M. Kawasaki and K. Saikawa,[arXiv:1012.4558 [astro-ph.CO]].

Bibliography

Evolution of string-wall networks and axionic domain wall problem
In collaboration with the members of ICRR and Tohoku Univ.
We study the cosmological evolution of domain wallsbounded by strings which arise naturally in axion models. If
we introduce a bias in the potential, walls become metastableand finally disappear. We perform two dimensional latticesimulations of domain wall networks and estimate the decayrate of domain walls. By using the numerical results, we givea constraint for the bias parameter and the Peccei-Quinn scale.
We also discuss the possibility to probe axion models by direct
detection of gravitational waves produced by domain walls.

[1] M. Kawasaki and K. Saikawa, [arXiv:1102.5628 [astroph.CO]].

58

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

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

Iwaitani, Nyukawa-cho, Takayama-shi, Gifu Prefecture 506-2254
N 36◦ 06′ , E 137◦33′ , 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 407-0201
N 35◦ 47′ , E 138◦30′ , 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◦ 25′ 26′′ , E 137◦19′ 11′′ , 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

59

NORIKURA OBSERVATORY
Introduction

Cosmic Ray Physics

Norikura Observatory (36.10 ◦N and 137.55◦E) was
founded in 1953 and attached to ICRR in 1976. It is locatedat 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.
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 was successful in the first winter, during which thebattery backed-up solar panels and/or wind power generators
kept supplying the electricity to the wireless LAN and ongoing cosmic-ray experiments.

For the modulation study[2], two small experiments havebeen operated continuously for a long time. One is a neutron monitor operated to study the correlation of solar activity and the cosmic ray flux. The other is a high counting muon telescope consisting of 36 m2 scintillation counters to study the time variation of cosmic rays with energiesof 10–100 TeV over 20 years. The neutron monitor data areopen to researchers worldwide as a world observation network point (WDC). The 5 years from 2000 corresponded tothe solar maximum (2000) to a declining phase in the solar
cycle 23. The sun spot number in 2004 is approximately one
fourth of the those at maximum. Nonetheless, there occurred
active cosmic-ray phenomena associated with Coronal Mass
Ejection (CME). As regards solar cosmic rays, although manyground level enhancement (GLE) phenomena took place every year, such GLEs were observed only by neutron monitors
in Japan, as the maximum cosmic-ray energy was several GeV
in the GLEs and the magnetic rigidity cutoff in Japan is approximately 10 GeV for charged particles initiating secondary
muons. The sunspot numbers in the solar cycle 23 was smaller
than those in the previous cycle 22, indicating less solar activities of cycle 23. Although the GLEs above 10 GeV were notobserved in cycle 23, the total number of GLEs were greater incycle 23 than in cycle 22. This suggests that the charged particle acceleration associated with CME was less frequent in
the cycle 23 than in the cycle 23. On the other hand, Forbush
decreases in galactic cosmic rays caused by CME in the Sun
were observed frequently in cycle 23, though the solar activities have been in a declining phase since 2000. The worldwide
observation of Forbush decreases may contribute significantly
to space weather study.
In addition, space weather observation is actively madeby a 25 m2 muon hodoscope at Norikura Observatory[1],[2],[3],[4],[5], [6],[7],[8]. A loss cone anisotropy is observed
by a ground-based muon hodoscope in operation at Norikura
Observatory in Japan for 7 hours preceding the arrival of aninterplanetary shock at Earth on October 28, 2003. Best fitting
a model to the observed anisotropy suggests that the loss conein this event has a rather broad pitch-angle distribution with ahalf-width about 50◦ from the interplanetary magnetic field(IMF). According to numerical simulations of high-energy
particle transport across the shock, this implies that the shock
is a ”quasi-parallel” shock in which the angle between themagnetic field and the shock normal is only 6◦ . It is alsosuggested that the leadtime of this precursor is almost independent of the rigidity and about 4 hour at both 30 GV formuon detectors and 10 GV for neutron monitors (see paper[7]).
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 de-Fig. 1. Norikura Observatory.

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
the aerosol removal mechanism in the atmosphere or for the
botanical study of the high altitude environment.

60

tected 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.
In 1990, Nagoya group constructed a solar neutron telescope consisting of scintillators and lead plates, which measures the kinetic energy of incoming neutrons up to several
hundred MeV. This telescope observed high energy neutrons
associated with a large flare occurred on the 4th of June, 1991.
The same event was simultaneously detected by the neutron
monitor and the high counting muon telescope of Norikura
Observatory. This is the most clear observation of solar neutrons at the ground level in almost ten years since the firstobservation at Jungfraujoch in 1982.
A new type of the large solar neutron telescope (64 m 2
sensitive area) was constructed by Nagoya group in 1996. It
consists of scintillators, proportional counters and wood absorbers piled up alternately. This takes a pivotal role among aworldwide network of ground based solar neutron telescopesof the same type in Yangbajing in Tibet, Aragatz in Armenia,
Gornergrat in Switzerland, Chacaltaya in Bolivia and Mauna
Kea in Hawaii. The Sun is being watched for 24 hours using
this network.

Fig. 2. New Solar-Neutron Telescope of Nagoya Group.

The Sun reached the maximum activity in 2000 and the active phase continued for the next few years. All the telescopesin Norikura Observatory, neutron telescope, neutron monitor,
muon telescope and muon hodoscope, have been operated almost continuously through the solar cycle 23 in order to obtaincomprehensive information on the solar flare phenomena. Important hints for understanding the mechanism of cosmic-ray
acceleration near the solar surface will be obtained by thesemeasurements, especially by energy spectra measured by thetiming information of arriving neutrons and muons.
Furthermore, the relation between the electric fields induced by thunderclouds is studied recently[10]. The electricfields with thunderclouds change the intensity of secondary
cosmic rays observed on the ground. This effect has been
investigated using several detectors located at Norikura Observatory where excesses of 1 % and more of the averagecounting rate are observed when the observatory is covered
with thunderclouds. A frequency analysis of the time seriesof days with such excesses for the period 26 October 1990 to
15 January shows the expected summer maximum in the rateof occurrence and, surprisingly, a 26-day variation. An electric field mill was installed to help determine the relationshipbetween the intensity variations and the strength and direction of the field near the detector system: the excess is usuallyobserved when a negative electric field (accelerating negative
charges downward) greater than 10 kV/m is present in the atmosphere above the observatory. Based on Monte Carlo simulations, it is predicted that excess counting rates measured
without charge discrimination will be expected as a consequence of the excess of positive muons among the secondary
cosmic rays.
Subsequently, during thunderstorms on 2008 September
20, an intense radiation burst, comprising γ rays and electrons,
was detected [11] by at the Norikura observatory. Outside theobservatory, a radiation detection system was set up on 2008
September 4, and operated it until 2008 October 2. The system has a radiation monitor and environmental sensors. The
radiation monitor consists of a spherical NaI scintillator with adiameter of 7.62 cm, and a 5 mm thick plastic scintillator withan area of 45 × 40 cm2 . The plastic scintillator is enclosed
in an aluminum box with the top and bottom being 1 mm and
3 mm thick, respectively. Each scintillator has a photomultiplier (HAMAMATSU R878) of its own, and each output signal is fed to a self-triggering electronics system, incorporatinga 12 bit ADC. The burst, lasting 90 seconds, was associatedwith thunderclouds rather than lightning. The photon spectrum, extending to 10 MeV, can be interpreted as consistingof bremsstrahlung γ rays arriving from a source which is 60- 130 m in distance at 90% confidence level. The observed
electrons are likely to be dominated by a primary population
escaping from an acceleration region in the source.
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. A few examples include a search for super heavy particles with plastic plates, a precise measurementof atmospheric gamma rays and muons, collection of cosmic
dusts contained in the snow,measurement of air fluorescencelight yield for ultra high-energy cosmic-ray observation andthe performance study of the balloon borne cosmic ray experiments.

Environmental Study
One of the interesting topics is atmospheric environment
especially relating with atmospheric aerosol particles and water soluble gases. Because of its height, AC power supply,
accommodation facility, and accessibility of cargos, the cosmic ray observatory at Mt. Norikura provides a very unique
opportunity for atmospheric observation, especially for freetropospheric conditions. (The atmosphere lower than a few
kilometer is highly affected by the ground. This height levelis named as ’atmospheric boundary layer’. The height of theboundary layer is about 4 km in daytime and about 2 km innighttime around Norikura area. The atmosphere higher than
this atmospheric boundary layer is called ’free troposphere’.)61

Originally, atmospheric observation at the cosmic ray observatory was initiated to study cosmogenic radionuclides with
Prof. Suzuki at Shizuoka University. During early stage ofthe research at Mt. Norikura, a local effect of air contamination was recognized. To reduce air contamination fromdiesel exhausts and other activities around the observatory,
an atmospheric observation hut (6 m2 ) was installed at thewest end (windward) of the observatory in September 1999.
From year 2000, continuous monitoring (mostly mid-May to
mid-October) of meteorology was started, number-size distribution of aerosols, dew point, aerosol chemical composition, ozone and radon concentrations, and column amount ofaerosols from sky radiometer and ceilometer. Monitoring ofozone and radon concentrations was extended during 2 winters from 2001 to 2003. During summer season, also collected
were rain, fog, water-condensed aerosol samples. These samples combined with other parameters were used in several thesis (master) works and provided useful information about future seeds of hygroscopic study of aerosols. During the past 5
years, the following results[12],[13],[14] were obtained at Mt.
Norikura.
(1) Polluted air pumping effects over central Japanese Alps insummerUnder the clear sky conditions in summer, polluted air
from mountain valley area is lifted up about 4km of altitude(1km above the mountain top) over Mt. Norikura. The heightof observatory is within the atmospheric boundary layer in thedaytime, and is out of (higher than) the atmospheric boundary
layer in nighttime. The ratio of aerosol volume concentration
for daytime (polluted valley wind) to nighttime (clean freetropospheric) conditions was about 10. The air pumping effects over central Japanese Alps carry about 10 time higher
concentration of aerosols to the free-troposphere over Japan
in summer. Under the high-pressure system centered over thenorthwest Pacific in typical summer condition, backward air
trajectories were originated from the northwest Pacific to Mt.
Norikura and forward trajectories returned to the north Pacificwith some deviations to east Russia and the Kurile Islands.
The air pumping effects over mountain area provide a strong
pollution source mechanism to the free-troposphere over thewestern Pacific region including East Asia.
(2) Seasonal variation of aerosol chemistry in free troposphere
An automated aerosol sampler was installed at the site in
September 2000 to obtain seasonal aerosol samples. The sampler collected aerosols from mid-May to mid-October in 2001
and 2002. Results of its analysis showed seasonal changes
in major and minor constituents of aerosols associating withchanges of dominant air mass type over Japan.
(3) Vertical profiles of aerosols and clouds near the top of theatmospheric boundary layer
Ceilometer (lidar with small output energy) was installedin summer 2002, and was operated in 4 summer seasons. The
aerosol and cloud profiles near the top of the atmosphericboundary layer have been observed. Some events of Asiandust, and of smoke from Siberian forest fire at lower free troposphere have been detected.

Botanical Study
It is predicted that ecosystems in high-latitudes and alpine
regions are sensitive to global climatic warming. The significant increasing trends in air temperature are found in the Hida
Mountains, where Mt. Norikura is located. Thus, effects ofclimatic change caused by global warming on alpine ecosystems must be urgently studied in the alpine region of central
Japan. The Hida Mountains, strongly influenced by cold-air
masses from Siberia in winter, receive some of the heaviest
snowfall in the world. Due to heavy snowfall, dynamics ofalpine ecosystems may be peculiar to the Hida Mountains.
However, few studies have been made because of difficulty
in approach to the alpine study site. The inter-university research program of ICRR, gave an opportunity to make an
intensive study all year around in the alpine region on Mt.
Norikura[15],[16].
(1) Tree line dynamics
The tree form of evergreen sub-alpine fir (Abies mariesii)
is studied at the upper distribution limit (2500m above sea
level)
on Mt. Norikura. Leader stems degenerate above themaximum snowpack line (3-4m high) , whereas branches
below the snowpack line grow densely. In winter, leaves
above snowpack line were severely damaged by environmental stresses, such as abrasion by wind-blown snow particles,
desiccation, photoinhibition. Longevity of leaves was shortened to 4-5 years due to high mortality rate in winter. In contrast, leaves below snowpack line were protected from environmental stresses and their longevity was 11 years. As a result, biomass below the snowpack line takes more than 80withclimate change should have unfavorable effects on tree line
Abies mariesii.
(2) Alpine region
Pinus pumila, an alpine prostrated pine, is dominant in
the alpine regions (2500∼3000m above sea level). At windprotected sites, Pinus pumila grows vigorously with the treeheight of 1-2m. They were beried in snowpack throughout the
winter. At the wind-exposed ridge, growth is suppressed withthe tree height of 0.2-0.5m. Throughout the winter, the surface of the pine community was exposed due to strong windat the ridge. Leeward leaves were sound, because pine stems
with high elasticity were prostrated and buried in snow. Thus,
alpine pine can catch and accumulate snow to protect itself.
This feature may be advantageous to alpine trees in comparison with sub-alpine trees (Abies mariesii). On the other hand,at the windward side (western), cuticular layer covering epidermal cells of leaf was abraded probably due to wind-blownsnow and ice particles. By spring, abraded leaves at the windward side were dead caused by desiccation and photoinhibition. Even Pinus pumila community could reduce its habitatin small snowfall condition caused by global warming.

62

Impact of global warming due to so-called greenhousegases like CO2, CH4 and others on vegetation ecology isamong the most serious environmental issues. To investigate how plants response to global warming, an experimentof greenhouse effect on vegetation has been continued at ahigh mountain, Mt. Norikura (3,025 m a.s.l.), central Japan,
since 1997. Five open-top chambers which are small greenhouses with a size of maximum open-top diameter, the maximum basal diameter and the height of the chamber were 47
cm, 85 cm and 30 cm, respectively, were set over alpine plantcommunities consisting of small woody plants and herbaceous
vegetation. At places inside and outside of the chambers, seasonal changes in vegetation growth and phenology were observed every month. Using automatic data-recorders, someclimate elements such as air and ground temperatures, humidity and rainfall have been observed every hour. Some results
through the experiment were quite remarkable. Due to thetemperature enhancement of about 0.8 ◦ C for air temperature and about 0.3 ◦ C for ground temperature, plant growth
rates and phenological changes showed notable differences
between inside and outside of the chambers. The responses towarming, however, were different by different plant species.
The results suggest[17],[18] that dominant species in plantcommunity should be replaced by the species with a highphysiological response to warming and with a growing form
extending tree crown.

Bibliography[1] “Precursors of geomagnetic storms observed by themuon detector network”, K. Munakata, J. W. Bieber, S.
Yasue, C. Kato, M. Koyama, S. Akahane, K. Fujimoto,
Z. Fujii, J. E. Humble, and M. L. Duldig, J. Geophys.
Res., Vol. 105, No.A12, pp. 27,457-27,468 (2000).
[2] “Solar cycle variations of modulation parameters ofgalactic cosmic- rays in the heliosphere”, K. Munakata,
H. Miyasaka, I. Sakurai, S. Yasue, C. Kato, S. Akahane,
M. Koyama, D. L. Hall, Z. Fujii, K. Fujimoto, S. Sakakibara, J. E. Humble, and M. L. Duldig, Adv. Space Res.,
Vol.29, No.10, pp.1527-1532 (2002).
[3] “A 1.7 year quasi-periodicity in cosmic ray intensity variation observed in the outer heliosphere”, C.
Kato, K. Munakata, S. Yasue, K. Inoue, and F. B.
McDonald, J. Geophys. Res., Vol.18, No.A10, p.1367,
doi:10.1029/2003JA009897 (2003).

J. W. Bieber, P. Evenson, R. Pyle, Z. Fujii, M. Tokumaru, M. Kojima, K. Marubashi, M. L. Duldig, J.
E. Humble, M. Silva, N. Trivedi, W. Gonzalez andN. J. Schuch, Geophys. Res. Lett., Vol.31, L19803,
doi:10.1029/2004GL020803 (2004).
[7] “A “loss-cone” precursor of an approaching shock observed by a cosmic-ray muon hodoscope on October 28,
2003”, K. Munakata, T. Kuwabara, S. Yasue, C. Kato,
S. Akahane, M. Koyama, Y. Ohashi, A. Okada, T. Aoki,
H. Kojima and J. W. Bieber, Geophys. Res. Lett., Vol.32,
L03S04, doi:10.1029/2004GL021469, 2005.
[8] “CME-geometry and cosmic-ray anisotropy observed bya prototype muon detector network”, K. Munakata, T.
Kuwabara, J. W. Bieber, P. Evenson, R. Pyle, S. Yasue,
C. Kato, Z. Fujii, M. L. Duldig, J. E. Humble, M. R.
Silva, N. B. Trivedi, W. D. Gonzalez and N. J. Schuch,
Adv. Space Res., doi:10.1016/j.asr.2003.05.064, 2005, inpress.
[9] “Acceleration below Thunder Clouds at Mount
Norikura”, by the Tibet hybrid experiment”, Y. Muraki
et al., Proceedings in the 28th International Cosmic Ray
Conference, (31 July - 7 August 2003, Tsukuba, Japan),Vol.7, pp 4177-4180.
[10] “Effects of atmospheric electric fields on cosmic rays”,
Y. Muraki et al., Phys. Rev. D, 69, 123010–1-13 (2004).
[11] “Observation of an energetic radiation burst frommountain-top thunderclouds”, H. Tsuchiya et al., Phys.
Rev. Lett., 102, 255003 (2009).
[12] K. Osada, M. Kido, C. Nishita, K. Matsunaga, Y.
Iwasaka, M. Nagatani, H. Nakada, Changes in ionic constituents of free tropospheric aerosol particles obtainedat Mt. Norikura (2770 m a. s. l.), central Japan, during
the Shurin period in 2000, Atmos. Environ., 36, 54695477, 2002.
[13] “Atmospheric diffusion process based on time change of
222 Rn vertical profile”, K. Yoshioka, Journal of Aerosol
Research, Japan, 17, 267-275, 2002 (in Japanese).
[14] “Free-tropospheric aerosols based on airplane andmountain observations”, K. Osada, Journal of Aerosol
Research, Japan, 15, 335-342, 2000 (in Japanese).

[4] “Exploration of the heliosphere by cosmic rays”, K. Munakata, published as the chapter 2 of Advances in SolarTerrestrial Physics, pp.101-116, edited by H. Oya, published by TERRAPUB, Tokyo (2004).

[15] “Diurnal changes in needle gas exchange in alpine Pinus pumila during snow-melting and summer seasons”,
A. Ishida, T. Nakano, S. Sekikawa, E. Maruta, T. Masuzawa, Ecological Research 16, 107-116 (2001).

[5] “Cosmic-ray modulation in the heliosphere: global andnear-earth measurements and modeling”, K. Munakata,
Rapporteur paper in 28th International Cosmic Ray
Conference, Vol.8, edited by T. Kajita et al., pp.251-276,
Univ. Acad. Press, Tokyo (2004).

[16] “Effects of high light and low temperature during harsh
winter on needle photodamage of Abies Mariesii growing at the forest limit on Mt. Norikura in Central Japan”,
J. Yamazaki, A. Ohashi, Y. Hashimoto, E. Negishi, S.
Kumagai, T. Kubo, T. Oikawa, E. Maruta, Plant Science
165, 257-264, (2003).

[6] “Geometry of an interplanetary CME on October 29,
2003 deduced from cosmic rays”, T. Kuwabara, K. Munakata, S. Yasue, C. Kato, S. Akahane, M. Koyama,

63[17] “Chemistry of surface water at a volcanic summit area,
Norikura, central Japan: Multivariate statistical approach”, K. Anazawa and H. Ohmori, Chemosphere, 45,
807-816, (2001).
[18] “Experimental research on vegetation response to artificial warming on a mid-latitude high mountain, central
Japan”, H. Ohmori, J.H. Iguchi, T. Ohta, A. Terazono
and K. Hikita, Geogr. Rev. Japan, 77, 301-320, (2004).

64

AKENO OBSERVATORYThe Observatory is in Akeno town of Hokuto-city situated
20 km west of Kofu and 130 km west of metropolitan Tokyo.
The location is at the longitude of 138.5◦E and the latitude of
35.5◦N. The altitude is ∼900 m above sea level (Fig.1).
The Observatory was established in 1977 as a research
center for air shower studies in the very high energy region.
It has been administered by the ICRR as a facility of jointuniversity-use.
The Akeno Air Shower Experiment started in 1979 withan array covering 1 km 2 area (1 km2 array). The array wasenlarged to 20 km2 in 1985 and was gradually expanded to
Akeno Giant Air Shower Array (AGASA) of approximately
100 km2 area by 1990.

Fig. 2. AGASA scintillation detector and data acquisition system.

Fig. 1. Aerial View of Akeno Observatory and 1 km2 array area

One of the distinctive features of Akeno experiments isthat the measurement was 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). The wide energy coverage wasaccomplished by the arrays of scintillation detectors of various inter-detector spacings from 3 m to 1 km and with different triggering conditions.
The AGASA was an air shower array composed of 111
scintillation detectors and 27 muon detectors. Each component was placed by about 1 km separation and covered theground area of 100 km2 in the neighboring villages of the observatory. All detectors were interconnected by optical fibers
for the precise timing determination and the data transmission (Fig.2). The AGASA was the largest air shower array inthe world. Its operation was ceased in January of 2004 after
the construction of Telescope Array (TA) had been funded in
2003.
The AGASA observed a total of 11 events with energies
exceeding 1020 eV in 13 years of operation, and heralded rich
physics of ultra-high energy cosmic rays now being exploredby the Pierre Auger Observatory in Argentina and the Telescope Array (TA) in Utah, USA.
The observatory currently supports two experiments by

the university users; one for the observation of galactic cosmic ray modulation by the muon telescope and another forthe rapid follow-up observation of gamma ray bursts by themulti-color robotic telescope. It is also used for supporting theoperation of TA and various research and development works
related to the measurement of very high energy cosmic rays.

65

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 was established in 1995 in order to operate Super-Kamiokande. The underground laboratories are located under Mt.Ikeno-yama andaccessible to the experimental site through a 1.7 km horizontal tunnel. The observatory also has surface research buildings
and a dormitory located at the distance of 15 minutes drivefrom the entrance of the mine. The Super-Kamiokande experiment had discovered neutrino oscillations through the observations of atmospheric and solar neutrinos (see the section for
Neutrino and Astroparticle Division). The atmospheric neutrino oscillation was confirmed by the K2K accelerator neutrino experiment, which was conducted between 1999 and2004. A new long baseline neutrino oscillation experiment(the T2K experiment) using a high intensity beam, 50 timesof the K2K neutrino beam, by the J-PARC proton accelerator
has started in 2009.

Fig. 1. Map of Kamioka observatory.

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 isa proto-type of the planned 3 km gravitational wave antenna
called LCGT, aiming to detect gravitational waves from extraterrestrial sources (see section of Astrophysics Gravity Division). Using the low radioactive background environment in
the Kamioka Mine, A dark matter experiment, called XMASS
is being prepared. The XMASS group has performed R&D
study using a small proto-type detector and subsequently, theconstruction of the 800kg liquid xenon detector was started in2007 and will be ready for data taking by the summer in 2010.
The R&D study of a tracking type detector for dark mattersearch by the Kyoto University group (the NEWAGE experi-ment) has also been performed in an underground laboratory.
The construction of the CANDLE experiment (Osaka Univ.),
a double beta decay experiment in the Kamioka Underground
Observatory, has started in 2009. The study to improve theneutrino detection sensitivity by adding gadolinium to SuperKamiokande is on going. Especially in 2009, a new cavern
dedicated for the R&D study of the gadolinium project was
excavated. In order to support those experiments and also related R&D works, the Observatory is equipped with low background Germanium detector, ICP-MS and so on to measureextremely low radioactive backgrounds.

Fig. 2. Super-Kamiokande detector.

Fig. 3. 100 m baseline laser interferometers for gravitational wave andgeophysics in Kamioka mine.

66

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 practical jobs of this center is the organization of neutrino-related meetings. On March
9, 2011, we hosted one domestic neutrino workshop on highenergy cosmic neutrinos. About 30 physicists participated inthis meeting.
Members of this center have been involved in the SuperKamiokande and T2K experiments, carrying out researches
in neutrino physics. Atmospheric neutrino data from SuperKamiokande give one of the most precise pieces of information on neutrino oscillations. With increased data, it ismore important to have better predictions of the neutrino flux.
Therefore, in addition to data analysis of the data from theseexperiments, we work on calculating the atmospheric neutrinoflux.
It is important that the general public knows about theachievements of the present science. For this reason, we holdpublic lectures every year. From FY2009, two public lectures
per year are co-sponsored by this Institute and the Institute for
the Physics and Mathematics of the Universe. The spring lecture is co-organized by RCCN and the Public Relation Officeof ICRR. The public lecture was held on April 17 (Sat), 2010
at Kashiwa Library. About 100 people heard the lecture.

Fig. 1. Public lecture held in Kashiwa in April 18, 2009.

RCCN, together with the computer committee of ICRR, isin charge of operating the central computer system in ICRR.
It had been highly utilized for the analyses and simulations ofvarious cosmic-ray physics. In 2010, the total disk size wasincreased by more than a factor of 2, allowing more data to
be studied by each research group. RCCN also supported theusers of the computer system, including physicists working
outside ICRR.
Since 2004, RCCN has been acting as a body for accepting the ICRR inter-university programs related to the low-background 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 that are related to this facility is described
elsewhere.

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APPENDICES

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

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

F. Inter-University Researches
G. List of Committee Members(a) Board of Councillors(b) Advisory Committee(c) Inter-University Research Advisory Committee

H. List of Personnel

68

A. ICRR Workshops and Ceremonies

GWADW2010 (Gravitational Wave Advanced Detector Workshop 2010)–Future directions for Laser Gravitational Wave Detectors–
Date: May 16–21, 2010
Place: Hearton Hotel Kyoto, Kyoto, Japan
Outline: The workshop was organized for experimentalists of gravitational wave detection in the world. Originally it used tobe held in annual base at Elba island in Italy. Since 2009, the workshop place becomes to be in rotation among Europe, America
and Japan. This was the first time in Japan. In this workshop, we laid the groundwork for future detectors of gravitational waves.
Leading the way would be lessons learned at CLIO, in particular, how to work underground and at cryogenic temperatures.
The ongoing operations at Enhanced LIGO, Virgo+, TAMA and GEO600 gave us an understanding of some of the problems to
be faced in building and operating second generation Advanced Detectors (Advanced LIGO, Advanced Virgo, LCGT, AIGO
and GEO-HF) and in planned third generation detectors like ET. They might also impact plans for space based antennae suchas LISA and DECIGO. The organizers hoped that young scientists and students would find the means to attend and this was
finally satisfied by the attendance of many young scientists.
Participants: 40 from Japan, 19 from USA, 15 from UK, 10 from Italy, 8 from France, 7 from Germany, 3 from Australia, 3from Netherlands, 1 from Russia, and 1 from Taiwan.

International Symposium on the Recent Progress of Ultra-High Energy Cosmic
Ray Observation
Date: Dec 10–12, 2010
Place: Nagoya Congress Center, Aichi, Japan
Outline: In this Symposium, recent progress of Ultra-High Energy Cosmic Ray (UHECR) observation was reviewed. Such
topics as the energy spectrum, mass composition, hadronic interactions at extremely high energy, anisotropy and arrival directions of UHECRs were reported and discussed. Future large scale ground experiments and space observatories were reviewed.
Participants: 59 from Japan, 19 from USA, 8 from Italy, 8 from Korea, 6 from Germany, 5 from France, 3 from Russia, 2from Belgium, 1 from China, 1 from Ireland, 1 from Mexico, and 1 from Spain.

B. ICRR Seminars
1. Apr 1, 2010: Akira Tonomura (HITACHI), ”Physics Explored by Electron Microscope”
2. Apr 5, 2010: Kaoru Yokoya (KEK), ”Current Status of Linear Collider Technology”
3. Apr 16, 2010: Akira Ukawa (Tsukuba University), ”Current Status and Future of Lattice QCD”
4. May 12, 2010: David Tanner (University of Florida), ”Seeking the unseen: gravitational waves with LIGO and axion
dark matter with ADMX”
5. May 14, 2010: Hironari Miyazawa (Univ. of Tokyo), ”Discovery of the muon by Yoshio Nishina”
6. May 21, 2010: Kota Murase (Tokyo Institute of Technology), ”Gamma-Ray Signals from Ultrahigh-Energy Cosmic-Ray
Sources and Implications of Ultrahigh-Energy Nuclei Production in the Sources”
7. May 28, 2010: Enrico Barausse (University of Maryland), ”Hamiltonian of a Spinning Test-particle in Curved Spacetime”

69

8. Jun 4, 2010: Kazuo Makishima (University of Tokyo), ”SUZAKU observation of magnetars—neutron stars with ultrastrong magnetic field”
9. Jun 25, 2010: Kazuoki Munakata (Shinshu University), ”Sidereal anisotropy of galactic cosmic ray intensity: Latest
results of two hemisphere observations by Tibet & IceCube”
10. Jul 16, 2010: Hideo Matsuhara (JAXA/ISAS), ”From AKARI to SPICA: Present and future of Space Infrared Astronomy”
11. Jul 23, 2010: Shigehiro Nagataki (Kyoto University), ”Numerical High-Energy Cosmic Rays and Astrophysics”
12. Jul 30, 2010: Hiroyuki Sagawa (ICRR), ”Recent results from the Telescope Array experiment”
13. Dec 15, 2010: Shuhei Okubo (Earthquake Research Institute, U. Tokyo), ”Solid State Earth Science and CosmicRay/Gravitational-wave Research”
14. Dec 28, 2010: Martin A. Lee (ICRR/U. New Hampshire), ”The Interaction of the Heliosphere with the Local Interstellar
Medium: Interstellar Gas, Pickup Ions, Anomalous Cosmic Rays and the Solar Wind Termination Shock”
15. Jan 24, 2011: Ichiro Nakatani (ICRR/Aichi University of Technology), ”Space Robot”
16. Feb 2, 2011: Jun Kataoka (Waseda University), ”Recent progress on high energy emission from AGN jets”

C. List of Publications(a) Papers Published in Journals
1. ”Measurement of K + production cross section by 8 GeV protons using high energy neutrino interactions in the SciBooNE
detector”, SciBooNE Collaboration (G. Cheng et al.), to be published in Phys.Rev.D, [arXiv:1105.2871 [hep-ex]].
2. ”Measurement of inclusive charged current interactions on carbon in a few-GeV neutrino beam”, SciBooNE Collaboration (Y. Nakajima et al.), Phys.Rev.D83:012005 2011, [arXiv:1011.2131 [hep-ex]].
3. ”Improved measurement of neutral current coherent π 0 production on carbon in a few-GeV neutrino beam”, SciBooNE
Collaboration (Y. Kurimoto et al.), Phys.Rev.D81:111102 2010, [arXiv:1005.0059 [hep-ex]].
4. ”Measurement of inclusive π 0 production in the Charged-Current Interactions of Neutrinos in a 1.3-GeV wide bandbeam”, K2K Collaboration (C. Mariani et al.), Phys.Rev. D83:054023, 2011, [arXiv:1012.1794 [hep-ex]].
5. ”Solar neutrino results in Super-Kamiokande-III”, Super-Kamiokande Collaboration (K. Abe et al.), Phys. Rev.
D83:052010, 2011, [arXiv:1010.0118 [hep-ex]].
6. ”Atmospheric neutrino oscillation analysis with sub-leading effects in Super-Kamiokande I, II and III”, SuperKamiokande Collaboration (R. Wendell and C. Ishihara et al.), Phys. Rev. D81:092004, 2010, [arXiv:1002.3471 [hepex]].
7. ”Improvement of low energy atmospheric neutrino flux calculation using the JAM nuclear interaction model”, M. Honda,
T. Kajita, K. Kasahara and S. Midorikawa, to be published in Phys. Rev. D, [arXiv:1102.2688 [astro-ph.HE]].
8. ”Atmospheric Neutrinos And Discovery Of Neutrino Oscillations”, T. Kajita, Proc. Japan Acad. B86, 303-321, 2010.
9. ”Further study of neutrino oscillation with two detectors in Kamioka and Korea”, F. Dofour, T. Kajita, E. Kearns and K.
Okumura, Phys. Rev. D81: 093001, 2010, [arXiv:1001.5165 [hep-ph]].
10. ”Status of Very High Energy Gamma Ray Astronomy and Future Prospects”, M.Teshima, Tenmmon Geppou, Vol 104-7,
2011 333.
11. ”A search for very-high energy gamma-ray emission from Scorpius X-1 with the MAGIC telescopes”, MAGIC Collaboration (J. Aleksi and M. Teshima et al.), Astrophys. J. Letters 735, 2011 L5, [arXiv:1103.5677].
12. ”MAGIC discovery of VHE Emission from the FSRQ PKS 1222+21”, MAGIC Collaboration (J. Aleksi and M. Teshima
et al.), Astrophys. J. Letters 730, 2011, L8, [arXiv:1101.4645].

7013. ”MAGIC observations and multiwavelength properties of the quasar 3C279 in 2007 and 2009”, MAGIC Collaboration(J.
Aleksi and M. Teshima et al.), Astron. Astrophys. 530, 2011, A4, [arXiv:1101.2522].
14. ”Observations of the Blazar 3C 66A with the MAGIC Telescopes in Stereoscopic Mode”, MAGIC Collaboration (J.
Aleksi and M.Teshima et al.), Astrophys. J. Lett. 726, 2010, 58, [arXiv:1010.0550].
15. ”Detection of very high energy γ -ray emission from the Perseus cluster head-tail galaxy IC 310 by the MAGIC
Telescopes”, MAGIC Collaboration (J. Aleksi and M. Teshima et al.), Astrophys. J. Lett. 723, 2010, L207-212,[arXiv:1009.2155].
16. ”Spectral Energy Distribution of Markarian 501: Quiescent State vs. Extreme Outburst”, VERITAS and MAGIC Collaboration(V.A.Acciari and M. Teshima et al.), Astrophys. J. 729, 2010, 2, [arXiv:1012.2200].
17. ”Insights Into the High-Energy Gamma-ray Emission of Markarian 501 from Extensive Multifrequency Observationsin the Fermi Era”, FERMI, MAGIC, VERITAS and MAGIC Collaboration(A.A.Abdo and M. Teshima et al.), to be
published in Astrophys. J., [arXiv:1011.5260].
18. ”Design Concepts for the Cherenkov Telescope Array”, CTA Consortium (R.Enomoto, S.Inoue, M. Ohishi, M. Teshima,
T. Yoshikoshi et al.), to be published in Astro Particle Physics, [arXiv:1008.3703].
19. ”GRB100906A: Ashra-1 observation of early optical emission”, Y. Asaoka et al., GCN Circular, 11291, 2010.
20. ”Cosmic-ray energy spectrum around the knee obtained by the Tibet experiment and future prospects”, M. Amenomori
et al., Advances in Space Research, 47, 629-639, 2011.
21. ”Cosmic-ray energy spectrum around the knee observed with the Tibet air-shower experiment”, M. Amenomori et al.,Astrophysics and Space Sciences Transactions, 7, 15-20, 2011.
22. ”Expansion of Linear Range of Pound-Drever-Hall Signal”, Shinji Miyoki, Souichi Terada,and Takashi Uchiyama, Appl.
Optics 49, 5217, 2010.
23. ”Optical properties measurement of an Al2 O3 mirror substrate for the Large-Scale Cryogenic Gravitational Wave Telescope (LCGT)”, M. Tokunari, et al., Class. Quantum Grav. 27, 185015, 2010.
24. ”Status of LCGT”, K. Kuroda (on behalf of the LCGT Collaboration), Class. Quantum Grav. 27, 084004, 2010.
25. ”Keck Spectroscopy of Faint 3 < z < 7 Lyman Break Galaxies: A High Fraction of Line Emitters at Redshift Six”, Stark,
D. P., R. S. Ellis, and M. Ouchi, The Astrophysical Journal, 728, L2, 2011, [arXiv:1009.5471 [astro-ph]].
26. ”The Subaru Lyα blob survey: a sample of 100-kpc Lyα blobs at z= 3”, Matsuda Y. et. al., Monthly Notices of theRoyal Astronomical Society, 410, L13, 2011, [arXiv:1010.2877 [astro-ph]].
27. ”Lyman-α Emitters and Lyman-Break Galaxies at z = 3-6 in Cosmological SPH Simulations”, Nagamine K., M. Ouchi,
V. Springel, and L. Hernquist, Publications of the Astronomical Society of Japan, 62, 1455, 2010, [arXiv:0802.0228[astro-ph]].
28. ”Statistics of 207 Lyα Emitters at a Redshift Near 7: Constraints on Reionization and Galaxy Formation Models”, Ouchi
M. et. al., The Astrophysical Journal, 723, 869, 2010, [arXiv:1007.2961 [astro-ph]].
29. ”Global amount of dust in the universe”, Fukugita M., [arXiv:1103.4191 [astro-ph]].
30. ”Characterization of Sloan Digital Sky Survey Stellar Photometry”, Fukugita M., N. Yasuda, M. Doi, J. E. Gunn, andD. G. York, The Astronomical Journal, 141, 47, 2011, [arXiv:1008.0510 [astro-ph]].
31. ”Supernovae in the Subaru Deep Field: the rate and delay-time distribution of type Ia supernovae out to redshift 2”,
Graur O. et. al., [arXiv:1102.0005 [astro-ph]].
32. ”Microwave Emission from the Edgeworth-Kuiper Belt and the Asteroid Belt Constrained from WMAP”,Ichikawa,
K. and M. Fukugita, to be published. [arXiv:1011.4796 [astro-ph]].
33. ”The Sloan Digital Sky Survey Quasar Lens Search. IV. Statistical Lens Sample from the Fifth Data Release”, Inada N.,
et. al., The Astronomical Journal, 140, 403, 2010, [arXiv:1005.5570 [astro-ph]].
34. ”A complete calculation for direct detection of Wino dark matter”, J. Hisano, K. Ishiwata and N. Nagata, Phys. Lett.
B690, 311, 2010, [arXiv:1004.4090 [hep-ph]].

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35. ”Reevaluation of Higgs-Mediated mu-e Transition in the MSSM”, J. Hisano, S. Sugiyama, M. Yamanaka and
M. J. S. Yang, Phys. Lett. B694, 380, 2011, [arXiv:1005.3648 [hep-ph]].
36. ”Gluon contribution to the dark matter direct detection”, J. Hisano, K. Ishiwata and N. Nagata, Phys. Rev. D82, 115007,
2010, [arXiv:1007.2601 [hep-ph]].
37. ”Charge-Breaking Constraints on Left-Right Mixing of Stau’s”, J. Hisano and S. Sugiyama, Phys. Lett. B696, 92, 2011,[arXiv:1011.0260 [hep-ph]].
38. ”Right-handed sneutrino dark matter and big-bang nucleosynthesis”, K. Ishiwata, M. Kawasaki, K. Kohri and T. Moroi,
Phys. Lett. B689, 163, 2010, [arXiv:0912.0781 [hep-ph]].
39. ”Primordial Black Holes as All Dark Matter”, P. H. Frampton, M. Kawasaki, F. Takahashi and T. T. Yanagida, JCAP
1004, 023, 2010, [arXiv:1001.2308 [hep-ph]].
40. ”Numerical study of Q-ball formation in gravity mediation”, T. Hiramatsu, M. Kawasaki and F. Takahashi, JCAP 1006,
008, 2010, [arXiv:1003.1779 [hep-ph]].
41. ”Inflation from a Supersymmetric Axion Model”, M. Kawasaki, N. Kitajima and K. Nakayama, Phys. Rev. D82, 123531,
2010, [arXiv:1008.5013 [hep-ph]].
42. ”Gravitational Waves from Collapsing Domain Walls”, T. Hiramatsu, M. Kawasaki and K. Saikawa, JCAP 1005, 032,
2010, [arXiv:1002.1555 [astro-ph.CO]].
43. ”Gravitational waves from kinks on infinite cosmic strings”, M. Kawasaki, K. Miyamoto and K. Nakayama, Phys. Rev.
D81, 103523, 2010, [arXiv:1002.0652 [astro-ph.CO]].
44. ”B-mode polarization induced by gravitational waves from kinks on infinite cosmic strings”, M. Kawasaki, K. Miyamoto
and K. Nakayama, Phys. Rev. D82, 103504, 2010, [arXiv:1003.3701 [astro-ph.CO]].
45. ”Kahler moduli double inflation”, M. Kawasaki and K. Miyamoto, JCAP 1102, 004, 2011, [arXiv:1010.3095 [astroph.CO]].
46. ”Destruction of 7 Be in big bang nucleosynthesis via long-lived sub-strongly interacting massive particles as a solution
to the Li problem”, M. Kawasaki and M. Kusakabe, Phys. Rev. D83, 055011, 2011. [arXiv:1012.0435 [hep-ph]].
47. ”Quantum Statistical Corrections to Astrophysical Photodisintegration Rates”, G. J. Mathews, Y. Pehlivan, T. Kajino,
A. B. Balantekin and M. Kusakabe, Astrophys. J. 727, 10, 2011, [arXiv:1012.0519 [astro-ph.SR]].
48. ”Prospects for direct detection of inflationary gravitational waves by next generation interferometric detectors”, S. Kuroyanagi, T. Chiba and N. Sugiyama, Phys. Rev. D83, 043514, 2011, [arXiv:1010.5246 [astro-ph]].
49. ”First very low frequency detection of short repeated bursts from magnetar SGR J1550-5418”, Tanaka, Y. T., et al.,Astrophys. J., 721, L24-L27, 2010.
50. ”Solar-type magnetic reconnection model for magnetar giant flares”, Masada, Y., et al., Pub. Astron. Soc. Japan, 104,
1093-1102, 2010.
51. ”Effect of the solar wind proton entry into the deepest lunar wake”, Nishino, M. N., et al. Geophys. Res. Lett., 37,
L12106.1-4, 2010.
52. ”In-flight performance and initial results of plasma energy angle and composition experiment (PACE) on SELENE(Kaguya)”, Saito, Y., et al., Space Sci. Rev., 154, 265-303, 2010.
53. ”Synchronized Northern Hemisphere Climate Change and Solar Magnetic Cycles during the Maunder Minimum”, Y.T.
Yamaguchi et al., PNAS, 2010.
54. ”Explosive volcanic eruptions triggered by cosmic rays: volcano as a bubble chamber”, T. Ebisuzaki et al., Gondwana
Research, 2010.
55. ”Is the Sun heading for another Maunder Minimum? -Precursors of the grand solar minima”, H. Miyahara et al., Journalof Cosmology, 8, 1970, 2010.
56. ”Variations of Solar Activity and Climate during the Past 1200 Years”, H. Miyahara, Journal of Geography, 119, 3, 510,
2010.

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57. ”Universality test of the charged Higgs boson couplings at the LHC and at B factories”, Alan S. Cornell, et al., Phys.
Rev. D81, 115008, 2010, [arXiv:0906.1652 [hep-ph]].

(b) Conference Papers
1. ”Messenger of new physics”, W. Rodejohann and M. Shiozawa, Proceeding of the Neutrino Oscillation Workshop(NOW2010), September, 2010, to be published in Nuclear Physics B Proceedings Supplement.
2. ”Study of gamma-ray production in neutral-current neutrino-oxygen interactions and the detection of neutrinos fromsupernova explosion.”, T. Mori, M. Sakuda, A. Tamii, H. Toki, M. Nakahata, and K. Ueno, AIP Conf.Proc. 1269,
418-420, 2010.
3. ”Asian Facilities”, M. Nakahata, Proceedings of Topical Workshop in Low Radioactivity Techniques (LRT2010), August, 2010.
4. ”Low background techniques in XMASS”, A. Takeda for the XMASS Collaboration, Proceedings of Topical Workshop
in Low Radioactivity Techniques (LRT2010), August, 2010.
5. ”Status of XMASS Experiment”, S. Moriyama, Proceedings of identification of dark matter 2010 (IDM2010), July,
2010.
6. ”XMASS”, M. Yamashita, Proceedings of Patras Workshop on Axions, WIMPs, WISPs , July, 2010.
7. ”Recent results on atmospheric neutrino oscillation from Super-Kamiokande”, Y. Obayashi for the Super-Kamiokande
Collaboration, Prepared for 35th International Conference on High Energy Physics: ICHEP 2010, Paris, France, 21-28
Jul 2010. Published in PoS ICHEP2010:313,2010.
8. ”Search for Nucleon Decays in Super-Kamiokande”, M. Miura for the Super-Kamiokande Collaboration, Prepared for35th International Conference on High Energy Physics: ICHEP 2010, Paris, France, 21-28 Jul 2010. Published in PoSICHEP2010:403,2010.
9. ”Solar neutrino results from Super-Kamiokande”, H. Sekiya for the Super-Kamiokande Collaboration, Prepared for 35th
International Conference on High Energy Physics: ICHEP 2010, Paris, France, 21-28 Jul 2010. Published in PoS ICHEP
2010:330,2010.
10. ”Construction and performance of XMASS 800kg detector”, J. LIU for XMASS collaboration, Proceedings of 24th
International Conference on Neutrino Physics and Astrophysics (Neutrino 2010), June, 2010.
11. ”Radon Removal from Liquid Xenon”, K. Martens for XMASS collaboration, Proceedings of 24th International Conference on Neutrino Physics and Astrophysics (Neutrino 2010), June, 2010.
12. ”Large Underground Water Cherenkov Detectors”, M. Shiozawa, Proceeding of the XXIV International Conference
on Neutrino Physics and Astrophysics (Neutrino2010), June, 2010. to be published in Nuclear Physics B Proceedings
Supplement.
13. ”Commissioning of the new electronics and online system for the Super-Kamiokande experiment”, S. Yamada, et. al. for
the Super-Kamiokande Collaboration, Y. Arai, K. Ishikawa, A. Minegishi, and T. Uchida, IEEE Trans.Nucl.Sci.57:428432, 2010.
14. ”Status and prospect of atmospheric neutrinos and long baseline studies”, T. Kajita, J. Phys. Conf. Ser. 203: 012012,
2010.
15. ”The Telescope Array experiment: Status and Prospects”, H. Tokuno et al. (Telescope Array Collaboration), Proceedingsof 14th International Conference On Calorimetry In High Energy Physics (CALOR2010), 10-14 May 2010, AIP Conf.
Proc.1238, 365-368, 2010.
16. ”Measurement of UHECRs by the Telescope Array (TA) experiment”, M. Fukushima for the Telescope Array Collaboration, Proceedings of XVI International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI2010),
28 Jun - 2 Jul 2010.
17. ”Results from the Telescope Array Experiment”, D. Ikeda for the Telescope Array Collaboration, Proceedings of the
22nd European Cosmic Ray Symposium (ECRS2010), 3-6 Aug 2010.

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18. ”Recent Results from the Telescope Array Experiment”, H. Sagawa for the Telescope Array Collaboration, Proceedingsof the International Symposium on the Recent Progress of Ultra-high Energy Cosmic Ray Observation (UHECR2010),
10-12 Dec 2010.
19. ”Absolute energy calibration of FD by an electron linear accelerator for Telescope Array”, T. Shibata et al., Proceedingsof UHECR2010, 10-12 Dec 2010.
20. ”Energy measurement and spectrum by the Telescope Array”, D. Ikeda for the Telescope Array Collaboration, Proceedings of UHECR2010, 10-12 Dec 2010.
21. ”Measurement of UHECR composition by TA”, Y. Tameda for the Telescope Array Collaboration, Proceedings of
UHECR2010, 10-12 Dec 2010.
22. ”Central Laser Facility Analysis at The Telescope Array Experiment”, Y. Takahashi et al. (the Telescope Array Collaboration), Proceedings of UHECR2010, 10-12 Dec 2010.
23. ”Comparison of CORSIKA and COSMOS simulation”, S.Y. Roh et al., Proceedings of UHECR2010, 10-12 Dec 2010.
24. ”Search for small clusters by auto-correlation analysis from Telescope Array”, T. Okuda et al. (Telescope Array Collaboration), Proceedings of UHECR2010, 10-12 Dec 2010.
25. ”An Event Reconstruction Method for the Telescope Array Fluorescence Detectors”, T. Fujii et al. (Telescope Array
Collaboration), Proceedings of UHECR2010, 10-12 Dec 2010.
26. ”Large scale anisotropy of UHECRs for the Telescope Array”, E. Kido for the Telescope Array Collaboration, Proceedings of UHECR2010, 10-12 Dec 2010.
27. ”Heliospheric signatures seen in the sidereal anisotropy of high-energy galactic cosmic ray intensity”, M. Amenomori etal., AIP Conf. Proc., 1302, 285-290, 2010.
28. ”Cryogenic Advanced Gravitational Wave Detectors (LCGT)”, K. Kuroda and LCGT Collaboration Proceedings of theNinth Asia-Pacific International Conference on Gravitation and Astrophysics, Edit. Jun Luo, Ze-Bing Zhou, HsiChina,
Hsien-Chi Yeh and Jong-Ping Hsu, Wuhan, China, 29 June-2 July 2009.
29. ”Shocks in the Heliosphere”, Terasawa, T., Chapter 12, IAGA Special Sopron Book Series vol. 4, ”The Sun, the Solar
Wind, and the Heliosphere”, ed. by M. P. Miralles and J. S. Almeida, Springer, 2011.
30. ”Anomalous deformation of the Earth’s bow shock in the lunar wake: Joint observations by Chang’E-1 and SELENE”,
Nishino, M. N., et al., Proceedings of American Geophysical Union Fall meeting, Paper P54B-07, 2010.
31. ”Effect of the solar-wind proton entry into the deepest lunar wake”, Nishino, M. N., et al., Proceedings of EGU General
Assembly, vol. 5, EPSC2010-473, 2010.
32. ”VLF detection of ionospheric disturbance caused by a magnetar giant gamma-ray flare”, Tanaka, Y. T., et al., Proceedings of 38th COSPAR Scientific Assembly, C11-0172-10, 2010.
33. ”Effect of solar-wind proton entry into the deepest lunar wake”, Nishino, M. N., et al., Proceedings of 38th COSPAR
Scientific Assembly, B01-0061-10, 2010.
34. ”Collisionless shock and particle acceleration”, Terasawa, T., Proceedings of the IAU symposium 274, 2010.
35. ”Identification of new physics and general WIMP search at the ILC”, M.Asano, et al., to be published in proceedings ofInternational Linear Collider Workshop 2010.
36. ”Simulation Study of W Boson + Dark Matter Signatures for Identification of New Physics”, T.Suehara, et al., to be
published in proceedings of International Linear Collider Workshop 2010.

74(c) ICRR Reports
1. ICRR-Report-568-2010-1”A complete calculation for direct detection of Wino dark matter”
Junji Hisano, Koji Ishiwata, and Natsumi Nagata.
2. ICRR-Report-569-2010-2”Reevaluation of Higgs-Mediated µ -e Transition in the MSSM”
Junji Hisano, Shohei Sugiyama, Masato Yamanaka, and Masaki Jung Soo Yang.
3. ICRR-Report-570-2010-3”Gluon contribution to the dark matter direct detection”
Junji Hisano, Koji Ishiwata, and Natsumi Nagata.
4. ICRR-Report-571-2010-4”Non-Gaussianity from Lifshitz Scalar”
Keisuke Izumi, Takeshi Kobayashi, and Shinji Mukohyama.
5. ICRR-Report-572-2010-5”Decaying Dark Matter in Supersymmetric Model and Cosmic-Ray Observations”
Koji Ishiwata, Shigeki Matsumoto, and Takeo Moroi.
6. ICRR-Report-573-2010-6”Inflation from a Supersymmetric Axion Model”
Masahiro Kawasaki, Naoya Kitajima, and Kazunori Nakayama.
7. ICRR-Report-574-2010-7”Kähler moduli double inflation”
Masahiro Kawasaki, and Koichi Miyamoto.
8. ICRR-Report-575-2010-8”Prospects for Direct Detection of Inflationary Gravitational Waves by Next Generation Interferometric Detectors”
Sachiko Kuroyanagi, Takeshi Chiba, and Naoshi Sugiyama.
9. ICRR-Report-576-2010-9”Running Spectral Index from Inflation with Modulations”
Takeshi Kobayashi, and Fuminobu Takahashi.
10. ICRR-Report-577-2010-10”Evolution of String-Wall Networks and Axionic Domain Wall Problem”
Takashi Hiramatsu, Masahiro Kawasaki, and Ken’ichi Saikawa.
11. ICRR-Report-578-2010-11”Destruction of 7 Be in big bang nucleosynthesis vis long-lived sub-strongly interacting massive particles as a solution to
the Li problem”
Masahiro Kawasaki, and Motohiko Kusakabe.
12. ICRR-Report-578-2010-12”Improved estimation of radiated axions from cosmological axionic strings”
Takashi Hiramatsu, Masahiro Kawasaki, Toyokazu Sekiguchi, Masahide Yamaguchi, and Jun’ichi Yokoyama.
13. ICRR-Report-579-2010-13”Cosmological constraints on dark matter models with velocity-dependent annihilation cross section”
Junji Hisano, Masahiro Kawasaki, Kazunori Kohri, Takeo Moroi, Kazunori Nakayama, and Toyokazu Sekiguchi.
14. ICRR-Report-580-2010-14”Study of gravitational radiation from cosmic domain walls”
Masahiro Kawasaki, and Ken’ichi Saikawa.

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D. Doctoral Theses
1. ”Study of pulse shape discrimination and low background techniques for liquid xenon dark matter detectors”,
K. Ueshima,
Ph.D. Thesis, Jan. 2011.
2. ”Optical Properties of Type Ia Supernovae and their Host Galaxies”,
K. Konishi, Ph.D. Thesis, Mar. 2011.

E. Public Relations(a) ICRR NewsICRR News is a newspaper published quarterly in Japanese to inform the Institute’s activities. This year’s editors were Hideo
Itoh. It includes :1. reports on investigations by the staff of the Institute or made at the facilities of the Institute,
2. reports of international conferences on topics relevant to the Institute’s research activities,
3. topics discussed at the Institute Committees,
4. list of publications published by the Institute [ICRR-Report, ICRR-Houkoku (in Japanese)],5. list of seminars held at the Institute,
6. announcements,
7. and other items of relevance.
The main topics in the issues in 2010 fiscal year were:
No.73 (Sep 30, 2010)• On the Study of Astrophysical Particle Acceleration, Toshio Terasawa.
• Status report of Telescope Array experiment, Hiroyuki Sagawa.
• Observation of Gamma Ray Bursts by Ashra, Kazuaki Ota.
• Staff reassignment.
• ICRR-Seminar.
• ICRR-Report.
No.74 (Nov 30, 2010)• Development of a precise on-board gravity-gradiometer, Sachie Shiomi.
• Start operation of the Small electron linear accelerator for Absolute energy calibration of Telescope Array Experiment,
Tatsunobu Shibata.
• Report on the training for ICRR technical staffs, Hiroyuki Sagawa.
• Beginning of the T2K experiment, Masato Shiozawa.
• Staff reassignment.
• ICRR-Seminar.

76• ICRR-Report.
No.75 (Feb 28, 2011)• Cosmic Reionization Probed with Subaru Telescope, Masami Ouchi.
• Cherenkov Telescope Array(CTA) project, Masahiro Teshima.
• Report on open campus 2009, Hideo Itoh.
• Staff reassignment.
• ICRR-Seminar.
• ICRR-Report.
No.76 (Mar 31, 2011)• Report on the Meeting for Presenting the Results of Inter-University Research in JFY2010, Takanori Yoshikoshi.
• Axions from Axionic strings, Masahiro Kawasaki.
• Staff reassignment.
• ICRR-Seminar.
• ICRR-Report.

(b) Public Lectures• ”Detecting Dark Matter”, Feb 26, 2011, Tokyo, Yoichiro Suzuki (ICRR, University of Tokyo).
• ”Searching Dark Matter”, Feb 23, 2011, Tokyo, Yoichiro Suzuki (ICRR, University of Tokyo).
• ”GSA Science Cafe”, Feb 12, 2011, Kamioka-cho, Hida-city, Gifu, Yoshinari Hayato (ICRR, University of Tokyo).
• ”ICRR tour”, Dec 10, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).
• ”Detection of Gravity Wave predicted by Einstein”, Nov 27, 2010, Kashiwa campus, University of Tokyo, Chiba, Masatake Ohashi (ICRR, University of Tokyo).
• ”About Dark Matter”, Nov 26, 2011, Kanazawa, Nishigawa, Yoichiro Suzuki (ICRR, University of Tokyo).
• ”New age of Cosmic Ray Physics”, Nov 20, 2010, Katsushika City Museum, Tokyo, Hideo Itoh (ICRR, University ofTokyo).
• ”SSH Kainan High School”, Nov 18, 2010, Kamioka-cho, Hida-city, Gifu, Jun Kameda (ICRR, University of Tokyo).
• ”Weather of the Space and the Earth”, Nov 14, 2010, University of Tokyo, Tokyo, Hiroko Miyahara (ICRR, Universityof Tokyo).
• ”Observe the Universe through an Underground Huge Water Tank”, Oct. 30, 2010, Kashiwa, Chiba, Yoshihisa Obayashi(ICRR, University of Tokyo)• ”Yoshiki High School”, Sep 15, 2010, Toita Girl’s Junior-Senior High School, Tokyo, Hideo Itoh (ICRR, University ofTokyo).
• ”Investigation of the Universe using particle physics”, Sep 14, 2010, Kamioka-cho, Hida-city, Gifu, Makoto Miura(ICRR, University of Tokyo).
• ”SSH Toyounaka High School”, Sep 6, 2010, Kamioka-cho, Hida-city, Gifu, Ko Abe (ICRR, University of Tokyo).
• ”SSH Senior High School Attached to Kyoto University of Education”, Aug 26, 2010, Kamioka-cho, Hida-city, Gifu,
Jun Kameda (ICRR, University of Tokyo).
• ”ICRR tour”, Aug 24, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).

77• ”Visualisation of Radiation and Cosmic Ray”, Aug 11, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).
• ”JST Project for girl students to choose the science course”, Aug 11, 2010, Kamioka-cho, Hida-city, Gifu, Yoshihisa
Obayashi and Katsuki Hiraide (ICRR, University of Tokyo).
• ”Particle physics and the Universe”, Aug 10, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).
• ”SSH Fujishima High School”, Aug 10, 2010, Kamioka-cho, Hida-city, Gifu, Hiroyuki Sekiya (ICRR, University ofTokyo).
• ”Yumeno Tamago Jyuku; Hida Academy Summer Seminar”, Aug 6, 2010, Kamioka-cho, Hida-city, Gifu, Atsushi
Takeda (ICRR, University of Tokyo).
• ”SSH Takamatsu First High School”, Aug 5, 2010, 5-1-5, Kashiwanoha, Kashiwa-city,Chiba , Shigetaka Moriyama(ICRR, University of Tokyo).
• ”SSH Sanda Shounkan High School”, Aug 5, 2010, Kamioka-cho, Hida-city, Gifu, Makoto Miura (ICRR, University ofTokyo).
• ”Particle physics and the Universe”, Aug 3, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).
• ”Hirameki Tokimeki Science”, Aug 3, 2010, Kamioka-cho, Hida-city, Gifu, Yoichiro Suzuki (ICRR, University ofTokyo).
• ”Hirameki Tokimeki Science”, Aug 2, 2010, Kamioka-cho, Hida-city, Gifu, Yoichiro Suzuki (ICRR, University ofTokyo).
• ”Visualisation of Radiation and Cosmic Ray”, Jul 30, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).
• ”SSH Kawagoe High School”, Jul 29, 2010, Kamioka-cho, Hida-city, Gifu, Atsushi Takeda and Yumiko Takenaga(ICRR, University of Tokyo).
• ”Cosmic Ray Physics and ICRR”, Jul 27, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).
• ”Investigation of the Universe using particle physics”, Jul 24, 2010, Niigata Prefectural Kokusai Joho High School,
Niigata, Hideo Itoh (ICRR, University of Tokyo).
• ”Investigation of the Universe using particle physics”, Jul 13, 2010, Tokyo City University Junior and Senior HighSchool, Tokyo, Hideo Itoh (ICRR, University of Tokyo).
• ”Elementary Particles and Cosmic Rays”, Jul 9, 2010, ICRR, Chiba, Hideo Itoh (ICRR, University of Tokyo).
• ”SSH Shizuoka-kita High School”, Apr 23, 2010, Kamioka-cho, Hida-city, Gifu, Ko Abe and Yumiko Takenaga (ICRR,
University of Tokyo).

(c) Visitors
KASHIWA Campus (Total: 7 groups, 41 peoples)• Chiba Advanced Technology Experience Program• The Japan Society of Mechanical Engineers• Induction course of the University of Tokyo• Others: 4 groups
KAMIOKA Observatory (Total: 143 groups, 3028 peoples)• Yumeno Tamago Jyuku (Hida Academy for High School Students)• MEXT Super Science High School (SSH) project: total 7 schools• Schools and Universities: total 29 groups• Schools and Universities: total 21 groups• Researchers: total 23 groups• Others: 91 groups

78

F.

Inter-University Researches

Numbers of Researchers
Number ofApplications

Number of
Adoptions

Number of
Researchers

Facility Usage
Kamioka Observatory
Norikura Observatory
Akeno Observatory
Emulsion and Air Shower Facilities in Kashiwa
Low-level Radio-isotope Measurement Facilities in Kashiwa
Gravitational Wave Facilities in Kashiwa
Computer Facilities in Kashiwa
Over Sea Facilities
Others

37
8
8
1
6
3
9
6
18

36
8
8
1
6
3
9
6
18

874
70
181
7
25
29
103
80
382

Collaborative Researches
Cosmic Neutrino Researches
High Energy Cosmic Ray Researches
Theoretical Researches or Rudimental Researches
Research Center for Cosmic neutrinos

28
43
20
5

27
43
20
5

739
682
289
40

OthersConferences

3

3

45

Research Titles
1. Development of low concentration radon detection system
2. Energy calibration for Super-Kamiokande
3. Study of solar neutrino energy spectrum
4. Neutrino workshop
5. Sidereal daily variation of ∼10TeV galactic cosmic ray intensity observed by the Super-Kamiokande
6. Study of Supernova Relic Neutrinos
7. Study in upward-going muons and high energy neutrinos
8. Precise measurement of Day/Night effect for B8 solar neutrinos
9. Study of Solar Neutrino Flux
10. Study of ambient gamma-ray and neutron flux at Kamioka Observatory
11. Study for the electron neutrino appearance search in the T2K experiment
12. Study of simulation for atmospheric neutrino
13. Study of nucleon decay p → ν K
14. Tokai to Kamioka Long Baseline Experiment T2K
15. 3-flavor Oscillation study in atmospheric neutrinos
16. Study of atmospheric neutrinos and neutrino oscillations

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17. Neutrino interaction study using accelerator data
18. Development of the new online DAQ system for Super-Kamiokande
19. Study for Supernova monitor
20. Search for proton decay via e+ π 0 mode
21. R&D of a Mton water Cherenkov Hyper-Kamiokande
22. Analysis of Spatial Distribution of Radon Family Underground and Its Dosimetry
23. Direction-sensitive dark matter search experiment
24. Development of metal complies loaded liquid scintillator for measurement of solar neutrinos and neutrinoloss β β decay
25. Development of InP detector for measurement of solar pp/7Beν
26. Study for lowering backgrounds of radioisotopes in large volume detectors
27. Study for upgrade of XMASS detector
28. Study for double beta decay of 48Ca
29. Integration of crustal activity observation around the Atotsugawa fault
30. A study on emission spectrum of liquid xenon
31. Seismic classification of underground facilities for low frequency ground based gravitational wave detectors
32. A search for Dark Matter using Liquid Xenon Detector
33. Design and Construction of Purification system for XMASS 800kg detector
34. Multi-Color Imager for Transients, Survey and Monstrous Explosions
35. Production and calibration of surface detectors for the Telescope Array experiment
36. A study of the hybrid trigger for the Telescope Array experiment
37. Observation of Galactic Cosmic ray by the Large Area Muon Telescope
38. R&D for a Small Atmospheric Cherenkov Telescope in Akeno Observatory
39. Observation of solar neutrons in solar cycle 24
40. Vegetation survey of alpine plants on Mt.Norikura
41. Observation of total ozone and UV solar radiation with Brewer spectrophotometer on the Norikura mountains
42. Space weather observation using muon hodoscope at Mt.Norikura
43. Study of particle acceleration in electric field using x and gamma rays from lightning and thunderclouds
44. Ecophysiological studies of alpine plants
45. Observation of the highest energy Solar Cosmic Rays
46. Observation of nightglow and its reflected and scattered light on the mountain47. Study of the composition of cosmic-rays at the knee
48. Observation of high-energy cosmic-ray electrons with emulsion chambers
49. Experimental Study of High-energy Cosmic Rays in the Tibet AS γ experiment
50. Development of advanced photon counter for the future IACT
51. Development of the optical fiber image transfer system for Ashra
52. Study of Galactic Diffuse Gamma Rays

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53. Study of absolute energy calibration air shower by compact Electron LINAC
54. Sidereal daily variation of 10TeV galactic cosmic-ray intensity observed by the Tibet air shower array
55. Study on High Energy Cosmic-Ray source by Observation Using Long Duration Balloon
56. Basic Study to Establish the CTA Japan Consortium
57. Cosmic ray interactions in the knee and the highest energy regions
58. A study on variation of interplanetary magnetic field with the cosmic-ray shadow by the sun
59. Acceleration processes: Comparative study of 1st and 2nd order processes
60. Observation of TeV gamma-ray spectra from galactic objects
61. Bolivian Air Shower Joint Experiment
62. A R&D for a new atmospheric monitoring system
63. Improvement of characteristics of the image sensor used in Ashra
64. Study on the Ultra-high Energy Cosmic Ray Future Projects
65. Observation of very-high-energy gamma-rays in Australia
66. Data Analysis of the UHECR data for the Auger Project III
67. Multiwavelength observation of extragalactic gamma-ray objects with CANGAROO telescope and Fermi gamma-ray
space telescope
68. Development of an atmospheric transmittance meter for the site survey of Cherenkov telescopes
69. Workshop on High Energy Gamma-Ray Astronomy
70. Data analysis of nearby galaxies and clusters of galaxies and their non-thermal radiation models
71. Observation with All-sky Survey High Resolution Air-shower detector Ashra
72. Monte Carlo simulation for the Tibet air shower array
73. Radiation and environment Measurement while thunder storm at TA site
74. Study of radio detection of highest energy cosmic rays
75. Study of Extremely-high Energy Cosmic Rays by Telescope Array
76. Development of an optical cavity to stabilize ultranarrow lasers
77. Development of Local Suspension Point Interferometer for CLIO (II)78. Gravitational Wave Detector in Kamioka (IX)
79. Development of an intensity stabilization system for a high-power laser for CLIO
80. Research of the Earths free oscillations based on simultaneous observations with a laser strainmeter and a superconducting gravimeter
81. data analysis using CLIO data
82. Development of DC-readout system for CLIO interferometer
83. Study of a LCGT cryostat toward ultra-high vacuum operation
84. Development of Sapphire Mirror Suspension for LCGT (VI)
85. R&D and Design of large-scale cryogenic gravitational wave telescope (XI)
86. Development of Local Suspension Point Interferometer for CLIO (XII)
87. Evolution of the universe and particle physics

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88. Comprehensive Researches on Cosmic Dusts
89. Detection of time variations for cosmogenic Be-7
90. Detection of low level radioisotopes in tree rings
91. Study of solar activity, cosmic rays and climate change based on the analysis of cosmogenic nuclides and stable isotopes
92. Chemical study for Antarctic micrometeorites
93. Determination of 26 Al in Antarctic meteorite samples
94. Continuous Measurement of Underground Laboratory Environment
95. Deposition Rate variation of natural activities 7 Be and 210 Pb
96. Simulation Study for the IceCube Neutrino Observatory
97. Precise calculation of the atmospheric neutrino flux
98. Future plan symposium for cosmic ray research

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G. List of Committee Members(a) Board of Councillors
KAJITA, Takaaki
TERASAWA, Toshio
KURODA, Kazuaki
NAKAHATA, Masayuki
YAMAGATA, Toshio
MATSUMOTO, Yoichiro
NISHIKAWA, Koichiro
EGUCHI, Toru
MIYAMA, Shoken
TORII, Shoji
MASAIKE, Akira
MURAKI, Yasushi
MAKINO, Fumiyoshi
SATO, Katsuhiko
KOMAMIYA, Yukio

ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
University of Tokyo
University of Tokyo
KEK
YITP, Kyoto University
National Astronomical Observatory
Waseda University
Kyoto University
Konan University
Institute of Space and Astronautical Science
IPMU, University of Tokyo
ICEPP, University of Tokyo(b) Advisory Committee
KAJITA, Takaaki
NOJIRI, Mihoko
SAITO, Naohito
YAMAMOTO, Hitoshi
AIHARA, Hiroaki
ITOW, Yoshitaka
MORI, Masaki
KAJINO, Fumiyoshi
MUNAKATA, Kazuoki
TOTANI, Tomonori
FUKUSHIMA, Masaki
SUZUKI, Yoichiro
KURODA, Kazuaki
TERASAWA, Toshio
NAKAHATA, Masayuki
KAWASAKI, Masahiro

ICRR, University of Tokyo
KEK
KEK
Tohoku University
University of Tokyo
STEL, Nagoya University
Ritsumeikan University
Konan University
Shinshu University
Kyoto University
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo(c) Inter-University Research Advisory Committee
NISHIJIMA, Kyoshi
OHASHI, Hideo
KANDA, Nobuyuki
MUNAKATA, Kazuki
TASAKA, Shigeki
TAMURA, Tadahisa
YAMAMOTO, Tokonatsu
OGIO, Shoichi
FUKUSHIMA, Masaki
OHASHI, Masatake
TAKITA, Masato
YOSHIKOSHI, Takanori
SHIOZAWA, Masato

Tokai University
Tokyo University of Marine Science and Technology
Osaka City University
Shinshu University
Gifu University
Kanagawa University
Konan University
Osaka City University
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo

83

H. List of Personnel
Director

KAJITA, Takaaki

Vice-Director

FUKUSHIMA, Masaki

Kamioka Observatory (Neutrino and Astroparticle Division)
Scientific Staff
NAKAHATA, Masayuki,
SUZUKI, Yoichiro,
MORIYAMA, Shigetaka,
SHIOZAWA, Masato,
ABE, Ko,
HIRAIDE, Katsuki,
KISHIMOTO, Yasuhiro,
KOBAYASHI, Kazuyoshi,
MIURA, Makoto,
NAKAYAMA, Shoei,
OGAWA, Hiroshi,
SEKIYA, Hiroyuki,
TAKEDA, Atsushi,
TOMURA, Tomonobu,
Administrative Staff
TAKAKURA, Koji
Technical Staff
KANBE, Tomio,
KUMAMARU, Seiichi,
ONOUE, Tatsuya
Research Fellow
TAKENAGA, Yumiko
Secretary
MAEDA, Yukari,
OKURA, Yoko,
Research Center for Cosmic Neutrinos (Neutrino and Astroparticle Division)
Scientific Staff
KAJITA, Takaaki,
KANEYUKI, Kenji,
OHASHI, Hideo
Technical Staff
SHINOHARA, Masanobu
Research Fellow
KAJI, Hiroshi,
LAING, Andrew Brian
Secretary
KITSUGI, Atsuko,
WATANABE, KeikoHigh Energy Cosmic Ray Division
Scientific Staff
FUKUSHIMA, Masaki,
RUBTSOV, Grigory,TERASAWA, Toshio,
TESHIMA, Masahiro,
OISHI, Michiko,
TAKITA, Masato,
SASAKI, Makoto,Technical Staff
KOBAYASHI, Takahide,
AOKI, Toshifumi,
KOIZUMI, Chikako,
Research Fellow
IKEDA, Daisuke,
CHEN, Ding,
AITA, Yuichi,
Secretary
OKAMURA, Takako,
TATSUMI, Fusako,
KOKUBUN, Yayoi,
FUKUI, Misa,

NONAKA, Toshiyuki,
SAKURAI, Nobuyuki,
LEE, Martin Alan,
ENOMOTO, Ryoji,

HAYATO, Yoshinari,
YAMASHITA, Masaki,
KAMEDA, Jun,
KOSHIO, Yusuke,
OBAYASHI, Yoshihisa,
TAKEUCHI, Yasuo,
YAMADA, Satoru
NOZAWA, Noriyuki,

TAKAMATSU, Midori

OKUMURA, Kimihiro,

TAKEDA, Masahiro,
SHIBATA, Tatsunobu,
SCHOLER, Manfred,
YOSHIKOSHI, Takanori,

ONISHI, Munehiro,
ASAOKA, Yoichi
HOSHI, Noboru,
MORIMOTO, Yusuke,
KONDO, Yoshimi,
KAWATA, Kazumasa,
MASUDA, Masataka,
OKI, Kaoru,

IKEDA, Kiriko,
NAKADA, Yuichiro
TAMEDA, Yuichiro,
OTA, Kazuaki

TOJO, Kaori

Akeno Observatory (High Energy Cosmic Ray Division)
Scientific Staff
SAGAWA, Hiroyuki
Technical Staff
OOKA, Hideyuki,
SHIMIZU, Kanetoshi
Norikura Observatory (High Energy Cosmic Ray Division)
Technical Staff
AGEMATSU, Yoshiaki,
ISHITSUKA, Hideki,
USHIMARU, Tsukasa,
YAMAMOTO, Kuniyuki

SHIMODAIRA, Hideaki,

84

Astrophysics and Gravity Division
Scientific Staff
KAWAMURA, Seiji,
MIYOKI, Shinji,
MIYAKAWA, Osamu,
NAKATANI, Ichiro,
KIMURA, Nobuhiro,
FUKUGITA, Masataka,
MIYAHARA, Hiroko,
KAWASAKI, Masahiro,
Research Fellow
SHIOMI, Sachie,
KUROYANAGI, Sachiko,
SEKIGUCHI, Toyokazu
Secretary
KIKUCHI, Rie,
Graduate Students
DoctorMaster

KIDO, Eiji,
LEE, Ka-pik,
UESHIMA, Kota,
SAITOH, Takanori,
KAWAKAMI, Etsuko,
RYO, Masaki,
KONISHI, Kohki,
MIYAMOTO, Hideaki,
TAKAHASHI, Yoshiaki,
TOYAMA, Takeshi,
INOUE, Daisuke,
ITOH, Takashi,
IYOGI, Kazuki,
HIRANO, Shigetoshi,
SAKAKIBARA, Yusuke,
KITAJIMA, Naoya,
TAKESAKO, Tomohiro,
NAGATA, Kumiko

Administration Division
Scientific Staff
ITOH, Hideo
Administrative Staff
MATSUZAWA, Noboru,
ARIDOME, Ryutaro,
AKIYAMA, Makiko,
SAITO, Akiko,

KURODA, Kazuaki,
UCHIYAMA, Takashi,
OISHI, Naoko,
SAITO, Yoshio,

OHASHI, Masatake,
TANNER, David Burham,
TAKAHASHI, Ryutaro,
SUZUKI, Toshikazu,

OUCHI, Masami,

MENARD, Brice,

HISANO, Junji,

IBE, Masahiro

KUSAKABE, Motohiko,

ISHIWATA, Koji,

MASHIMA, Chieko,

SAKAI, Akiko

McLACHLAN, Thomas Fukuei,
YOKOZAWA, Takaaki,

UENO, Ko,

KOBAYASHI, Takeshi,
SAIKAWA, Kenichi,

MIYAMOTO, Koichi,
SUGIYAMA, Shohei,

OBI, Yoshio

SODA, Takashi,
HIRAI, Shun,NISHIIE, Hironori,

YOSHIGOE, Koichi,
SHINOZAKI, Akihiro,

SEKIGUCHI, Takanori,
NAGATA, Natsumi,
YAMAMOTO, Yusuke,

TAKEDA, Naoyuki,

SETO, Mikako,
OGURA, Satoshi,
FUJIE, Tamiko,
TAKANO, Eri,

SASADA, Takaaki,
KANEKO, Saho,
MARUMORI, Yasuko,
YAMAGUCHI, Akiko