INSTITUTEFORCOSMIC RAY RESEARCH
UNIVERSITY OF TOKYOANNUAL REPORT(APRIL 2008 – MARCH 2009)

Editorial Board
YOSHIKOSHI, Takanori
OHASHI, Masatake
TAKENAGA, Yumiko
ITOH, HideocInstitutefor 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

14

Astrophysics and Gravity Division36

Observatories and a Research Center.........................................................................

52

Norikura Observatory

53

Akeno Observatory

57

Kamioka Observatory

58

Research Center for Cosmic Neutrinos

59.............................................................

61..............................................................................

61........................................................

62

Appendix A.

ICRR Workshops and Ceremonies

Appendix B.

ICRR Seminars

Appendix C.

List of Publications — Fiscal Year 2008(a) Papers Published in Journals(b) Conference Papers(c) ICRR Reports

Appendix D.

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

68

Appendix E.

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

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

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

71

Appendix G.

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

75............................................................................

76(a) Board of Councillors(b) Advisory Committee(c) User’s Committee
Appendix H.

List of Personnel

PREFACE
This report summarizes the scientific activities of the Institute for Cosmic Ray Research(ICRR) of the University of Tokyo in the Japanese FY 2008.
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 asl, Mt. Norikura, Gifu prefecture),
and Akeno Observatory (Yamanashi prefecture). In addition, there are 3 major experimental
facilities outside of Japan. They are located in Utah in USA, Yangbajing in Tibet, China, andWoomera 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 are described in this report. One of the highlights isthe start of the full operation of the Telescope Array experiment, which is a very large scalecosmic ray experiment to study the highest energy cosmic rays. We hope that this report isuseful for the understanding of the current research activities of ICRR. Finally, we appreciatevery much the strong support of our colleagues in this research field, the University of Tokyoand the Japanese Ministry of Education, Culture, Sports, Science and Technology. They are
indispensable 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
Board of Councillors

Faculty Council

Research Division
Neutrino and Astroparticle DivisionHigh Energy Cosmic Ray Division
Astrophysics and Gravity Division

Director
Vice-Director

Advisory Committee

Facilities
Kamioka Observatory
Akeno Observatory
Norikura Observatory
Research Center for Cosmic Neutrinos
Low-level Radioisotope Measurement Facility

User's Committee

Administration Division

Number of Staff Members in 2008
Scientific
Staff

Technical
Staff

Research
Fellows

21
13
8
1
43

4
8
0
0
12

4
6
3
0
13

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

Administrators
andSecretaries
15
4
2
13
34

44
31
13
14
102

FY 2003–2008 Budget
Personnel
expenses
Nonpersonnel
expenses
Total

2003

2004

2005

2006

2007

2008

434 874

539 000

465 000

566 000

624 000

632 000

1 785 449

1 902 000

1 822 000

812 000

1 253 000

1 121 000

2 220 323

2 441 000

2 287 000

1 378 000

1 877 000

1 753 000
(in 1 000 yen)

1

RESEARCH DIVISIONS
Neutrino and Astroparticle Division
Overview
Super-Kamiokande Experiment
T2K Experiment
XMASS ExperimentHigh Energy Cosmic Ray Division
Overview
CANGAROO-III Project
TA: Telescope Array Experiment
Tibet ASγ Project
Ashra Project

Astrophysics and Gravity Division
Overview
Gravitational Wave Group
CLIO Project
LCGT Project

Sloan Digital Sky Survey
Theory Group
Neutrino mass, Dark Matter and Baryon Asymmetry via TeV-Scale Physics without Fine-Tuning
Light Higgs boson scenario in the SUSY seesaw model
D-term assisted Anomaly Mediation in E6 motivated models
Precision Measurements of Little Higgs Parameters at the International Linear Collider
Non-linear evolution of matter power spectrum in modified theories of gravity
Flavor physics in supersymmetric theories
Probing reheating temperature of the universe with gravitational wave background
Direct/indirect detection signatures of non-thermally produced dark matter
Non-Gaussianity from isocurvature perturbations
Hilltop Non-Gaussianity
Cosmic Rays from Dark Matter Annihilation and Big-Bang Nucleosynthesis
Cosmological Moduli Problem from Thermal Effects
Neutrino Signals from Annihilating/Decaying Dark Matter in the Light of Recent Measurements of Cosmic Ray Electron/Positron Fluxes
Upperbound on Squark Masses in Gauge-Mediation Model with Light Gravitino
A Realistic Extension of Gauge-Mediated SUSY-Breaking Model with Superconformal Hidden Sector
Non-Gaussianity from Symmetry
Primordial Curvature Fluctuation and Its Non-Gaussianity in Models with Modulated Reheating
Exact gravitational lensing by cosmic strings with junctions

2

NEUTRINO AND ASTROPARTICLE DIVISION
Overview
This division aims to study particle physics that is notaccessible within accelerator facilities, with prime interestsin 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 at J-PARC (T2K) is expected to start in 2009 with the
SK detector as the far detector of the experiment. High precision measurement of oscillation parameters and the third oscillation pattern (the effect of the mixing angle θ13 ) will be
investigated by T2K.
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 mass using neutrinoless double beta decay, and low energy solar neutrinos. An R&D study for the liquid xenon detector has been
performed at the underground laboratory and the constructionof the 800 kg detector started in 2007.
Recent progress of research activities in the Neutrino andAstroparticle division is presented here.

Super-Kamiokande experiment
New electronics system
To ensure stable observation for the next 10∼20 years andto improve sensitivity of the detector, the SK electronics system was fully upgraded in September 2008.
Figure 1 shows a picture of our new front-end electronics,
QBEE (QTC-Based Electronics with Ethernet). The QBEE
is a TKO-standard module which has 24 input channels. Essential components on the QBEE for the analog signal processing and digitization are the QTC (Charge-to-Time Converter) ASIC [1] and the multi-hit TDC. The QTC detects
PMT signals by individual built-in discriminators and drives
output timing signals whose width represents the integrated
charge of the PMT signal. Timing information on both edges

Fig. 1. New front-end electronics, QBEE. PMT signals are fed throughthe backplane (left side). The Ethernet cable for the data readout
and the board control is connected at the front panel (right side)
as well as the UTP cable for the 60MHz system clock input.

of a QTC output signal is digitized by the AMT-3 multi-hit
TDCs. An FPGA then reads and processes the data stored
in the TDC internal buffer continuously by a unit of 17 μ sec.
The QBEE realizes high-speed signal processing by combining the pipelined components like the QTC, TDC and FPGA.
The QBEE has an on-board calibration pulser which is used
for monitoring and correcting the charge measurement by the
QTCs under possible ambient temperature changes.
The high-speed QTC was developed as a custom ASIC
in CMOS 0.35μ m technology. Figure 2 shows a picture of
the internal circuit of the QTC chip. The QTC has three input channels per chip. Each channel has three gain ranges:
Small, Medium, and Large. The gain ratio of three ranges,
which can be adjusted by external resistor networks, is set to1. The overall charge dynamic range of the QTC is 0.21: 17 : 49
2500pC, which is about 5 times wider than that of the previous front-end electronics used in SK. The width of the charge
integration gate in the QTC is set to 400nsec. The charge integration circuits are triggered by the input PMT signal itself(self-triggering scheme). To reduce charge leakage, the PMT
signal to be integrated is delayed by a second-order voltagecontrolled voltage source (VCVS) low-pass filter (LPF) in the
QTC. Soon after the end of the charge gate, the discharging
timer operates for ∼350nsec Input signals within ∼250nsec
after the discharge gate are ignored. In total, processing time
for one input signal is ∼1000nsec.
The charge and timing resolutions of the QBEE for the
single p.e. level signals are 10% and 0.3nsec, respectively,

3both better than the intrinsic resolutions of the 20-inch PMTs
in SK. The QBEE achieves good charge linearity over a wide
dynamic range. The charge nonlinearity (i.e. deviation from a
linear fitted function) is within ±1% and satisfies our requirements. The discriminators in the QTC can be operated with a−0.3mV threshold, equivalent to 1/10p.e.s, without sufferingfrom intrinsic electrical noise or channel crosstalk.
A total of 553 QBEEs are used in SK, 472 for the innerdetector PMTs, 80 for the outer detector PMTs, 1 for a special use to record the flash timings of light sources for various
detector calibrations. All the QBEEs operate synchronized
by a common 60MHz master clock, which is generated by
the MCLK module (see Fig. 3). The MCLK module also
generates a 17 μ sec-cycle periodic trigger for the TDCs on
the QBEE. The combination of the periodic TDC trigger andthe high-speed signal processing by the QBEEs enables us torecord every hit of all the PMTs, including hits by PMT’s darkcurrent. This “record every hit” data acquisition is one of themost prominent features of the new electronics system. In theprevious system, event triggers were issued when the numberof hit PMTs exceeded a certain threshold and only the PMT
signals in a 1.3μ sec window around the event trigger were
processed by front-end electronics. To achieve the “record
every hit” data acquisition, the speed of data readout from thefront-end electronics and subsequent data processing by the
online PC system is also important.
We adopted an Ethernet technology for data readout fromthe QBEE. The network interface sub-board attached to the
QBEE has an FPGA network firmware called SiTCP and gives
a 100BASE-TX data transfer. In the previous electronics system, 20 front-end electronics modules shared a TKO bus fordata readout and the transfer speed of a TKO bus was about

1200

1000

number of events / 100nsec

Fig. 2. The internal circuit of the QTC ASIC.

4MB/sec. The Ethernet enables a parallel readout from the
QBEEs. The measured data throughput of a QBEE achieves
11.75MB/sec, which is almost the theoretical limit of the
100BASE-TX and fast enough to realize the “record every hit”
data acquisition. In addition, implementing the digital readout
on the ethernet daughterboard suppresses readout noise compared to backplane readout, and allows us to achieve a low
single photo electron threshold.
The data processed by the QBEEs are collected by 20
Front-end PCs via Ethernet cables and network switches. The
hit data are then sorted in time order and sent to the Merger
PCs. A software-trigger program is running on the Merger PC
to extract an event from all the hit data of all the PMTs. A basic condition of the software-trigger is based on the numberof hit PMTs in a certain time window. The special conditions
triggered by an external signal input are also prepared for detector calibrations. The software-triggered event data are collected by the Organizer PC and recorded on a disk. A large
amount of the data taken by the “record every hit” scheme aresuccessfully processed by the parallel distributed processingin the online system.
The data-taking by the new electronics system started on
September 6th, 2008. The present phase of the experiment
after the electronics system replacement is called SK-IV. The
SK-IV detector performance/sensitivity is much improved forvarious observations. For example, the result of a test using ahigh-rate flashing light pulser shows that the SK-IV can takethe data from a supernova neutrino burst up to a rate of 6 million events/10sec with no data loss. This limit is about 100
times as large as that of the previous SK phases and is about1000 times as large as an expected event rate in case of a supernova at the galactic center. The detection of μ → e decays
is very important to classify interactions in neutrino oscillation analyses or nucleon decay searches. Figure 4 shows the
decay time distribution of the μ → e decay events. The detection efficiency after 1 μ sec from the parent muon event timing
reaches almost 100%. The high-speed front-end electronics
with a better impedance matching to the PMT signal cable
gives a better detection efficiency for μ → e decays in SK-IV.

800

600

400

200

0

0

1

2

3

4

5

6

7

8

decay time (μsec)

Fig. 3. The MCLK module. The 60MHz master clock and 17 μ seccycle periodic trigger are produced as LVDS signals from the RJ45
jack on the front-panel.

Fig. 4. Decay time of the μ → e decay events. The curve shows thenumber of electrons by muon decays which is estimated by themuon lifetime and the total number of stopping muon events. The
hatched histogram shows the detected μ → e decay events.

4The “record every hit + software-trigger” system will also enable us to detect a delayed signal by the 2.2MeV γ -ray after
the neutron capture, which was not feasible with the previous
electronics system, because the signal by a 2.2MeV γ -ray is
too faint for a hardware trigger. Tagging of neutrons using
a delayed 2.2MeV γ -ray signal will help us to reduce background events in a search for supernova relic neutrino events.
The SK-IV observation has been very stable. We hopeto achieve brand-new results using the data taken by the newelectronics system soon.

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 geomagnetic effect on primarycosmic rays is negligible.
SK-I observed 11,866 fully-contained (FC) events and898 partially-contained (PC) events during 1489 days of datataking and SK-II observed 6684 FC events and 430 PC events
during 804 days. FC events deposit all of their Cherenkov
light in the inner detector, while PC events have exiting tracks
which deposit some Cherenkov light in the outer detector. The
neutrino interaction vertex was required to have been reconstructed within the 22.5 kiloton fiducial volume, defined to be> 2 m from the PMT wall.
The FC events were classified into “sub-GeV” (Evis <1330 MeV) and “multi-GeV” (Evis > 1330 MeV) samples.
Among FC events, single-ring events are identified as e-likeor μ -like based on a Cherenkov ring pattern. The momentum resolution of SK-II is slightly worse than SK-I. This isbecause the number of ID PMTs in SK-II is about half that of
SK-I. However, the performance of the vertex reconstruction,
the ring counting, and the particle identification in SK-II arealmost the same as in SK-I. Some fraction of the multi-ring
events is also subdivided into e-like and μ -like events using
the event pattern of the most energetic Cherenkov ring in each
event.
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 the otheris “upward stopping muons” which come into and stop insidethe detector. The mean neutrino energy of upward throughgoing muons and upward stopping muons is ∼100 GeV
and ∼10 GeV, respectively. SK-I observed 1856 upward
through-going muons and 458 upward stopping muons during 1646 day livetime exposure and SK-II observed 889 and
228 events during 828 days, respectively.
The zenith angle distributions for each samples comparedwith atmospheric neutrino M.C. predictions are shown in
Fig. 5. The prediction is based on the recent precise measure-

SK-1+2 Sub-GeV 1-ring e-like 0mue

SK-1+2 Sub-GeV 1-ring e-like 1mue

600

140

500

120

400

100
80

300

60

200

40

100

20

0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
cosθ

0
2

SK-1+2 Sub-GeV 1-ring mu-like 0mu

SK-1+2 Sub-GeV 1-ring mu-like 1mu

250

500

200

400

150

300

100

200

50

100

2.2

2.4

2.6 log momentum
2.8
3(MeV/c)3.20-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
cosθ

0-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
cosθ

80
70
60
50
40
30
20
10
0
2

100

SK-1+2 Sub-GeV 1-ring mu-like 2mue

80
60
40
20
2.2

2.4

2.6 log momentum
2.8
3(MeV/c)3.2

SK-1+2 Sub-GeV 2-ring pi0-like
350
300
250
200
150
100
50
0
2

SK-1+2 Sub-GeV 1-ring pi0-like

2.2

2.4

2.6 log momentum
2.8
3(MeV/c)3.2

SK-1+2 Multi-Gev 1-ring mu-like
200
180
160
140
120
100
80
60
40
20
0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosθ

SK-1+2 Multi-Gev Multi-ring mu-like
180
160
140
120
100
80
60
40
20
0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosθ

SK-1+2 PC through

250
200
150
100
50
0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosθ

SK-1+2 Upmu non-showering

0
2

2.2

2.4

2.6 log momentum
2.8
3(MeV/c)3.2

SK-1+2 Multi-Gev 1-ring e-like
220
200
180
160
140
120
100
80
60
40
20
0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosθ

SK-1+2 Multi-Gev Multi-ring e-like

140
120
100
80
60
40
20
0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosθ

SK-1+2 PC stop
50
40
30
20
10
0
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosθ

SK-1+2 Upmu stopping

180
160
140
120
100
80
60
40
20
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1cosθ

SK-1+2 Upmu showering

500
400
300
200
100
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
cosθ

100
80
60
40
20
0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
cosθ

Fig. 5. The zenith angle distributions for each data sample. cosΘ =1means down-going particles. The red histograms show the MC
prediction without neutrino oscillation. The green histograms
show the Monte Carlo prediction for νμ ↔ ντ oscillations withsin2 2θ = 1.0 and Δm2 = 2.1 × 10−3 eV2 .

ments of primary cosmic rays by BESS, AMS and a three dimensional calculation of the neutrino flux by Honda et al. The
hadronic interaction model of cosmic rays is also improvedin the calculation. The μ -like data from SK exhibit a strong
up-down asymmetry in zenith angle (Θ) while no significant
asymmetry was observed in the e-like data. The data werecompared with the Monte Carlo expectation without neutrino
oscillations and the best-fit expectation for νμ ↔ ντ oscillations. The oscillated Monte Carlo reproduced the zenith angle
distributions of the data well.
We carried out a neutrino oscillation analysis using theentire SK-I and II atmospheric neutrino data set. Figure 6
shows the allowed neutrino oscillation parameter regions forνμ ↔ ντ oscillations. The best fit oscillation parameters are
sin2 2θ = 1.0 and Δm2 = 2.1 × 10−3eV2 . The allowed oscillation parameter range is sin 2 2θ > 0.95 and Δm2 = (1.7 −2.7) × 10−3eV2 at 90 % C.L.
SK-I + SK-II

-2

1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

1

0.8

10

2

10

L/E (km/GeV)

3

10

4

-2

2
2

99% C.L.
90% C.L.
68% C.L.

-3

0.7

10

Fig. 7. Ratio of the data to the MC events without neutrino oscillation(points) as a function of the reconstructed L/E together with thebest-fit expectation for 2-flavor νμ ↔ ντ oscillations (red line). The
error bars are statistical only.

10

99% C.L.
90% C.L.
68% C.L.

10

1.8Δm (eV )Δ m223 (eV 2 )10

Data/Prediction (null oscillation)

5

0.9

1
2
sin 2 θ23

10

-3

0.7

0.8

0.9

1

2

Fig. 6. Allowed region of νμ → ντ neutrino oscillation parameters obtained by SK using contained atmospheric neutrino events andupward-going muon events.

The atmospheric neutrino data is well described by neutrino oscillations as shown above. In this case, the survival
probability of a νμ is given by a sinusoidal function of L/E,
where L is the travel distance. E is the neutrino energy. However, the sinusoidal L/E dependence of this survival probability of νμ has not yet been directly observed. We used a
selected sample of these atmospheric neutrino events, thosewith good resolution in L/E, to search for an oscillation maximum in the L/E distribution.
The neutrino energy, E, was estimated from the total energy of charged particles observed in the inner detector. The
flight length of neutrinos, L, which ranges from approximately
15 km to 13,000 km depending on the neutrino zenith angle,
was estimated from the reconstructed neutrino direction. The
neutrino direction was taken to be along the total momentum
vector of all observed particles. Since the correlation between
the neutrino directions and the directions of observed particles is taken into account in the Monte Carlo simulations, weapplied the same analysis techniques to both real events andsin 2θ
Fig. 8. 68, 90 and 99 % C.L. allowed oscillation parameter regions for
2-flavor νμ ↔ ντ oscillations obtained in the L/E analysis.

Monte Carlo events. We applied a cut to reject low energy or
horizontal-going events since they have either large scattering
angles or large dL/dΘzenith .
Figure 7 shows the observed L/E distribution of the ratio of data events to unoscillated MC events. In the figure,a dip which corresponds to the first oscillation maximum,
is observed around L/E = 500 km/GeV. The distribution
was fit assuming νμ ↔ ντ oscillations. The best-fit expectation shown in the figure corresponds to (sin2 2θ , Δm2 ) =(1.00, 2.2 × 10−3eV2 ). Figure 8 shows the contour plot of
the allowed oscillation parameter regions. This result is consistent with that of the oscillation analysis using zenith angle
distributions. The observed L/E distribution gives the first direct evidence that the neutrino survival probability obeys thesinusoidal function predicted by neutrino flavor oscillations.
Another interest is an observation of ντ in the atmospheric
neutrinos since there has not yet been evidence for appear-

6
10-2

Likelihood

TAU+BKG
BKG
DATA
2
Δ m23
(eV 2)

Number of Events

100

75

50

25
10-3

0
-1

-0.5

0

cosθ

0.5

0

0.1

1

0.2

0.3

0.4

0.5

0.4

0.5

2

sin θ1310-2

ance of ντ charged current interactions due to νμ ↔ ντ oscillations. We have performed a search for the ντ appearance
by using the SK-I atmospheric neutrino data [2]. The analysis is based on two statistical methods: a likelihood analysis
and a neural network. Since τ ’s produced in the Super-K detector would immediately decay into many hadrons, the event
pattern would be similar to that of high-energy multi-ring νeevents. Using the statistical difference in τ -like and background events, we have derived variables to select an enrichedsample of ντ charged current events in the atmospheric neutrino data. The differences appear in the energy spectrum, thenumber of charged pions in the final state, and in the fractionof lepton energy with respect to neutrino energy. We optimized a combination of the variables and defined a likelihood
function so that the signal to noise ratio becomes maximal.
We also use the neural network for the analysis. Before theseanalyses, we applied pre-selection cuts on: (1) fiducial volume, (2) multi-GeV, and (3) the most energetic ring is e-like.
After the pre-selection cuts based on the likelihood andneural network, we fit the zenith angle distribution of the ντenriched sample to a combination of the expected ντ and theatmospheric neutrinos (νμ and νe ) including oscillations at
sin2 2θ = 1.0 and Δm2 = 2.1 × 10−3 eV2 . Fig. 9 shows thefitted zenith angle distribution. Using τ selection efficiencies
estimated by Monte Carlo study, we concluded the number oftau events during the SK-I exposure is 138 ± 48+14.8−31.6 with the+16.0
likelihood analysis and 134 ± 48−27.2 with the neural network
while 78.4 ± 26 and 8.4 ± 27 are expected for each analysis.
Thus the fitted results are found to be consistent with pure
νμ ↔ ντ oscillations and ντ appearance.
Two flavor neutrino oscillations successfully describe the
SK atmospheric neutrino data. However, contributions byelectron neutrino oscillations have not been observed yet. We
extended our neutrino oscillation analysis in order to treat
three neutrino flavors. For the analysis, Δm223 ∼ Δm213 ≡Δm2 >> Δm212 was assumed. If the parameter θ13 in the2
Δ m23(eV 2)

Fig. 9. The zenith angle distribution for tau candidate events in thelikelihood analysis. The dashed histogram (background neutrinos)
and the solid line (excess of ντ ) show the best fit for the data.

10-3

0

0.1

0.2

0.3
2

sin θ13
Fig. 10. The allowed region for (Δm2 , sin2 θ13 ) for the normal (upper
figure) and inverted (lower figure) hierarchy. We assumed positiveΔm2 . The red and blue contours correspond to allowed regions
obtained by this analysis. The hatched region corresponds to 90%
C.L. excluded area by CHOOZ experiment.

mixing matrix of lepton sector (MNS matrix) is finite, neutrino oscillations among νμ ↔ νe may be observed. Moreover, the mixing parameter is affected by potentials caused
by matter and oscillations are expected to be resonantly enhanced around 5 GeV. Therefore, we can expect an increaseof upward-going Multi-GeV e-like events. Fig. 10 shows theresult of the three-flavor neutrino oscillation analysis. Though
there was no significant excess of electrons, we set an upper
limit on θ13 . More statistics are needed to improve sensitivity[3].
We also studied deviations of sin2 θ23 from 0.5 assuming
θ13 = 0. If the contribution of 1-2 parameters (Δm212 , sin2 θ13 )are considered, the enhancement (or reduction) of low energy
νe flux is expected in the case of θ23 < (>)π /4. The oscillation analysis was performed with and without 1-2 oscillation
2 distributions as a funcparameters. Figure 11 shows χ 2 − χmin2
tion of sin θ23 for oscillations with 1-2 parameters (solid line)
and without 1-2 parameters (dotted line). There was no sig-

7
5

solar terms off

4

solar terms on

0.4

εeτ

4.5

0.35
0.3

3.5

2

Δχ

99% C.L.
90% C.L.
68% C.L.

0.25

3
2.5

0.2

2

0.15

1.5

0.1

1

0.05

0.5

0

0.4

0.5
2
sin θ23

−0.4

−0.2

0

0.2

0.6
0.2

ε ττ

0

SK−I + SK−II

2 distributions as a function of sin2 θ for oscillations
Fig. 11. χ 2 − χmin23
with 1-2 parameters (solid line) and without 1-2 parameters (dottedline).

0.15
0.1

0.4

ε ee

SK−I + SK−II
99% C.L.
90% C.L.
68% C.L.

0.05

nificant discrepancy of θ23 from π /4. sin2 θ23 is constrained
too 0.44 ≥ sin2 θ23 ≥ 0.55 at one σ level.
In addition to neutrino oscillations, several attempts areproposed to explain the atmospheric neutrino problem. We
tested the possibility of νμ − ντ oscillation + non standard
neutrino-matter interactions, flavor changing neutral current
and lepton non universality. We obtained no evidence of
NSI signal, we set 90% C.L. limits for the NSI parameters,|εμτ | < 1.1 × 10−2 , −4.9 × 10−2 < εττ − εμ μ < 4.9 × 10−2 ,|εeτ | < 0.16 and −0.05 < εττ < 0.06.
We performed several studies to search for astrophysical sources of high energy neutrinos using the SuperKamiokande-I neutrino induced upward-going muon data.
The data set consists of 2359 events with a minimum energy
1.6 GeV, of which 1892 are through-going and 467 stop within
the detector. No statistically significant evidence for point
sources or any diffuse flux from the galactic plane is found.
The 90 % C.L. upper limits on upward-going muon flux fromastronomical sources which are located in the southern hemisphere and always under the horizon for Super-Kamiokandeare (1 ∼ 4) × 10−15cm−2 s−1 [4] [5].

Solar neutrinos
SK detects solar neutrinos through neutrino-electron scattering, ν + e → ν + e, with which the energy, direction andtime of the recoil electron are measured. Due to its large fiducial mass of 22.5 kilotons, SK gives the most precise measurement of the solar neutrinos’ flux with accurate information of
the energy spectrum and time variations. For this precisionexperiment precise calibrations are performed for the energy
scale, energy resolution, angular resolution and the vertex position resolution using a LINAC and 16 N radioisotope generated by a DT neutron generator.
In this year, we have started to improve SK-III data analysis. We have locate a 0.5nsec order problem in the timing
calibration, then fixed the 10cm level vertex shift. This will

0
−0.05
−0.1
−0.15
−0.2
0

0.1

0.2

0.3

ε e0.4τFig. 12. Allowed NSI parameters region for εee v.s.εeτ (top) andεeτ v.s.εττ (bottom).

reduce the systematic error on solar neutrino flux by the vertex
shift. The water quality during SK-III period are also studied
precisely, then obtained water absorption parameter as a function of time. The data reduction cuts are also under optimizing
to SK-III data.
We have also lowered energy threshold of SK-III detector
from 5.0MeV to 4.5MeV on April 16. These are total energy of recoil electrons. Figure 13 shows the low-energy data
reduction steps from April 16, 2008 until the end of SK-III(August 17, 2008). SK-III shows a lower event rate in thecentral 13.3kt in the final data sample, though the event rates
in SK-III are consistent with those in SK-I in the 22.5kt fiducial volume.
Figure 14 shows the angular distributions of the final
data sample in the central 13.3kton region. The backgroundrates in the 5.0-5.5MeV region have been improved in SK-III,though the signal rate is consistent. We are planning to summarize the SK-III solar neutrino results in 2009.
SK-IV has been started in September. The software trigger system is used in SK-IV, so essentially there is no trigger
threshold. Since the current data acquisition computer poweris limited, we are currently accumulating the solar neutrino

8

data with the same energy threshold level as SK-III. Now, weare trying to introduce the new computer system to achieve
100% event selection efficiency at 3.5MeV in electron totalenergy.

Search for nucleon decay

Fig. 13. The data reduction steps in SK-III during April 16 and August
17 in 2008. The colored lines are from SK-III, and the black plots
are from SK-I. The tight fiducial volume cut to select central 13.3kt
is applied to the data below 6.0MeV. The 22.5kton fiducial volume
is applied above 6.0MeV.

Fig. 14. The angular distribution in the central region of the SK detector. The blue and red plots correspond to SK-I and SK-III, respectively. The vertical and horizontal length are 23.6m and R2 ≤180m2 , and the fiducial volume is 13.3kton in these plots.

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) and 49.2 kt·yrs(SK-II) resulting in 141 kt·yrs data in total. Various nucleon
decay modes have been looked for in SK but we have foundno 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 anddiscovery of the signal would give us the information of themass of the gauge mesons. To discriminate the signal from theatmospheric neutrino background, we reconstruct the number of particles (Cherenkov rings) and reconstruct the total
visible energy corresponding to parent proton mass and total momentum corresponding to the proton’s Fermi momentum. The signal efficiency and the estimated atmospheric
neutrino background for SK-I are 44.9% and 0.20 events in
91.7 kt·yrs. Even with about one half (19%) of the photocoverage area in SK-II, we achieved high detection efficiencyof signals (43.7%) and low background levels (0.11 events in
49.2 kt·yrs). The BG rate was confirmed by an artificial neutrino beam by using 1-kton water Cherenkov detector [6]. Because there are no candidate events in SK-I and SK-II data,
we obtained a lower limit on the partial lifetime of the proton;τ /B p→e+ π 0 > 8.2 × 1033 years at 90% confidence level [7].
Moreover, we have performed extensive search for nucleon decays into a charged lepton (e+ or μ + ) and a meson(π 0 , π − , η , ρ 0 , ρ − , or ω ). Among these decay modes, wehave observed two candidate events for p → μ + η with the
expected background of 0.45 events in the exposure of SK-I
+ SK-II. In other modes, we have observed at most one event
while expected background is in the order of 0.1. Figure 15
shows obtained upper limits on the partial proton lifetime.
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, we
looked for 236 MeV/c monochromatic muons from the decayof K + . Figure 16 shows the comparison between data andfitting results of the muon momentum distribution for singlering μ -like events. We observed no excess of signal. In othermodes, there are no significant signal excess. Therefore weconclude that there is no evidence of nucleon decays and we
calculated partial lifetime limits taking into account systematic uncertainties. Obtained limits are 2.3 × 1033, 1.3 × 1032,
1.3 × 1033 and 1.0 × 1033 years at 90% confidence level for
p → ν̄ K + , n → ν̄ K 0 , p → μ + K 0 , and p → e+ K 0 modes, respectively.
We also looked for neutron-antineutron oscillation (conversion) in the water that violates Baryon number by 2. The9antineutron annihilates with a nearby nucleon (proton or neutron) producing multiple secondary pions and gammas whichemit isotropic Cherenkov photons with a visible energy of 1
GeV. In the full SK-I data, the number of observed candidates
is 23 events while expected backgrounds is 24. We have set
the upper limit on the neutron-antineutron conversion rate to
1.99 × 1032 years at 90% confidence level. This limit gives
the upper limit on the oscillation time of a free neutron as
2.49 × 108 sec at 90% confidence level and can be comparedwith the reactor experiment limit of 0.86 × 108 sec.

p → e+ π0
p → μ+ π0
p → e+ η
p → μ+ η
p → e+ ρ0
p → μ+ ρ0

Supernova neutrinos

p → e+ ω

Kamiokande and IMB observed neutrino burst from supernova 1987a. Those observations confirmed that the energy release by neutrinos is about several×1053erg. SuperKamiokande is able to detect several thousand neutrino events
if it happens near the center of our galaxy. Until now, noclear neutrino burst from a supernova was observed in SuperKamiokande.
Currently, we have been improving the the Supernova
Relic Neutrino (SRN) search in SK. The SRN is the diffuse
supernova neutrino background from all the supernovae in thepast. It is expected that the SRN would become dominant in
18–40MeV energy region, though they haven’t been observed
yet.
In SK detector, we have applied the special data selections
to enhance the SRN candidates. The energy region was 18–
82MeV, and the fiducial volume was 22.5kton. All the cut
criteria are under retuning, including the fiducial volume cut
and the energy threshold.

p → μ+ ωn → e+ π−
n → μ+ π−

SK−I+IIIMB−3n → e+ ρ−+

Kam−I+II
FREJUS

−

n→μ ρ

31

10

32

10

33

10

34

10

Lifetime limit (years)

Fig. 15. The lifetime limits on the partial lifetime of protons.

Bibliography
dataatmνMC (best fit)+p→νK MC

number of events

60

40[2] Super-Kamiokande Collaboration, “A measurement of
atmospheric neutrino flux consistent with tau neutrino appearance”, Submitted to Phys. Rev. Lett., hepex/0607059.
[3] Super-Kamiokande Collaboration, “Three flavor neutrino oscillation analysis of atmospheric neutrinos inSuper-Kamiokande”, Phys. Rev. D 774 (2006) 032002.

20

0
200

[1] H. Nishino et al., “High-Speed Charge-to-Time Converter ASIC for the Super-Kamiokande Detector’ ’, Tobe submitted to Nucl. Inst. and Meth. A.

[4] Super-Kamiokande Collaboration, “High energy neutrino astronomy using upward-going muons in SuperKamiokande-I’ ’ Astrophys. J. 652, (2006) 198.
225

250

275

300

μ momentum (MeV/c)
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.

[5] Super-Kamiokande Collaboration, “Search for Diffuse
Astrophysical Neutrino Flux Using Ultrahigh Energy
Upward-going Muons in Super-Kamiokande-I.” Astrophys. J. 652, (2006) 206.
[6] 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]].

10

T2K Experiment[Spokesperson : T. Kobayashi]High Energy Accelerator Research Organization, Japan,
Tsukuba 305-0801
In collaboration with the members of:
ICRR, University of Tokyo, Japan; Kyoto University, Japan;
KEK, High Energy Accelerator Research Organization,
Japan; Kobe University, Japan; Osaka City University, Japan;
Hiroshima University, Japan; Tohoku University, Japan; University of Tokyo, Japan; Miyagi Edu. University, Japan;
Chonnam National University, Korea; Seoul National University, Korea; Dongshin University, Korea; Gyeongsang
National University, Korea; Kyungpook National University, Korea; Sejong University, Korea; Sungkyunkwan University, Korea; Boston University, USA; Brookhaven National Lab, USA; Colorado State University, USA; Duke
University, USA; Louisiana State University, USA; Stony
Brook University, USA; University of California at Irvine,
USA; University of Colorado, USA; University of Pittsburgh,
USA; University of Rochester, USA; University of Washington, Seattle, USA; TRIUMF, Canada; University of Alberta, Canada; University of British Columbia, Canada; University of Regina, Canada; University of Toronto, Canada;
University of Victoria, Canada; York University, Canada;
University of Oxford, UK; Imperial College London, UK;
Lancaster University, UK; Queen Mary, University of London, UK; Sheffield University, UK; STFC/Rutherford Appleton Laboratory/Daresbury Laboratory, UK; The University of Liverpool, UK; University of Warwick, UK; Universitat Autonoma de Barcelona IFAE, Spain; IFIC Universityof Valencia, Spain; INRM, Russia; CEA/DAPNIA Saclay,
France; IPN Lyon (IN2P3), France; LLR Ecole polytechnique(IN2P3), France; LPNHE-Paris, France; RWTH Aachen University, Germany; INFN Sezione di Roma, Italy; Napoli
University, Italy; Padova University, Italy; Rome University,
Italy; ETHZ, Swiss; University of Geneva, Swiss; University of Warsaw, Poland; A. Soltan Institute for Nuclear Studies, Poland; H.Niewodniczanski Institute of Nuclear Physics,
Poland; Technical University, Poland; University of Silesia,
Poland; Wroclaw University, Poland; Institute for Nuclear Research, Russia;

may be possible to search for CP violation in the lepton sector and to measure the CP phase, δ , which is one of the lastparameters of the neutrino oscillation. Therefore, several next
generation experiments, which utilize high intensity neutrino
beams, have been planned for the further investigation of theneutrino oscillations. The Tokai to Kamioka long baseline
neutrino oscillation experiment (T2K) is one of the new generation experiments. The intense neutrino beam is produced
by using a new high intensity proton synchrotron accelerator
at the J-PARC site in Tokai village. As a far detector to study
neutrino oscillation phenomena, the T2K experiment utilizes
Super-Kamiokande(SK), which is located at 295 km from thebeam production target.
In the design of the neutrino beam line for T2K, the concept of off-axis beam 1 is introduced. With this method, it
is possible to efficiently produce a low energy neutrino beamwith narrow energy spread from the high energy proton beam.
Also, it is possible to tune the peak energy by changing thedirection of the beam direction. Based on this concept, the direction of the neutrino beam is intentionally shifted from thedirection of the SK detector by a few degrees and also the direction of the beam is tunable. The initial peak position of theneutrino beam energy is adjusted to ∼ 650 MeV by setting theoff-axis angle to ∼ 2.5◦ to maximize the neutrino oscillation
effects at the SK detector. The generated neutrino beam isprimarily νμ with a small contamination of νe , which is estimated to be ∼ 0.4% at the flux peak. The T2K neutrino beam
is expected to be almost two orders of magnitude more intensecompared to the K2K neutrino beam. The construction of thebeamline facility for the T2K experiment has been completed
in spring of 2009 and the physics run is expected to start by
the end of FY2009.
90% CL θ13 Sensitivity

10−1

10−2
2
Δ m23
(eV 2)[7] 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]].

10−3
Systematic Error Fraction
5% sys error
10% sys error
20% sys error
CHOOZ Excluded

The K2K experiment established the method of theaccelerator-based long baseline neutrino oscillation experiment and successfully confirmed the neutrino oscillation phenomena. Meanwhile, several experiments have measured 2
out of 3 neutrino mixing angles and 2 mass differences using
accelerator, atmospheric, solar and reactor neutrinos. However, one mixing angle, θ13 , has not been measured and has
only been found to be small. The experimental sensitivityof the θ13 measurement is still limited by statistics and thus,
there is a chance to measure the value with a much more intense neutrino beam. Furthermore, if θ13 is large enough, it

−4

10 −3
10

10−2
10−1
sin2 2 θ13 sensitivity

1Fig. 1. Expected sensitivity to θ13 by T2K (750 kW beam, 5 years of
running) as a function of Δm223 compared with current best limit by
the CHOOZ reactor experiment.

As described, one of the motivations of this experiment*1 Long Baseline Neutrino Oscillation Experiment BNL E889 proposal,(1995).

11

is to measure the neutrino oscillation parameter θ13 , which isonly known to be small (sin2 2θ13  0.1) by the previous experiments. It is of great interest to know the value of a nonzero
θ13 or how close to zero θ13 is. The T2K experiment will try
to measure θ13 using the electron neutrino appearance channel
and there is a possibility to be the first experiment to observe
the neutrino oscillation signature with the appearance channel.
Figure 1 shows T2K’s expected sensitivity to θ13 as a function of Δm223 . The shaded region is the excluded region by the
CHOOZ experiment. As shown in this figure, the T2K experiment has more than one order of magnitude better sensitivity
compared to the current best limit.
If the measured θ13 is large enough, it will be possible
to investigate CP violation in the lepton sector with further
extension of this experiment.
Another major purposes of this experiment are precise
measurements of θ23 and Δm223 . Owing to the high statistics, the precisions of these parameters are expected to be almost one order of magnitude better than before. So far, θ23
mixing is known to be very large and almost maximal fromthe Super-Kamiokande, K2K and the MINOS experiments. If
sin2 2θ23 = 1, it may suggest an underlying new symmetry.
To achieve the expected precision, we have been working
to improve the SK detector, to understand the detector and to
improve the analysis methods. In the following sections, someof the works are described briefly.
Detector Upgrade
The reconstruction work of Super-Kamiokande was completed in 2006 and all the PMTs were installed just as in SK-I.
It will help the T2K experiment in search for the electron neutrino appearance, to distinguish the π 0 backgrounds from theνe signal more efficiently.
In summer 2008, the electronics and the DAQ systems
were replaced and newly developed ADC/TDC modules
called QBEE were installed. The new QBEE boards consistof the custom analog ASIC chips and the multi-hit TDC chips.
This new system allows us to observe the T2K neutrino eventswith good stability and accuracy.
The trigger system of the new DAQ system is software
based and the T2K neutrino beam induced events are stored
using the beam extraction timing from the accelerator. With
this scheme, it is possible to record all the PMT hit information around the beam arrival timing as the T2K events. In order to make this system work, the beam timing is required to
be transferred within a few seconds. This time, we have prepared the dedicated network line from the J-PARC accelerator
to the Kamioka site to transfer the necessary timing information as soon as the protons are extracted. This system has
been tested using the dummy timing information for several
months. As a result, the typical latency to transfer the beamtiming was measured to be less than several tens of ms, which
is much shorter than the 3 second allowance, and the trigger
system was confirmed to work as designed.
Precise Detector Calibration
The response of the far detector, SK, must be well understood in order to maximize the sensitivities to oscillation

parameters such as θ13 , θ23 , and Δm223 . In the electron appearance search, single π 0 production backgrounds can fakesingle-ring electron signals when one of the two γ rings is not
identified. Even if a small portion of νμ induced events are
mis-identified as electrons, it will be a serious background.
Therefore, we have started to study the ring identificationand the particle identification capabilities of the detector very
carefully. It is also important to reduce the uncertainty in theabsolute energy scale measurement (2.5%) in order to achievea Δm223 measurement with ∼ a few% accuracy. Moreover,further calibration of the fundamental properties such as the
charge and timing responses of each PMT, the light attenuation and scattering in water, and the light reflection by thedetector materials are indispensable.
Software Upgrade
All measurements of the physical quantities of an event,such as the vertex position, the number of Cherenkov rings,
the momentum, the particle type and the number of the decay electrons, are automatically performed based on the reconstruction algorithms. The analysis software can be sharedwith the one for the atmospheric neutrino analysis. However,
the energy region in our interest for the T2K experiment islimited and thus, there is room to optimize the software forthe particular analysis for the T2K experiment. This work has
started, especially in the π 0 rejection studies.
Also, the R&D work of the possible near detector to measure the left right symmetry of the neutrino beam has been
started in RCCN in order to investigate the feasibility of the
future extension.

Bibliography[1] Y. Itow et al., The JHF-Kamioka neutrino project,(2001), hep-ex/0106019.

XMASS experiment
XMASS is a multi-purpose experiment using liquid xenon
that aims at the detection of cold dark matter, search for neutrinoless double beta decay, and detection of low energy solar
neutrinos. Construction of a one-ton liquid xenon detector(100 kg fiducial volume) was approved in 2007 and will bedone in 2009. This detector is expected to search for dark
matter with a sensitivity that is improved by a factor of 100
over that in existing experiments.

Liquid xenon detectors
There are three motivations for developing liquid xenon
detectors.
1. Astronomical observations suggest that there is dark
matter (non-luminous particles with mass) in the universe. One of the most likely candidates for dark matter
is a weakly interacting massive particle (WIMP), suchas the lightest supersymmetric particle. The recoil ofa xenon nucleus due to an interaction with dark matter
will produce scintillation light in liquid xenon.

12

2. The Super-Kamiokande experiment shows that neutrinos have mass. However, we do not yet know their absolute mass or whether they are Majorana or Dirac type.
The Xenon nuclei with mass number 136 is the double
beta nuclei best suited for this research.
3. The energy spectrum of solar neutrinos has been measured only above 5 MeV by SK and SNO and that of
low-energy solar neutrinos (pp, 7 Be neutrinos, etc.) has
not yet been measured. A 10-ton liquid xenon detector will be able to detect pp neutrinos and 7 Be neutrinos by detecting ν +e scattering, at a rate of 10 and
5 events/day, respectively.
For all these purposes, background caused by gamma raysoutside the liquid xenon must be suppressed. The key idea in
reducing background is that gamma rays can be absorbed byliquid xenon itself (self-shielding). A sphere of liquid xenon
absorbs low energy gamma rays from the outside within theouter 10-20 cm thick layer and realizes a low background radiation in the central volume. WIMPs and neutrinos, however,interact throughout the detector. Therefore, if the vertices ofthe events can be reconstructed, WIMPs and neutrinos canbe observed in a low background environment by extracting
only events observed deep inside the detector. The event reconstruction can be accomplished by observing photons withmany photo multipliers mounted outside the fiducial volume.
Liquid xenon has the following advantages to realize this idea:• With the high atomic number of xenon (Z = 54) andthe high density of liquid xenon (∼ 3 g/cm3), external
gamma-rays can be absorbed within a short distancefrom the detector wall (self-shielding).
• A large light yield of 42,000 photons/MeV, which is as
good as a NaI(Tl) scintillator, enables good event reconstruction as well as detection of small energy signals
such as dark matter recoil.
• The 175-nm-wavelength scintillation light of liquid
xenon can be detected by a photomultiplier tube (PMT)comprising a bi-alkaline photocathode with a quartz
window.
• Purification is easier than with other materials (e.g. distillation is possible).
• Isotope separation is possible. It is possible to enrich
136 Xe for double beta decay or deplete 136 Xe for solar
neutrino measurements.
We have been studying liquid xenon detectors since 2000.
A 3 kg fiducial volume liquid xenon detector has been developed for R&D study and test data obtained. Event reconstruction, self-shielding and low internal activity have been confirmed. The description of the one-ton liquid xenon detector in
the following sections represents the first phase of this project.
The detector aims to detect cold dark matter particles with improved sensitivity by a factor of 100. The second phase of the
XMASS project requires a larger detector with more than 10tons of liquid xenon. The detector is intended for a detailed
study of dark matter, and detection of low energy solar neutrinos. The search for neutrinoless double beta decay withthe 10-ton detector needs additional efforts in the reduction of
background activity in a few MeV energy regions.

Fig. 1. The central part of the proposed one-ton liquid xenon detector
intended for dark matter search. The detector has a sensitivity of
10−45 ∼ 10−44 cm2 in cross section, which is two orders of magnitude better than the current best limit in the world.

Fig. 2. Expected sensitivity of the proposed one-ton liquid xenon detector. See http://dmtools.berkeley.edu/

One-ton detector
We plan to make the one-ton detector to search for dark
matter down to 10−45 ∼ 10−44cm2 in cross section which is
two orders of magnitude better than the current best limit in
the world. Figure 1 shows the central part of the detector.
Its background and sensitivity were evaluated by Monte Carlosimulations which were validated by the current experimental
results. The advantages of our detector design are as follows:
1. Extension of the detector is straightforward because thetarget substance is liquid.
2. The energy threshold is as low as 5 keV since the photoelectron yield is high.
3. Purification of the target substance is easy because
xenon is naturally in a gas phase.
4. It is possible to use pulse shape analysis to select nuclear recoil events.
The expected sensitivity for particle dark matter is better
than the current experimental limits by two orders of magnitude. Figure 2 shows the expected sensitivity of the one-ton
detector.

Construction of the one-ton detector
The construction of the one-ton detector started in 2007
and is to be completed by 2009. Important progress related tothe construction has been made.

13

reduce such contaminations, we have constructed and tested
a recirculation system with the 3 kg fiducial volume liquid
xenon detector. At present, reduction of water vapor in liquid xenon has been observed but no clear reduction of radon
contamination observed. Some other candidates of filters will
be tested in 2009.
References
1. Y. Suzuki et al., “Low energy solar neutrino detection
by using liquid xenon”, Aug. 2000, hep-ph/0008296.
Fig. 3. A water tank (left side) for shielding from gamma ray and neutrons. The liquid xenon detector will be located at the center of thetank.

Construction of radiation shield
Ambient gamma rays and neutrons are serious sources ofbackground, and pure water is one of the best materials for
reducing it. We designed a liquid xenon detector immersedin the cylindrical water tank shown in Fig. 3. It is 10 m indiameter and 11 m high. Its construction completed and an
inner structure for supporting the detector is going to be done.
A water purification system will be prepared by the summer
in 2009.
Mass production of PMTs
The central part of this detector is shown in Fig. 1. The
PMTs (shown as many cylinders) are one of the main components of this part. The PMTs consists of a hexagonal photo
cathode to maximize the photo sensitive area of the detector. They are specially developed and designed for this experiment since the scintillation wavelength is very short (175 nm)
and the operating temperature is low (-100C). In addition, thePMT materials including base parts were carefully selected
and evaluated with a low background germanium detector.
Production of 650 PMTs started at the end of fiscal year 2008,
and is to be completed by the end of summer in 2009.
Detail design of the liquid xenon vessel
In the Fig. 1, PMT holder and liquid xenon vessel are also
shown. Copper was chosen as their material because of its
purity and high atomic number. Detail design of holder andvessel was done and ready for construction.
Development of a distillation tower
Radioactive contamination in xenon contributes background for dark matter signals. 85 Kr in xenon is one potential
source of radioactive contamination. In order to reduce krypton contamination, a distillation system was developed which
is able to process 6 kg Xe/hour and achieve better than 10 −5
reduction in krypton concentration. This system will be tested
in early summer in 2009.
Recirculation system for liquid xenon
We may need to purify liquid xenon before or during detector operation to reduce possible contamination. One example is water vapor which absorbs scintillation light. Anotherexample is radon gas which is a source of background. To

2. S. Moriyama, “XMASS EXPERIMENT I”, Proceedings of the International Workshop on Technique andApplication of Xenon Detectors, Kashiwa, Japan, 3-4
Dec. 2001.
3. Y. Suzuki, “XMASS”, presentation at the Identificationof Dark Matter (IDM2008), Stockholm, Sweden, 18-22
August 2008.
4. M. Yamashita,“XMASS experiment”, presentation at
the 16th YKIS Conference, Progress in Particle Physics
2008, Kyoto, Japan, 16-19 February 2009.

14

HIGH ENERGY COSMIC RAY DIVISION
Overview
Three major research activities of the High Energy Cosmic Ray Division are the study of very high energy gamma
rays by the CANGAROO group, extremely high energy cosmic rays by the Telescope Array (TA) group, and very highenergy cosmic rays and gamma rays by the Tibet ASγ Collaboration. It is particularly worth noting that TA started fulloperation in the spring of this fiscal year. Other activities, suchas 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 CANGAROO project (Collaboration of Australia andNippon for a GAmma-Ray Observatory in the Outback) isa set of large imaging atmospheric Cherenkov telescopes tomake a precise observation of high-energy air showers originated by TeV gamma rays. It started as a single telescopewith a relatively small mirror (3.8 m in diameter) in 1992. In
1999 a new telescope with a 7-m reflector has been built, andnow it has a 10-m reflector with a fine pixel camera. The main
purpose of this project is to explore the violent, non-thermal
universe and to reveal the origin of cosmic rays. An array offour 10-m telescopes has been completed in March 2004 sothat more sensitive observations of gamma rays are realizedwith its stereoscopic imaging capability of Cherenkov light.
Several gamma-ray sources have been detected in the southern sky and detailed studies of these sources are now ongoing.
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 just started taking data as the largest array viewing thenorthern 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 suc-cessive 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), has been developed and thefirst-phase stations have been installed near the Mauna Loa
summit in the Hawaii Island. It will monitor optical and particle radiation from high-energy transient objects with a wide
field-of-view. The optical system is under tuning and real observation will start soon.

CANGAROO-III Project[Spokespersons : R.W. Clay, M. Mori, 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; School of Allied Health
Sciences, Kitasato University, Kanagawa, Japan; Departmentof 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 Institutesof 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 University, Kanagawa, Japan; Department of Physics,
Hiroshima University, Hiroshima, Japan; Department of Basic
Physics, Tokyo Institute of Technology, Tokyo, Japan; 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. Three of the four telescopes (called T2, T3
and T4 in the order of construction) have been used in observations since 2005 as the first telescope, completed in 2000
and having been used as CANGAROO-II, has degraded and isequipped with a different electronics system from the others.
A stereoscopic triggering system was installed at the beginning of 2005 and has been working properly, rejecting mostsingle 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.
In February 2008, a considerable number of segment mirrors of T4, corresponding to about 10% of the total mirrorarea, were blown off by heavy storm. Part of them was fixedand put back to the telescope in March 2008. Since May 2008,
two of the four telescopes (T3 and T4) have been used in observations as the reflectivity of T2 mirrors has degraded seriously. The T3 and T4 mirrors were cleaned using tap water in
May 2008 and their reflectivities calibrated using muon ring
events were improved by more than 10%.

CANGAROO-III Results
In 2008, CANGAROO-III papers of five celestial objects
were published in journals: the blazar PKS 2155–304 [2], thepulsar wind nebula MSH 15–52 [3], Kepler’s supernova remnant [4], the unidentified TeV source HESS J1804–216 [5],and the Galactic Plane [6]. One paper of the clusters of galaxies Abell 3667 and Abell 4038 was also submitted to a journal[7]. Results of relatively recent papers are summarized below.
Kepler’s Supernova Remnant [4]Kepler’s supernova remnant (SNR) is 400 years oldand both younger (Cas A) and older (RX J0852.0–4622,
RX J1713.7–3946, etc.) SNRs are known to be TeV gammaray sources. Therefore, one might expect a similar level of
TeV gamma-ray emission also from Kepler’s SNR, if the SNR
age is a dominant factor in cosmic-ray acceleration.
CANGAROO-III observed Kepler’s SNR in April 2005
for an effective observation time of 874 min. No statisticallysignificant gamma-ray signal has been detected from the SNR
and we have estimated 2σ flux upper limits corresponding to
the 10–30% Crab level. They are plotted in Figure 1 together
with model predictions obtained by Berezhko et al. (2006)2
considering a reasonably wide range of possibilities for the
distance of the SNR (3.4–7.0 kpc), the supernova explosion
energy ((0.5–2.0)×1051 erg), and the ambient matter density(0.4–6.0 cm−3 ). Limitations on the allowed parameter range
in the model were discussed in comparison with the flux upper
limits.
*2

Berezhko, E. G., Ksenofontov, L. T., & Völk, H. J. 2006, A&A, 452, 217

log10 Eγ Fγ [erg/(cm2s)]

15

-11

-12

-13

-14

-15
7

8

9

10

11

12

13
14
log10 Eγ [eV]Fig. 1. Spectral energy distributions for Kepler’s SNR. The

black lines with arrows at both ends are the 2σ flux upper
limits obtained by CANGAROO-III. The colored curves arespectra predicted from hadronic models by Berezhko et al.
(2006), obtained assuming the distance to Kepler’s SNR
to be 4.8 kpc and varying the supernova explosion energy
and the ambient matter density.

HESS J1804–216 [5]A Galactic plane survey was performed in 2004 by the
H.E.S.S. IACTs with a flux sensitivity of 0.02 Crab for gamma
rays above 200 GeV. Fourteen new gamma-ray sources weredetected at significance levels above 4σ , and 11 of the sources
either have no counterpart or possible counterparts with significant positional offsets. HESS J1804–216 is one of thebrightest, and its spectrum is softest in this survey; the flux
is about 0.25 Crab above 200 GeV with a photon index of
2.72 ± 0.06. In addition, with a size of ∼ 22 , it is one of
the most extended TeV gamma-ray sources.
We observed HESS J1804–216 with the CANGAROO-III
IACTs from May to July in 2006. We detected very high energy gamma rays above 600 GeV at the 10σ level in an effective exposure of 76 hr. We obtained a differential flux of(5.0 ± 1.5stat ± 1.6sys) × 10−12(E/1 TeV)−α cm−2 s−1 TeV−1
with a photon index α of 2.69 ± 0.30stat ± 0.34sys, which isconsistent with that of the H.E.S.S. observation in 2004. We
also confirmed the extended morphology of the source. By
combining our result with multiwavelength observations, we
discussed the possible counterparts of HESS J1804–216 andthe radiation mechanism based on leptonic and hadronic processes for a SNR and a pulsar wind nebula (PWN). An example is shown in Figure 2 for the leptonic model for the PWNof PSR B1800–21 with a time-dependent rate of electroninjection.
Galactic Plane [6]The Galactic Plane is known to be a very bright sourceof gamma rays in the GeV energy band. Its gamma-ray spa-

×10-610 3

t < 1000 years
10 2
10t > 15000 years
GLAST
1year

1
10 -1

Integral flux (E>600GeV)(phs/cm2/sec/str)νF ν [eV cm -2 s -1]

16

0

-0.2
-1

10

10 -4
10

-5

10 -9 10 -7 10 -5 10 -3 10 -1 10 10 3 10 5 10 7 10 9 10 11 10 13 10 15
Energy [eV]Fig. 2. Spectral energy distribution and the leptonic model

curves for the pulsar wind nebula of PSR B1800–21 witha time-dependent rate of electron-injection with an age
τ = 16 kyr, an initial spin-down timescale τ0 = 700 yr, a braking index of the pulsar nbr ∼ 1.6, a spectral index of injected electrons Γe = 1.5, and a magnetic field B = 8 μ G.
The right-hand curves show the inverse Compton component, and the left-hand curves show the synchrotron emissions. The dot-dashed curves show the spectra producedby old electrons (t < 1000 yr), and the dotted curves show
the spectra produced by young electrons (t > 15000 yr).
The thin solid curves represent their medium per 1000 yr(1000 < t < 15000 yr), and the thick solid curves show their
total.

tial profile and spectrum across the entire galactic plane were
measured by satellite experiments such as SAS-II, COS-B,
and CGRO. Among these, the EGRET detector on the CGRO
was sensitive to GeV gamma-rays, and the observations using
this detector provided the detailed spatial and spectral characteristic features of gamma-ray emission from the Galactic
Plane up to 30 GeV. Above this energy, some models of the
diffuse gamma-ray emission predict very hard spectra, extrapolations of which are detectable at TeV energies by using thecurrent generation of IACTs.
In 2004, we searched for very high energy (VHE) gammaray emission from the Galactic Plane using the CANGAROOIII stereoscopic IACT system. Two different longitude regionsof  = −19◦ .5 and  = +13◦.0 on the Galactic Plane wereobserved in July and August 2004 for 8.0 hr and 5.9 hr, respectively. We analyzed events that triggered three telescopes
aiming to measure the diffuse emission component. No significant signal associated with the Galactic Plane was found fromeither of the regions (Figure 3). Assuming that the gamma-ray
spectrum is described by a single power-law for energies ranging between a few GeV and TeV, lower limits of the power-law
spectral indices were found to be 2.2 for both of the regionswith a 99.9% confidence level (CL). This result is consistent
with the other VHE measurements and constrains a hypothesis in which a very hard (∼ 2.0) cosmic ray electron spectrum
was introduced to explain the EGRET GeV anomaly.

Integral flux (E>600GeV)(phs/cm2/sec/str)

10 -2
-3

l=-19.5

0.2

-0.5

0
0.5
1
Galactic latitude (deg)×10-6
l=+13.0

0.1
0

-0.1
-1

-0.5

0
0.5
1
Galactic latitude (deg)Fig. 3. The latitude profiles of the flux intensity for  = −19◦ .5

and  = +13◦ .0, obtained by projecting two-dimensional excess count maps onto  = const. lines. The raw count profile was divided by the acceptance and the solid angles foreach projection bin. The bin size in the latitude direction
was selected to be 0◦ .2. Vertical bars represent fitting errors in each data subset.

Clusters of Galaxies [7]Clusters of galaxies are candidate sites for the origin ofultra high energy (UHE) cosmic rays because accretion andmerger shocks in clusters may accelerate particles to high energies, A prediction was presented for gamma-ray emission
from a cluster of galaxies at a detectable level with the current
generation of IACTs. The gamma-ray emission is produced
via inverse Compton (IC) upscattering of cosmic microwave
background (CMB) photons by electron-positron pairs generated by collisions of UHE cosmic rays in the cluster.
We observed two southern clusters of galaxies, Abell 3667
and Abell 4038, searching for VHE gamma-ray emission
with the CANGAROO-III telescope system in 2006. The
ON-source observation times are 29.7 hr and 23.6 hr for
Abell 3667 and Abell 4038, respectively. The analysis showedno significant excess around these clusters (significance maps
shown in Figure 4), yielding upper limits on the gamma-ray
emission. From a comparison of the upper limit for the northwest radio relic region of Abell 3667 with a model prediction,
we derived a lower limit for the magnetic field of the regionof ∼ 0.1 μ G. This shows the potential of gamma-ray observations in studies of the cluster environment. We also discussed
the flux upper limit from cluster center regions with a model ofgamma-ray emission from neutral pions produced in hadronic
collisions of cosmic-ray protons with the intra-cluster medium(Figure 5). The derived upper limits of the cosmic-ray energy densities within this framework are ∼ 20 eVcm−3 for
Abell 3667 and ∼ 40 eVcm−3 for Abell 4038, which are anorder of magnitude higher than that of our Galaxy.

17

-1.

0.

1.

2.

Declination (J2000, deg)

-1

Integral flux [cm sec ]

-2.

-2

-56.0
-56.5
-57.0

10

-8

EGRET
10

10

10

-9

-10

-11

-57.5
10

304
303
302
Right Ascension (J2000, deg)10

Γ=-2.1
Γ=-2.3-12w IR absorption

-13

10

Declination (J2000, deg)

-2.

-1.

0.

1.

2.

358.0 357.5 357.0 356.5 356.0
Right Ascension (J2000, deg)

10

10

2

10

3

Photon energy [GeV]gion of Abell 4038 with the gamma-ray emission spectrum
via π 0 -decay process, normalized to the EGRET upper
limit. The EGRET upper limit is indicated by the arrow at
100 MeV, and the lines are the gamma-ray spectrum fromthe proton power-law indices of Γ = −2.1 and −2.3 with anenergy cutoff of 200 TeV. The gamma-ray absorption effectby IR photons are represented by dot-dashed lines, where
the P0.4 model in Aharonian et al. (2006)3is adopted.

-28.0

-29.0

1

Fig. 5. Gamma-ray flux upper limits for the cluster core re-

-27.5

-28.5

-1

lying on both sides. Shock accelerated electrons are expected
to generate sub-TeV gamma rays through the IC process in thelobes.
CANGAROO-II observed the western X-ray lobe regionin August and September 2001, and in July and September
2002. The total observation times are 85.2 hr for ON source
and 80.8 hr for OFF source. In the ON-source observations,the tracking position was set at “p1” indicated in Figure 6,
from which the hardest power-law X-ray spectrum was ob-

Fig. 4. Two-dimensional significance maps around the clus-

05D 15’Dec.

ters. The map centers correspond to the position of thecD galaxy of each cluster, and at each point a smoothing algorithm within 0◦ .6 × 0◦ .6 was applied. Contoursof other wavelengths (X-ray and radio) are over-plotted.
The top panel is for Abell 3667, where the white contours show ROSAT hard-band data and orange contours
show SUMSS 843 MHz radio data. The bottom panel is for
Abell 4038, where white contours show ROSAT hard-banddata and orange contours show VLA 1.4 GHz radio data.
Our point-spread function is also shown at the bottom-rightcorner.

w1

SS433
05D 00’SS 433 is a close proximity binary system consisting of acompact star and a normal star. It is located at the center of
the SNR W 50. Jets of material are directed outwards fromthe vicinity of the compact star symmetrically to the east andwest. Non-thermal hard X-ray emission is detected from lobes*3 Aharonian, F. A., et al. 2006, Nature, 440, 1018

p2

p1
04D 45’CANGAROO-II Observations of SS 433/W 50
[8]

w2

p3

Western Lobe
19h12m

11m

10m

09m

08m

R.A.
Fig. 6. 4.75 GHz radio contour map of W 50 overlaid on X-ray

images of the western X-ray lobe (dots) obtained by ASCA.
Solid white circles show the regions reported by the ASCAteam in 2000. We label these regions “p1”, “p2” and “p3”.
Solid black circles show the regions reported by the ROSAT& ASCA team in 1997, which are labeled “w1” and “w2”.

102Synchrotron/IC

10

IC on CMB
IC on IRRadioASCACANGAROO−II

p1

1

10−1

10−2
−9

ν Fν [ eV cm−2 sec−1 ]

10

10−7

10

−5

10

102

Synchrotron/IC

10

IC on CMB
IC on IRRadioASCACANGAROO−II

−3

10−1

10

3

10

10

5

107

10

9

1011

13

15

10
10
Energy [ eV ]p2

Integral Flux (photons cm-2 s-1)

ν Fν [ eV cm−2 sec−1 ]18

PSR B1706-44
-10

10

10-11

10-12

1

10-13

10−1

10−2
−9

ν Fν [ eV cm−2 sec−1 ]

10

10−7

10

−5

10

102

Synchrotron/IC

10

IC on CMB
IC on IRRadioASCACANGAROO−II

−3

10−1

10

3

10

10

5

107

10

9

1011

13

15

10
10
Energy [ eV ]

10−1

10−2
−9

10−7

10

−5

10

−3

10−1

10

3

10

10

5

107

10

9

1011

13

1

10
Energy (TeV)

Fig. 8. Integral gamma-ray fluxes from PSR B1706–44 ob-

p3

1

10

10-1

15

10
10
Energy [ eV ]Fig. 7. Synchrotron/IC model fitting to the spectral energy dis-tributions at “p1” (top), “p2” (middle) and “p3” (bottom). The
X-ray fluxes are from ASCA and the radio fluxes are calculated from the result of the Effelsberg 100 m telescope foreach frequency. The 99% CL upper limit fluxes of this work
are shown by down-arrows. The thick solid lines represent
the synchrotron/IC spectra. Two components (CMB andIR) of IC are shown by the dashed lines and the dottedlines, respectively.

tained by ASCA. No significant excess of sub-TeV gamma
rays has been found at 3 regions (“p1”, “p2” and “p3” shownin Figure 6) of the western X-ray lobe of the SS 433/W 50
system. The 99% CL upper limits to the fluxes of gamma rays
at energies greater than 850 GeV have been derived as 1.5,
1.3, and 0.79 in unit of 10−12 photons cm−2 s−1 for “p1”, “p2”and “p3”, respectively. The synchrotron/IC model has been
applied to the multiwavelength spectrum together with radio
and X-ray data (Figure 7). Lower limits to the magnetic fieldstrengths have been estimated to be 4.3 μ G for the brightest
X-ray emission region (“p2”) and 6.3 μ G for the far end fromSS 433 in the western X-ray lobe (“p3”).

Reanalysis of CANGAROO-I Data [9]Old CANGAROO-I data have been reanalyzed for
PSR B1706–44, SN 1006, and the Vela pulsar region in response to the results reported for these sources by the H.E.S.S.
Collaboration. Although detections of TeV gamma-ray emission from these sources were claimed by CANGAROO moretained using the CANGAROO-I data. The 95% CL upper
limits to the integral flux from PSR B1706–44 obtained fromthe 1993, 1993 + 1994, 1997, and 1998 data are indicatedby the filled circle, filled square, filled triangle, and filled upside-down triangle, respectively. The open circle indicatesthe integral flux estimated by Kifune et al. (1995)4using the1993 data. The horizontal bars represent the systematic
errors of the threshold energies. The 99% CL upper limit
curves obtained by H.E.S.S. are indicated by the thin solid,
dashed, and dotted lines. The thick solid line is the integral spectrum converted from the preliminary CANGAROO-II result (Kushida et al. 20035 ). The open square andfilled star indicate the results from the Durham group and
BIGRAT, respectively.

than 10 years ago, upper limits to the TeV gamma-ray signals
from PSR B1706–44 and SN 1006 derived by H.E.S.S. areabout an order of magnitude lower. The H.E.S.S. group detected strong diffuse TeV gamma-ray emission from Vela butwith a morphology differing from the CANGAROO result.
In the reanalysis, in which gamma-ray selection criteria have been determined exclusively using gamma-ray
simulations and OFF-source data as background samples,no significant TeV gamma-ray signals have been detectedfrom compact regions around PSR B1706–44 or within thenortheast rim of SN 1006. The upper limits to the integral gamma-ray fluxes at the 95% CL have been estimated for the 1993 data of PSR B1706–44 to be F(> 3.2 ±1.6 TeV) < 8.03 × 10−13 photons cm−2 s−1 , for the 1996 and1997 data of SN 1006 to be F(> 3.0 ± 1.5 TeV) < 1.20 ×
10−12 photons cm−2 s−1 and F(> 1.8 ± 0.9 TeV) < 1.96 ×
10−12 photons cm−2 s−1 , respectively. These results are plotted in Figure 8 and Figure 9 together with the other previous
results.
The reanalysis did result in a TeV gamma-ray signal fromthe Vela pulsar region at the 4.5σ level using 1993, 1994,
and 1995 data. The excess was located at the same posi*3 Kifune, T. et al. 1995, ApJL, 438, L91*5 Kushida, J. et al. 2003, 28th ICRC (Tsukuba), 4, 2493

SN 1006
10-11

10-12

Integral Flux (photons cm-2 s-1)

Integral Flux (photons cm-2 s-1)

19
10-10

HESS J0835-455

10-11

10-12

10-13

10-1

1

10
Energy (TeV)

Fig. 9. Integral gamma-ray fluxes from the NE rim of SN 1006

obtained using the CANGAROO-I data. The 95% CL upper
limits to the integral fluxes are indicated by the filled circle(1996 data with the selection criteria optimized for the 0◦ .3
offset) and the filled square (1997 data). The open circle
and open square are the integral fluxes estimated by Tanimori et al. (1998)6using the 1996 and 1997 data, respectively. The thick solid line is the integral spectrum converted
from the CANGAROO-I differential spectrum (Tanimori etal. 20017). The horizontal bars represent the systematic
errors of the threshold energies. The 99.9% CL upper limits obtained by H.E.S.S. are indicated by the gray band fora range of assumed photon indices (2 to 3). The open triangle indicates the preliminary CANGAROO-II result (Haraet al. 20018).

tion, 0◦ .13 to the southeast of the Vela pulsar, as that reported in the original analysis. We have investigated the effect of the acceptance distribution in the field of view of the
3.8 m telescope, which rapidly decreases toward the edge ofthe field of the camera, on the detected gamma-ray morphology. The expected excess distribution for the 3.8 m telescope has been obtained by reweighting the distribution of
HESS J0835–455 measured by H.E.S.S. with the acceptanceof the 3.8 m telescope. The result is morphologically comparable to the CANGAROO excess distribution, although theprofile of the acceptance-reweighted H.E.S.S. distribution ismore diffuse than that of CANGAROO. The integral gammaray flux from HESS J0835–455 has been estimated for thesame region as defined by H.E.S.S. from the 1993–1995 dataof CANGAROO to be F(> 4.0 ± 1.6 TeV) = (3.28 ± 0.92) ×
10−12 photons cm−2 s−1 , which is statistically consistent with
the integral flux obtained by H.E.S.S. as shown in Figure 10.

Other Activities
A light-weight and cost-effective metal mirror has
been developed for replacing current mirrors used in the*5 Tanimori, T. et al. 1998, ApJL, 497, L25*6 Tanimori, T. et al. 2001, 27th ICRC (Hamburg), 6, 2465
*8 Hara, S. et al. 2001, 27th ICRC (Hamburg), 6, 2455

10-13

1

10
Energy (TeV)

Fig. 10. Integral gamma-ray fluxes from the Vela pulsar region(0◦ .8 radius centered on HESS J0853–455) obtained fromthe CANGAROO-I data. The open circle represents theintegral flux from the 1993 to 1995 data and the filled circle represents the 95% CL upper limit to the flux from the1997 data. The horizontal bars represent the systematic
errors of the threshold energies. The solid line is the integral spectrum converted from the differential spectrumof HESS J0853–455 measured by H.E.S.S. assuming a
power law with an exponential cutoff.

CANGAROO-III telescopes or for the next generation
Cherenkov telescopes. A sample mirror of 20 cm diameter
was made grinding its surface and is currently checked for
performance. Methods of surface coating have also been investigated. For upgrading photomultiplier tube (PMT) cameras of the CANGAROO-III telescopes, a super bialkali PMT,
new preamplifiers, and Cockcroft-Walton breeder circuits for
PMTs have been tested or developed. Compact data acquisition circuits utilizing analog memory cells (AMCs) havebeen developed for recording Cherenkov light signals withhigher time resolution (∼ 1 GHz) and lower power consumption. Cheap implementation of a GPS compass module has
been developed for auto calibrations of the telescope attitude.
Its calibration accuracy should be better than 0 ◦ .1 in principle.
This technology will be important in the next generation observatory of many (∼ 100) IACTs, dramatically reducing timeand effort of manually tuning their rotation axes.

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

http://vesper.icrr.

[2] Y. Sakamoto et al., Astrophys. J., 676, 113 (2008).
[3] T. Nakamori et al., Astrophys. J., 677, 297 (2008).
[4] R. Enomoto et al., Astrophys. J., 683, 383 (2008).
[5] Y. Higashi et al., Astrophys. J., 683, 957 (2008).

20[6] M. Ohishi et al., Astropart. Phys., 30, 47 (2008).
[7] R. Kiuchi et al., Astrophys. J., 704, 240 (2009).
[8] Sei. Hayashi et al., Astropart. Phys., 32, 112 (2009).
[9] T. Yoshikoshi et al., Astrophys. J., 702, 631 (2009).

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; Kanagawa Univ.,
Yokohama, Japan; KEK/IPNS, Tsukuba, Japan; Kinki Univ.,
Higashi-Osaka, Japan; Kochi Univ., Kochi, Japan; Musashi
Inst. of Tech., Tokyo, Japan; Nat. Inst. of Rad. Sci., Chiba,
Japan; Osaka City Univ., Osaka, Japan; Pusan Nat. Univ.,
Pusan, Korea; Rutgers Univ., Piscataway, NJ, USA; Saitama
Univ., Saitama, Japan; Tokyo Inst. of Tech., Tokyo, Japan;
Tokyo Univ. of Science, Noda, Japan; Univ. of Denver, Denver, CO, USA; Univ. of Utah, Salt Lake City, UT, USA; Univ.
of Yamanashi, Kofu, Japan; Waseda Univ., Tokyo, Japan;
Yonsei Univ., Seoul, Korea

112.9◦W, alt. ∼1400 m). The construction was completed in
2007, and TA is fully operating from March 2008.

Overview of TA

Ground Array of the ph-1 TA

The TA project was proposed in 2000 [1] to investigate
the origin of super-GZK cosmic rays by employing a large
array of fluorescence telescopes with about 100 times larger
acceptance than AGASA. The HiRes experiment, however,presented an energy spectrum indicating the GZK-cutoff inthe 27th ICRC and the result was later published [2].
With contradictory results on the existence of GZK cutoff
appearing, it became urgent to understand the experimental
bias in the energy and the acceptance determination of superGZK cosmic rays. We initiated constructing a composite detector with AGASA-like ground array and TA fluorescencetelescopes [3]. We call it as the phase-1 TA (ph-1 TA). We expect simultaneous measurement of the same EHECRs by thedetectors of two different types will sort out the systematics
of two methods. It will guide us to a reliable determination of
the primary energy and the acceptance of EHECRs.
The phase-1 TA consists of a large plastic scintillator array and three stations of air fluorescence telescopes overlooking the array from periphery as shown in Fig.1. The groundarray will give an aperture of about 1900 km 2 sr for zenith
angles below 60◦ , which is approximately an order of magnitude larger than that of AGASA. The fluorescence telescope
will have a stereoscopic aperture of about 860 km 2 sr with
10% duty factor at 1020 eV. The telescope will also supply
information on the primary particle species by measuring thelongitudinal shower profile. It is located in the West Desertof Utah, 140 miles south of Salt Lake City (lat. 39.3◦N, long.

Fig. 1. Detector Arrangement of the ph-1 TA. The locations of 507
surface detectors are indicated by filled black boxes. The three
fluorescence telescope stations are marked by filled green boxes.
The three communication towers are marked by orange circles.
The central laser facility is marked by a blue cross.

The ground detector array consists of 507 plastic scintillators on a grid of 1.2 km spacing. It covers the ground area of
about 700 km2 . The trigger efficiency is ∼100% for cosmic
rays with energies more than 10 19 eV with zenith angle lessthan 45◦ .
The counter is composed of two layers of plastic scintillator overlaid on top of each other. The scintillator (CIMS-G2;
CI Kogyo Ltd.) is 1.2 cm thick, 3 m2 large and is read out
by 104 wave length shifter fibers installed in grooves on thesurface. Both ends of the fibers are bundled and optically connected to the photomultiplier (9124SA; Electron Tubes Ltd.).
The signal from each PMT is continuously digitized witha 12-bit flash ADC with 50 MHz sampling. When both of the
PMTs record more than 1/3 of the muon signal (Level-0 trigger), wave forms are stored with a time stamp supplied by the
GPS (M12+ Timing Oncore Receiver; Motorola, Inc.). Thisrate of local buffering is less than 1 kHz. For the event timing, we took a GPS timing (PPS; pulse per second) prior to
the event occurrence and a fractional time of one second is
added using clock frequency of 50 MHz DAQ system. The
absolute location and the altitude of each SD is measured by
the GPS of each SD electronics operated in ’3D fix mode’
before the commissioning period. The accuracy is expected
to be better than 0.3m in horizontal direction and better than
0.5m in altitude. After the commissioning period, the GPS
is changed to ’position hold mode’. The relative timing between remotely separated counters will be better than ±20 ns

21

by the GPS, which is sufficient to supply good resolution forthe determination of the arrival direction.
When both of the PMT signals exceed a trigger threshold of three muons (Level-1 trigger), the timing is recorded
in a local trigger list. The content of the list is transmitted toa branch DAQ board by the wireless LAN at 1 Hz. The list
contains less than 100 events for normal counters. To covercommunication in the whole surface detector array, the array is divided into three regions. The branch DAQ board isinstalled on a communication tower built at the periphery of
the array for each region. Each surface detector is assigned
to one of the three branch DAQ boards on the tower. A colinear antenna which is indirectional in azimuth is connectedto each branch DAQ board. An air shower event is identified by the branch DAQ firmware by requiring clustered hits
(at least three adjacent counters) with a coincidence timing
within 8 μ sec (Level-2 trigger). The trigger rate of air shower
events taken at each tower is around 0.003 Hz.
When an air shower trigger is generated in a branch DAQ
board, a command is sent to all counters, and relevant countersstoring the event within ±32μ sec respond by transmitting thewave form data to the branch DAQ board. We employ a commercially produced wireless transmitter using 2.4 GHz spread
spectrum technology, and we use the speed of 2 Mbps. The
dead-time-less DAQ operation is aimed with the high transmission speed together with a large buffering memory at eachcounter. The data in a branch DAQ board on the tower aretransmitted to an industrial PC board inside a cabinet at the
tower site. The data taken in the PC board at the tower sites
are then transmitted via 5.7GHz wireless communication network and stored in a mass storage at the Cosmic Ray Centerin DELTA which is located to the east of the TA site. Fig.2
shows an air shower event taken with surface detectors.
We have been taking data for the whole ground array since
March 2008. We have 507 surface detectors in the field after we deployed remaining four counters in November 2008.
Since three DAQ sub-arrays were operated independently,
there was inefficiency of shower trigger around the boundaries
of neighboring DAQ sub-arrays. We installed cross-boundary
trigger between neighboring regions to make the Level-2 trigger efficiency uniform inside the whole region except the border of the array in November 208. One of the three tower PCs
was defined as a central PC and trigger information from twoother tower PCs is transmitted to the central PC via towerto-tower wireless LAN communication. We do not have inefficiency of Level-2 trigger around the boundaries of DAQ
sub-arrays now.
We developed a real-time system that works in the background to monitor a variety of information for SD calibrationand maintenance. The gain of the whole SD system is determined by the histogram of the penetrating ’muon’ signals
accumulated locally at the SD. Pulse charges of about 420k
muons are histogrammed locally at the SD and sent out every
10 minutes for the recording. A typical result of the energy
deposit histogram of the ’muon’ signals fit with the MC isshown in Fig. 3. Here COSMOS MC is used for air shower
simulation and GEANT4 is used for detector simulation.
We are developing a new air shower full MC simulation
system for the precise measurement of ultra-high energy cos-Fig. 2. Air Shower Event Observed with Surface Detectors. The
top panel shows charge map of surface detectors which observed
more than 1/3 of a muon signal. The horizontal axis and verticalaxis represent longitude and latitude in detector ID, respectively.
The radius of the circle is proportional to the logarithm of the energy deposition. The color bar shows triggered timing in micro
second. The middle panel shows timing map. The vertical axis is
triggered timing and the horizontal axis is the distance in detector
ID. The bottom panel shows wave form distributions from the detectors. Red lines show upper layer scintillator signal and green
lines show lower layer’s signal.

mic rays based on parallel computing COSMOS MC using a
PC cluster. We estimate energy of ultra-high energy cosmic
rays by using total energy deposited at a certain distance fromthe shower core. We define S(800) as the total energy deposited in the SD which is located at a distance of 800m fromthe shower core. Fig. 4 shows zenith angle dependence ofS(800) obtained for 1020 eV proton using a QGSJET2 hadron22

Fig. 3. An example of the energy deposit histogram of the ’muon’signals. Open circles are the measured spectrum and the solid
curve is expected energy deposit by the simulation.

Fig. 4. Zenith angle dependence of the energy deposition S(800) incase of 1020 eV primary proton with QGSJET2 interaction model.
We average the azimuth angle dependence of S(800) from theshower core.

interaction model.

Fluorescence Telescope
The ph-1 TA has three fluorescence stations. The fluorescence station in the southeast is called the Black RockMesa (BRM) site. The southwestern station is called the Long
Ridge (LR) site and the station in the north is called the Middle Drum (MD) site.
Twelve reflecting telescopes are installed at each of the
BRM and LR stations and cover the sky of 3◦ -34◦ in elevationand 108◦ in azimuth looking toward the center of the groundarray.
The air shower image is detected by a mosaic PMT cameraon the focal plane. A set of 16×16 PMTs (Hamamatsu 6234)
with a hexagonal window is used for one camera. Each PMT
covers 1.1◦ ×1.0◦ patch of the sky.
A signal from the PMT is amplified by a factor of 50 byFig. 5. Flux of light from an air shower event by the fluorescence telescope. Flux of light from data is shown together
with expected light from total contribution, fluorescence, direct
Cherenkov, Rayleigh-scattered Cherenkov and aerosol-scattered
Cherenkov by black, red, pink, green and blue curves, respectively.

the pre-amplifier and is sent to a Signal Digitizer and Finder(SDF). The SDF module receives the signal with a shaping filter and digitizes it with a 12-bit, 40 MHz FADC. Consecutive
four samplings are added by the following FPGA. A trace offluorescence signal is searched in pipeline at the FPGA employing a sliding sum algorithm for every 25.6 μ s of the time
window. The dc component from the night sky background isestimated every 1 ms and is subtracted.
The result of the “hit” search by the SDF is reported to a
Track Finder (TF) in the same VME crate and an air shower
track is searched in one camera. A track is found when fiveor more adjacent PMTs are fired. A looser track definition
is applied to a camera-crossing event. The results of all TF
modules are concentrated to a Central Trigger Decision (CTD)
module and the decision of data acquisition is made. The wave
form data stored in the SDF memory are read out to “a cameraPC” in parallel. Data are transferred from the camera PCs
and collected to a storage PC by Ethernet during the daytime.
Fig.5 shows an example of the flux of light from an air shower
event observed by the fluorescence telescope.
The calibration of the telescope sensitivity is important
for the measurement of energy. Characterizing parameters ofeach component such as the mirror reflectivity, filter transmission, PMT quantum efficiency and the electronics gain were
measured piece by piece at the production or in situ [8]. The
relative gain of all PMTs were adjusted in situ by the Xenon
Flasher installed at the center of the mirror. The light from theflasher is diffused and filtered by BG3. The Xenon Flasher
supplies a light pulse of good uniformity (<3%) to all PMTs
in a camera.
There are three “standard” PMTs installed in a camera.
The efficiency and the gain of the standard PMT are calibrated
before installing to a camera and their values are transmitted
to other PMTs by the Xenon Flasher calibration. A tiny YAP(YAlO3 :Ce) scintillator with 50 Bq 241 Am source is embeddedin the BG3 filter of the standard PMT. The calibration of thestandard PMT will be monitored by the YAP pulser.
For the calibration of the standard PMT, we developed
a light source using a Rayleigh scattering of nitrogen laser

23

Fig. 7. Examples of CLF laser tracks. (left) the laser beam wasblocked around the middle of the lower view by the cloud. (right)
the laser shot image was taken at a clear night. Color bars show
ADC counts.
Fig. 6. The extinction coefficient as a function of the height from theground. The results from vertical LIDAR shots are shown by theblue line and the green line for high energy shots and low energy
shots, respectively. The black line is the exponential curve connected between the data at 0 km obtained by the slope method
and the data obtained at the lowest height. The red dot line showsthe extinction coefficient of pure Rayleigh scattering calculated
from radiosonde data measured at Elko in Nevada where 340 km
apart from the TA site.

(337 nm) in the nitrogen atmosphere. The power of laser ismeasured pulse by pulse to an accuracy of 5% and the known
cross section of Rayleigh scattering is applied to calculate theintensity of the scattered light.
A LIDAR (LIght Detection And Ranging) system locatedat the Black Rock Mesa station is used for the atmosphericmonitoring. It consists of a pulsed Nd:YAG laser (the third
harmonic, 355 nm) and a telescope attached to an alto-azimuth
mount and sharing the same optical axis. The laser can beshot to any direction and the back-scattered light is received
by the telescope to analyze the extinction coefficient along thepath of the laser. Fig. 6 shows an example of the extinction
coefficient as a function of the height from the ground.
We also built a laser shooting facility (Central Laser Facility: CLF) in the middle of the array. The intensity of the laser
shot is monitored to 5% accuracy and the Rayleigh scattering
at high altitude can be considered as a “standard candle” observable at all stations. The comparison of the received light
gives a reliable information for the difference and the changeof atmospheric conditions. The CLF operation started in December 2008. Fig. 7 shows examples of CLF laser tracks.
For monitoring the cloud in the night sky, we installed an
infra-red CCD camera (IR camera) at the Black Rock Mesa
station, and take data of the night sky every hour during FD
observation. The camera measures sky temperature in a fieldof view (FOV) of 25.8◦×19.5◦ and digitizes in 320×236 pixels. The camera is mounted on a steering table and its orientation is changed in elevation and azimuthal directions via PC
control. Fig. 8 show examples of pictures of the IR camera fora clear and a partly-cloudy skies, and the distribution of pixel
data D. The pixel data D = 1100 corresponds to ∼20◦C and
D = 1200 to ∼0◦ C. We developed a statistical analysis method
to judge the sky condition by defining the (clear/cloudy) flagof the IR images from the distribution of the pixel data and thethresholds. We found that most of the sky seen from the sta-Fig. 8. Examples of IR pictures and distributions of the pixel data D ofa clear and a partly cloudy skies (for lower elevation angle, 10.5◦ .).
The vertical line for each distribution is the median D50

tion is covered with clouds if there is a cloud in one directionin the FOV of the camera. Therefore this information obtained
from the IR camera can be used for the FD data selections.
In order to confirm the absolute energy scale of the fluorescence detector in situ, we plan to operate a compact electron linear accelerator (TA-LINAC) about 100 m away fromthe fluorescence station and inject an electron beam verticallyup into the atmosphere. A beam of 109 electrons with energyof 40 MeV and a duration of 1 μ s well simulates a shower
energy deposition of ∼4×1016 eV 100 m away from the station, which corresponds to a shower of ∼4×1020 eV 10 km
away. The calibration is obtained by comparing the observed
fluorescence signal with the expected energy deposition calculated by the GEANT simulation [9]. The accelerator was
designed with a collaboration of KEK accelerator physicists
and was assembled in KEK. We finished testing the basic performance of the accelerator in KEK by the end of 2008. The

24

Prospects

Fig. 9. Electron Linac. (top) the linac which was assembled in KEK,
and (bottom) the one which was installed at the FD site.

The construction of the ph-1 TA was completed in 2007 by
the collaboration of Japanese, Korean, and American physicists. The Japanese fund for ph-1 TA was approved in 2003
by the Grants-in-Aid for Scientific Research (Kakenhi) of Priority Areas. The US fund is supported by the US National
Science Foundation (NSF) through awards PHY-0307098 andPHY-0601915 (University of Utah) and PHY-0305516 (Rutgers University). The US proposal includes a construction of
TALE, a Low Energy extension of TA down to 1017 eV, toinvestigate the modulation of CR composition and spectrum
expected by the galactic to extra-galactic transition of CR origins.
The Auger group calibrated the ground array energy estimator ρ (1000), the muon density 1000 m away from theshower center, by the measurement of shower energy from thefluorescence telescope. The Auger group and the HiRes grouppublished the results of energy spectrum, which are consistent
with GZK cutoff [4, 5] with their energy scales determined by
the method of fluorescence telescope.
For the anisotropy, the Auger group claimed there is a correlation between the arrival directions of the highest energy
cosmic rays and the positions of AGN [6] while the HiResgroup reported that no correlations have been found [7].
For composition in EHE region, the Auger data suggests
a change to a heavier composition while HiRes data is consistent with constant elongation rate which stays with proton.
The energy measurement of ph-1 TA therefore is less sensitive to the unknown composition of the primary cosmic rays
and the details of hadronic interactions at EHE, whereas its
sensitivity to the composition determination using the muoncontent is limited. It is our belief that the characteristic features of ph-1 TA, the sampling of electromagnetic shower energy, the unique calibration of fluorescence generation, usage of HiRes-I telescopes in TA site, and the measurement in
the Northern Hemisphere, will make an essential contribution
to the understanding of the intricate problem of GZK cutoff,anisotropy, and composition of EHECRs.

Bibliography
Fig. 10. An example of an air shower event which was observed simultaneously by surface detectors and three FD stations.

main accelerator part was installed in a 40-feet commercial
container. We transported the accelerator system from Japan,
and deployed it to the BRM site in March 2008. Fig. 9 shows
the pictures of the completed TA-LINAC in KEK and the installed one at the FD site.
The Middle Drum FD station was constructed using refurbished equipment from the old HiRes-I observatory at Dugway in Utah. HiRes mirrors are 20% smaller in area than the
mirrors in the BRM and LR FD stations. The MD fluorescence detector also observes at elevation angles from 3 to 31
degrees.
Three FD stations are fully operated from November of
2007. Fig. 10 show an example of an air shower event which
was observed simultaneously by surface detectors and three
FD stations.

[1] The Telescope Array Project: Design Report, July, 2000.
[2] T.Abu-Zayyad et al., Phys. Rev. Lett. 92 (2004) 151101;
T.Abu-Zayyad et al., Astropart. Phys. 23 (2005) 157.
[3] M.Fukushima et al., Proc. of 28th ICRC, Tsukuba, 2(2003) 1025; S.Kawakami et al., Proc. of 28th ICRC,
Tsukuba, 2 (2003) 1033; F.Kakimoto et al., Proc. of 28th
ICRC, Tsukuba, 2 (2003) 1029; M.Fukushima, Proc. of
APPI2003 workshop, KEK Proceedings 2003-6.
[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] J. Abraham et al. (Pierre Auger Collaboration), Astropart. Phys. 29 (2008); J. Abraham et al. (Pierre Auger
Collaboration), Science 318 (2007) 939;

25[7] R.U. Abbasi et al. (HiRes Collaboration), Astropart.
Phys. 30 (2008) 175-179.
[8] H. Tokuno et al., Nucl. Instr. and Meth. A601 (2009)364-371.

Tibet III Air Shower Array (2003)

36,900 m2[9] T. Shibata et al., Ncul. Instr. and Meth. A597 (2008) 6166.

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-counters
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 degree 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 spec-

FT Detector (512)FT Detector w/ D−PMT(249)15 m

Density Detector (28)789 detectors

Fig. 1. Schematic view of the Tibet III array.

troscopically 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
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) Cosmic-ray anisotropy in the multi-TeV region with highprecision,(4) Global 3-dimensional structure of the solar and interplanetary magnetic fields by observing the Sun’s shadow incosmic rays.

26

E2.5 × dJ/dE (GeV1.5/sr/m2/s)

10

JACEE
RUNJOB
Grigorov

103

KASCADE(QGSJET)KASCADE(SIBYLL)
CASA-MIAAKENO(1984)
Tibet-III(ICRC2003)
This work(QGSJET+HD)
This work(QGSJET+PD)

2

10This work(SIBYLL+HD)

105

106

107

108
Energy (GeV)

Fig. 2. From [1]. The differential energy spectra of all particles
obtained by the present work using mixed composition models
compared with other experiments. For the following references;
JACEE (Asakimori et al. 1998),RUNJOB (Apanasenko et al.
2001), Grigorov (Grigorov et al. 1971), KASCADE (Antoni etal. 2005), CASA-MIA (Glasmacher et al. 1999), AKENO(1984)(Nagano et al. 1984), Tibet-III(ICRC2003) (Amenomori et al.
2003a), see [1].

Differential Flux x E 2.5 (cm −2 s −1 TeV1.5 )

−10

4

10

−11

10

HEGRA
H.E.S.S.
MAGIC
WhippleCANGAROO III
Tibet HD
Tibet III
−12

10

0.1

1
10
Energy (TeV)

100

Fig. 3. From [3]. Differential energy spectrum of γ -rays from the
Crab Nebula obtained using the data collected from 1999 November to 2005 November with the Tibet-III array in comparison withthe results from IACTs. For more detail and references, see [3].

We will introduce a part of the results obtained in this fiscal year.
As shown in Fig. 2, we obtain an updated all-particle energy spectrum of primary cosmic rays in a wide range from1014 eV to 1017 eV using 5.5×107 events collected in the period from 2000 November through 2004 October by the TibetIII air-shower array located at 4300 m above sea level (atmospheric depth of 606 g/cm2 ). The size spectrum exhibits a
sharp knee at a corresponding primary energy around 4 PeV.
This work uses increased statistics and new simulation calculations for the analysis. We performed extensive Monte Carlocalculations and discuss the model dependences involved in
the final result assuming interaction models of QGSJET01c
and SIBYLL2.1 and primary composition models of heavy
dominant (HD) and proton dominant (PD) ones. Pure proton and pure iron primary models are also examined as extreme cases. The detector simulation was also made to improve the accuracy of determining the size of the air showers
and the energy of the primary particle. We confirmed thatthe all-particle energy spectra obtained under various plausible model parameters are not significantly different from eachother as expected from the characteristics of the experimentat the high altitude, where the air showers of the primary energy around the knee reaches near maximum development andtheir features are dominated by electromagnetic components
leading to the weak dependence on the interaction model or
the primary mass. This is the highest-statistical and the bestsystematics-controlled measurement covering the widest energy range around the knee energy region.
The Tibet-III air shower array, consisting of 533 scintillation detectors, has been operating successfully at Yangbajing in Tibet, China since 1999. Using the dataset collectedby this array from 1999 November through 2005 November,
we obtained the energy spectrum of γ -rays from the Crab
Nebula[3] , expressed by a power law as (dJ/dE) = (2.09 ±E2 dF/dE (MeV cm−2 s−1)

10–3

10–4

Polar Cap Model
Outer Gap Model
EGRET

10–5

H.E.S.S. pulsed
H.E.S.S. On−Off
HEGRA
Whipple

10–6

MAGIC
CELESTE

10–7

TIBET

102

103

104

105
106
Energy (MeV)

107

108

Fig. 4. From [3]. Upper limits on the pulsed γ -ray flux from the Crabpulsar observed by the Tibet-III array (arrows with thick solid line),
together with results from other experiments. The long-dashedcurve and dashed curve represent the fluxes expected from theouter gap and polar cap models, respectively. For more detail andreferences, see [3].

0.32) × 10−12 (E/3 TeV)−2.96±0.14cm−2 s−1 TeV−1 in the energy range of 1.7 to 40 TeV. As shown in Fig. 3, this result is
consistent with other independent γ -ray observations by imaging air Cherenkov telescopes.
We also search for gamma rays from the Crab pulsar with
33 ms periodicity and find no significant signal. Accordingly,
we set flux upper limits on the pulsed gamma-ray flux, as
shown in Fig. 4.
In this analysis, we carefully checked and tuned the performance of the Tibet-III array using data on the Moon’s
shadow in comparison with a detailed Monte Carlo simulation. The shadow is shifted to the west of the Moon’s apparent position as an effect of the geomagnetic field, although
the extent of this displacement depends on the primary energy
positively charged cosmic rays. This finding enables us to estimate the systematic error in determining the primary energy
from its shower size. This error in our experiment is estimatedto be less than ±12% including uncertainties in the chemical

27
Energy (TeV) / Z

Energy (TeV) / Z

45.4

−0.6

−0.2
−0.3
−0.4

Data
MC
MC Best fit
MC +−10%

−0.5

−0.7
10

100

Σρ FT

1000

Fig. 5. From [3]. Dependence of shower size on the displacementof the Moon’s shadow in the east-west direction. The filled circles
show the experimental data, and open squares represent the MC
simulation. The solid curve is fitted to the MC events, and dashedcurves show a ±10% deviation from the solid curve, respectively.
The upper scale indicates the logarithmic mean of E/Z (TeV / Z)in each ∑ ρFT bin. For more detail, see [3].

composition of primary cosmic rays and in the hadronic interaction models, as is shown in Fig. 5. This energy scale estimation is the first attempt among cosmic-ray experiments atground level. The systematic pointing error is also estimatedto be smaller than 0◦ .011, as shown in Fig. 6. The deficit
rate and position of the Moon’s shadow are shown to be very
stable within a statistical error of ±6% year by year. Thisguarantees the long-term stability of point-like source observation with the Tibet-III array. These systematic errors areadequately taken into account in our study of the Crab Nebula.
The solar activity in Cycle 23 gradually changes to final
minimum phase. The Sun’s shadow generated by multi-TeV
cosmic-ray particles has been continuously observed with the
Tibet-II and Tibet-III air shower array in 1996 through 2008
during almost whole period of the Solar Cycle 23. We haveshown that the Sun’s shadow is strongly affected by the solar
and interplanetary magnetic fields changing with the solar activity. We present yearly variation of the Sun’s shadow above
10 TeV in association with the Solar Cycle 23, in unit of deficit
significance in Fig. 7 and in unit of deficit intensity in Fig. 8,
respectively. We observe the solar minimum still continue in2008, as is indicated by the corresponding sunspot number
observation. We keep an eye on the Sun’s shadow next year
to see whether it will still remain at high significance or not.

2.94 4.20 6.46 11.4

21.6

45.4

0

Displacement (degrees)

Displacement (degrees)

−0.1

0.1

−0.1

South

North

21.6

0

West

East

0.1

2.94 4.20 6.46 11.4

−0.6

−0.2
−0.3
−0.4

Data
MC

−0.5

−0.7
10

Data Best fit

100

Σρ FT

1000

Fig. 6. From [3]. Dependence of shower size on the displacementof the Moon’s shadow in the north-south direction. The filled
circles and open squares represent experimental data and theMC simulation, respectively. The solid line denotes the fitting to
the experimental data assuming a constant function, resulting in0.◦ 008 ± 0.◦ 011. The upper scale indicates the logarithmic mean of
E/Z (TeV/Z) in each ∑ ρFT bin. For more detail, see [3].

Fig. 7. Observed yearly variation of the Sun’s shadow depth (significance map.

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

Fig. 8. Observed yearly variation of the Sun’s shadow depth, (intensity
map).

28

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.

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. 9, 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 addition 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 con-Fig. 9. Tibet AS + MD (red curve) integral flux sensitivity (5σ or 10
events/1yr) for a point source.

Fig. 10. Prototype muon detector viewed from outside, just before
being covered with soil.

structed in Tibet to demonstrate the technical feasibility, costestimate, validity of our Monte Carlo simulation, as is shownin Figs. 10 and 11. Single muon peak is clearly observed in
the prototype muon detectors. Preliminary analysis indicatesthat our MC simulation reproduces real data quite reasonably.
Detailed comparison is under way.

Fig. 11. Prototype muon detector viewed from inside.

29

Tibet ASγ collaboration
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582

Fig. 12. Illustration of YAC array.

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. ofTokyo, Kashiwa, Japan; Konan Univ., Kobe, Japan; Shibaura
Inst. of Technology, Saitama, Japan; Department of Physics,
Shinshu Univ., Matsumoto, Japan; Center of Space Scienceand Application Research, Beijing, China; Tsinghua Univ.,
Beijing, China; Waseda Univ., Tokyo, Japan; NII, Tokyo,
Japan; Sakushin Kakuin Univ., Utsunomiya, Japan; AMNC,
Utsunomiya Univ., Utsunomiya, Japan; Tokyo Metropolitan
Coll. of Industrial Technology, Tokyo, Japan; Shonan Inst. ofTechnology, Fujisawa, Japan; RIKEN, Wako, Japan; Schoolof General Education, Shinshu Univ. Matsumoto, Japan.

Bibliography
Papers in refereed journals[1] “The all-particle spectrum of primary cosmic rays in thewide energy range from 10 14 eV to 1017 eV observedwith the Tibet-III air-shower array”, M. Amenomori etal., ApJ 678 1165–1179, (2008).

Fig. 13. Expected cosmic-ray iron energy spectra with Tibet AS +YAC.

(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
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, as is illustrated in Fig. 12 to distinguish the heavy component making
the knee by measuring the difference in lateral distribution ofenergetic air shower cores.
This will be the first experiment to selectively measure theenergy spectrum of the heavy component in the knee energy
region and will demonstrate that the knee of the all particle
energy spectrum is really composed of heavy nuclei. Figure 13 shows the expected energy spectra of cosmic-ray ironnuclei depending on theoretical models. Tibet AS + YAC has
a strong model discrimination power.

[2] “The energy spectrum of all-particle cosmic rays aroundthe knee region observed with the Tibet-III air-shower
array”, M. Amenomori et al., Advances in Space Research, 42 467–472, (2008).
[3] “Multi-TeV Gamma-Ray Observation from the Crab
Nebula Using the Tibet-III Air Shower Array Finely
Tuned by the Cosmic-Ray Moon’s Shadow”, M.
Amenomori et al., ApJ 692 61–72, (2009).
Papers in conference proceedings[4] “Analysis of primary cosmic ray proton and helium components at the knee energy region with the Tibet hybrid
experiment”, M. Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007,
vol.2, 117–120, (2008).
[5] “Chemical composition of cosmic rays at the kneemeasured by the Tibet air-shower-core detector”, M.
Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 121–124,(2008).
[6] “Future plan for observation of cosmic gamma rays in
the 100 TeV energy region with the Tibet air shower array : physics goal and overview”, M. Amenomori et al.
(The Tibet ASγ Collaboration), Proceedings of the 30th

30International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.2, 353–356, (2008).
[7] “Future plan for observation of cosmic gamma rays in
the 100 TeV energy region with the Tibet air shower array : simulation and sensitivity”, M. Amenomori et al.
(The Tibet ASγ Collaboration), Proceedings of the 30th
International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.2, 357–360, (2008).
[8] “A search for 100 TeV celestial gamma rays with
the Tibet air shower array and a future prospect”, M.
Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 575–578,(2008).

laboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007,
vol.5, 529–532, (2008).
[16] “Implication of the sidereal anisotropy of 5 TeV cosmic ray intensity observed with the Tibet III air shower
array”, M. Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic
Ray Conference, Merida, Mexico, 3-11 July 2007, vol.5,
593–596, (2008).
[17] “Study on TeV gamma Ray Emission from Cygnus Region Using the Tibet Air Shower”, M. Amenomori et al.
(The Tibet ASγ Collaboration), Proceedings of the 30th
International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.2, 695–698, (2008).

[9] “Seven-year observation of multi-TeV gamma rays fromthe Crab Nebula with the Tibet air shower array”, M.
Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 799–802,(2008).

[18] “Two-dimensional observation on TeV Cosmic-ray solar
diurnal variation using the Tibet Air Shower Array”, M.
Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.5, 577–580,(2008).

[10] “Search for pulsed multi-TeV gamma rays from the
Crab pulsar with the Tibet III air shower array”, M.
Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 783–786,(2008).

[19] “The study of Periodic Variation of Cosmic Ray intensity with the Tibet III Air Shower Array”, M.
Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.5, 609–612,(2008).

[11] “Gamma-hadron separation of parent particles of air
showers above several 10 TeV energies using TibetIII air-shower array”, M. Amenomori et al. (The Tibet
ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11
July 2007, vol.2, 583–583, (2008).

[20] “A Monte Carlo study to measure the energy spectraof the primary heavy components at the knee using a
new Tibet AS core detector array and a large underground muon detector array”, J. Huang et al. (The Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11
July 2007, vol.2, 329–312, (2008).

[12] “Study of discrimination between cosmic gamma rays
and protons at multi-TeV energies with the Tibet air
shower array”, M. Amenomori et al. (The Tibet ASγ
Collaboration), Proceedings of the 30th International
Cosmic Ray Conference, Merida, Mexico, 3-11 July
2007, vol.3, 1493–1493, (2008).
[13] “The cosmic ray all-particle spectrum in the wide energy range from 10 14 eV to 1017 eV observed with the
Tibet-III air shower array”, M. Amenomori et al. (The
Tibet ASγ Collaboration), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11
July 2007, vol.4, 103–106, (2008).
[14] “Zenith angle dependence of the size spectrum of air
showers around the knee observed with the Tibet air
shower array”, M. Amenomori et al. (The Tibet ASγ
Collaboration), Proceedings of the 30th International
Cosmic Ray Conference, Merida, Mexico, 3-11 July
2007, vol.4, 99–102, (2008).
[15] “Sun’s Shadow in the Solar Cycle 23 Observed with the
Tibet Air Shower Array and Comparison with Simulation Studies”, M. Amenomori et al. (The Tibet ASγ Col-[21] “Tibet Air Shower Array: Results and Future Plan”, M.
Amenomori et al. (The Tibet ASγ Collaboration), Proceedings of TAUP2007, Sendai, Japan, Journal of Conference Series vol.120, 062024-1-3, (2008).

The Ashra Project
Overview
Ashra (All-sky Survey High Resolution Air-shower detector) [1, 2, 3] is a project to build an unconventional opticaltelescope complex that images very wide field of view, covering 77% of the sky, yet with the angle resolution of a few
arcmin, sensitive to the blue to UV light with the use of image intensifier and CMOS technology. The project primarily aims to observe Cherenkov and fluorescence lights fromthe lateral and longitudinal developments of very-high-energy
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.

31

We started observation of optical transients and pilot
observation of Cherenkov tau neutrinos with some of thelight collectors in 2008. By analyzing the accumulated
data from these observations, we have already searched for
optical and VHE-neutrino emissions, for example, in thefield of GRB081203A around the Swift/BAT-triggered GRBtime [4, 5, 6].
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:would 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.
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 [7]. This is useful to investigate events clusteredaround the galactic and/or extragalactic sources. This in turnFig. 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 fromJapan. 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

32

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.

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.
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.

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

Observation

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

As a first step, we have started the observation of optical transients. During observation, Optical images were con-stantly 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.
We have accumulated more than 1500 hours of observation
time within one year of observation. Good weather rate of
90% shows the superiority of our site and operation efficiencyof 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 definedby observed time divided by observable time. Table2 summarizes coincidence events with satellite GRB triggers[8][9]. In
those events, our wide field covers the GRB position at the
GRB trigger time. Observed period shows the time period
relative to GRB trigger time. In this time period, the GRB
position is within our filed of view.
The next step is to start observation of Cherenkov air
showers using the light collector towards Mauna Kea. It may
detect Cherenkov signals originated from tau neutrinos whichinteracts with the mountain and/or the earth as described in
the section below. We prepared the optical and photoelectric
image pipeline system in that light collector. The installationof trigger and DAQ system was performed. Pilot observation
to confirm the detection principle of tau neutrino has been carried out [6].
Search for early optical transients
We constructed a 2/3-scale prototype Ashra detector on
Haleakala to verify the optical performances. From October 2004 to August 2005 at the observatory, We made good
observations for 844 hours out of 1,526 hours of the moonless nighttime. The fine resolution (arc-minutes) in the ultra wide field of view (0.5 sr) has already been demonstratedusing a 2/3-scale model. Our wide field observation covered the HETE-2 WXM error box at the time of GRB041211.
2,000 images were taken every 5 s with 4-s exposure from thetime 1h7m before GRB041211 to 1h41m after GRB041211.
We detected no objects showing time variation in the WXM
error box. It indicates the 3-sigma limiting magnitudes ofB∼11.5 magnitude [10]. This is compared with other observations [11, 12]. We also successfully performed two more
observations coincident with Swift: GRB050502b [13] andGRB050504 [14].

33Satellite
Swift
Swift
Swift
Fermi
Fermi

Trigger Number
322590324362336489262607680
262701807

GRB Name
N/A
N/A
GRB081203A
GRB090428
GRB090429C

Trigger Time080828 UT 08:15:09.33
080910 UT 12:52:21.68
081203 UT 13:57:11.57
090428 UT 10:34:38.46
090429 UT 12:43:25.70

Observed Period [sec]-2.3×103 – 1.1×104-4.3×103 – 7.7×103-1.2×104 – 5.6×103-8.1×103 – 5.9×103-4.1×103 – 7.1×103

Table 2. Summary of coincidence events with satellite GRB triggers[8][9]. Listed events are those which GRB trigger position are within our
FOV at the GRB trigger time.

Fig. 4. Trajectory of the GRB081203A counter part in the field of view.

The Ashra-1 light collector unit on Mauna Loa has theachieved resolution of a few arcmin, viewing 42 degree circle
region of which center is located at Alt = 11.7 deg, Azi = 22.1
deg. The sensitive region of wavelength is similar with the
B-band. Utilizing this light collector, we have searched for
optical counterpart in the field of GRB081203A [15] aroundthe Swift/BAT-triggered GRB time (T0). Figure 4 shows the
trajectory of the GRB position in our field of view. We preliminary analyzed 83 images covering the field of GRB081203A
every 7.2s with 6s exposure time respectively during theobservation between T0-300s and T0+300s. We detected
no new optical object within the PSF resolution around the
GRB081203A determined by Swift-UVOT [16]. Around theSwift-BAT trigger time, we have obtained data in every 7.2
seconds with 6sec exposure. The examples of obtained preliminary S/N (signal to noise ratio) maps including the trigger time can be found at [1]. As a result of our preliminary
analysis, the following 3-sigma limiting magnitudes are derived. The limiting magnitudes were estimated in comparison
with stars in Tycho-2 Catalog to be distributed between 11.7
and 12.0. Figure 5 shows limiting optical magnitudes vs timecomparing with the other measurements [4].

Fig. 5. Summarized lightcurve for GRB081203A around the trigger
time. 3-sigma limiting magnitudes of our observation (labeled as
Ashra-1) and other observations are compared as a function oftime after GRB. The horizontal axis is in linear scale. The verticalaxis in the right is only for the data by Swift XRT (gray data), where
the scale is arbitrary.

Search for Cherenkov tau neutrinos
We used a detection technique called ‘the Earth-skimming
neutrino’. This detection technique was originally proposed
in 1990’s [17] and already used by other observations. The
essence of this technique is separation of target and detection.
Small cross section of first interaction of neutrino favors densematerial, while fine imaging of the interaction does not. If thefirst interaction is separated from the following interactions,
we can evade from the above contradiction.
Reaching the Earth, a neutrino enters into the Earth’s crustand mountains, interacts with materials via charged current interaction, and produces a lepton. The lepton propagates in thecrust with loss of its energy. If it is a tau lepton, it decays after
exit to the atmosphere, and generates detectable air shower.
The length of the propagation of tau lepton in the rock makes
a cluster around a few 10 km above 10 17 eV due to the energy
loss. Hence we can detect tau neutrinos of decades of energies
with a fixed geological formation.
This detection technique has a maximum sensitivity
around 100 PeV. Using this technique, we aim to connect PeV

34

to EeV by lowering the energy threshold of neutrino observation with air light. PeV is the energy range where ice andwater Cherenkov experiments have their maximum sensitivities, while EeV is the energy range where experiments with
air shower have. For that aim, we think that detection of
Cherenkov radiation from air shower is important. In orderto detect Cherenkov radiation emitted forward, shower front
must be directed to the detector. Therefore, we chose a geometry widely viewing rock of over 10km thickness, that is,
mountain. We designed an observation facing the mountain(Figure 6). In this observation, we used a light collector to-

Fig. 6. Conceptual figure of this observation (the Earth-skimming neutrino detection technique). The right mountain is Mauna Kea andthe left is Mauna Loa.

ward Mauna Kea.
Cherenkov tau shower observation
We intended an observation in order to study neutrino
emissions from transient objects. Also, performance checkof our trigger system is another aim of this observation.
Before the observation, we simulated neutrino signals
generated by tau leptons emerging from Mauna Kea (Figure 7). Then, we calibrated the detector with artificial sources,
such as an LED and a radiant source. Furthermore, we verified the system’s performance by an observations of cosmic
rays (protons). Cosmic-ray observation was carried out withan FOV closer to the zenith than in the neutrino observation.
Figure 8a shows an example of obtained image of Cherenkov
radiation from air-showers, and Figure 8b shows a simulated
event by CORSIKA. We can see that the obtained data resembles the simulated event. It demonstrates well the strength of
the high angular resolution of our detector. As shown by thecomparison of Figure 7 with the data (Figure 8a), our detector
has an ability of detecting air showers from neutrinos.

Fig. 7. Example of simulated neutrino event.

The observation for neutrino emission was executed in aduration from October to December in 2008 (Table 3). Fortunately we accomplished highly efficient observation. As aresult we observed a GRB, GRB081203A, in a period before
and after its occurrence, tens of GRBs after their occurrence,and tens of active galactic nuclei (AGN).
The obtained data were analyzed. In order to estimate
the sensitivity we must take into account spurious events generated by background cosmic rays. In principle, the Earthskimming neutrino detection technique is free from background events, thanks to the screening effect of the Earth’s
rock. Also, the FOV of this observation is nearly horizontal,
hence thick atmosphere screens the normal cosmic-ray events.
We studied the screening effects and confirmed the absence of
background events from background sources. Then, the mostfrequent background was Cherenkov radiation from muonsthat interact with the detector itself. We simulated the radiation, and carefully removed them from the data.
Results of tau neutrino search
We did not discover any candidate of neutrino emission in
the range from tens of PeV to EeV. We set preliminary upper limits to the fluence and flux of source models, related tothe mechanism for the particle acceleration in transient objects. All the following limits are derived with 95% confidence level.
For GRB081203A precursor, we set a limit
E φ (E) < 5.4 × 10−8 [cm−2 ], assuming a spectrum extended up to 5 EeV. For GRB081203A late prompt emission,
the obtained limit is E 2 φ (E) < 4.3 [erg cm−2 ]. Combinationof the two observations for GRB081203A, the upper limit forneutrino emission [6] and the optical observation with ourdetector [5], leads to the conclusion that it is not contradictory
to the normal particle acceleration. This discussion can beconsidered as a beginning of ‘multi-particle astronomy’[18].
For GRB afterglow, the limit leads E 2 φ (E) < 19 [erg cm−2 ].
Note that this limit is set by the source integrated analyses.
Furthermore, neutrino emission from AGN was studied.
The limit for diffuse flux is about 2nd order of magnitudelarger than that by other experiments, but better than Auger
experiment at 100 PeV. In addition to that, we set a meaningful upper limit, E 1.4 φ (E) < 1.3 × 10−12[cm−2 s−1 PeV0.4 ],based on a source model assuming proton synchrotron
emission. This limit corresponds to a diffuse flux rejected byexperiments. However, it should be noted that our result is
not affected by the source distribution in the universe becauseof a limit for point sources.
By means of Cherenkov tau shower observation, our detector is sensitive to neutrinos with energies of 1 ∼ 100 PeV.
This energy range is just between the maximum sensitivities
of ice experiments and other air-shower experiments. For future neutrino experiments, pointing accuracy in this region
will become more important, in order to localize transient
objects and investigate the mechanism of the particle acceleration in individual sources. The Ashra detector may beconsidered as a promising candidate to realize ‘multi-particle
astronomy’[18], which is necessary to understand particle acceleration in the universe.

35(a) data(b) simulated event

Fig. 8. Example of air-shower image from the cosmic-ray observation. The conditions for simulated event are as follows; proton, energy = 1EeV,
core distance = 266m, angular resolution = 9 arcmin, and thinning = 10−6 . The color shows pixel value (max. is 255 counts).

Table 3. Observation time for Cherenkov tau neutrinos. Duty factor is defined by the observed time divided by the total time including daytime
and full moon periods.

Period (UT)
2008/10/28 – 11/11
2008/11/15 – 12/10

Max. Observable
Time [hr]
95.5
164.6

Bibliography[1] http://www.icrr.u-tokyo.ac.jp/∼ashra[2] Sasaki, M., 2003, “Very High Energy Particle Astronomy with All-sky Survey High Resolution Air-shower
Detector (Ashra)”, Progress of Theoretical Physics Supplement, vol. 151, pp. 192–200.

Observed Time [hr](duty factor)
75.3 (17%)
140.5 (20%)[12] Sasaki, M., et al., 2005. “Observation of Optical transients with the Ashra Prototype,” Proc. 29th Intl. Cosmic
Ray Conf. Pune 5, 319–322.
[13] Sasaki, M., et al., 2005. GCN Circ. 3499.
[14] Sasaki, M., Manago, N., Noda, K., Asaoka, Y., 2005.
“GRB050502b: Early Observation,” GCN Circ. 3421.

[3] Sasaki, M., et al., 2008, “The Ashra Project” Proc. 30th
Intl. Cosmic Ray Conf. Merida 3, 1559.

[15] Parsons, A. M., et al., GCN Circ. 8595

[4] Aita, Y., et al., 2008, GCN Circ. 8632.

[16] De Pasquale, M., et al.,GCN Circ. 8603.

[5] Ogawa, S., et al., 2009, “Ashra Optical Transient Observation”, 31th Intl. Cosmic Ray Conf. (Lodz), ID1410.

[17] Fargion, D.,
ph/9704205).

[6] Noda, K., et al., 2009, “VHE neutrino pilot observation
with the Ashra detector”, 31th Intl. Cosmic Ray Conf.
(Lodz), ID313.

[18] Sasaki, M., 2000, in Proc. of ICRR workshop”ICRR2000 Satellite Symposium: Workshop of Comprehensive Study of the High Energy Universe”.

[7] Sasaki,M., et al., 2002, “Design of UHECR telescopewith 1 arcmin resolution and 50◦ field of view”, Nucl.
Instrum. Methods, vol. A492, pp. 49–56.
[8] http://gcn.gsfc.nasa.gov/swift grbs.html[9] http://gcn.gsfc.nasa.gov/fermi grbs.html[10] Sasaki, M., et al., 2004. GCN Circ. 2846.
[11] Sasaki, M., et al., 2005. “Status of Ashra project,” Proc.
29th Intl. Cosmic Ray Conf. Pune 8, 197–200.

2002,

ApJ 570 909 (arXiv:astro-

36

ASTROPHYSICS and GRAVITY DIVISION
Overview
Astrophysics and Gravity Division consists of Gravitational Wave Group, The Sloan Digital Sky Survey Groupand Theory Group. The Gravitational Wave Group conducts
R&Ds for LCGT project jointly with researchers of gravitational wave experiment and theory in Japan. The main itemsof those R&Ds are TAMA project and CLIO project. The
Sloan Digital Sky Survey Group continues accumulating dataof images and spectroscopic observation of galaxies and publishing papers in collaboration with worldwide researchers.
Theory Group conducts both theoretical study of the Universe
and astroparticle physics.

Gravitational Wave Group
Status of TAMA Project[Spokesperson : Kazuaki Kuroda]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of: TAMA collaboration
NAOJ, Tokyo; KEK, Tsukuba; UEC, Tokyo; Osaka City
Univ., Osaka; Kyoto Univ., Kyoto; Osaka Univ., Osaka; Niigata Univ., Niigata

cannot be improved anymore without a drastic change of thesuspension system utilizing more sophisticated actuator.

Achievement of TAMA
The achieved sensitivity of TAMA at the time of Data Taking Run 9 was reported in the previous Annual report (20052006).[1] Although there was a gap between the achieved sensitivity and the practically attainable one, at low frequencies,
we could demonstrate that the basic techniques for the interferometer operation was acquired by the fulfillment of the target noise curve at frequencies more than 800 Hz, where theoptical system properly worked and the control system wasappropriate. The noise spectrum at frequencies lower than
30 Hz was disturbed by non-stationary ground motion and thespectrum in a frequency range from 30 Hz to 300 Hz was determined by the actuator noise to stabilize the mirror alignment mainly due to relatively larger seismic noise at Mitaka
campus of NAOJ. In order to identify the noise source governing the spectrum in the frequency range from 30 Hz to 800 Hz,
we had installed the Seismic Attenuation System (SAS) [2]for four main mirrors and improved the performance of antivibration at low frequencies. The sensitivity improvement isshown in Fig 1 under the SAS system.

*9 J. H. Taylor and J. M. Weisberg, Astrophysical J., 345 (1989) 434.

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 9 , 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 eye ofmankind to inspect the universe. In order to directly observe
gravitational waves, we aim to construct the Large scale Cryogenic Gravitational wave Telescope (LCGT).
For the first step of constructing sensitive laser interferometer, we developed a 300 m baseline interferometric gravitational wave detector, TAMA, at the Mitaka campus of the
National Astronomical Observatory of Japan (NAOJ) and several observations had been conducted. TAMA project started
in April, 1995, as a five-year project and it was extended by
two years after 1999. TAMA is organized by researchers belonging to universities and national laboratories. We achieved
nine data-taking runs that span from two to eight weeks, which
ended in 2004. About TAMA project, we had presented its
development of Seismic Attenuation System (SAS) newly installed for four main mirrors and tried to achieve its design
sensitivity. However, we finally found that the sensitivity at
low frequencies were limited by so-called up-conversion noise
possibly arising from the suspension and actuation system and

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the sensitivity has been improved by about one order at 100 Hz.
The sensitivity was not limited by the alignment control noise as
shown in the plot, but limited by another unidentified noise source,which turned out to be some up-conversion noise as reported as
the following.

By this improvement at low frequencies, we had expectedthat we could overcome the actuator noise that governed thesensitivity at low frequencies less than 300 Hz. However, thisexpectation was negatively broken by the observed sensitivity, which showed the existence of some noise source at thesefrequencies. In order to inspect this noise source, we checked

37
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ment”, TAUP 2007, September 11-15, 2007, Sendai.
[4] K. Araiet al., “Recent Progress of TAMA 300”, TAUP
2007, September 11-15, 2007, Sendai.
[5] B. Abbott et al., Phys. Rev. D 72 (2005) 122004.

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been empirically observed, which limits the sensitivity at low frequencies less than 300 Hz.

the up-conversion noise that was found by LIGO project. This
was arising from the Barkhousen effect in the bar magnets
that were used for as part of actuation system for the controlof the mirror. Actually, we applied a large excitation force
at pendulum mode of the main mirror through the actuation
magnet-coil system and observed the noise appeared at higher
frequencies.
Figure 2 shows the noise spectrum taken by this methodwith changing the amplitude of the applied force. One canclearly perceive the effect of some up-conversion mechanism.
The blue curve in the figure accords to the expected upconversion noise under normal pendulum motion. This result
empirically showed the existence of an up-conversion noisein the suspension system of TAMA. We can guess its physicalreason of this phenomenon, such as magnetism, non-linearityof the pendulum, and so on. Note that this phenomenon has
not been observed at CLIO interferometer placed at quieter
site by two orders less in noise amplitude. We have not succeeded to identify its origin. We may need a drastic changeof the suspension and actuation system (full manpower withmoney) to escape from this new noise. However, since theeffect of this new noise reduces rapidly in more than quadric,the effect is not certainly dominant underground at Kamioka
as indicated by the recent result of CLIO.
In regard with data analysis, we had made reports with
LIGO project at the time when the sensitivity of TAMA300
had competitiveness [5, 6]. Without new observation, persistent activity on the development of data analysis was conducted using existing TAMA 300 observation data.[7, 8]

Bibliography[1] H. Tagoshi it et al., Phys. Rev. D 63(2001)062001-1-5.
[2] R. Takahashi et al., Class. Quantum Grav. 25 (2007)
114036.
[3] D. Tatsumi et al., “TAMA 300 interferometer develop-[7] H. Tagoshi et al., “Results of Searches for inspiraling
compact star binaries from TAMA 300fs observationin 2004-2004”, TAUP 2007, September 11-15, 2007,
Sendai.
[8] N. Kanda et al.,lq‘Short gravitational wave signal
searches in TAMA 300 data: stellar collapse and blackhole”, TAUP 2007, September 11-15, 2007, Sendai.

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
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 planed LCGT (3 km cryogenic interferometerat Kamioka). The site of CLIO, near the Super-Kamiokande
neutrino detector, is shown in Fig. 3. The tunnel was dug in
2002, and a 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 theannual report (2003–2004). Four sets of cryostats and wholevacuum system were installed (annual report 2004–2005). We
started the operation of CLIO in 2006 (annual report 2006).

One of the aims of CLIO is to demonstrate the thermal
noise suppression by cooling the mirrors. The main mirrors are cooled at 20 K by refrigerators.
√ The lowest noiselevel of CLIO is designed√
to be 10−19m/ Hz around 100 Hz,
which would be 10−18m/ Hz if cryogenics is not applied [2].
The current best sensitivity at the room temperature was obtained in the end of 2006. The displacement
sensitivity ar√round 300Hz reached at 6 × 10−19m/ Hz. Of special note is
its high strain sensitivity below 20Hz. It is comparable with
LIGO sensitivity in spite of much shorter baseline. Now weare reducing the excess noise to realize the thermal noise limited sensitivity. And we have checked the cooling of mirrors
not to harm the sensitivity in 2007.

38

Fig. 3. Location of the CLIO interferometer.

Fig. 4. Overview of the CLIO interferometer.

Once the objective is attained, the CLIO interferometeris used to observe gravitational wave events in parallel with
the TAMA interferometer until completion of the constructionof LCGT. The merits of the underground site are lower seismic noise and temperature stability. The former characteristic
makes interferometer locking easily controlled, and the latterassures long-term stable operation (LISM) [3].
The 57-hours observation data were taken at February
2007 and analyzed for continuous gravitational wave fromthe pulsar J0835-4510 (Vela pulsar) at twice its rotation frequency ( 22.38 Hz). We use an analysis method based ona matched filtering with a correction of pulsar spin down, aDoppler effect caused by the relative motion between the pulsar and the Earth, and so on. We obtained an upper limit ofh0(U.L.) = 5.3 × 10−20 at 99.4 % confidence level. This value

Fig. 5. a sapphire mirror and cryogenic suspension system.

corresponds to the upper limit on the ellipticity of the neutronstar, ε = 29 [4].
We have achieved the target sensitivity for the room temperature on November 5th (Fig. 6) 2008 which is limited by
the fundamental noise sources, seismic noise in the low frequency, pendulum thermal noise and mirror thermal noise between 20 Hz and 100 Hz and shot noise in the high frequency.
We emphasis that what the sensitivity is limited by two kindof thermal noises in the room temperature means that CLIOis qualified to observe thermal noise reductions by cooling the39

mirrors in the next step.

Fig. 6. CLIO displacement noise spectrum: The black curve is thecurrent best sensitivity at room temperature. This spectrum is represented by the thermal noises of pendulum and mirror.

Actually we cooled down one of the four mirrors as thefirst step of full process of cooling all mirrors and showed thatthe cooling did not contaminate the noise floor obtained at theroom temperature. An effect of cooling will be seen drastically as a mirror thermal noise reduction when the second
mirror is cooled down since the two front mirrors are dominant to determine the floor level of the mirror thermal noise.
We have already started cooling down the second mirror in
July and we are currently making efforts to hunt other technical noises caused by this second cooling process such as
mirror contaminations or shrinking wires.

Communications Technology, Hirosaki University, Tohoku
University, Niigata University, Rikkyo University, Waseda
University, Nagaoka University of Technology, Hiroshima
University, Ryukyu University, Department of Astronomy(Beijing Normal University), Center for Astrophysics (University of Science and Technology, China), Institute for HighEnergy Physics (Chinese Academy of Science), Purple Mountain Observatory (China), Industrial Technology Research Institute (Taiwan), Inter University Centre for Astronomy & Astrophysics (IUCAA), Physics Department of Physics (University of Western Australia), Laboratory of Laser Interferometry (Sternberg State Astronomical Institute, Moscow
Univ.), Louisiana State University, MPI-AEI, California Institute of Technology, Rochester Institute of Technology,
Columbia University, Birmingham University, Glasgow University, Maryland University.

Introduction
The organization of LCGT was augmented by creating a
position of the project manager since October, 2008. We reformed the working groups that share tasks of LCGT construction and revised documents that describe the design of
LCGT. Five coordinators were newly introduced to be positioned above the working groups of LCGT and they chair related working groups as follows;• Facility– tunnel construction– crust strain meter

Bibliography[1] S. Takemoto, et al., Journal of Geodynamics 41 (2006)
23.
[2] M. Ohashi, et al., Class. Quantum Grav. 20 (2003) S599.
[3] S. Sato, et al., Phys. Rev. D 69 (2004) 102005.
[4] T. Akutsu, et al., Class. Quantum Grav. 25 (2008)
184013.

• Vacuum&Suspension– vacuum system– anti-vibration&suspension system– cryostat system– refrigerator system• Interferometer– interferometer support system

LCGT Project– interferometer control system[Spokesperson : Kazuaki Kuroda]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582– digital control system

In collaboration with the members of:
National Astronomical Observatory (Japan), KEK, Physics
Department (University of Tokyo, UT), Department of Advanced Material Science (UT), Earthquake Research Institute (UT), Department of Earth Science and Astronomy(UT), Institute for Laser Science (University of ElectroCommunications), Department of Physics (Osaka City University), Department of Physics (Osaka University), Physics
Department (Kyoto University), Yukawa Institute (Kyoto University), Advanced Research Institute for Sciences and Humanities (Nihon University), System Engineering (Hosei University), Ochanomizu University, Agency of Industrial Science and Technology, National Institute of Information and• Laser– laser source system– input&output optical system– mirror design&fabrication• data analysis– data analysis– data collecting system– computer facility40

Under the MOU among three Institute (ICRR) and organizations (NAOJ and KEK) which is an extension of the previous MOU among three directors since 1994, we prepared
to form an executive panel of LCGT consisting of membersof those three directors with three representatives of research.
The panel is effect since 1st, April, 2009.
We promote LCGT project for the first priority of future
project in ICRR supported by all gravitational wave physicists
in Japan and oversea collaborators.

Objective of LCGT
After the discovery of the highly relativistic binary neutron star system 10 , a new young binary pulsar was detected
11 . The former discovery increased the coalescence rate from10−6 to 10−5 a year in a galaxy as big as our Galaxy 12 andthe latter pushed up by another factor of six. Although it wasgood news for the detection of gravitational waves, we stillneeded to wait for long time to detect by the presently existing detectors. This was the reason why we planed LCGT
(Large-scale Cryogenic Gravitational wave Telescope). The
objective of LCGT is to detect at least one gravitational wave
event in a year. There are many other possible gravitational
wave sources in the universe other than the coalescence ofbinary neutron stars. However, the coalescence of binary neutron stars differs completely from other sources in the sensethat its wave form is precisely predicted, and its existence has
certainly been confirmed.

Table 1. LCGT design parameters to detect binary neutron-star coalescence events in 230 Mpc.

Item
Baseline LengthInterferometer
Optical PowerBeam radius at End
Main Mirror

Suspension
pendulum
VacuumParameter
3 km
One setPower recycled Fabry-Perot-Michelson with RSE
Laser:150 W; Finesse:1550
Input power at BS: 825 W
Cavity power 800 kW
3 cm
Sapphire 30 kg, 20 K
Diameter 25 cm
Mechanical Q:108
Frequency: 1 Hz; Q:1 × 108
10 K≤ 10−7 Pa

Status of LCGT Project
The target sensitivity of LCGT is to observe binary neutron star coalescence events occurring at 230 Mpc with S/N=8
13 in its optimum configuration. This is ten-times more sensitive than that of the LIGO (I), and by two orders more thanthat of TAMA at their most sensitive frequencies.[2] This
will be attained by an interferometers located underground(as in Fig. 7), using a three-kilometer length baseline, cooling mirrors at cryogenic temperature, and a high-power laser
source employing 150 W output. The optical configuration isa power recycled Fabry-Perot-Michelson interferometer withthe resonant-sideband-extraction (RSE) scheme (in Fig. 8).
The detailed design of the control system was tested for the
resonant sideband extraction scheme.[3] Table 1 lists the important parameters of LCGT, which were revised three times
from the original design.[4] Ultimate sensitivity of a laser interferometer is determined by seismic noise at low frequencies(10-30 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 thephoton recoil force noise. This requires that thermal noise isreduced both by decreasing the temperature and by decreasing*10 M. Burgay, et al., Nature, 426 (2003) 531.
*11 D.R. Lorimer, et al., Astrophysical J. 640(2006) 428.
*12 C. Kim, V. Kalogera and D. R. Lorimer, Astrophysical J. 584 (2003) 985.
*13 The signal-to-noise-ratio so far was 10 considering high rate of nonstationary noise that dominated in TAMA. However, recent improvementof handling noise assures us to adopt widely accepted number, 8Fig. 8. Optical design of LCGT. The optical configuration is a power
recycled Fabry-Perot-Michelson interferometer with the resonant-sideband-extraction (RSE) scheme.

the internal mechanical loss (i.e., increasing the mechanical Q
of vibration modes). The source of thermal noise comes fromboth mirror internal vibration, mechanical loss of the opticalcoating and swing noise of the pendulum suspending the mirror. The reduction of thermal noise is attained by cooling boththe mirror and the suspension system that suspends the mirror.
The laser system is designed by the experience of TAMA
laser that is an injection locking master-slave laser pumped
laser diodes. The output of the master laser (2 W) is injected into a slave laser of 100 W under a scheme of injectionlocking. The output of the slave is amplified to 150 W by an
optical amplifier (Fig. 9).
Figure 10 compares the sensitivity curve of LCGT withthose of TAMA, CLIO (a 100 m prototype cryogenic interferometer placed underground of Kmioka mine), GEO, Virgoand LIGO (initial LIGO, Adv. LIGO). 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 will be proven by

41

Fig. 7. The interferomter of LCGT is placed underground at Kamioka mine for fairly quiet seismic motion.

λFig. 9. A laser source system for LCGT. The output of the master
laser (2 W) is injected into a slave laser of 100 W under a schemeof injection-locking.

the on-going project of CLIO. Although the improvement, especially two orders of magnitude at low frequencies, is adventurous, it is not impossible until the construction period of
LCGT that needs four years after the beginning of the construction.
The main effort on the research and development for
LCGT has been placed on cryogenic mirrors for the past years.
The implementation of cryogenic mirrors is one of the moststraight-forward solutions to improve the sensitivity.
The design of the cryogenic mirror system is shown in
Fig. 11. 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 froman alignment control platform that is suspended with an insulator 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 the cryogenic system and the vibration isolator are

Fig. 10. LCGT sensitivity (dotted red curve) compared with those of
TAMA (red one), CLIO (a 100m prototype cryogenic interferometer
placed underground of Kmioka mine, light blue one), GEO (greenone), LIGO (initial LIGO, blue one, Adv. LIGO, dotted black one)and Virgo (orange one). The horizontal axis is frequency [Hz] andthe vertical√ axis represents sensitivity spectrum for gravitational
waves [1/ Hz].

42

put inside a common high-vacuum chamber.

Fig. 11. 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.

R&D
Basic Research for cryo-mirror system
To realize the cryo-mirror concept, the following researchsubjects were conducted and reported:
1. Removal of heat produced by high-power laser illumination (annual report 1997-1998 and also in references[5])
2. Holding the high Qs of the mirror internal modes andsuspension pendulum [6]3. Reducing the contamination of mirror surfaces (annual
report 2000?2001 and also in [7]).
4. Estimating heat production by optical loss in the mirror[8].
5. Alignment control of mirrors in a cryogenic environment [9]6. Low mechanical loss of the optical coating (annual report 2003-2004 and also in reference [10])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 themirror. With respect to the last item, we reported on a measurement 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 was sapphire, which has alarge 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 was 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. This is the significant merit of
the cryogenic mirror system.
For a practical cryogenic detector, more practical R&Ds
will be needed for the installation of cryogenic mirrors. Oneof the earliest R&D activities along this line was the Kashiwa
cryogenic interferometer system reported in the annual report(2000–2001; 2002–2003; 2003–2004). By this Kashiwa cryogenic interferometer, we learned the necessity of several practical R&D items and began to construct the CLIO interferometer in Kamioka to establish techniques for the cryogenic
interferometer (2005?2006 annual reports).
Parametric instability of high power cavities
The most serious problem was pointed by Braginskii. 14
Large power density of Fabry-Perot cavity may cause socalled parametric instability, which is produced by the coupling between optical cavity modes with elastic vibration
modes of the mirror substrate. Since the sapphire has larger
elastic wave velocity, the number density of elastic modes
is fewer than that of synthesized silica mirror, which is thecase of advanced LIGO. And also the coupling constant between optics and mechanics is smaller in LCGT than in advanced LIGO due to the smaller beam size of LCGT. This
merit comes from the adoption of cryogenics of LCGT[11].
Recent publication shows the effective suppression of the increase of the instability by adopting a negative feedback directly applied to the mirror.[12]Substrate selection device
LCGT adopts cryogenic mirrors to reduce thermal noisein place of expanding laser beam radius that is planed both in
the Advanced LIGO and the Advanced Virgo. Al2 O3 monocrystal is selected as the cryogenic mirror substrate because
it has excellent mechanical and thermal properties. However,there were some optical problems to be solved. High opticalabsorption and in-homogeneity of refractivity are concernedwith the reproducibility of large ingots exceeding 20 cm.
While some small-sized Al2 O3 crystal substrates had good absorption quality and better homogeneity enough to satisfy the*14 Braginskii, et al., Physics Lett. A 305 (2002)111.

43

LCGT requirement, larger samples (10cm in diameter, 6cm
in length) had less quality [13]. Moreover, we know that the
fabrication technology of Al2 O3 crystal to date is not mature
enough to consistently produce large substrates of adequate
quality. In order to inspect optical homogeneity of large piecesof Al2 O3 crystal for the production of better quality, we developed a scanning technique of birefringence measurement withhigh sensitivity and reported the determination of the opticalaxis of the uni-axial crystal and the measurement of the fluctuation of birefringence. We established a tool to distinguishthe quality required to pass the specification of LCGT by thisR&D in the annual report (2006–2007).
Other R&Ds
Apart from the above R&D issues, a high power laser system that produces more than 100 W is continually being developed by a group in Advanced Material Science, Schoolof New Frontier Science, University of Tokyo. Also, researchers at KEK tested the mechanical strength of suspension fiber of sapphire crystal [15] and the result of heat radiation leaking from room temperature tube to the cryogenic
chamber was quantitatively measured as reported in the section of CLIO.[16] We steadily advance towards the realizationof LCGT by these R&D activities.

Summary and Scope of LCGT
We have restructured the organization and added minorchanges to the design of LCGT. Persistent R&Ds have beensuccessfully conducted and we are ready to construct the interferometer of LCGT at any time.

Bibliography[1] M. Ohashi et al. “Status of LCGT and CLIO”, TAUP
2007, September 11-15, 2007, Sendai.
[2] K. Kuroda et.al., “Current status of LCGT”, Seventh
Edoardo Amaldi conference on gravitational waves,
Sydney, July 8-14, 2007.
[3] F. Kawazoe et al., presented at Amaldi 7 meeting,
Sydney, July 8-14, 2007.
[4] 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.
[5] T. Uchiyama, et.al., Phys. Lett. A 242 (1998) 211.
[6] T. Uchiyama, et.al., Phys. Lett. A 261 (1999) 5;ibid
A273(2000)310.
[7] S. Miyoki, et al., Cryogenics 40 (2000) 61: ibid 41(2001) 415.

[8] T. Tomaru, et al., Phys. Lett. A 283 (2001) 80.
[9] N. Sato, et al., Cryogenics 43 (2003) 425.
[10] K. Yamamoto, et al., Class. Quantum Grav. 21 (2004)
S1075.
[11] Parametric Instability in the LCGT arm cavity, K.
Yamamoto, et al., J. Phys. Conference series 122,
012015, 2008.
[12] Mathew Evans, GWADW09, May 11-15, 2009, Fortlauderdale, Florida.
[13] M. Tokunari et al., J. Phys.: Conference Series 32 (2006)
432.
[14] Z. Yan, et al., Applied Optics 40(2006) 1.
[15] T. Suzuki, et al., Seventh Edoardo Amaldi conferenceon gravitational waves, Sydney, July 8-14, 2007.
[16] T. Tomaru, et al., J. Phys. Conference series 122,
012009, 2008.

Sloan Digital Sky Survey[Spokesperson : Masataka Fukugita]
ICRR, University of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of:
University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 1130033, Japan; Nagoya University, Chikusa, Nagoya 464-8602,
Japan; National Astronomical Observatory of Japan, 2-211 Osawa, Mitaka, Tokyo 181-8588, Japan; Tohoku University, Aramaki, Aoba, Sendai 980-8578, Japan; Japan Women’s
University, 2-8-1, Mejirodai, Bunkyo-ku, Tokyo, 112-8681,
Japan; The University of Chicago, 5640, South Ellis Ave.,
Chicago, IL 60637, USA; Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, IL 60510, USA; Institute forAdvanced Study, Einstein Drive, Princeton, NJ 08540, USA;
Johns Hopkins University, Baltimore, MD 21218, USA; Los
Alamos National Laboratory, Los Alamos, NM 87545, USA;
Max-Planck-Institute for Astronomy, Königstuhl 17, D-69117
Heidelberg, Germany; Max-Planck-Institute for Astrophysics,
Karl Schwarzschildstrasse 1, D-85748 Garching, Germany;
New Mexico State University, P.O. Box 30001, Dept 4500,
Las Cruces, NM 88003, USA; University of Pittsburgh, 3941
O’Hara St., Pittsburgh, PA 15260, USA; Princeton University, Princeton, NJ 08544, USA; United States Naval Observatory, P.O. Box 1149, Flagstaff, AZ 86002-1149; Universityof Washington, Box 351580, Seattle, WA 98195, USA
The SDSS completed its originally planned phase of operations — SDSS-I — on 30 June 2005 after five years of operation. The goal initially set was to cover 10,000 square degrees

44of sky, but at the time the production survey began, the Five
Year Baseline was developed to provide a more realistic metric against which the progress was evaluated. This decreased
the target area to 8,387 square degrees (7,642 square degrees
in the northern sky and 745 square degrees in the southernsky). The imaging carried out over 5 years has sustained theplanned pace. At the end of the survey 97% of the baseline
area were observed for the northern-sky baseline and 99%
of southern-sky baseline were completed. Spectroscopic surveys, however, are somewhat behind the schedule. Only 74%of the baseline area were observed for the north (100% for thesouth). This is due to unusually poor weather conditions in thespring of 2003 and in the winter of 2004. The time consuming spectroscopic runs were severely affected. Otherwise, all
the operations have been working smoothly (98% is the mean
uptime fraction), producing the data as expected. Software
has undergone extensive fine tunings and all the data were rereduced for a number of times, which are now made public
as The Data Release of the Sloan Digital Sky Survey I to VII(DR1-DR7), the last one comprising 8,423 square degrees ofimaging and 8,032 square degrees of spectroscopic surveys
done to 14 July 2008. This database contains 230 million objects including 1,374,080 objects with spectroscopic information. These numbers include 928,567 galaxies and 118,664
quasars obtained with the uniform selection criteria.
The SDSS has entered a new phase, SDSS-II, continuing
through July, 2008. SDSS-II have carried out three distinct
surveys — the Sloan Legacy Survey, SEGUE (The Sloan Extension for Galactic Understanding and Exploration), and the
Sloan Supernova Survey — to address fundamental questions
about the nature of the Universe, the origin of galaxies andquasars, and the formation and evolution of our own Galaxy,
the Milky Way.
The Sloan Legacy Survey is the continuation of SDSS-I
to complete spectroscopic survey to fill the gap in the Northern Galactic Cap which was not observed during SDSS-I due
to poor weather conditions. Constructing the largest possible single contiguous survey volume will improve the following three main results: the determination of the power spectrum, the photometric calibration, and the legacy which SDSS
will supply to the astronomical world. The goal is contiguous region of 7,808 square degrees in both imaging and spectroscopy.
SEGUE is mining the stellar content of the Milky Way inorder to create a detailed 3-dimensional map of the Galaxy.
SEGUE will image 3,320 square degrees mostly at |b| < 30◦
and obtain spectra of 240,000 stars in the disk and spheroid,
revealing the age, composition and phase space distributionof stars within the various Galactic components. These stellar excavations will provide essential clues to the structure,formation, and evolution of our Galaxy. SEGUE has finishedwith imaging of 3240 square degrees and 237,388 stellar spectra.
The Sloan Supernova Survey is a time-domain survey involving repeat imaging of the same region of the sky (theSDSS Southern equatorial stripe; about 2.5 degree wide by∼120 degree long) every other nights over the course of three
3-month campaigns (Sep-Nov). A primary scientific motivation is to detect and measure multi-band light-curves for ∼200

Type Ia supernovae in the redshift range z = 0.1 − 0.3. This
sample, with excellent photometric calibration, should provide insights into systematics of SNe Ia as calibrated standard candles. The survey of the three years (2005-2007)
have been finished successfully and found 494 spectroscopically confirmed SNe Ia in the redshift range between 0.05
and 0.40. About 85% of SNe Ia are discovered before maximum light. Follow-up spectra were taken at various telescopes
through collaboration including MDM(2.4m), NOT(2.6m),
APO(3.5m), NTT(3.6m), KPNO(4m), WHT(4.2m), Subaru(8.2m), HET(9.2m), Keck(10m), and SALT(10m).
The prime scientific goals of the SDSS are focused on extragalactic themes, such as the large-scale structure of galaxies
over a very large volume of the Universe, and detailed characterisations of the galaxy properties and those of quasars.
The clustering of galaxies observed in the SDSS, whenmapped in three dimensional space, looks very similar to that
expected in the model of the Universe dominated by cold
dark matter (CDM) with density fluctuations starting fromnearly scale-invariant adiabatic perturbations, as predicted in
the model of inflation. As a quantitative measure this density
field is characterised by the statistic called the power spectrum, the squared amplitude of the Fourier modes of fluctuations, which is written,
P(k) = |δk |2 =



d 3 rξ (r)e−ik·r(1)

where ξ (r) is the two-point correlation function of galaxies.
The important result is an accurate derivation of this power
spectrum from galaxy clustering over the scale from 10 to
200 Mpc, and the demonstration that it joins smoothly thespectrum derived from the temperature field imprinted on thecosmic microwave background measured by Wilkinson Microwave Anisotropy Probe (WMAP) (see Fig. 1). Combinedwith WMAP that explores the Universe at z ≈ 1000, this lends
the most convincing support to the standard model of structure formation in the Universe based on the ΛCDM model.
Moreover, the large-scale structure data of SDSS reduced theparameter degeneracies that exist within the CMB analyses;
the combined data of WMAP and SDSS yield the cosmological parameters Ωm = 0.29 ± 0.04, ΩΛ = 0.71 ± 0.04 and
H0 = 71 ± 4 km s−1 Mpc−1 at the year of 2004. Two years
later, 3-year WMAP data was released. It includes the newmeasurement of the low-l polarization power spectrum, which
detects the reionization signature and determines the corresponding optical depth. This measurement breaks the severe
degeneracy in the 1-year WMAP data and causes the dramatic
tightening of the constraints on various important cosmological parameters. Now the value added by other datasets isclearly reduced. However, the information from large scale
structure of galaxies give substantial improvements by cutting
error bars.
SDSS has applied another selection of galaxies — the selection of luminous red galaxies (LRG). Approximately 10%
of SDSS galaxies belong to this category. The advantageof this selection is to allow us to explore much deep sky.
The sight increases from 600h−1 Mpc (z = 0.2) to 1200h−1
Mpc (z = 0.4), quadrupling the survey volume compared withthe main galaxy sample. The constraints on cosmological45

Fig. 1. The power spectrum of galaxy clustering scaled to the present
epoch (SDSS galaxies) plotted with four other independent measures, extending four decades on spatial resolution, and demonstrating remarkable consistency. These data provide fundamental
constraints on cosmological models. Figure is taken from Tegmark
et al. Astrophys. J. 606, 702 (2004).

parameters obtained by combining 3-year WMAP data andSDSS LRG measurements are Ωm = 0.239 ± 0.018, ΩΛ =0.761 ± 0.018 and H0 = 73 ± 2 km s−1 Mpc−1 . This set istaken as an authoritative in the astronomy community.
Baryonic acoustic oscillations (BAO) is a reminiscenceof the sound wave oscillation in the pre-recombination era,
which is most dramatically seen in CMB multipoles. In real
space this leads to a peak in the two-point correlation function
ξ (r) at about rs = 100h−1 Mpc. In Fourier space this processleads to oscillations in the power spectrum. The wavelength ofthese oscillations will be ks = 2π /rs = 0.06h Mpc−1 . Eisenstein et al. (2005) has detected this acoustic peak in correlation function of SDSS LRG and determine the curvature of
the Universe to 1% accuracy, ΩΛ +Ωm = 1.01±0.01, which iscomparable to the latest WMAP3+SDSS LRG analysis. The
analysis of the main galaxies and LRGs in the SDSS DR5
sample determines Ωm = 0.256 ± 0.029 using the dependenceof rs on the matter density Ωm (Fig. 2). This value of the matter density is derived from the locations of BAO in the galaxy
power spectrum and in the CMB. This is an extremely clean
geometrical cosmological measurement, as the physics of the
BAO production is well understood. With larger samples anda wider redshift range, the BAO “standard ruler” can be used
to constrain the cosmology at high precision through the comoving distance-redshift relation. Forthcoming surveys will
be designed to exploit this effect.
Although CDM models seem to be very successful onlarge scales, one of the most serious challenges facing CDM
models is the so-called “missing satellite” problem. CDM
models predicts at least 1-2 orders of magnitude more lowmass sub-halos at the present epoch compared to the observed
abundance of dwarf galaxies surrounding the Milky Way andM31. All-sky photographic surveys cover most of the sky, but
are limited to surface brightnesses of ∼ 25.5 mag arcsec−2 .

Fig. 2. Ratio of the power spectra calculated from the SDSS to theoverall shape of the measured power spectra (filled circles with
1σ errors). Solid lines represents the BAO predicted by a CDM
model with matter densities given in each panel and h = 0.73, anda 17% baryon fraction. As can be seen, the observed oscillations
approximately match those predicted for 0.2 ≤ Ωm ≤ 0.3. Figure istaken from Percival et al. Astrophys. J. 657, 51 (2007).

46

0.04

17 < g < 19

19 < g < 19.5

19.5 < g < 20

20 < g < 20.5

0.02

0.00

-0.02

wGQ(θ)

0.04

Fig. 3. Locations of Milky Way satellites in Galactic coordinates. Filled
circles are satellites discovered by SDSS, and open circles arepreviously known Milky Way dSphs. Figure is taken from Belokurov et al. Astrophys. J. 654, 897 (2007).

0.02

0.00

-0.02

0.01

20.5 < g < 21

0.04

0.1

θ (degrees)

1

0.02

0.00

The selection effects are also difficult to model with accuracy.
The SDSS makes it possible to carry out a systematic survey for satellite galaxies, which are detectable through overdensity of stars in position-color-magnitude space. A total of
10 new Milky Way satellites with effective surface brightness
μV ≥ 28 mag arcsec−2 have been discovered in SDSS data
(Fig. 3) in addition to the previously known 9 Milky Way
dwarf spheroidals. Some preliminary studies of these indicate that they may be dark matter dominated. We need moreinvestigation to see if these are the “missing satellites”.
Gravitational lensing is also a subject to which the SDSS
is making a significant contribution in a number of ways. The
SDSS is one of the first few that observed a weak effect ofgravitational lensing of galaxy images by foreground galaxies. The lensing effect appears as distorted images of galaxies
due to the gravitational shear field, but it is only on the order of a few percent, compared with the order of unity effectof randomly oriented galaxies that have intrinsically different
shapes. Millions of galaxies are needed to extract this small
signal from noise of the order of unity. With the SDSS galaxy
sample, this distortion was unambiguously detected, showing that the mass concentration around galaxies behaves asr−0.8 as a function of distance r, consistently with the famous
r−1.8 law of the galaxy-galaxy correlation. Another effect ofgravitational lensing by foreground galaxies is a magnification of distant sources, cosmic magnification. Gravitational
magnification has two effects. First, the flux received fromdistant sources is increased, resulting in a relatively deeper
apparent magnitude limited survey. Second, the solid angle
is stretched, diluting the surface density of source images on
the sky. The net result of these competing effects is an induced cross-correlation between physically separated populations that depends on how the loss of sources due to dilution isbalanced by the gain of sources due to flux magnification. Using ∼ 200, 000 quasars and 13 million galaxies, cosmic magnification has been detected for the first time at 8σ level (Fig.
4).
The large quasar sample of the SDSS also provides an
excellent platform to search for classical strong gravitational
lenses of quasar images, i.e., splitting of images. 16 lenses

-0.02

0.01

0.1

θ (degrees)

1

Fig. 4. Measurement of wGQ (θ ), cross-correlation between foreground galaxies and distant quasars, as a function of quasar
g-band magnitude. The dark solid curve is the fitting model. Figure
is taken from Scranton et al. Astrophys., J. 633, 589 (2005).

are found from 46000 quasar images. Among the novel casesthat deserve special scientific discussion, we quote the largeseparation lensed quasar, SDSS J1004+4112 of four images
with their maximum separation being 14.6 arcsec and SDSS
J1029+2623 with two images with their separation of 22.5
arcsec (Figure5). These are the case where split lensed images are further enhanced by a cluster of galaxies. A statistical analysis to infer cosmological and mean galaxy parameters from the lens sample yielded Ωm = 0.26 ± 0.08,ΩΛ = 0.74 ± 0.17, consistent with the values derived from
WMAP and SDSS power spectrum analysis.
As it became apparent already at imaging first light, theSDSS project has made unrivalled contributions to our understanding of high redshift quasars from its commissioning
phase. By now the project has found 19 quasars with redshift
higher than 5.7 (i- dropout quasars) from ∼6,600 square degrees — Among them 8 are with z > 6: there are no z > 6
quasars reported from other projects. The highest redshift is
6.42, which means that the light was emitted only 0.84 Gyrafter the Big Bang. These high-z quasars, together with asample for lower-z, show the abundance of luminous quasars
declining exponentially with redshift from z ≈ 3 towards early
epochs. This is a significant constraint on the model of quasar
formation at high redshifts.
Also important aspect with high redshift quasars is thatthey allowed us to observe a change of the ionisation stateof the intergalactic medium (IGM) in a high redshift universe.
We know that a free electron and a proton recombine to form aneutral hydrogen atom at z ≈ 1000 − 1500. We also know that
IGM was again highly reionised before z ≈ 3. When and how
the reionisation took place is a matter of significant interest

47

Fig. 5. gri composite SDSS image of SDSS J1029+2623. The quasar
images (blue stellar objects) are indicated by A and B. G1 and G2(red extended objects) are likely to be member galaxies of a lensing cluster at z ∼ 0.55. Figure is taken from Inada et al. Astrophys.
J. (Letters) 653, L97 (2006).

Fig. 7. Bright-end slope of the Quasar Luminosity Function as a function of redshift determined from a linear least-squares fit to theMi (z = 2) < −25. The slope of the luminosity function significantly
flattens with redshift z > 3. Figure is taken from Richards et al.
Astron. J. 131, 2766 (2006).

taining 77,429 quasars in 5,740 square degrees. The longawaited quasar luminosity function (the work requires proper
understanding of the selection function) was determined forwell-defined and homogeneous sample consisting of 15,343
quasars within an effective area of 1622 square degrees. Derived luminosity function has a flatter bright-end slope at highredshift than at low redshift (Fig. 7). This slope change mustbe accounted for in models of the evolution of accretion onto
supermassive black holes.

Theory Group

Fig. 6. Evolution of optical depth combined with the Lyα , Lyβ , andeff ≈ (1 + z)>10.9 ,Lyγ results. At z > 5.5, the best-fit evolution has τGP
indicating an accelerated evolution. Figure is taken from Fan et al.
Astron. J. 132, 117 (2006).

from the point of view of galaxy formation. The SDSS quasar
spectra show the flux shortwards the Lyman α line rapidly
vanishing at z ≥ 6 (called the Gunn-Peterson trough), indicating the change of state of the IGM at this redshift (Figure
6). Cosmic reionisation is also evident from the WMAP 3year data and its epoch zr = 8 ± 2 is consistent with SDSS
result if we consider the error of optical depth determinedfrom WMAP data. A problem newly created is the question whether the star formation activity, as inferred from faintgalaxy observations, is sufficient to ionise the entire IGM atz ≈ 6.
Besides high redshift quasars, a large number of quasars
are collected and their properties are being studied. We
have released four catalogues of quasars, the fourth one con-

Neutrino mass, Dark Matter and Baryon
Asymmetry via TeV-Scale Physics without
Fine-Tuning[Spokesperson : M. Aoki]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of Toyama U. and Universidad Autónoma de Madrid.
We propose an extended version of the standard model,
in which neutrino oscillation, dark matter, and baryon asymmetry of the Universe can be simultaneously explained by
the TeV-scale physics without assuming unnatural hierarchy
among the mass scales. Tiny neutrino masses are generated at
the three loop level due to the exact Z2 symmetry, by which
stability of the dark matter candidate is guaranteed. The extra
Higgs doublet is required not only for the tiny neutrino masses
but also for successful electroweak baryogenesis. The model
provides discriminative predictions especially in Higgs phenomenology, so that it is testable at current and future collider
experiments.

48

Bibliography[1] M. Aoki, S. Kanemura, and O. Seto, Phys. Rev. Lett. 102(2009) 051805, [arXiv:0807.0361 [hep-ph]].

Light Higgs boson scenario in the SUSY
seesaw model[Spokesperson : M. Asano]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, Sokendai, Univ.
of Toyama and Kyoto Univ..
In the light Higgs boson scenario in which the lightest
Higgs boson mass is lighter than 114 GeV, we discuss consistency with see-saw mechanism. Using lepton flavor violating charged lepton decays, we investigate the mass bound forthe right-handed neutrino. We show that this scenario would
be testable in future experiments. We also discuss the effectof the modification of renormalization group equations by theright-handed neutrinos on the b → sγ process and the relicabundance of dark matter in the light Higgs boson scenario.

Bibliography[1] M. Asano, T. Kubo, S. Matsumoto and M. Senami,
arXiv:0807.4922 [hep-ph].

D-term assisted Anomaly Mediation in E6
motivated models[Spokesperson : M. Asano]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, KEK, Tohoku
Univ. and Nagoya Univ..
In E6 GUTs model, we investigate effects of D-term contributions which can tachyonic slepton problem in anomaly
mediated supersymmetry breaking scenario. We show mass
spectrum at several sample points. There would be a distinct signature of this scenario at the LHC. We also discuss
some characteristic features of the neutralino dark matter inthis model.

Bibliography[1] M. Asano, T. Kikuchi and S. G. Kim, arXiv:0807.5084[hep-ph].

parameter point of the model. ¿From the simulation result,
we also discuss the determination of other model parameters
and its impact on the future measurement of the thermal abundance of the dark matter relics in our universe.

Bibliography[1] E. Asakawa, M. Asano, K. Fujii, T. Kusano, S. Matsumoto, R. Sasaki, Y. Takubo and H. Yamamoto,arXiv:0901.1081 [hep-ph], to be published in Phys. Rev.
D.

Non-linear evolution of matter power spectrum in modified theories of gravity[Spokesperson : T. Hiramatsu]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of Univ. of Tokyo andUniv. of Portsmouth.
Recently considerable efforts have been made to study thepossibility of a large distance modification of General Relativity, which may account for the late-time acceleration of the
Universe. We focus on the non-linear behaviour of the matter
power spectrum in some viable theoretical models of modified gravity, f (R) gravity models and the DGP brane-worldmodel. The present work is based on an improved cosmological perturbation theory developed in our previous paper,
called closure theory. We developed a numerical algorithm tosolve a set of the integral-differential equations derived fromthe closure theory [1]. Using this scheme, we predicted thematter power spectrum in a f (R) gravity model proposed by
Hu and Sawicky and the DGP model at the 1-loop level[2].
We found that, in all cases, the resultant power spectra tend toconverge to the prediction in GR on small scales, which is realised by the Vainstein effect (DGP) or the Chameleon effect( f (R)). In addition, we checked that the Parametrized-PostFriedmann formalism by Hu and Sawicky can be also used inthese modified theories of gravity if small modifications of themodel parameters are allowed.

Bibliography[1] T. Hiramatsu, A. Taruys, Phys. Rev. D79 (2009) 103526,[arXiv:0902.3772 [astro-ph.CO]].
[2] K. Koyama, A. Taruya and T. Hiramatsu, Phys. Rev. D79(2009) 123512, [arXiv:0902.0618 [astro-ph.CO]].

Precision Measurements of Little Higgs Parameters at the International Linear Collider Flavor physics in supersymmetric theories[Spokesperson : M. Asano]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582[Spokesperson : J. Hisano]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582

In collaboration with the members of ICRR, Meiji Gakuin
Univ., KEK, Tohoku Univ. and Univ. of Toyama.

In collaboration with the members of Univ. of Tokyo, Munich
Tech. Univ., and Tohoku Univ..

In the Littlest Higgs model with T-parity, we study production processes of new gauge bosons at the international linear
collider. Through Monte Carlo simulations of the production
processes, we show that the heavy gauge boson masses canbe deter- mined very accurately at the ILC for a representative

In the supersymmetric (SUSY) extension of the standard model (SM), CP- and/or flavor-violating SUSY-breaking
terms are introduced, and they lead to rare processes, such as
EDMs and charged-lepton flavor violating processes. Theseobservables are known to be sensitive to source of the SUSY

49

breaking and also physics beyond the SUSY SM. In [1], we
systematically evaluated the predictions for the EDMs at the
beyond-leading-order (BLO) within supersymmetric frameworks with flavor-violating soft terms. We found that the BLO
contributions to the EDMs dominate over the leading-order(LO) effects in large regions of the supersymmetric parameter
space. Next, in [2] we reevaluated the charged-lepton flavor
violating processes in the SUSY seesaw model and discussed
correlation of the Br(μ → eγ ) and other observables within
the prospect of the MEG experiment sensitivity.

tight constraints on such nonthermal production scenarios ofneutralino dark matter.

Bibliography

ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR and IPMU.

[1] J. Hisano, M. Nagai and P. Paradisi, arXiv:0812.4283[hep-ph].
[2] J. Hisano, M. Nagai, P. Paradisi and Y. Shimizu,
arXiv:0904.2080 [hep-ph].

Probing reheating temperature of the universe with gravitational wave background[Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, Univ. of Tokyoand RESCEU.
Thermal history of the universe after big-bang nucleosynthesis (BBN) is well understood both theoretically and observationally, and recent cosmological observations also begin
to reveal the inflationary dynamics. However, the epoch between inflation and BBN is scarcely known. In this paper weshow that the detection of the stochastic gravitational wave
background around 1Hz provides useful information about
thermal history well before BBN. In particular, the reheating temperature of the universe may be determined by future space-based laser interferometer experiments such as DECIGO and/or BBO if it is around 106−9 GeV, depending on thetensor-to-scalar ratio.

Bibliography

Bibliography[1] M. Nagai and K. Nakayama, Phys. Rev. D 78 (2008)
063540 [arXiv:0807.1634 [hep-ph]].

Non-Gaussianity from isocurvature perturbations[Spokesperson : K. Nakayama]

We develop a formalism to study non-Gaussianity in both
curvature and isocurvature perturbations. It is shown that nonGaussianity in the isocurvature perturbation between dark
matter and photons leaves distinct signatures in the CMB
temperature fluctuations, which may be confirmed in future experiments, or possibly, even in the currently available observational data. As an explicit example, we consider the QCD axion and show that it can actually induce
sizable non-Gaussianity for the inflationary scale, Hinf =O(109 − 1011) GeV. We also study a scenario that large nonGaussianity arises from the baryon asymmetry of the Universe. There are baryogenesis scenarios containing a light
scalar field, which may result in baryonic isocurvature perturbations with some amount of non-Gaussianity. As an example
we consider the Affleck-Dine mechanism and show that a flat
direction of the supersymmeteric standard model can generatelarge non-Gaussianity in the curvature perturbations.

Bibliography[1] M. Kawasaki, K. Nakayama, T. Sekiguchi,
T. Suyama and F. Takahashi, JCAP 0811 (2008)
019 [arXiv:0808.0009 [astro-ph]].
[2] M. Kawasaki, K. Nakayama and F. Takahashi, JCAP
0901 (2009) 002 [arXiv:0809.2242 [hep-ph]].

[1] K. Nakayama, S. Saito, Y. Suwa and J. Yokoyama, JCAP
0806 (2008) 020 [arXiv:0804.1827 [astro-ph]].

[3] M. Kawasaki, K. Nakayama, T. Sekiguchi,
T. Suyama and F. Takahashi, JCAP 0901 (2009)042 [arXiv:0810.0208 [astro-ph]].

Direct/indirect detection signatures of nonthermally produced dark matter

Hilltop Non-Gaussianity[Spokesperson : K. Nakayama][Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582

ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR.
We study direct and indirect detection possibilities of neutralino dark matter produced non-thermally by e.g. the decayof long-lived particles, as is easily implemented in the case ofanomaly or mirage mediation models. In this scenario, large
self-annihilation cross sections are required to account for thepresent dark matter abundance, and it leads to significant enhancement of the gamma-ray signature from the Galactic Center and the positron flux from the dark matter annihilation. It
is found that GLAST and PAMELA will find the signal or give

In collaboration with the members of ICRR and IPMU.
We study non-Gaussianity induced by a pseudo NambuGoldstone boson with a cosine-type scalar potential. We focus on how the non-Gaussianity is affected when the pseudo
Nambu-Goldstone boson rolls down from near the top of thescalar potential where the deviation from a quadratic potential
is large. We find that the resultant non-Gaussianity is similar to that obtained in the quadratic potential, if the pseudo
Nambu-Goldstone boson accounts for the curvature perturbation; the non-Gaussianity is enhanced, otherwise.

50

Bibliography

Neutrino
SignalsfromAnnihilating/Decaying
Dark
MatterintheLight[1] M. Kawasaki, K. Nakayama and F. Takahashi, JCAP
of
RecentMeasurementsofCosmicRay
0901 (2009) 026 [arXiv:0810.1585 [hep-ph]].
Electron/Positron Fluxes
Cosmic Rays from Dark Matter Annihilation[Spokesperson : K. Nakayama]
and Big-Bang Nucleosynthesis[Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, Lancaster Univ.,
and Tohoku Univ..
Recent measurements of cosmic-ray electron and positron
fluxes by PAMELA and ATIC experiments may indicate theexistence of annihilating dark matter with large annihilation
cross section. We show that the dark matter annihilation in
the big-bang nucleosynthesis epoch affects the light element
abundances, and it gives stringent constraints on such annihilating dark matter scenarios for the case of hadronic annihilation. Constraints on leptonically annihilating dark mattermodels are less severer. We also show that the dark matter annihilation scenarios to explain the positron excess may also becompatible with the discrepancy of the cosmic lithium abundances between theory and observations. The wino-like neutralino in the supersymmetric standard model is a good example for it.

Bibliography[1] J. Hisano, M. Kawasaki, K. Kohri and K. Nakayama,
Phys. Rev. D 79 (2009) 063514 [arXiv:0810.1892 [hepph]].
[2] J. Hisano, M. Kawasaki, K. Kohri, T. Moroi and
K. Nakayama, Phys. Rev. D 79 (2009) 083522[arXiv:0901.3582 [hep-ph]].

Cosmological Moduli Problem from Thermal Effects[Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR and IPMU.
We estimate the cosmological abundance of a modulus
field that has dilatonic couplings to gauge fields, paying particular attention to thermal corrections on the modulus potential. We find that a certain amount of the modulus coherent
oscillations is necessarily induced by a linear thermal effect.
We argue that such an estimate provides the smallest possible modulus abundance for a given thermal history of the
Universe. As an example we apply our results to a saxion,a bosonic supersymmetric partner of an axion, and derive atight bound on the reheating temperature. We emphasize thatthe problem cannot be avoided by fine-tuning the initial deviation of the modulus field, since the minimal amount of themodulus is induced by the dynamics of the scalar potential.

Bibliography[1] K. Nakayama and F. Takahashi, Phys. Lett. B 670 (2009)434 [arXiv:0811.0444 [hep-ph]].

ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR and Lancaster
Univ..
The excess of cosmic-ray electron and positron fluxes
measured by the PAMELA satellite and ATIC balloon experiments may be interpreted as the signals of the dark matterannihilation or decay into leptons. In this letter we show thatthe dark matter annihilation/decay which reproduces the electron/positron excess may yield a significant amount of highenergy neutrinos from the Galactic center. In the case, futurekilometer-square size experiments may confirm such a scenario, or even the Super-Kamiokande results already put constraints on some dark matter models.

Bibliography[1] J. Hisano, M. Kawasaki, K. Kohri and K. Nakayama,
Phys. Rev. D 79 (2009) 043516 [arXiv:0812.0219 [hepph]].

Upperbound on Squark Masses in GaugeMediation Model with Light Gravitino[Spokesperson : S. Sugiyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, KEK, and Univ.
of Tokyo.
We examine stabilities of our supersymmetry-breaking
false vacuum in a low-energy direct gauge mediation modelof SUSY breaking. The stability required in the hightemperature early universe leads to upperbounds on massesof squarks and gluino as mq̃  1 TeV and mg̃  1 TeV for thelight gravitino of mass m3/2  16 eV.

Bibliography[1] J. Hisano, M. Nagai, S. Sugiyama, T. T. Yanagida,
arXiv:0804.2957 [hep-ph].

A Realistic Extension of Gauge-Mediated
SUSY-Breaking Model with Superconformal
Hidden Sector[Spokesperson : S. Sugiyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR.
The sequestering of supersymmetry (SUSY) breaking parameters, which is induced by superconformal hidden sector, is one of the solutions for the μ /Bμ problem in gaugemediated SUSY-breaking scenario. However, it is found thatthe minimal messenger model does not derive the correct electroweak symmetry breaking. In this paper we present a model

51

which has the coupling of the messengers with the SO(10)GUT-symmetry breaking Higgs fields. The model is one of
the realistic extensions of the gauge mediation model with superconformal hidden sector. It is shown that the extension isapplicable for a broad range of conformality breaking scale.

Bibliography[1] M. Asano, J. Hisano, T. Okada, S. Sugiyama,
arXiv:0810.4606 [hep-ph].

Non-Gaussianity from Symmetry[Spokesperson : T. Suyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with a member of IPMU
We pointed out that a light scalar field fluctuating around asymmetry-enhanced point can generate large non-Gaussianity
in density fluctuations. We named such a particle as an ”ungaussiton”, a scalar field dominantly produced by the quantum
fluctuations,generating sizable non-Gaussianity in the density
fluctuations. We derived a consistency relation between the
4/3
bispectrum and the trispectrum, τNL = 103 fNL , which can beextended to arbitrary high order correlation functions. If sucha relation is confirmed by future observations, it will strongly
support this mechanism.

Bibliography[1] T. Suyama and F. Takahashi, JCAP 0809 (2008) 007[arXiv:0804.0425 [astro-ph]].

Primordial Curvature Fluctuation and Its
Non-Gaussianity in Models with Modulated
Reheating[Spokesperson : T. Suyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with members of ICRR, Saga Univ. andAoyama-Gakuin Univ.
We investigated non-Gaussianity in the modulated reheating scenario where fluctuations of the decay rate of the inflation generate adiabatic perturbations, paying particular attention to the non-linearity parameters fNL , τNL and gNL as wellas the scalar spectral index and tensor-to-scalar ratio whichcharacterize the nature of the primordial power spectrum. We
found that the non-linearity between the decay rate and themodulus field which determines the decay rate can generatemuch greater non-Gaussianity. We also discussed a consistency relation among non-linearity parameters which holds inthe scenario and find that the modulated reheating yields a different one from that of the curvaton model.

Bibliography[1] K. Ichikawa, T. Suyama, T. Takahashi and
M. Yamaguchi, Phys. Rev. D 78 (2008) 063545[arXiv:0807.3988 [astro-ph]].

Exact gravitational lensing by cosmic
strings with junctions[Spokesperson : T. Suyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
We pointed out that the results by Brandenberger et al.
in Phys.Rev.D77:083502(2008) that the geometry around thestraight cosmic strings with stationary junctions is flat to linear
order in the string tension can be immediately extended to any
order.

Bibliography[1] T. Suyama, Phys. Rev. D 78 (2008) 043532[arXiv:0807.4355 [astro-ph]].

52

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

53

NORIKURA OBSERVATORY
1.

Introduction

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.

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.

2.

Cosmic Ray Physics

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 flare

54

accelerates the proton and ion to high energy and they are detected on the Earth soon after the flare. Among the particles
generated by the flare, high energy neutrons provide the mostdirect information about the acceleration mechanism as theycome straight from the flare position to the Earth without deflected by the magnetic field.
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.
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 and the performance study of theballoon borne cosmic ray experiments.

3.

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’.)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[11],[12],[13] were obtained at Mt.

55

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.

4.

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[14],[15].
(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
the maximum 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.
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 tothe temperature enhancement of about 0.8◦C for air temperature and about 0.3◦C for ground temperature, plant growth

56

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[16],[17] 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).
[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).
[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).
[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,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] 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.
[12] “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).
[13] “Free-tropospheric aerosols based on airplane andmountain observations”, K. Osada, Journal of Aerosol
Research, Japan, 15, 335-342, 2000 (in Japanese).
[14] “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).
[15] “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).
[16] “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).
[17] “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).

57

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.

various R & D works for the development of detectors used
for the observation high energy cosmic rays.

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 TA in
Utah, USA.
The observatory is now used as a support base for the operation of TA. It also supports two related experiments and58

KAMIOKA OBSERVATORY
Kamioka observatory is located at 1000m 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, will inject first neutrino beam to the Super-Kamiokande
detector in April, 2009.

The R&D study of a tracking type detector for dark mattersearch by the Kyoto University group (the NEWAGE experiment) has also been performed in an underground laboratory.
A double beta decay experiment, the CANDLE experiment(Osaka Univ.), is planned to be located in the Kamioka Underground Observatory. In order to support those experiments
and also related R&D works, the Observatory is equipped withlow background Germanium detector, ICP-MS and so on tomeasure extremely low radioactive backgrounds.

Fig. 2. Super-Kamiokande detector.

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 autumn in 2009.

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

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RESEARCH CENTER FOR COSMIC NEUTRINOS
The Research Center for Cosmic Neutrinos was established in April, 1999. The main objective of this Center is to
study neutrinos based on data from various observations andexperiments. In order to promote studies of neutrino physics,
it is important to provide the occasion to discuss theoreticalideas and experimental results on neutrino physics. Therefore, one of the most important practical jobs of this Center isthe organization of neutrino-related meetings. On Jun. 27th,
2008, we hosted one domestic neutrino workshop on ”Current
status of neutrino physics”. About 41 physicists participatedin this meeting.
Members of this Center have been involved in the SuperKamiokande, K2K and T2K experiments, carrying out researches in neutrino physics. Atmospheric neutrino data fromSuper-Kamiokande give one of the most precise pieces of information on neutrino oscillations. With increased data, it
is more important to have better predictions of the neutrino
flux. Therefore, in addition to data analysis of the above experiments, we work on predicting the atmospheric neutrino
flux. In order to accurately predict this flux, it is important toknow details of the data based on measurements of primaryand secondary cosmic-ray fluxes. For this reason, we have aclose collaboration with researchers working on cosmic-ray
flux measurements.
It is important that the general public knows about theachievements in the present science. For this reason, we havea public lecture every year. In FY2008, we held the public
lecture on April 12 (Sat) at Kashiwa. Two active scientists
working on the neutrino physics lectured on the latest researchfindings of the neutrino physics. About 86 people heard thelectures.

Fig. 1. Public lecture held in Kashiwa in April 12, 2008.
This Center, together with the computer committee of
ICRR, is in charge of operating the central computer system
in ICRR. The computer system was upgraded in Jan. 2008by about a factor of 5 to 10 in the performance relative to theprevious one, and it had been highly utilized for the analysis
and simulation of the various cosmic-ray physics. This Center

also supported the users of the computer system, including thephysicists working outside ICRR.
Since 2004, this Center has been acting as the 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
for the measurements of cosmic radioactive isotopes. The scientific activities that are related to this facility is described
elsewhere.

Fig. 2. Computer facility operated since Jan. 2008.

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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 Report

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) User’s Committee

H. List of Personnel

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A. ICRR Workshops and Ceremonies
Inauguration Ceremony and Symposium of Telescope Array
Date: August 25th, 2008
Place: Media Hall of Kashiwa Library, University of Tokyo, Kashiwa, Japan
Outline: The construction of the Telescope Array (TA) experiment was completed in Utah, USA and it started an observationof ultra-high energy cosmic rays in March, 2008. The Collaborators of TA are from USA, Korea, Russia and Japan. An
inauguration ceremony of TA was held on August 25th, 2008 inviting Prof. K. Hirao, Vice President of University of Tokyo
for Research, Prof. Tom Parks, Vice President for Research, University of Utah and Prof. Jim Whitmore, Program Director,
National Science Foundation. The TA collaborators, researchers in the field and representatives of the industry assembled
together to celebrate the start of TA. After the ceremony, a mini-symposium was held. Prof. K. Sato of physics department
presented the study of the propagation of ultra-high energy cosmic rays and his expectation to TA’s observation. Prof. M.
Fukushima of ICRR’s TA group gave a report of the construction and stated a prospect of physics.
Participants: 101 from Japan, 6 from USA and 1 from Korea.

B. ICRR Seminars
1. Apr 10, 2008: Masaki Asano (ICRR, University of Tokyo), ”Neutralino Dark Matter in Light Higgs Boson Scenario”
2. Apr 17, 2008: Takashi Hiramatsu (ICRR, University of Tokyo), ”Evolution of cosmological perturbations in a braneworld scenario”
3. Apr 25, 2008: Yuki Shimizu (ICRR, University of Tokyo), ”CALET: high energy cosmic ray experiment on the
ISS/JEM”
4. May 9, 2008: Hirohisa Sakurai (Yamagata University), ”Time variations of cosmogenic nuclide and solar activities”
5. May 30, 2008: Kentaro Terada (Hiroshima University), ”In-situ isotope analysis of extraterrestrial materials by Ion
microprobe”
6. Jun 17, 2008: Venya Berezinsky (INFN, Laboratori Nazionali del Gran Sasso), ”Ultra High Energy Cosmic Rays: from
Galactic to Extragalactic Cosmic Rays”
7. Jun 24, 2008: Mohammad S. Athar (Aligarh Muslim University, India), ”Neutrino Nucleus Cross Sections”
8. Jul 9, 2008: Hiroaki Yamamoto (LIGO, Caltech), ”Current status of Advanced LIGO”
9. Jul 9, 2008: Takashi Uchiyama (ICRR, University of Tokyo), ”Toward Large-scale Gravitational Wave Detector in Japan(CLIO to LCGT)”
10. Jul 11, 2008: Gary Varner (University of Hawaii), ”Microwave Radio Detection of UHE Air Showers”
11. Sep 26, 2008: Kumiko Kotera (Institute of Astrophysics of Paris), ”The Optical Depth of the Universe Seen throughUltrahigh Energy Cosmic Ray Spectacles”
12. Oct 27, 2008: Hiroyuki Nakanishi (Kagoshima University), ”Square Kilometer Array Project”
13. Nov 7, 2008: Hiroko Miyahara (ICRR, University of Tokyo), ”Variations of solar activity and the galactic cosmic rays
during the last 1200 years deduced from cosmogenic nuclides”
14. Dec 1, 2008: Shoji Torii (Waseda University), ”Cosmic Ray Electron (+Positron) Spectrum Observed by Antarctica
Balloon Flights and Its Interpretations”
15. Dec 2, 2008: Gerasimos Rigopoulos (University of Helsinki), ”On the Infrared divergences of Inflationary Perturbations”

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16. Dec 12, 2008: Hiroshi Miyakawa (ICRR, University of Tokyo), ”Development of the next generation gravitational wave
detector”
17. Dec 16, 2008: Hiro Tajima (SLAC National Accelerator Laboratory), ”Gamma-ray Universe revealed by Fermi Gammaray Space Telescope”
18. Dec 24, 2008: Toshio Terasawa (Tokyo Institute of Technology), ”Particle Acceleration and Propagation: Plasma Physics
and Cosmic Rays”
19. Jan 9, 2009: Carsten Rott (Ohio State University), ”Neutrino Oscillation Measurements at the South Pole”
20. Feb 27, 2009: Federico Urban (University of British Columbia), ”The cosmological constant as a manifestation of theconformal anomaly”
21. Mar 17, 2009: German Hermann (Max-Planck-Institut fuer Kernphysik), ”Ground-based gamma-ray astrophysics: today
and tomorrow”
22. Mar 24, 2009: Marco Casolino (INFN and Physics Department of University of Rome), ”Pamela Experiment”

C. List of Publications — Fiscal Year 2008(a) Papers Published in Journals
1. ”Supernova detection”, M. Nakahata, J.Phys.Conf.Ser.136:022042, 2008.
2. ”Search for Proton Decay via p → e+ π 0 and p → μ + π 0 in a Large Water Cherenkov Detector”, Super-Kamiokande
Collaboration (H. Nishino et al.), Phys.Rev.Lett.102:141801, 2009.
3. ”Kinematic reconstruction of atmospheric neutrino events in a large water Cherenkov detector with proton identification”, Super-Kamiokande Collaboration (M. Fechner et al.), Phys.Rev.D79:112010, 2009.
4. ”First Study of Neutron Tagging with a Water Cherenkov Detector”, Super-Kamiokande Collaboration (H. Watanabe etal.), Astroparticle Physics 31, 320-328, 2009.
5. ”Future of neutrino experiments”, T. Kajita, Pramana 72:109-117, 2009.
6. ”Working group report: Neutrino physics”, Sandhya Choubey et al, Pramana 72:269-275, 2009.
7. ”Future neutrino oscillation experiment with 2 detectors at Kamioka and Korea”, T. Kajita, J.Phys.Conf.Ser.120:052045,
2008.
8. ”Atmospheric neutrinos and the implications to cosmic ray interactions”, T. Kajita, Nucl.Phys.Proc.Suppl.175:301-306,
2008.
9. ”Distillation of Liquid Xenon to Remove Krypton”, XMASS Collaboration (K. Abe et al.), Astroparticle Physics 31,
290-296, 2009.
10. ”Measurement of single charged pion production in the charged-current interactions of neutrinos in a 1.3-GeV wide bandbeam”, K2K Collaboration (A. Rodriguez et al.), Phys.Rev.D78:032003, 2008.
11. ”Probing nonstandard neutrino physics by two identical detectors with different baselines”, N. C. Ribeiro et al., Phys.
Rev. D 77, 073007, 2008.
12. ”CANGAROO-III Observations of the 2006 Outburst of PKS 2155-304”, Y. Sakamoto et al., Astrophys. J. 676, 113,
2008.
13. ”Observation of an Extended Very High Energy Gamma-Ray Emission from MSH 15-52 with CANGAROO-III”, T.
Nakamori et al., Astrophys. J. 677, 297, 2008.
14. ”CANGAROO-III Search for Gamma Rays from Kepler’s Supernova Remnant”, R. Enomoto et al., Astrophys. J. 683,
383, 2008.

63

15. ”Observation of Very High Energy Gamma Rays from HESS J1804-216 with CANGAROO-III Telescopes”, Y. Higashi
et al., Astrophys. J. 683, 957, 2008.
16. ”Very high energy gamma-ray observations of the Galactic Plane with the CANGAROO-III telescopes”, M. Ohishi etal., Astropart. Phys. 30, 47, 2008.
17. ”CANGAROO-III Search for TeV Gamma-Rays from Two Clusters of Galaxies”, R. Kiuchi et al., Astrophys. J. in press,
2009, arXiv:0908.3301 [astro-ph.HE].
18. ”Search for VHE Gamma Rays from SS433/W50 with the CANGAROO-II Telescope”, Sei. Hayashi et al., Astropart.
Phys. in press, 2009, arXiv:0909.0133 [astro-ph.HE].
19. ”Reanalysis of Data Taken by the CANGAROO 3.8 Meter Imaging Atmospheric Cherenkov Telescope: PSR B1706-44,
SN 1006, and Vela”, T. Yoshikoshi et al., Astrophys. J. 702, 631, 2009.
20. ”End-to-end absolute Energy calibration of atmospheric fluorescence telescopes by an electron linear accelerator”, T.
Shibata et al., Nucl. Instr. and Methods A597, 61-66, 2008.
21. ”Multi-TeV Gamma-Ray Observation from the Crab Nebula Using the Tibet-III Air Shower Array Finely Tuned by the
Cosmic-Ray Moon’s Shadow”, M. Amenomori et al., The Astrophysical Journal, 692, 61-72, 2009.
22. ”The energy spectrum of all-particle cosmic rays around the knee region observed with the Tibet-III air-shower array”,
M. Amenomori et al., Advances in Space Research, 42, 467-472, 2008.
23. ”The all-particle spectrum of primary cosmic rays in the wide energy range from 1014 eV to 1017 eV observed with the
Tibet-III air-shower array”, M. Amenomori et al., The Astrophysical Journal, 678, 1165-1179, 2008.
24. ”Conduction Effect of Thermal Radiation in a Metal Shield Pipe in a Cryostat for a Cryogenic Interferometric Gravitational Wave Detector”, T. Tomaru et al., Jpn. J. Appl. Phys. 47, 3, 1771-1774, 2008.
25. ”Effect of energy deposited by cosmic-ray particles on interferometric gravitational wave detectors”, K. Yamamoto, etal., Phys. Rev. D78, 022004, 2008.
26. ”Search for continuous gravitational waves from PSR J0835-4510 using CLIO data”, T. Akutsu, et al., Class. Quantum
Grav. 25 184013, 2008.
27. ”Status of LCGT and CLIO”, M. Ohashi, Journal of Physics: Conference Series, 120, 032008, 2008.
28. ”The Sixth Data Release of the Sloan Digital Sky Survey ”, Adelman-McCarthy, J. K. et al., ApJS, 175, 297-313, 2008.
29. ”Implications for Galaxy Evolution from Cosmic Evolution of the Supernova Rate Density”, T. Oda, et al., PASJ, 60,
169, 2008
30. ”First-Year Spectroscopy for the Sloan Digital Sky Survey-II Supernova Survey”, C. Zheng, et al., AJ, 135, 1766-1784,
2008.
31. ”The Subaru/XMM-Newton Deep Survey (SXDS). II. Optical Imaging and Photometric Catalogs”, H. Furusawa, et al.,ApJS, 176, 1-18, 2008.
32. ”A Measurement of the Rate of Type Ia Supernova at Redshift z ∼ 0.1 from the First Season of the SDSS-II Supernova
Survey ”, B. Dilday, et al., ApJ, 682, 262-282, 2008.
33. ”Luminosity Function Constraints on the Evolution of Massive Red Galaxies since z ∼ 0.9”, R. Cool, et al., ApJ, 682,
919-936, 2008.
34. ”The Milky Way Tomography with SDSS. II. Stellar Metallicity”, Ivezić, Ž., et al., ApJ, 684, 287-325, 2008.
35. ”Light-curve studies of nearby Type Ia supernova with a Multiband Stretch method”, N. Takanashi, et al., MNRAS, 389,
1577-1592, 2008.
36. ”The Sloan Digital Sky Survey-II: Photometry and Supernova Ia Light Curves from the 2005 Data”, J. A. Holtzman, etal., AJ, 136, 2306-2320, 2008.
37. ”Delay Time Distribution Measurement of Type Ia Supernova by the Subaru/XMM-Newton Deep Survey and Implications for the Progenitor”, T. Totani, et al., PASJ, 60, 1327, 2008.

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38. ”Discovery of an Unusual Optical Transient with the Hubble Space Telescope”, K. Barbary, et al., ApJ, 690, 1358-1362,
2009.
39. ”Neutrino mass, Dark Matter and Baryon Asymmetry via TeV-Scale Physics without Fine-Tuning”, M. Aoki, et al.,Phys. Rev. Lett. 102, 051805, 2009.
40. ”Precision Measurements of Little Higgs Parameters at the International Linear Collider”, E. Asakawa, et al.,arXiv:0901.1081 [hep-ph], to be published in Phys. Rev. D.
41. ”Chasing the non-linear evolution of matter power spectrum with numerical resummation method: solution of closure
equations”, T. Hiramatsu, et al., Phys. Rev. D79, 103526, 2009.
42. ”Non-linear Evolution of Matter Power Spectrum in Modified Theory of Gravity”, K. Koyama, A. Taruya and T. Hiramatsu, Phys. Rev. D79, 123512, 2009.
43. ”CP Violation in Bs Mixing in the SUSY SU(5) GUT with Right-handed Neutrinos”, J. Hisano, et al., Phys. Lett. B669,
301, 2008.
44. ”Discriminating Electroweak-ino Parameter Ordering at the LHC and Its Impact on LFV Studies”, J. Hisano, et al., JHEP
0906, 044, 2009.
45. ”Formation of intermediate-mass black holes as primordial black holes in the inflationary cosmology with running spectral index”, T. Kawaguchi, et al., MNRAS 388, 1426, 2008.
46. ”Big-Bang Nucleosynthesis and Gravitino”, M. Kawasaki, et al., Phys. Rev. D78, 065011, 2008.
47. ”Electron and Photon Energy Deposition in Universe”, T. Kanzaki, et al., Phys. Rev. D78, 103004, 2008.
48. ”Isocurvature fluctuations in Affleck-Dine mechanism and constraints on inflation models”, S. Kasuya, et al., JCAP
0810, 017, 2008.
49. ”Probing reheating temperature of the universe with gravitational wave background”, K. Nakayama, et al., JCAP 0806,
020, 2008. [arXiv:0804.1827 [astro-ph]].
50. ”Direct/indirect detection signatures of non-thermally produced dark matter”, M. Nagai, et al., Phys. Rev. D78, 063540,
2008. [arXiv:0807.1634 [hep-ph]].
51. ”Non-Gaussianity from isocurvature perturbations”, M. Kawasaki, et al., JCAP 0811, 019, 2008. [arXiv:0808.0009[astro-ph]].
52. ”Non-Gaussianity from Baryon Asymmetry”, M. Kawasaki, et al., JCAP 0901, 002, 2009. [arXiv:0809.2242 [hep-ph]].
53. ”A General Analysis of Non-Gaussianity from Isocurvature Perturbations”, M. Kawasaki, et al., JCAP 0901, 042, 2009.
[arXiv:0810.0208 [astro-ph]].
54. ”Hilltop Non-Gaussianity”, M. Kawasaki, et al., JCAP 0901, 026, 2009. [arXiv:0810.1585 [hep-ph]].
55. ”Positron/Gamma-Ray Signatures of Dark Matter Annihilation and Big-Bang Nucleosynthesis”, J. Hisano, et al., Phys.
Rev. D79, 063514, 2009. [arXiv:0810.1892 [hep-ph]].
56. ”Cosmological Moduli Problem from Thermal Effects”, K. Nakayama, et al., Phys.
[arXiv:0811.0444 [hep-ph]].

Lett.

B670, 434, 2009.

57. ”Neutrino Signals from Annihilating/Decaying Dark Matter in the Light of Recent Measurements of Cosmic Ray Electron/Positron Fluxes”, J. Hisano, et al., Phys. Rev. D79, 043516, 2009. [arXiv:0812.0219 [hep-ph]].
58. ”Cosmic Rays from Dark Matter Annihilation and Big-Bang Nucleosynthesis”, J. Hisano, et al., Phys. Rev. D79,083522, 2009. [arXiv:0901.3582 [hep-ph]].
59. ”Primordial Helium Abundance from CMB: a constraint from recent observations and a forecast”, K. Ichikawa, et al.,Phys. Rev. D78, 043509, 2008.
60. ”Probing the Effective Number of Neutrino Species with Cosmic Microwave Background”, K. Ichikawa, et al., Phys.
Rev. D78, 083526, 2008.
61. ”Cosmological Constraints on Isocurvature and Tensor Perturbations”, M. Kawasaki, et al., Prog. Theor. Phys. 120,
995, 2008.

6562. ”Upperbound on Squark Masses in Gauge-Mediation Model with Light Gravitino”, J. Hisano, et al., Phys. Lett. B665,
237, 2008. [arXiv:0804.2957 [hep-ph]].
63. ”A Realistic Extension of Gauge-Mediated SUSY-Breaking Model with Superconformal Hidden Sector”, M. Asano, etal., Phys. Lett. B673, 146, 2009. [arXiv:0810.4606 [hep-ph]].
64. ”Non-Gaussianity from Symmetry”, T. Suyama, et al., JCAP 0809, 007, 2008.
65. ”Primordial Curvature Fluctuation and Its Non-Gaussianity in Models with Modulated Reheating”, K. Ichikawa, et al.,Phys. Rev. D78, 063545, 2008.
66. ”Exact gravitational lensing by cosmic strings with junctions”, T. Suyama, Phys. Rev. D78, 043532, 2008.
67. ”Hidden particle production at the ILC”, K. Fujii, et al., Phys. Rev. D78, 015008, 2008.

(b) Conference Papers
1. ”Kamiokande and Super-Kamiokande results on Neutrino Astrophysics”, M. Nakahata, Proceedings of XIII International
Workshop on ”Neutrino Telescopes”, Venice, Italy, March 2009.
2. ”Development of a large area gas photomultiplier with GEM/μ PIC”, H. Sekiya, Proceedings of the 34th International
Conference on High Energy Physics(ICHEP2008) Jul 29 - Aug 5, 2008 - Philadelphia, PA, arXiv:0809.3319
3. ”Search for Nucleon Decay in Super-Kamiokande”, M. Miura, LXIVth Recontres de Moriond, Electroweak interactions
and Unified Theories 7-14th March 2009.
4. ”Future possibilities with the J-PARC neutrino beam” T. Kajita, Proceedings of the 23rd International Conference on
Neutrino Physics and Astrophysics (Neutrino 2008), Christchurch, New Zealand, 26-31 May 2008. J. Phys. Conf. Ser.
136:022020, 2008.
5. ”Summary of the 3rd International Workshop on a Far Detector in Korea for the J-PARC Beam” T. Kajita, et al., Proceedings of 3rd International Workshop on a Far Detector in Korea for the J-PARC Neutrino Beam, Tokyo, Japan, 30,
p151-160, Sep-1 Oct 2007.
6. ”Reach of Future Accelerator and Reactor Neutrino Efforts” T2K Collaboration (Y. Obayashi for the collaboration),
Presented at Flavor Physics and CP Violation (FPCP 2008), Taipei, Taiwan, 5-9 May 2008. e-Print: arXiv:0807.4012[hep-ex].
7. ”T2KK sensitivity with more systematic error terms” K. Okumura, Far Detector in Korea for the J-PARC Neutrino Beam,
p57-60.
8. ”Future possibilities with the J-PARC neutrino beam” T. Kajita, Proc. Of the XXIII International Conference on Neutrino
Physics and Astrophysics, J. of Physics. Conference Series Vol.136, 022020, 2008.
9. ”Highlights in the T2KK workshops in 2005 and 2006” T. Kajita, et al., Proc. of the 3rd International Workshop on a
Far Detector in Korea for the J-PARC Neutrino Beam, pp3-14, 2008.
10. ”Summary of the 3rd International Workshop on a Far Detector in Korea for the J-PARC Beam” T. Kajita, et al., Proc.
of the 3rd International Workshop on a Far Detector in Korea for the J-PARC Neutrino Beam, pp151-160, 2008.
11. ”Future of neutrino experiments” T. Kajita, Proc. of the 10th Workshop on High Energy Physics Phenomenology,
Pramana 72, pp109-117, 2009.
12. ”Status and prospects for solar and atmospheric neutrinos” T. Kajita, Proc. of the 10th International Workshop on
Neutrino Factories, Superbeams, and Betabeams (NuFact08), Proceedings of Science (NuFact08), p006, 2008.
13. ”The implications from CANGAROO-III observations of TeV blazar PKS 2155-304”, K. Nishijima, et al., HIGH ENERGY GAMMA-RAY ASTRONOMY: Proceedings of the 4th International Meeting on High Energy Gamma-Ray
Astronomy, AIP Conf. Proc. 1085, 486-489, 2008.
14. ”CANGAROO-III observation of gamma rays from the Galactic Center”, T. Mizukami, et al., HIGH ENERGYGAMMA-RAY ASTRONOMY: Proceedings of the 4th International Meeting on High Energy Gamma-Ray Astronomy,
AIP Conf. Proc. 1085, 364-367, 2008.
15. ”Status of CANGAROO-III”, R. Enomoto et al., HIGH ENERGY GAMMA-RAY ASTRONOMY: Proceedings of the
4th International Meeting on High Energy Gamma-Ray Astronomy, AIP Conf. Proc. 1085, 661-663, 2008.

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16. ”Proceedings of the 5th Fluorescence Workshop”, El Escorial - Madrid, Spain, 16-20 September 2007
17. ”GRB081203A: Ashra-1 observation of early optical and VHE-neutrino emission”, The Ashra-1 collaboration(Y. Aita,
et al.), GCN GRB OBSERVATION REPORT, 8632, 2008.
18. ”MONITORING OF AEROSOLS AND CLOUDS USING AN IMAGING LIDAR BASED ON A HIGHRESOLUTION, WIDE FIELD-OF-VIEW TELESCOPE”, H. Kuze, et al., The 2008 International Laser Radar Conference (ILRC24), S05P11, Boulder, Colorado, USA, June 23-27, 2008.
19. ”Analysis of primary cosmic ray proton and helium components at the knee energy region with the Tibet hybrid experiment”, The Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray
Conference, Merida, Mexico, 3-11 July 2007, vol.2, 117-120, 2008.
20. ”Chemical composition of cosmic rays at the knee measured by the Tibet air-shower-core detector”, The Tibet AS γ
Collaboration(M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.2, 121-124, 2008.
21. ”Future plan for observation of cosmic gamma rays in the 100 TeV energy region with the Tibet air shower array :physics goal and overview”, The Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International
Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 353-356, 2008.
22. ”Future plan for observation of cosmic gamma rays in the 100 TeV energy region with the Tibet air shower array :simulation and sensitivity”, The Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International
Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 357-360, 2008
23. ”A search for 100 TeV celestial gamma rays with the Tibet air shower array and a future prospect”, The Tibet AS γ
Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.2, 575-578, 2008.
24. ”Seven-year observation of multi-TeV gamma rays from the Crab Nebula with the Tibet air shower array”, The Tibet AS γ
Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.2, 799-802, 2008.
25. ”Search for pulsed multi-TeV gamma rays from the Crab pulsar with the Tibet III air shower array”, The Tibet AS γ
Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.2, 783-786, 2008.
26. ”Gamma-hadron separation of parent particles of air showers above several 10 TeV energies using Tibet-III air-shower
array”, The Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 583-583, 2008.
27. ”Study of discrimination between cosmic gamma rays and protons at multi-TeV energies with the Tibet air shower array”,
The Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference,
Merida, Mexico, 3-11 July 2007, vol.3, 1493-1493, 2008.
28. ”The cosmic ray all-particle spectrum in the wide energy range from 1014 eV to 1017 eV observed with the Tibet-III air
shower array”, The Tibet AS γ Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray
Conference, Merida, Mexico, 3-11 July 2007, vol.4, 103-106, 2008.
29. ”Zenith angle dependence of the size spectrum of air showers around the knee observed with the Tibet air shower array”,
Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida,
Mexico, 3-11 July 2007, vol.4, 99-102, 2008.
30. ”Sun’s Shadow in the Solar Cycle 23 Observed with the Tibet Air Shower Array and Comparison with Simulation
Studies”, Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference,
Merida, Mexico, 3-11 July 2007, vol.5, 529-532, 2008.
31. ”Implication of the sidereal anisotropy of 5 TeV cosmic ray intensity observed with the Tibet III air shower array”,
Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida,
Mexico, 3-11 July 2007, vol.5, 593-596, 2008.
32. ”Study on TeV gamma Ray Emission from Cygnus Region Using the Tibet Air Shower”, Tibet ASγ Collaboration (M.
Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007,
vol.2, 695-698, 2008.

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33. ”Two-dimensional observation on TeV Cosmic-ray solar diurnal variation using the Tibet Air Shower Array”, Tibet AS γ
Collaboration (M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico,3-11 July 2007, vol.5, 577-580, 2008.
34. ”The study of Periodic Variation of Cosmic Ray intensity with the Tibet III Air Shower Array”, Tibet ASγ Collaboration(M. Amenomori et al.), Proceedings of the 30th International Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007,
vol.5, 609-612, 2008.
35. ”A Monte Carlo study to measure the energy spectra of the primary heavy components at the knee using a new Tibet AS
core detector array and a large underground muon detector array”, J. Huang et al., Proceedings of the 30th International
Cosmic Ray Conference, Merida, Mexico, 3-11 July 2007, vol.2, 329-332, 2008.
36. ”Tibet Air Shower Array: Results and Future Plan”, Tibet ASγ Collaboration (M. Amenomori et al.), Proceedings of
TAUP2007, Sendai, Japan, Journal of Conference Series 120, 062024-1-3, 2008
37. ”Neutralino dark matter in light Higgs boson scenario”, M. Asano, et al., 16th International Conference on Supersymmetry and the Unification of Fundamental Interactions (SUSY08), (16-21 Jun 2008, Seoul, Korea), AIP Conf. Proc. 1078,
566, 2009.
38. ”Measurements of the model parameter in the littlest Higgs model with T-parity”, M. Asano, et al., International Linear
Collider Workshop (LCWS08 and ILC08), (16-20 Nov 2008, Chicago, Illinois), arXiv:0901.4863 [hep-ph].
39. ”Charged Lepton-Flavor Violation in Beyond-Standard Models”, J. Hisano, Flavor Physics and CP Violation (FPCP
2008), (Taipei, Taiwan, 5-9 May 2008), arXiv:0807.0149 [hep-ph].
40. ”Supersymmetry and cosmology: Inflation, gravitino and axion”, M. Kawasaki, GRAND UNIFIED THEORIES: CURRENT STATUS AND FUTURE PROSPECTS AIP Conf. Proc. 1015, 226, 2008.
41. ”Inflationary cosmology of axion models in supergravity”, K. Nakayama, AIP Conf. Proc. 1040, 61, 2008.
42. ”Gravitational wave background as a probe of reheating temperature of the universe”, K. Nakayama, et al., AIP Conf.
Proc. 1078, 515, 2009.
43. ”Transition of the 11-year solar cycle and its effect on climate change”, H. Miyahara, Proceedings of the symposium on”Historical Records and Modern Science”, 2008.
44. ”Study on cosmic ray variations using beryllium-10 in Dome Fuji Shallow Ice core”, H. Miyahara, et al., Malt Annual
Report, 2008.
45. ”Variation of the solar cycle length during the grand solar minimum in the 4th century B.C. deduced from 14C contents
in Japanese camphor tree rings”, K. Nagaya, et al., Summaries of Researches Using AMS at Nagoya University(XX),2008.

(c) ICRR Reports
1. ICRR-Report-526-2008-1”Search for TeV Gamma-ray Emission from Clusters of Galaxies with CANGAROO-III Imaging Atmospheric
Cherenkov Telescopes”
Ryuta Kiuchi
2. ICRR-Report-527-2008-2 (October 31, 2008)”Non-Gaussianity from isocurvature perturbations”
Masahiro Kawasaki, Kazunori Nakayama, Toyokazu Sekiguchi, Teruaki Suyama and Fuminobu Takahashi
3. ICRR-Report-528-2008-3 (September 16, 2008)”Non-Gaussianity from Baryon Asymmetry”
Masahiro Kawasaki, Kazunori Nakayama and Fuminobu Takahashi
4. ICRR-Report-529-2008-4 (October 1, 2008)”A General Analysis of Non-Gaussianity from Isocurvature Perturbations”
Masahiro Kawasaki, Kazunori Nakayama, Toyokazu Sekiguchi, Teruaki Suyama and Fuminobu Takahashi
5. ICRR-Report-530-2008-5 (October 9, 2008)”Hilltop Non-Gaussianity”
Masahiro Kawasaki, Kazunori Nakayama and Fuminobu Takahashi

68

6. ICRR-Report-531-2008-6 (October 10, 2008)”Positron/Gamma-Ray Signatures of Dark Matter Annihilation and Big-Bang Nucleosynthesis”
Junji Hisano, Masahiro Kawasaki, Kazunori Kohri and kazunori Nakayama
7. ICRR-Report-532-2008-7 (February 6, 2009)”A Realistic Extension of Gauge-Mediated SUSY Breaking Model with Superconformal Hidden Sector”
Masaki Asano, Junji Hisano, Takashi Okada, and Shohei Sugiyama
8. ICRR-Report-533-2008-8 (November 4, 2008)”Cosmological Moduli Problem from Thermal Effects”
Kazunori Nakayama and Fuminobu Takahashi
9. ICRR-Report-534-2008-9 (January 21, 2009)”Precision Measurements of Little Higgs Parameters at the International Linear Collider”
Eri Asakawa, Masaki Asano, Keisuke Fujii, Tomonori Kusano, Shigeki Matsumoto, Rei Sasaki, Yosuke Takubo andHitoshi Yamamoto
10. ICRR-Report-535-2008-10 (December 17, 2008)”Neutrino Signals from Annihilating/Decaying Dark Matter in the Light of Recent Measurements of Cosmic Ray Electron/Positron Fluxes”
Junji Hisano, Masahiro Kawasaki, Kazunori Kohri and Kazunori Nakayama
11. ICRR-Report-536-2008-11 (January 23, 2009)”Cosmic Rays from Dark Matter Annihilation and Big-Bang Nucleosynthesis”
Junji Hisano, Masahiro Kawasaki, Kazunori Kohri, Takeo Moroi and Kazunori Nakayama
12. ICRR-Report-537-2008-12 (February, 2009)”Search for Nucleon Decay into Charged Antilepton plus Meson in Super-Kamiokande”
Haruki Nishino
13. ICRR-Report-538-2008-13 (February 9, 2009)”Study of Non-Standard Neutrino Interactions with Atmospheric Neutrino Data in Super-Kamiokande”
Mitsuka Gaku

D. Doctoral Theses
1. ”Study of Non-Standard Neutrino Interactions with Atmospheric Neutrino Data in Super-Kamiokande”,
G. Mitsuka,
Ph.D Thesis, Mar. 2009.
2. ”Search for Nucleon Decay into Charged Antilepton plus Meson in Super-Kamiokande”,
H. Nishino,
Ph.D Thesis, Mar. 2009.
3. ”Search for TeV Gamma-Ray Emission from the Supernova Remnant W44 with the CANGAROO-III Telescopes”,
Yohei Yukawa,
Ph.D. Thesis, Mar. 2009.

69

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
H.Sagawa. 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 2008 fiscal year were:
No.66 (Jun 6, 2008)• Address from new director of ICRR, Takaaki Kajita.
• Address from ex-director of ICRR, Yoichiro Suzuki.
No.67 (Nov 30, 2008)• XMASS experiment, Yoichiro Suzuki.
• Detection for eigenfrequency of the Earth, Yoshiaki Tamura.
• Commemoration about ex-director of ICRR, Yoji Totsuka, Takaaki Kajita.
• Commemoration about Yoji Totsuka, Masayuki Nakahata.
• Report on ICRR open campus 2008, Hideo Itoh.
• Announcements.
• Self-introduction/Staff reassignment.
• ICRR-Seminar/Report.

(b) Public Lectures• ”Science Cafe for Novel Prize of Physics 2008”
Mar 1 2009, Kashiwa, Chiba,
Hideo Itoh(ICRR, University of Tokyo)• ”Neutrino on Elementary Particles”
Jan 12 2009, Saga,
Hideo Itoh(ICRR, University of Tokyo)• ”Concern between elementary particles and the universe”
Dec 12 2008, Mitaka, Tokyo,
Hideo Itoh(ICRR, University of Tokyo)• ”Pioneer of Elementary Particle Physics and Advanced Study of the one”
Jan 25 2009, Daiba, Tokyo,
Hideo Itoh(ICRR, University of Tokyo)

70• ”Modern Picture of the Universe”
Mar 15 2009, Higashi-Nakano, Tokyo,
Hideo Itoh(ICRR, University of Tokyo)• ”About Novel Prize of Physics 2008”
Mar 15 2009, Higashi-Nakano, Tokyo,
Hideo Itoh(ICRR, University of Tokyo)• ”What’s symmetry? -About Novel Prize 2008”
Nov 15 2008, Matsue, Shimane,
Hideo Itoh(ICRR, University of Tokyo)• ”Concern between elementary particles and the universe”
Mar 14 2009, Matsue, Shimane,
Hideo Itoh(ICRR, University of Tokyo)• ”Searching the universe using small small particles”
Apr 18 2008, Kashiwa, Chiba,
Hideo Itoh(ICRR, University of Tokyo)• ”Message from the universe”
Oct 18 2008, Katsushika, Tokyo,
Hideo Itoh(ICRR, University of Tokyo)• ”How to search the cosmic ray”
Jan 15 2009, Yubari, Hokkaido,
Hideo Itoh(ICRR, University of Tokyo)• ”Picture of the universe using elementary particles and cosmic ray”
Apr 18 2008, Kashiwa, Chiba,
Hideo Itoh(ICRR, University of Tokyo)• ”Picture of the universe using elementary particles and cosmic ray”
Jul 18 2008, Atsugi, Kanagawa,
Hideo Itoh(ICRR, University of Tokyo)• ”Public Lecture on Neutrino”,
April 12 2008, Kashiwa, Chiba,”Studying mysteries of neutrino using neutrino beam”, Tsuyoshi Nakaya (Kyoto University).
”Neutrino is dominating the universe -Role of neutrino in cosmology-”, Naoshi Sugiyama (ICRR, University of Tokyo).

(c) Visitors
KASHIWA Campus (Total: 3 groups, 31 people)• Chiba Advanced Technology Experience Program• MEXT Science Partnership Project (SPP): total 2 schools
KAMIOKA Observatory (Total: 136 groups, 2981 people)• Yumeno Tamago Jyuku (Hida Academy for High School Students)• MEXT Super Science High School (SSH) project: total 4 schools• Schools and Universities: total 34 groups• Others: 97 groups

71

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
Over Sea Facilities
Other

39
10
4
2
6
4
16
18

39
10
4
2
6
4
16
18

554
73
96
19
35
94
153
241

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

35
45
9
10

35
45
9
10

502
516
167
80

OthersConferences
Special Activity on Abroad

3
0

3
0

55
0

Research Titles
1. Energy calibration for Super-Kamiokande
2. Study of solar neutrino energy spectrum
3. Study of simulation for atmospheric neutrino
4. Study of nucleon decay p → ν K
5. Study of the low energy solar neutrinos
6. Study of solar neutrino energy spectrum
7. Precise measurement of Day/Night effect for B8 solar neutrinos
8. Sidereal daily variation of 10TeV galactic cosmic-ray intensity observed by the Super-Kamiokande
9. Study for Supernova monitor
10. Development of the new online DAQ system for Super-Kamiokande
11. Study of flavor identification of atmospheric neutrinos
12. Study for the electron neutrino appearance search in the T2K experiment
13. Study in upward-going muons and high energy neutrinos
14. Study of Supernova Relic Neutrinos
15. Search for Nucleon Decay
16. Development of neutrino-nucleus interactions for the precise neutrino oscillation experiment

72

17. Search for proton decay via e+ π 0 mode
18. R&D of a 1Mton water Cherenkov Hyper-Kamiokande
19. Study of atmospheric neutrinos and neutrino oscillations
20. Neutrino interaction study using accelerator data
21. R&D of J-PARC-Kamioka Long Baseline Experiment T2K
22. Study for lowering backgrounds of radioisotopes in large volume detectors
23. Direction-sensitive dark matter search experiment
24. Study of purification system for liquid xenon
25. Development of InP detector for measurement of solar ν
26. Design of detector for dark matter search by using simulation
27. Study on absorption and scattering of vacuum ultraviolet light in liquid xenon
28. A study on emission spectrum of liquid xenon
29. Study of ambient gamma-ray and neutron flux at Kamioka Observatory
30. Development of low concentration radon detection system
31. R&D for the Astroparticle Detector by using Liquid Xenon
32. 3-flavor Oscillation study in atmospheric neutrinos
33. Scintillation efficiency for the liquid xenon detector
34. Direct dark matter search with liquid xenon detector
35. Study for double beta decay of 48Ca
36. Study of the formation and the evolution of the Universe with prompt observations of gamma-ray bursts
37. Observation of Galactic Cosmic ray by the Large Area Muon Telescope
38. Observation of the highest energy Solar Cosmic Rays
39. Observation of solar neutrons in solar cycle 24
40. Ecophysiological studies of alpine plants
41. A Study of the Radiation Damage to Polyimide film
42. Space weather observation using muon hodoscope at Mt.Norikura
43. Continuous observation of microbarographs at high mountains
44. Study of particle acceleration in electric field using X and gamma rays from lightning and thunderclouds
45. Observation of nightglow and its reflected and scattered light on the mountain
46. Adaptive strategies in community structure and leaf characteristics of alpine plants related to snow gradient
47. Field test of natural electric power supply at Mt. Norikura-dake
48. Observation of high-energy cosmic-ray electrons with emulsion chambers
49. A study of cosmic ray interactions by hybrid experiment on Mt. Chacaltaya
50. Study of Galactic Diffuse Gamma Rays
51. Observation of TeV gamma-ray spectra from galactic objects
52. Data Analysis of the UHECR data for the Auger Project

73

53. Basic Study for Cherenkov Telescopes of Next Generation
54. A R&D for a new atmospheric monitoring system
55. Study of the composition of cosmic-rays at the knee
56. CANGAROO-III Observation of gamma-rays in the southern sky
57. Study of the emission mechanism of unidentified TeV gamma-ray source based on the multi-wavelength spectrum
58. Observation with All-sky Survey High Resolution Air-shower detector Ashra
59. Experimental Study of High-energy Cosmic Rays in the Tibet AS γ experiment
60. Development of advanced photon counter for the future IACT
61. Sidereal daily variation of 10TeV galactic cosmic-ray intensity observed by the Tibet air shower array62. Improvement of characteristics of the image sensor used in Ashra
63. Cosmic ray interactions in the knee and the highest energy regions
64. Bolivian Air Shower Joint Experiment
65. Application of Fast Image-delay Tube to Sky Survey for Cosmic Rays
66. Measurement of the temperature characteristics of YAP for TA fluorescence detectors
67. R&D for the Next Generation VHE Gamma-Ray Telescope
68. Observation of very-high-energy gamma-rays in Australia
69. Composition Study with the Telescope Array Data
70. Development of the optical fiber image transfer system for Ashra
71. A study on variation of interplanetary magnetic field with the cosmic-ray shadow by the sun
72. Workshop on ’“High Energy Gamma-ray Astrophysics”
73. Optical observations of transient high-energy sources in the southern sky
74. Search for High Energy Gamma-ray Emission from Star Forming Regions and Theoretical Research
75. Improvement of the CANGAROO-III immediate data analysis system
76. Observation of UHE cosmic rays and TeV gamma rays with Ashra detector
77. Study of absolute energy calibration air shower by compact Electron LINAC
78. Study of radio detection of highest energy cosmic rays
79. Study of Extremely-high Energy Cosmic Rays by Telescope Array
80. Study on High Energy Cosmic-Ray source by Observation Using Long Duration Balloon
81. R&D and Design of large-scale cryogenic gravitational wave telescope (IX)
82. Study of effective thermal shielding method for the LCGT cryostat
83. Development of Sapphire Mirror Suspension for LCGT (IV)
84. Development of a high-power laser system for CLIO
85. Gravitational Wave Detector in Kamioka (VII)86. digital Control of CLIO and Its Analysis
87. An research of the Earths free oscillations based on simultaneous observations with a laser strainmeter and a superconducting gravimeter

74

88. Evaluation of a fiber-coupled laser stabilization system
89. Evolution of the universe and particle physics
90. Deposition Rate variation of natural activities 7 Be and 210 Pb
91. Continuous Measurement of Underground Laboratory Environment
92. Chemical study for Antarctic micrometeorites
93. Determination of 26 Al in small Antarctic meteorite samples
94. Comprehensive Researches on Cosmic Dusts
95. Detection of time variations for cosmogenic Be-7, Na-22
96. Detection of low level radioisotopes in tree rings
97. Precise calculation of the atmospheric neutrino flux
98. Monte Carlo Simulation Data Generation for the IceCube experiment
99. Neutrino workshop

75

G. List of Committee Members(a) Board of Councillors
KAJITA, Takaaki
FUKUSHIMA, Masaki
SUZUKI, Yoichiro
KAWASAKI, Masayuki
YAMAMOTO, Masayuki
HIRAO, Kimihiko
TAKASAKI, Tadafumi
EGUCHI, Toru
MIYAMA, Shoken
SATO, Fumitaka
YAMAZAKI, Toshimitsu
MURAKI, Yasushi
MIZUTANI, Kouhei
INOUE, Hajime
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
Konan University
University of Tokyo
Konan University
Saitama University
Institute of Space and Astronautical Science
ICEPP, University of Tokyo(b) Advisory Committee
KAJITA, Takaaki
TORII, Shoji
KAJINO, Fumiyoshi
ITOW, Yoshitaka
TERASAWA, Toshio
SAITOH, NaotoNISHIKAWA Koichiro
KODAMA, Hideo
AIHARA, Hiroaki
FUKUSHIMA, Masaki
MORI, Masaki
FUKUGITA, Masataka
NAKAHATA, Masayuki
SUZUKI, Yoichiro
KURODA, Kazuaki

ICRR, University of Tokyo
Waseda University
Konan University
STEL, Nagoya University
Tokyo Institute of Technology
KEK
KEK
KEK
University of Tokyo
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) User’s Committee
KAJINO, Fumiyoshi
NISHIJIMA, Kyoshi
TORII, Shoji
OGIO, Shoichi
MATSUBARA, Yutaka
YOSHIDA, Shigeru
SAKURAI, Takahisa
MUNAKATA, Kazuki
OHASHI, Masataka
HAYATO, Yosinari
SAGAWA, Hiroyuki
KANEYUKI, Kenji
TAKITA, Masato
HISANO, Junji

Konan University
Tokai University
Waseda University
Osaka City University
Nagoya University
Chiba University
Yamagata University
Shinshu 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

76

H. List of Personnel
Director

KAJITA Takaaki

Vice-Director

FUKUSHIMA Masaki

Kamioka Observatory (Neutrino and Astroparticle Division)
Scientific Staff
SUZUKI Yoichiro,
NAKAHATA Masayuki,
TAKEUCHI Yasuo,
SHIOZAWA Masato,
YAMASHITA Masaki,
MIURA Makoto,
KOSHIO Yusuke,
KAMEDA Jun,
ABE Ko,SEKIYA Hiroyuki,
NAKAYAMA Shoei,
OGAWA Hiroshi,
Chief Secretary
KAIZU Satoshi
Technical Staff
MIZUHATA Minoru,
KANBE Tomio,
Research Fellow
TAKENAGA Yumiko,
WATANABE Hideki
Secretary
OKURA Youko,
MAEDA Yukari,
Research Center for Cosmic Neutrinos (Neutrino and Astroparticle Division)
Scientific Staff
KAJITA Takaaki,
KANEYUKI Kenji,
SAKURAI Yoshihisa
Technical Staff
SHINOHARA Masanobu
Research Fellow
SHIMIZU Yuki,
TANIMOTO Naho,
Athar Mohammad Sajjad
Secretary
WATANABE Keiko,
KITSUGI Atsuko
High Energy Cosmic Ray Division
Scientific Staff
FUKUSHIMA Masaki,
ENOMOTO Ryoji,
SASAKI Makoto,
TAKEDA Masahiro,
OHISHI Michiko,Technical Staff
AOKI Toshifumi,
Research Fellow
TOKUNO Hisao,
KAWATA Kazumasa,
WANG Xiao,
Secretary
SAWANO Sumiko,
TATSUMI Fusako

MORI Masaki,
YOSHIKOSHI Takanori,
HAYASHIDA Naoaki,
OHNISHI Munehiro,
KOBAYASHI Takahide
SHIBATA Tatsunobu,
KONDO Yoshimi,
KIUCHI Ryuta
KOKUBUN Yayoi,

MORIYAMA Shigetaka,
HAYATO Yoshinari,
OBAYASHI Yoshihisa,
TAKEDA Atsushi,
YAMADA Satoru,
KOBAYASHI Takashi
KUMAMARU Seiichi
OKADA Eri
OKUMURA Kimihiro,
KAJI Hiroshi,

TAKITA Masato,
SAKURAI Nobuyuki,
ASAOKA Yoichi
NONAKA Toshiyuki,
HUANG Jing,YAMAKAWA Toshie,

AKENO Observatory (High Energy Cosmic Ray Division)
Scientific Staff
SAGAWA Hiroyuki
Technical Staff
OHOKA Hideyuki,
KAWAGUCHI Masami
Norikura (High Energy Cosmic Ray Division)
Technical Staff
YAMAMOTO Kuniyuki,
ISHITSUKA Hideki,
Astrophysics and Gravity Division
Scientific Staff
FUKUGITA Masataka,
OHASHI Masatake,
MIYOKI Shinji,
Research Fellow
HIRAMATSU Teruaki,
AOKI Mayumi
Secretary
KIKUCHI Rie

AGEMATSU Yoshiaki,
SHIMODAIRA Hideaki

USHIMARU Tsukasa,

KURODA Kazuaki,
YASUDA Naoki,
UCHIYAMA Takashi
ASANO Masaki,

KAWASAKI Masahiro,HISANO Junji,
SUYAMA Teruaki,

77

Graduate Students
DoctorMaster

IKEDA Daisuke,
YUKAWA Yohei,
SAKO Takashi,
AITA Yuichi,
UESHIMA Kota,
NISHINO Haruki,
McLACHLAN Thomas Fukuei,
AGATSUMA Kazuhiro,
KANZAKI Toru,
NAKAYAMA Kazunori,
KONISHI Kohki
YAMAKAWA Yuichi,
KUNISAWA Toshiki,
NAGAI Yuichiro,
HIGASHI Yuhei,
UENO Koh,
YOKOZAWA Takaaki,
SAITOH Takanori,
SAIKAWA Kenichi,
OKADA Takashi,
YOKOZAWA Takaaki,

Administration Division
Scientific Staff
ITOH Hideo
Administrative Staff
NAGANEO Nobuyoshi,
IRIE Makoto,
AKIYAMA Makiko,
SAITO Akiko,
IIDA Nobuyuki

KIDO Eiji,

TAKETA Akimichi,

NODA Koji,
IIDA Takashi,
ISHIHARA Chizue,

CHONAN Tsutomu,
MITSUKA Gaku,
IKEDA Motoyasu,

TAKAYAMA Tsutomu,

SEKIGUCHI Toyokazu,

RYOKI Shinichi,
INOUE Daisuke,

NAKAYAMA Koichi,

NAKAJIMA Yuha,

KOHZUMA Yuki,

MORIOKA Tomoko,
MIYAMOTO Koichi,
KAWAKAMI Etsuko,
RYO Masaki

ARASHIBA Soichi,
YAMAMOTO Yusuke,

SETO Mikako,
MATSUMOTO Kenichi,
NISHIMORI Tomoe,
MARUMORI Yasuko,

SASADA Takaaki,
ARIDOME Ryutaro,
YAMAGUCHI Akiko,