INSTITUTEFORCOSMIC RAY RESEARCH
UNIVERSITY OF TOKYOANNUAL REPORT(APRIL 2007 – MARCH 2008)

Editorial Board
OHASHI, Masatake
OBAYASHI, Yoshihisa
TAKITA, Masato
KANEYUKI, Kenji
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 Division32

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

49

Norikura Observatory

50

Akeno Observatory

54

Kamioka Observatory

56

Research Center for Cosmic Neutrinos

57................................................................

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

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

61

Appendix D. Doctoral Theses.............................................................................

66

Appendix E. Public Relations.............................................................................

66

Appendix A. ICRR International Workshops
Appendix B. ICRR Seminars

Appendix C. List of Publications — 2006 fiscal year(a) Papers Published in Journals(b) Conference Papers(c) ICRR Report(a) ICRR News(b) Public Lectures(c) Visitors
Appendix F. Inter-University Researches...................................................................

68

Appendix G. List of Committee Members..................................................................

72............................................................................

73(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 2007.
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 and Poland).
Many exciting scientific activities are described in this report. One of the highlights is thestart of the Telescope Array experiment, which is a very large scale cosmic ray experiment tostudy the highest energy cosmic rays. We hope that this report is useful for the understanding of the current research activities of ICRR. Finally, we appreciate very much the strong
support of our colleagues in this research field, the University of Tokyo and the Japanese
Ministry of Education, Culture, Sports, Science and Technology. They are indispensable forthe continuing, and exciting scientific outcome of ICRR.

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

The ICRR building at Kashiwa,
Chiba, Japan.

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

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 Arrayexperiment under construction in
Utah, USA for the study 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 2007
Scientific
Staff

Technical
Staff

Research
Fellows

18
13
8
0
39

5
11
0
0
16

3
10
4
1
18

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

Administrators
andSecretaries
13
4
1
13
31

39
38
13
14
104

FY 2002–2007 Budget
Personnel
expenses
Nonpersonnel
expenses
Total

2002

2003

2004

2005

2006

2007

460 332

434 874

539 000

465 000

566 000

624 000

1 518 065

1 785 449

1 902 000

1 822 000

812 000

1 253 000

1 978 397

2 220 323

2 441 000

2 287 000

1 378 000

1 877 000
(in 1 000 yen)

1

RESEARCH DIVISIONS
Neutrino and Astroparticle Division
Overview
Super-Kamiokande Experiment
K2K 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
TAMA Project
LCGT Project
CLIO Project
Sloan Digital Sky Survey
Theory Group
Lepton Flavour Violating τ Decays in the Left-Right Symmetric Model
Probing Majorana Phases and Neutrino Mass Spectrum in the Higgs Triplet Model at the LHC
Unitarity bounds in the Higgs model including triplet fields with custodial symmetry
Neutralino Dark Matter in Light Higgs Boson Scenario
Relic abundance of dark matter in universal extra dimension models with right-handed neutrinos
Primordial Non-Gaussianity in Multi-Scalar Slow-Roll Inflation
Non-Gaussianity in the modulated reheating scenario
Primordial Non-Gaussianity in Multi-Scalar Inflation
Non-Gaussianity, Spectral Index and Tensor Modes in Mixed Inflaton and Curvaton Models”Flavored” Electric Dipole Moments in Supersymmetric Theories
Stability of Metastable Vacua in Gauge Mediated SUSY Breaking Models with Ultra Light Gravitino
Cosmological constraints on neutrino injection
Affleck-Dine leptogenesis via multiscalar evolution in a supersymmetric seesaw model
Formation of IMBHs as PBHs in the inflationary cosmology with running spectral index
Increasing effective number of neutrinos by decaying particles
Baryon Asymmetry in Heavy Moduli Scenario
Nonthermal dark matter in mirage mediation
Cosmological implications of supersymmetric axion models
Space laser interferometers can determine the thermal history of the early Universe
Cosmological Constraints on Isocurvature and Tensor Perturbations
Primordial Helium Abundance from CMB: a constraint from recent observations and a forecast
Probing the Effective Number of Neutrino Species with Cosmic Microwave Background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
11,146 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 θ 13 ) 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 had been
performed at the underground laboratory and the constructionof the 800 kg detector was started from 2007.
Recent progress of research activities in the Neutrino andAstroparticle division is presented here.

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, (ν μ + 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 12,180 fully-contained (FC) events and911 partially-contained (PC) events during 1489 days of datataking and SK-II observed 6605 FC events and 427 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

Table 1. Summary of the atmospheric ( μ /e)data /( μ /e)MC (≡ R) ratio
measurement.

SK-I
Data
Sub-GeV
e-likeμ -likeR
Multi-GeV
e-likeμ -like(FC+PC)
R

SK-II
MC

Data

MC

3353
2879.83227
4212.80.658±0.016±0.035

1842
1554.51723
2215.40.656±0.022±0.033

746
680.5
1562
2029.50.702+0.032−0.030 ±0.101

417
426.2
806
1103.80.746 +0.047−0.044 ±0.056

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” (E vis <1330 MeV) and “multi-GeV” (E vis > 1330 MeV) samples.
The numbers of observed and predicted events for sub- andmulti-GeV energy regions in SK are summarized in Table 1.
The prediction is based on the recent precise measurements ofprimary cosmic rays by BESS, AMS and a three dimensional
calculation of the neutrino flux by Honda et al. The hadronicinteraction model of cosmic rays is also improved in the calculation.
Among FC events, single-ring events are identified as elike or μ -like based on a Cherenkov ring pattern. All the PC
events were assigned to be multi-GeV μ -like. Using the number of e-like and μ -like events, the ratio of (μ /e) was obtained
and it is significantly smaller than the expectation as shown in
the table. The momentum resolution of SK-II is slightly worse
than SK-I. This is because the number of ID PMTs in SK-II
is about half that of SK-I. However, the performance of thevertex reconstruction, the ring counting, and the particle identification in SK-II are almost the same as in SK-I.
The zenith angle distributions for the sub- and multi-GeV
samples are shown in Fig. 1. 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 were compared with the Monte Carlo expectation
without neutrino oscillations and the best-fit expectation forνμ ↔ ντ oscillations. The oscillated Monte Carlo reproduced
the zenith angle distributions of the data well. Some fraction of the multi-ring events is also subdivided into e-like andμ -like events using the event pattern of the most energetic
Cherenkov ring in each event. Fig. 2 shows the zenith angle
distribution of multi-ring events which also agrees well withthe expectation from neutrino oscillations.
Energetic atmospheric ν μ ’s passing through the Earth in-

3

SK-I + SK-II
Sub-GeV μ-like

Number of Events

Number of Events

Sub-GeV e-like
600
500
400
300
200
100

225
200
175
150
125
100
75
50
25
0
-1

-0.5
0
0.5
cosΘ
Multi-GeV e-like

1

Number of Events

Number of Events

0
-1

800
700
600
500
400
300
200
100
0
-1

-0.5
0
0.5
1
cosΘ
Multi-GeV μ-like + PC

500
400
300
200
100

-0.5

0

0.5

0
-1

1

-0.5

cosΘ

0

0.5

1

cosΘ

teract 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. Fig. 2 shows thezenithangle distributions of those upward muons. They agreewith the MC expectation assuming neutrino oscillations.
We carried out a neutrino oscillation analysis using theentire SK-I and II atmospheric neutrino data set. Fig. 3
shows the allowed neutrino oscillation paramteer regions forνμ ↔ ντ oscillations. The best fit oscillation parameters are
sin2 2θ = 1.0 and Δm 2 = 2.5 × 10−3eV2 . The allowed oscillation parameter range is sin 2 2θ > 0.93 and Δm 2 = (1.9 −3.1) × 10−3eV2 at 90 % C.L.

Fig. 1. The zenith angle distributions for sub-GeV e-like, sub-GeV
μ -like, multi-GeV e-like and multi-GeV (FC+PC) μ -like events.
cosΘ =1 means 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
with sin2 2θ = 1.0 and Δm2 = 2.5 × 10−3 eV2 .

-2

SK-I + SK-II2

2

Δm (eV )

10

180
160
140
120
100
80
60
40
20
0
-1

Multi-ring μ-like

Multi-ring e-like

Number of Events

180
160
140
120
100
80
60
40
20
0
-1

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

250
200
150

-3

10

100

-0.5

0

0.5

-0.5
0
0.5
1
cosΘ
Upward Through Going μ
600
500

cosΘ

0

0.9

1

Fig. 3. Allowed region of νμ → ντ neutrino oscillation parameters obtained by SK using contained atmospheric neutrino events andupward-going muon events.

400
300
200
100

-0.8 -0.6 -0.4 -0.2

0.8

0
-1

1

cosΘ
Upward Stopping μ0.7

sin22θ

50

Number of Events

Number of Events

Number of Events

SK-I + SK-II

0-1-0.8 -0.6 -0.4 -0.2

0

cosΘ

Fig. 2. The zenith angle distributions for multi-ring sub-GeV μ -like(upper left) and multi-ring multi-GeV μ -like (lower left) samples.
The zenith angle distributions of upward stopping muons (upper
right) and upward through-going muons (lower right). The red histograms show the MC expectation without neutrino oscillations.
The green histograms show the expected flux for the νμ ↔ ντ oscillation with sin2 2θ = 1.0 and Δm2 = 2.5 × 10−3 eV2 .

The atmospheric neutrino data is well described by neutrino oscillations as shown above. In this case, the survival
probability of a ν μ 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 ν μ 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

4
-2

2

2

Δm (eV )10

99% C.L.
90% C.L.
68% C.L.
-3

10
0.7

0.8

0.9

sin 2θ
Fig. 5. 68, 90 and 99 % C.L. allowed oscillation parameter regions for
2-flavor νμ ↔ ντ oscillations obtained in the L/E analysis.

Likelihood

2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

1

2

TAU+BKG

100

Number of Events

Data/Prediction (null oscillation)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 andMonte Carlo events. We applied a cut to reject low energy or
horizontal-going events since they have either large scattering
angles or large dL/dΘ zenith .
Fig. 4 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 ν μ ↔ ντ oscillations. The best-fit expectation shown in the figure corresponds to (sin 2 2θ , Δm2 ) =(1.00, 2.3 × 10 −3eV2 ). Fig. 5 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 the sinusoidal function predicted by neutrino flavor oscillations.

BKG
DATA
75

50

25

1

10

10

2

10

3

10

4

L/E (km/GeV)
Fig. 4. 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.

Another interest is an observation of ν τ in the atmospheric
neutrinos since there has not yet been evidence for appearance of ντ charged current interactions due to ν μ ↔ ντ oscillations. We have performed a search for the ν τ appearance
by using the SK-I atmospheric neutrino data [4]. 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 ν eevents. 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.

0
-1

-0.5

0

0.5

1

cosθ
Fig. 6. 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.

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 ν τenriched sample to a combination of the expected ν τ and theatmospheric neutrinos (ν μ and νe ) including oscillations at
sin2 2θ = 1.0 and Δm 2 = 2.1 × 10−3 eV2 . Fig. 6 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 thewiththeneuralnetwork
likelihood analysis and 134 ± 48 +16.0−27.2
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5

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, Δm 223 ∼ Δm213 ≡Δm2 >> Δm212 was assumed. If the parameter θ 13 in the
mixing matrix of lepton sector (MNS matrix) is finite, neutrino oscillations among ν μ ↔ 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. 7 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[5].

neutrino. We assume that the mass variation of the neutrinos
depends only upon the electron density of the environment,a possible effect from radiative couplings of active neutrinos
and electrons. To test for this density dependence, we replace Δm2 in the equation for the oscillation probability with
an effective mass difference that is proportional to the electron density of the medium, Δm 2 → Δm2 × ( ρρ0e )n , where ρeis the electron density of the matter, n parameterizes the density dependence and ρ 0 is set at 6.02 × 1023e/cm3 . Figure 8
shows the relative-χ 2 confidence level contours on the Δm 2
versus n plane. A minimum χ 2 =174.3/178 d.o.f. is obtainedat (n,Δm2 )=(-0.04, 1.95 × 10 −3eV 2 ). This result is consistent
with the standard 2-flavor oscillation result [6].

-2

2

2

2

Δm (eV )2

Δm (eV )

10

-3

10

-3

SK 90% C.L.
SK 99% C.L.
CHOOZ 90% CL exclude

10
0

0.1

0.2

0.3

0.4

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

-0.5 -0.4 -0.3 -0.2 -0.1 0

0.1 0.2 0.3 0.4 0.5

n

0.5

2

sin θ13-2

Fig. 8. relative- χ 2 confidence level contours on the Δm2 versus nplane.

10

2

2-Δm (eV )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 [7] [8].

-3SK 90% C.L.
SK 99% C.L.
CHOOZ 90% CL exclude

10
0

0.1

0.2

0.3

0.4

0.5

2

sin θ13
Fig. 7. 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.

We also consider possible consequences of the mass varying neutrino (MaVaN) model. In this model, the neutrino masscan vary depending on the matter density along the path of the

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 neutrino flux with accurate informationof 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.

10

10

10

10

-3

Number of events/day/22.5kt/0.5MeV

10

2

Δm in eV

2

6

-4

-5

-6

4

After noise reduction
After pre-ambient BG cut
After spallation cut
After ambient BG reduction
Final data sample
Mark; SK-I PRD73 112001
Color; SK-III After SLE 110 days

10
3

10

2

10
10
1

-7

-1

10

6
10

10

8

10

-8

Fig. 10. The data reduction steps in SK-III in the 22.5 kton fiducial
volume. The colored lines are from SK-III, and the black plots arefrom SK-I.

νe→νμ/τ (95%C.L.)

-9

-4

10

-3

10

10

-2

12
14
Energy [MeV]

-1

10

1

10
10
2
tan (Θ)2

Fig. 9. The excluded areas from SK-I and SK-II. The purple region is
SK-II only, and the light blue region is SK-I with SK-II. The blackline shows SK-I only. [1]

1.5

1.5

1

1

0.5

0.5

Events/day/bin

In this year, we have submitted the final results of
the SK-II solar neutrino analysis [1]. The live-time is791 day between 2002 Dec. 24 and 2006 Oct. 5. The
analysis energy threshold for the flux measurement set
at 7.0 MeV. The obtained number of signal events is+483.387212.8 +152.9−150.9(stat.)−461.6 (syst.). The corresponding B solar
6−2 −1
neutrino flux is 2.38± 0.05 (stat.) +0.16
s .
−0.15 (syst.) ×10 cm
This is consistent with the SK-I result. Figure 9 shows the excluded areas from SK-I and SK-II. The evidence of increased
exclusion can be seen with the addition of SK-II data in theplot.
The SK-III solar neutrino observation with a 5 MeV energy threshold was started from Jan. 24, 2007. We have applied preliminary analysis tools, which are basically identicalto SK-I, then compared the first SK-III SLE data with SK-I.
The data used for this analysis were from January 24 until October 4, 2007. The live time was 110 days for the 5–20 MeV
data sat.
Figure 10 shows the low-energy data reduction steps.
Most of the additional low-energy background events can be
reduced by the pre-ambient BG cut. Then, agreement of SKIII and SK-I in 22.5 kton looks quite good.
However, if we choose the central 7.5 kton region of the
SK detector, the observed event rate in SK-III is lower than
SK-I. Figure 11 shows the angular distributions of the final
data sample in the different energy region in the 7.5 kton center region. The background rates in the lower energy region

0
-1
1.5

0
cosθsun 5.0-5.5MeV

1

0
-1
2

0
cosθsun 5.5-6.5MeV

10cosθsun 8-14MeV

1

1
1
0.5

0
-1

0
cosθsun 6.5-8MeV

1

0
-1

Fig. 11. The angular distribution in the central region of the SK detector. The red and blue plots correspond to SK-I and SK-III, respectively. The vertical and horizontal lengths are 16m and R2 ≤150 m2 , and the fiducial volume is 7.5 kton in these plots.

7

shows improvement in SK-III though the signal rates looks
consistent. We think this is due to the water system upgrades
and improved analysis tools in SK-III. We are currently accumulating more low-energy data.

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 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 the photo-coverage area about half (19%) in SKII, we achieved high detection efficiency of signals (43.7%)
and low background levels (0.11 events in 49.2 kt·yrs). 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.
In addition, we looked for SUSY favored decay modes
which include K mesons in 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 decay of K + .
Figure 12 shows the comparison between data and fitting results of muon momentum distribution for single-ring μ -likeevents. We observed no excess of signal. In other modes,
there are no significant signal excess. Therefore we conclude
that there is no evidence of nucleon decays and we calculatedpartial lifetime limits taking into account systematic uncertainties. Obtained limits are 2.3 × 10 33, 1.3 × 1032, 1.3 × 1033
and 1.0 × 10 33 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
antineutron 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 × 10 8 sec.

number of events

Search for nucleon decay

data
atmνMC (best fit)+p→νK MC

60

40

20

0
200

225

250

275

300

μ momentum (MeV/c)
Fig. 12. The comparison between data and fitting results of muon momentum distribution for single-ring μ -like events. The filled circles
show data with statistical errors. The solid line shows p → ν̄ K +MC. The dashed line shows the best fitted atmospheric neutrino
MC with free normalization.

Supernova neutrinos
Kamiokande and IMB observed the neutrino burst fromsupernova 1987a. Those observations confirmed that the energy release by neutrinos is about several×10 53erg. SuperKamiokande is able to detect several thousand neutrino events
if it happens near the center of our galaxy. Until now, no clear
neutrino burst from a supernova has been observed in SuperKamiokande. We have performed 3 kinds of neutrino burst
searches in SK-I and SK-II and published the results [2].
In this year, we have summarized the preliminary resultsof the Supernova Relic Neutrino (SRN) search in SK-I and
SK-II. The SRN is the diffuse supernova neutrino backgroundfrom all the supernovae in the past. It is expected that the SRN
would become dominant in 18–40 MeV energy region though
they haven’t been observed yet. So far, SK-I gives the moststringent flux limit for past supernovae.
In SK detector, we have applied special data selections
to enhance the SRN candidates. The energy region was 18–
82 MeV, and the fiducial volume was 22.5 kton. The live time
for this analysis is the same as that for the solar neutrino analysis; that is, 1496 days in SK-I and 791 days in SK-II. The
number of events after all data reductions was 218 events in
SK-I and 115 events in SK-II. The event rates in the final data
samples are consistent between SK-I and II.
The dominant backgrounds are decay electrons from invisible atmospheric ν μ and atmospheric ν e . In SK-II, the remaining spallation products are also seen around 20 MeV due
to worse energy resolution. We have applied a spectrum fit
to estimate the possible SRN contributions. Figure 13 showsthe energy spectrum of the final data samples and the fitting
results in SK-I and SK-II. From this analysis, the best fit was
no SRN contribution in both SK-I and II.
We have obtained the preliminary SRN flux limits fromthe spectrum fits. The updated SRN flux upper limit fromonly SK-I data is 1.25/cm 2/sec at 90% C.L. The same limit

8

30
25
20
15
10
5
0

20

30

40

50

60

70

K2K Experiment (completed)SK2 spectrum fitting
Number of event /791days /4MeV

Number of event /1496days /4MeV

SK1 spectrum fitting

80

Energy (MeV)

16
14
12
10
8
6
4
2
0

20

30

40

50

60

70

80

Energy (MeV)

Fig. 13. The preliminary fitting results from the SRN analysis. The
left(right) plot shows SK-I(SK-II) result. The solid red points areobserved data. The dashed lines are each component of the fitting. The green-dashed, red-dashed, blue-dashed, and yellow–
dashed lines correspond to the decay electrons from the invisible
muons, atmospheric νe , remaining spallation products, and SRN
signal, respectively. The black solid line is the sum of the best-fitted components. .

from only SK-II is 3.68/cm 2/sec. The combined preliminary
SRN flux limit from SK-I and SK-II is 1.08/cm 2/sec. We aretrying to improve this analysis.

Bibliography[1] Super-Kamiokande Collaboration, “Solar Neutrino
Measurements in Super–Kamiokande–II”, Submitted to Phys. Rev. D, arXiv:0803.4312[hep-ex].
Additional information in http://www-sk.icrr.utokyo.ac.jp/sk/lowe/sk2 data/[2] Super-Kamiokande Collaboration, “ Search for Supernova Neutrino Bursts at Super-Kamiokande ”, Astrophys J. 669 (2007) 519, arxiv:0706.2283[astro-ph].
[3] Super-Kamiokande Collaboration, “A Measurement ofAtmospheric Neutrino Oscillation Parameters by SuperKamiokande I”, Phys. Rev. D 71 (2005) 112005.
[4] Super-Kamiokande Collaboration, “A measurement of
atmospheric neutrino flux consistent with tau neutrino appearance”, Submitted to Phys. Rev. Lett., hepex/0607059.
[5] Super-Kamiokande Collaboration, “Three flavor neutrino oscillation analysis of atmospheric neutrinos inSuper-Kamiokande”, Phys. Rev. D 774 (2006) 032002.
[6] Super-Kamiokande Collaboration, “Search for MatterDependent Atmospheric Neutrino Oscillations in SuperKamiokande”, Phys. Rev. D 77 (2008) 052001.
[7] Super-Kamiokande Collaboration, “High energy neutrino astronomy using upward-going muons in SuperKamiokande-I” Astrophys. J. 652, (2006) 198.
[8] Super-Kamiokande Collaboration, “Search for Diffuse
Astrophysical Neutrino Flux Using Ultrahigh Energy
Upward-going Muons in Super-Kamiokande-I.” Astrophys. J. 652, (2006) 206.

The observed neutrino mass difference, Δm 2 ∼ 3 ×
10−3 eV2 , means an oscillation length of a few hundred km for
one GeV neutrinos. Hence the oscillation can be experimentally tested using an artificial neutrino beam with the detector
placed a few hundred km away from the neutrino production
point.
The K2K experiment was designed to detect this oscillation effect and to determine the oscillation parameters precisely [1]. The neutrino beam created at KEK with a mean energy of 1.3 GeV was sent to the SK detector, 250 km west of
KEK, every 2.2 seconds for a duration of 1.1 μ s. At the KEK
site, we prepared a near detector complex which consists of a
1 kt water Cherenkov detector and fine grained detectors, at a
distance of 300 m from the target. We have analyzed the datataken from June 1999 to November 2004, which corresponds
to 9.2 × 10 19 protons on target.
There are several beam monitors, proton profile monitors,
a muon monitor, and a pion monitor placed along the neutrino
beam line to monitor the quality of the beam. The π ± decay
length is about 200 m; therefore the neutrino beams at the nearand the far detectors are not scaled exactly by a 1/r 2 law. The
flux ratio of the near to the far detectors was obtained from thebeam Monte Carlo (MC) simulation, taking into account the
spread and the emittance of the beam at the target, the production of pions, the focusing effect by the horn and the decay ofpions to neutrinos. The simulation results were verified by thepion monitor.
The beam flux and the spectrum were measured by thenear detectors. The ICRR group had the responsibility forthe construction and the analysis of the 1 kt near detector,
in addition to providing the data collected at SK. The coverage of PMTs in the 1 kt near detector is 40% of the total
inner detector surface, the same as for SK-I. The 1 kt detector
provides the information on the absolute neutrino flux. Theenergy spectrum of the beam is evaluated by using both the
1 kt and the fine grained detectors. The observed spectrum iswell reproduced by the MC simulation. With additional constraints from the pion monitor, the neutrino energy spectrum
was predicted for the far detector. Systematic errors due tothe detector biases and the uncertainties of the neutrino interactions were carefully studied. Also, the data taken at the
1 kt detector enable us to study neutrino interactions in the
GeV region. Examples include the neutral current (NC) interactions using single π 0 events [4], the nuclear de-excitation
gamma rays from the NC interaction, and the neutrino interaction backgrounds for the nucleon decay searches.
A GPS system is used for the synchronization of the KEK
12 GeV Proton Synchrotron and the Super-Kamiokande detector. SK identified 112 fully contained events induced by
the K2K beam. This number is compared with 158 +9.4
−8.7 (syst)
events that are expected assuming no-oscillation. The deficit
in the observed event number is consistent with the ν μ disappearance from the neutrino oscillation.
The neutrino energy spectrum is reconstructed from theobserved 58 μ -like single ring events using the energy and thescattering angle of the muons, as shown in Figure 1, where
the data are compared with the MC simulation both with and2Δm (eV )

9

1.4
1.2
1
0.8
0.6
0.4
0.2
0

Null Osci.

2

18
16
14
12
10
8
6
4
2
0

Nexp(1Rμ) = 90.1

-2

10
0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Eνrec(GeV)-3

10Null Oscillation

–

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Eνrec(GeV)

K2K-I & K2K-II-1Δm2 [ eV ]

10

-2

10

-3

10

-4

10

0

68%
90%
99%
0.25

0.5

0.75

2

1

sin (2θ)Fig. 2. Allowed regions of νμ -ντ oscillation parameters. Blue, green
and red lines are 68.4%, 90% and 99% C.L. contours, respectively.

without the neutrino oscillation. The observed neutrino spectrum is reproduced well with the oscillation, and the probability for the absence of neutrino oscillation is 0.001% (4.4σ ).
The allowed region for the ν μ − ντ oscillation parameters,
shown in Fig. 2 [5], is consistent with the atmospheric neutrino result.
A νμ − νe oscillation search is also performed based on
the full K2K data, by looking for the ν e appearance. We applied a new e/π 0 separation technique to reduce the π 0 background from NC π 0 interactions in the single ring e-like event
sample[3].
One candidate event is remained after applying the selection to enrich the ν e quasi elastic interaction, while 1.7
events are expected from the MC simulations. Since thenumber of observed events is consistent with the expectedbackground, we set an upper bound on the ν μ − νe oscil-

10–

CHOOZ 90%C.L.(νe →νx)
K2K 90%C.L. (νμ →νe)

-40Fig. 1. The upper panel shows the reconstructed Eν distribution fromsingle ring fully contained events at SK. The blue line is the best
fit spectrum and the red line shows the expected spectrum without
oscillation. The lower figure shows the same figure but the verticalaxis is normalized by the expected spectrum without oscillation.

2

-1

10

0

0.2

0.4

0.6

0.8
1
sin22θμe

Fig. 3. The upper bound on ν μ − νe oscillation parameters at 90% and
99% C.L. based on 9.2 × 1019 protons on target.

lation parameters, which is shown, together with the limit
from CHOOZ, in Figure 3 for sin 2 2θ23 ∼ 1. The K2K experiment excludes the region sin 2 2θμ e > 0.13 at a 90% C.L.
when Δm223 = 2.8 × 10−3 eV2 [6].
Other than the neutrino oscillation parameter determinations, we have completed and published the results of a studyof the atmospheric neutrino background for proton decay
searches via p → e+ π 0 in the ring imaging water Cherenkov
detectors[7]. We used the data taken with the 1 kt water
Cherenkov detector, which uses the same target material anddetection technique as SK. The accumulated numbers of neutrino interactions are equivalent to the atmospheric neutrino
exposures of 15.9 and 4.5 Megaton·years (or 700 and 200
years of SK) for the CC and NC background events, respectively. A re-weighting method, using the neutrino fluxes andthe detection efficiencies, is used to estimate the background
event rate in the search for proton decay in SK. The obtained+0.45
background rate for E ν < 3 GeV is 1.63+0.42−0.33 (stat.)−0.51 (syst.)
events/Megaton·years. Here, about 76% of the background
events are expected to be generated in this energy range,Eν < 3 GeV, according to the study with our Monte-Carlosimulation. This is the first estimation of the background event
rate for SK-type water Cherenkov detectors based on the datafrom an experiment. The obtained results are found to be consistent with the estimation by the full simulation of the SK
detector and the neutrino interactions.

Bibliography[1] K2K collaboration, Detection of accelerator produced
neutrinos at a distance of 250 km, Phys. Lett. B, 511,
178–184, 2001.
[2] K2K collaboration, Indication of neutrino oscillation in
a 250 km long baseline experiment, Phys. Rev. Lett., 90,
041801, 2003.
[3] K2K collaboration, Search for Electron Neutrino Appearance in a 250 km Long-baseline Experiment, Phys.

10

Rev. Lett., 93, 051801, 2004.
[4] K2K collaboration, Measurement of single pi0 production in neutral current neutrino interactions with waterby a 1.3 GeV wide band muon neutrino beam, Phys.
Lett. B, 617, 255, 2005.
[5] K2K collaboration, Evidence for muon neutrino oscillation in an accelerator-based experiment Phys. Rev. Lett.,
94, 081802, 2005.
[6] K2K collaboration, An Improved search for ν μ → νe oscillation in a long-baseline accelerator experiment, Phys.
Rev. Lett., 96, 1811801, 2006.
[7] K2K Collaboration, Experimental study of the atmospheric neutrino backgrounds for proton decay topositron and neutral pion searches in water Cherenkov
detectors, Phys. Rev. D., 77, 032003, 2008.

T2K Experiment (under construction)[Spokesperson : K. Nishikawa]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;
The K2K experiment successfully confirmed the neutrino
oscillation phenomena and established the method of theaccelerator-based long baseline neutrino oscillation experiment. Meanwhile, precise measurements of accelerator, atmospheric, solar and reactor neutrinos have been done and 2out of 3 neutrino mixing angles and 2 mass differences havebeen measured. However, the remaining mixing angle, θ 13 ,has not been measured and has only been found to be small. If
there is a much more intense neutrino beam, it will be possible
to measure θ13 . Furthermore, if θ 13 is large enough, there is apossibility to search for CP violation in the lepton sector andto measure the CP phase, δ , which is one of the last parameters of the neutrino oscillation. Therefore, next generation
experiments, which utilize much intense beams, was planned
for the further investigation of the neutrino oscillations, havebeen proposed. Among of them, the Tokai to Kamioka long
baseline neutrino oscillation experiment (T2K) is under construction and expected to start in 2009. The intense neutrino
beam will be produced by a new high intensity proton synchrotron accelerator being constructed at the J-PARC site in
Tokai village. T2K utilizes Super-Kamiokande as a far detector, located at 295 km from the beam production point.
The T2K neutrino beam is about 50 times more intensethan the K2K beam. The neutrino beam line of T2K utilizes
the so-called off-axis technique 1 in order to have a tunabilityof the peak energy and a narrow energy spread of the neutrino
beam. The peak position of the neutrino beam energy will
be adjusted to ∼ 650 MeV by setting the off-axis angle to∼ 2.5◦ . With this configuration, it is possible to maximize theneutrino oscillation effects at a distance of 295 km when themass squared difference is about Δm 2 = 2.8 × 10−3eV2 . The
beam primarily consists of ν μ with a contamination of ∼ 0.4%
νe at the flux peak.
As described, one of the motivations of this experimentis to measure the neutrino oscillation parameter θ 13 , which isonly known to be small (sin 2 θ13 < 0.04) by reactor experiments. It is of great interest to know the value of a nonzero
θ13 or how close to zero θ 13 is; a new underlying symmetry
may be required to explain this. In the case of nonzero θ 13 ,T2K may observe the appearance of electron neutrinos for the
first time. Also, there is a possibility to observe the neutrino
oscillation signature with an appearing experiment for the firsttime.
Figure 1 shows T2K’s expected sensitivity to θ μ e as afunction of Δm 223 . Note that sin2 (2θμ e ) = 12 sin2 2θ13 .
If the measured θ 13 is large enough, it will be possible
to investigate CP violation in the lepton sector with further
extension of this experiment.
The other purposes are precise measurements of θ 23 andΔm223 . Owing to the high statistics, these parameters will bemeasured almost one order of magnitude more precisely than
before. Figure 2 shows the expected accuracy of the measurement of sin 2 2θ23 and Δm223 [1]. So far, θ 23 mixing is
known to be very large and consistent with unity from the*1 Long Baseline Neutrino Oscillation Experiment BNL E889 proposal,(1995).

-1

2

10

δ(sin 2θ)11

-1

Δm 2 (eV 2)

10

10

-2

CHOOZ
excluded

-2

10
10

-3

T2K 5 year

-3
10

90% C.L. sensitivities

-4

10

10

-3

10

-2

10

-1

1

2

3
4
-3
2
Δm (x10 eV )

2

3
4
-3
2
Δm (x10 eV )1

sin22θμe-32Super-Kamiokande, K2K and the MINOS experiments. If
sin2 2θ23 = 1, it may suggest an underlying new symmetry.
To achieve these precise measurements, the SuperKamiokande detector has several to-do items in the near future: (1) detector upgrade, (2) precise detector calibration, and(3) software upgrade. Details of these items are described below.
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 a search for electron neutrino appearance, to distinguish single π 0 production backgrounds from the ν e signal more effectively.
In 2008, the electronics and DAQ systems are planned
to be replaced. Newly-developed ADC/TDC modules called
QBEEs will be installed. The new QBEE boards consist of acustom analog ASIC and multi-hit TDC chips. The new system will allow us to observe T2K neutrino events with goodstability and accuracy.
Precise Detector Calibration
The response of the far detector must be well understoodin 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 fake single-ringelectron signals when one of the two γ rings is not identified.
Even a small portion of muon events mis-identified as electrons could also be a serious background. Therefore, we will
study the ring identification and the particle identification capabilities of the detector very carefully. It will also be important to reduce the uncertainty in the absolute energy scalemeasurement (2.5%) in order to achieve a Δm 223 measurementwith ∼ 1% accuracy. Moreover, further calibration of the fundamental properties such as the charge and timing responses

10

δ(Δm )

Fig. 1. Expected sensitivity to θμ e by T2K as a function of Δm223 compared with current best limit by the CHOOZ reactor experiment.
Note that sin2 (2θμ e ) = 12 sin2 2θ13 .

2

-4

10

-5

10

1

2

Fig. 2. T2K’s expected accuracy of the measurement of sin2 2θ23 andΔm223 as a function of Δm223 [1].

of each PMT, the light attenuation and scattering in water, andthe light reflection by the detector 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. Improvements and re-tuning of thesealgorithms to meet the physics goals of T2K are underway.

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

12(100 kg fiducial volume) was approved in 2007. 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.

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.

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.

• Isotope separation is possible. It is possible to enrich
136 Xe for double beta decay or deplete 136 Xe for solar
neutrino measurements.

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 evevents/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/cm 3), 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).

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.

One-ton detector
We plan to make the one-ton detector to search for dark
matter down to 10 −45 ∼ 10−44 cm2 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.

13

we need to reduce it by circulating liquid xenon. Therefore wehave constructed a circulation system for the one-ton detector
and plan to test it with a smaller detector in 2008.

Fig. 2. Expected sensitivity of the proposed 800kg liquid xenon detector. See http://dmtools.berkeley.edu/

Development 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 experimentsince the scintillation wavelength is very short (175 nm) andthe operating temperature is low (-100 ◦C). In addition, thePMT materials are carefully selected and evaluated with a low
background germanium detector. The PMTs have been tested
in liquid xenon and are now ready for production.
References
1. Y. Suzuki et al., “Low energy solar neutrino detection
by using liquid xenon”, Aug. 2000, hep-ph/0008296.
2. S. Moriyama, “XMASS EXPERIMENT I”, Proceedings of the International Workshop on Technique andApplication of Xenon Detectors, Kashiwa, Japan, 3-4
Dec. 2001.

Fig. 3. A water tank for shielding from gamma ray and neutrons. The
liquid xenon detector is located at the center of the tank.

Construction of the one-ton detector
The construction of the one-ton detector started in 2007
and is expected to be completed by 2009. Important progress
related to the construction has been made.
Excavation of experimental halls
As a part of an extension program of the Kamioka observatory, two experimental halls were excavated. Installation of
the one-ton xmass detector in one of the halls was approved by
the observatory. The hall is 15 m wide, 21 m deep and 15 m
high. The excavation was finished in early 2008, and basic
outfitting is planned to be finished by the end of 2008.
Design of a 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 immersed in
the cylindrical water tank shown in Fig. 3. The tank is 10 m indiameter and 11 m high. The tank has been designed and weare ready to accept bids for the construction.
Circulation system for liquid xenon
We may need to purify liquid xenon before or during detector operation to reduce possible contamination. For example, water vapor in liquid xenon absorbs scintillation lights;
thus, it needs to be removed to maintain transparency. Anotherexample is radon gas which is emanated from detector components. If the radon produces more background than expected,

3. K. Abe, “XMASS, status of 800kg detector design”,
presentation at the Joint Meeting of Pacific Region
Particle Physics Communities (DPF2006), Honolulu,
Hawaii, USA, 29 October - 3 November 2006.
4. M. Nakahata,“Status of XMASS experiment”, presentation at the sixth international Heidelberg conferenceon dark matter in astro and particle physics (dark2007),
Sydney, Australia 24-28 September 2007.

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 raysby the Telescope Array (TA) group, and very high energy cosmic rays and gamma-rays by the Tibet ASγ Collaboration.
Remarkably, TA has been completed and started this fiscal
year. Other activities, such as experiments utilizing the Akeno
observatory, the Norikura observatory, the Mt. Chacaltaya observatory (jointly operated with Bolivia), and the emulsionpouring 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 Cherenkov telescopes to make a precise observation of high-energy air showers originated by TeV
gamma-rays. It started as a single telescope with a relatively
small mirror (3.8 m in diameter) in 1992. In 1999 a new telescope with a 7-m reflector has been built, and now it has a
10-m reflector with a fine pixel camera. The main purposeof this project is to explore the violent, non-thermal universe
and to reveal the origin of cosmic-rays. An array of four
10-m telescopes has been completed in March 2004 so that
more sensitive observation of gamma-rays is realized with its
stereoscopic imaging capability of Cherenkov light. Several
gamma-ray sources have been detected in the southern sky
and detailed study 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 10 20 eV. The Telescope Array (TA), alarge plastic scintillator array with air fluorescence telescopes
has just been constructed in Utah, USA, which will succeed
AGASA and measure the EHECRs with an order of magnitude larger aperture than that of AGASA to unveil the origin of super-GZK cosmic rays discovered by AGASA. It has
been completed and just started taking data as the largest arrayviewing the northern sky.
An air shower experiment aiming to search for celestial
gamma-ray point sources started in 1990 with Chinese physicists at Yangbajing (Tibet, 4,300 m a.s.l.) and has been successful. This international collaboration is called the Tibet
ASγ Collaboration. An extension of the air shower array wascompleted in 1995 and an emulsion chamber has been combined with this air shower array since 1996 to study the primary cosmic rays around the knee energy region. After successive extensions carried out in 1999, 2002 and 2003, thetotal area of the air shower array amounts to 37,000 m 2 . The
sun’s shadow in cosmic rays affected by the solar magnetic
was observed for the first time in 1992, utilizing its good angular 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; Dept.
of Radiological Sciences, Ibaraki Prefectural University of
Health Sciences, Ibaraki, Japan; Faculty of Science, Ibaraki
University, Ibaraki, Japan; Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Kanagawa, Japan; School of Allied Health Sciences, Kitasato University, Kanagawa, Japan; Department of Physics, Konan University, Hyogo, Japan; Department of Physics, Kyoto University, Kyoto, Japan; Solar-Terrestrial Environment Laboratory, Nagoya University, Aichi, Japan; National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Tokyo, Japan; Faculty of Engineering, Shinshu University, Nagano, Japan; Department of Physics, Tokai University,
Kanagawa, Japan; Department of Physics, Yamagata University, Yamagata, Japan; Faculty of Management Information,
Yamanashi Gakuin University, Yamanashi, Japan [1].

Status of the Project
CANGAROO is an acronym for the Collaboration of Australia and Nippon (Japan) for a GAmma Ray Observatory
in the Outback. As its third-generation experimental setup,
the CANGAROO-III stereoscopic Cherenkov telescope system has been in operation since March 2004 with four imaging
Cherenkov telescopes of 10 m diameter in the desert area near
Woomera, South Australia (136 ◦47 E, 31◦ 06 S, 160m a.s.l.).
Stereoscopic observations of atmospheric Cherenkov light images produced by particle showers caused by high-energy particles bombarding the earth allow effective discrimination of

15

CANGAROO-III results
Radio galaxy Cen A/globular cluster ω Cen [2]We have observed the giant radio galaxy Centaurus A andthe globular cluster ω Centauri in the TeV energy region. The
observations were carried out in March and April 2004. In total, approximately 10 hours data were obtained for each target.
No statistically significant gamma-ray signal has been foundabove 420 GeV over a wide angular region (a one-degree radius from the pointing center) and we derive flux upper limits
using all of the field of view. Implications for the total energyof cosmic rays and the density (see Fig. 1) of the cold dark
matter are considered.

Log10[EF/(eV/cm2/s)]

4
3.5
3
2.5
2
1.5
1
0.5
0
-0.5
-1

BJ3

port the results of observations made in 2004 and 2006 whichyield upper limits on the TeV gamma-ray flux, which are compared with a theoretical prediction (see Fig. 2). In addition,
we set upper limits on the TeV flux for four high energy objects which are located within the same field of view of theobservation: the super-bubble 30 Dor C, the Crab-like pulsar
PSR B0540−69, the X-ray binary LMC X-1, and the supernova remnant N157B.

1.5

log10(EF/cm -2s -1eV)

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) are currently usedin observations as the first telescope, completed in 2000 andhaving been used as CANGAROO-II, has degraded and isequipped a different electronics system from the others. A
stereoscopic triggering system was installed at the beginningof 2005 and has been working properly, rejecting most single muon events, which are the major background component
at low energies. We are continuing observations of various
candidates of celestial gamma-ray emitters on moonless, clear
nights.

1

0.5
0

-0.5
-1
-1.5
11.5

12

12.5

13
13.5
log10(E/eV)

Spectral energy distribution. The blue points and line are obtained from the 2004 data and the black from the 2006 data.
The red points are the CANGAROO-II upper limits from 2001
data. The green points are the H.E.S.S. data from 2003. Thelines are obtained from the theoretical prediction. The solidand dashed curves are the predictions of the gamma-ray flux
8249 and 7300 days after the supernova, respectively.
Fig. 2.

D
G

J1CI

J2

11 11.5 12 12.5 13 13.5 14 14.5
Log10[E/eV]

Fig. 1. SED for the jet region of Cen A. The open circle isthe prediction. The black square with the arrow is the
H.E.S.S. upper limit. The open diamonds are our upper
limits. The expected gamma-ray yield with a total electronenergy of 10 54 erg with a 100 TeV cutoff energy is shownby the dashed curve.

Supernova Remnant 1987A [3]Optical images of SN 1987A show a triple ring structure.
The inner (dust) ring has recently increased in brightness andin the number of hot spots suggesting that the supernova shock
wave has collided with the dense pre-existing circumstellar
medium, a scenario supported by radio and X-ray observations. Such a shocked environment is widely expected to result in the acceleration of charged particles, and the accompanying emission of very high energy gamma-rays. Here, we re-Blazar PKS 2155-304 [4]We have observed the high-frequency-peaked BL Lacertae (HBL) object PKS 2155−304 between 2006 July 28 (MJD
53944) and August 2, triggered by the H.E.S.S. report that thesource was in a high state of TeV gamma-ray emission. A
signal was detected at the 4.8 σ level in an effective live timeof 25.1 hours during the outburst period. The flux of VeryHigh Energy gamma-rays from the CANGAROO-III observations shows the variability on the time scale of less thana few hours (see Fig. 3). The averaged integral flux above
660 GeV is (1.6 ± 0.3 stat ± 0.5syst ) × 10−11 cm−2 sec−1 whichcorresponds to ∼ 45% of the flux observed from the Crab nebula. Follow-up observations between August 17 (MJD 53964)
and 25 indicate the source activity had decreased.
Pulsar Wind Nebula? MSH 15-52 [5]We have observed the supernova remnant MSH 15−52(G320.4−1.2), which contains the gamma-ray pulsar PSR
B1509−58, from April to June in 2006. We detectedgamma rays above 810 GeV at the 7 sigma level during
a total effective exposure of 48.4 hours. We obtained adifferential gamma-ray flux at 2.35 TeV of (7.9 ± 1.5 stat ±1.7sys )×10−13 cm−2 s−1 TeV−1 with a photon index of 2.21±
0.39stat ± 0.40sys, which is compatible with that of theIntegral flux (>660GeV)[ cm-2s-1 ]1680

×10-12

60
40
20
-0
-20
-40
53944

53945

53946

53947

53948

53949

53950

MJD
Fig. 3. Light curve of PKS 2155−304 using all the data at zenith angle less than 30 ◦ between 2006 July 28 and August 2,

expressed by the integral flux above 660 GeV. Closed triangles and closed circles indicate the results from 2 f old–SZ and
3 f old–SZ datasets, respectively. Dashed line indicates an average integral flux during this observation period. The bin widthis 40 minutes. The shaded areas indicate the H.E.S.S. observation periods.

H.E.S.S. observation in 2004. The morphology shows extended emission compared to our Point Spread Function (seeFig. 4). We consider the plausible origin of the high energy
emission based on a multi-wavelength spectral analysis andenergetics arguments.
-33.

-6.

21.

48.

75.

Declination(J2000) [deg]-58.0

cm−2 s−1 TeV−1 with a photon index α of 2.69 ± 0.30 stat ±0.34sys, which is consistent with that of the H.E.S.S. observation in 2004. We also confirm the extended morphology ofthe source. By combining our result with multi-wavelength
observations, we discuss the possible counterparts of HESS
J1804−216 and the radiation mechanism based on leptonic
and hadronic processes for a supernova remnant and a pulsar
wind nebula.

-58.5

-59.0

-59.5

-60.0

PSF
230
229
228
227
Right Ascension (J2000) [deg]Fig. 4. Morphology of gamma-ray like events, smoothed witha Gaussian of σ = 0.23◦ . Our PSF is also shown by
a dashed circle(68% containment radius). The squares
and the cross represent tracking positions and the pulsar position, respectively. Solid contours show VHE gamma-ray emission as seen by H.E.S.S. and dotted contours
by ROSAT 0.6-2.1 keV. The region between thin dotted circles are used for the background study.

Unidentified HESS source HESS1804-216 [6]We observed the unidentified TeV gamma-ray source
HESS J1804−216 with the CANGAROO-III atmospheric
Cerenkov telescopes from May to July in 2006. We detectedvery high energy gamma rays above 600 GeV at the 10σ levelin an effective exposure of 76 hr (see Fig. 5). We obtained adifferential flux of (5.0±1.5 stat ±1.6sys)×10−12 (E/1 TeV)−αFig. 5. Smoothed morphology of gamma-ray–like events with

our PSF of 0.23 ◦ radius. Dashed contours show the
VHE gamma-ray emission seen by H.E.S.S. . The thicksolid contours (green) show the 20 cm radio emission
from G8.7−0.1 recorded by the VLA. The thin solid contours (white) show the X-ray emission detected by the
ROSAT satellite. The solid circle indicates the position of
G8.31−0.09. The cross indicates the PSR B1800−21 position. The triangle and the square indicate the position of
Suzaku Src1 and Suzaku Src2, respectively.

17

TeV, lower limits of the power-law spectral indices were foundto be 2.2 for both of the regions with a 99.9% confidence level(see Fig. 7). 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.

Differential flux (phs/cm2/sec/TeV/str)

Supernova Remnant Kepler [7]Kepler’s supernova, discovered in October 1604, produced a remnant that has been well studied observationallyin the radio, infrared, optical, and X-ray bands, and theoretically. Some models have predicted a TeV gamma-ray flux thatis detectable with current Imaging Cherenkov Atmospheric
Telescopes.
We report on observations carried out in 2005 April with
the CANGAROO-III telescope. No statistically significant excess was observed, and limitations on the allowed parameter
range in the model are discussed as shown in Fig. 6.

10
1

CANGAROO-III U.L.
EGRET

10-1

2.2
2.4
2.6

-2

10

-3

-3

nH (cm )

10

-4

10

-5

10

-6

10

10-7

10

-8

l=-19.5

10

-9

10

-10

10

-1

4

5

6

7

8

9
d (kpc)Differential flux (phs/cm2/sec/TeV/str)

10 10-4

1

-3

10

10-2

10
1

CANGAROO-III U.L.
EGRET

-1

10

2.2
2.4
2.6

-2

10

Fig. 6. The allowed region in the plane of the distance (d) ver-sus ambient density (n H ), based on the neutral pion decay γ -ray emission model where we assume that the total number spectrum of protons is proportional to a powerlaw with an exponential cutoff and the value of the conversion efficiency from the explosion energy to the cosmic-ray
energy is 10%. The solid, dashed, and dotted lines indicate the upper limits obtained from the observed 2σ upper
limits, compared with the integral fluxes of the models forthe power-law indices 2.1, 1.9, and 2.3, respectively. The
colors of the lines represent the cutoff energy of protons;
the black, red, and blue ones are obtained with the values
1015 , 1014 , and 1013 eV, respectively. The allowed regions
lie under these upper-limit lines. The hatched region indicates the region which satisfies the Sedov-Taylor solutionof the apparent radius of the Kepler’s SNR, 100” at 400
yr with the explosion energy 0.5 ∼ 2 × 10 51 erg. The dot–dashed lines are obtained from the approximate analytic
blast-wave positions of the radius 100”. The red and blue
ones are obtained assuming the ejecta power-law index
n = 6 and n = 14, respectively, with ejecta mass of 1.4M
with the explosion energy 10 51 erg.

Galactic Plane [8]In 2004, we searched for very high energy (VHE) gammaray emission from the Galactic Plane using the CANGAROOIII stereoscopic observation system. Two different longitude
regions ( = −19 ◦.5 and  = +13 ◦.0) on the Galactic Plane
were observed during July and August 2004. We analyzed
events that triggered three telescopes aiming to measure thediffuse emission component. No significant signal associatedwith the Galactic Plane was found from either of the regions.
Assuming that the gamma-ray spectrum is described by a single power law for energies ranging between a few GeV and

10-1
1
10
Energy (TeV)

-3

10

-4

10

-5

10

-6

10

10-7
-8

l=+13.0

10

-9

10

-10

10 10-4

-3

10

10-2

10-1
1
10
Energy (TeV)

Fig. 7. Relation between the upper limit values of the flux ob-

tained by the CANGAROO-III and the extrapolation of the
EGRET data. The arrows show the CANGAROO-III flux
upper limit The lines show the extrapolation of the EGRET
1-2 GeV data point, with some sets for different spectral
index value.

Cluster of galaxies [9]As accretion and merger shocks in clusters of galaxies
may accelerate particles to high energies, clusters are candidate sites for the origin of ultra-high-energy (UHE) cosmicrays. Recently, a prediction was presented for gamma-ray
emission from a cluster of galaxies at a detectable level withmodern imaging atmospheric Cherenkov telescopes. The
gamma-ray emission was produced via inverse Compton upscattering of cosmic microwave background (CMB) photons
by electron-positron pairs generated by collisions of UHE cosmic rays in the cluster. We have observed two clusters ofgalaxies, Abell 3667 and Abell 4038, searching for very-highenergy gamma-ray emission in 2006. The analysis showed no18significant excess around these clusters, yielding upper limits
on the gamma-ray emission. By comparing the upper limit for
the north-west radio relic region of Abell 3667 with the model
prediction, we can derive a lower limit for the magnetic fieldof the region of ∼0.1μ G (see Fig. 8). This shows the potentialof gamma-ray observations in studies of the cluster environment. We also discuss the flux upper limit from cluster center regions with a model of gamma-ray emission from neutralpions produced in hadronic collisions of cosmic-ray protons
with the intra-cluster medium (ICM). The derived upper limitof the cosmic-ray energy density within this framework was 1
order higher than that of our Galaxy.

[5] T. Nakamori et al., Astron. Astrophys. 677, 297 (2008).
[6] Y. Higashi et al., Astrophys. J., in press (2008).
[7] R. Enomoto et al., Astrophys. J., in press (2008).
[8] M. Ohishi et al., Astropart. Phys., in press (2008).
[9] R. Kiuchi et al., submitted for publication (2008).

TA: Telescope Array Experiment
Spokespersons:-1Integral flux [cm sec ]M. Fukushima / ICRR, University of Tokyo
P. Sokolsky / Dept. of Physics, University of Utah-2

B=0.1[μG]

Collaborating Institutions:

B=0.3[μG]
10

10

10

10

-11

B=1.0[μG]

-12

-13

-14

10

-1

1

10

Photon energy [TeV]Fig. 8. Derived gamma-ray flux upper limits from NW Relic re-gion of Abell 3667 (filled squares) with the predicted gamma-ray fluxes. The model was scaled with the mass andthe distance of Abell 3667 to that of Coma-like cluster, andis shown in the case of magnetic field of 0.1μ G, 0.3μ G, and1.0μ G.

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. ofTokyo, Kashiwa, Japan; INR, Moscow, Russia; Kanagawa
Univ., Yokohama, Japan; KEK/IPNS, Tsukuba, Japan; Kinki
Univ., Higashi-Osaka, Japan; Kochi Univ., Kochi, Japan; Los
Alamos Nat. Lab., Los Alamos, NM, USA; 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 New Mexico, Albuquerque, NM, USA;
Univ. of Utah, Salt Lake City, UT, USA; Utah State Univ.,
Logan, UT, USA; Waseda Univ., Tokyo, Japan; Yamanashi
Univ., Kofu, Japan; Yonsei Univ., Seoul, Korea

Super-GZK Cosmic Rays
Summary
We have been carrying out stereo observations of subTeV gamma-rays with CANGAROO-III since March 2004.
There has been a significant progress in the analysis of thestereoscopic observations. On the HESS sources MSH 15-52
and J1804-216, our new results are consistent with the recent
H.E.S.S. results. Upper limits were given for the nearby radiogalaxy, Cen A, the globular cluster, ω Cen, supernova remnants, SN 1987A, Kepler’s SNR, Galactic Plane, and clusters of galaxies. For the flaring activity of PKS 2155-304 in
July/August 2006, we detected time-varying gamma-ray flux
from this source. Observations and analyses of other sources
are in progress and results will be reported soon.

Bibliography[1] Collaboration
website:http://icrhp9.icrr.u-tokyo.ac.jp .
[2] S. Kabuki et al., Astrophys. J., 668, 968 (2007).
[3] R. Enomoto et al., Astrophys. J. 671, 1939 (2007).
[4] Y. Sakamoto et al., Astrophys. J. 676, 113 (2006).

The AGASA air shower ground array observed 11
extremely-high energy cosmic rays (EHECRs) exceeding theenergy of 10 20 eV in 13 years of operation. The rate of such
events is consistent with a continued spectrum with a powerlaw of E−2.7 and the expected GZK-cutoff structure due to theinteraction of EHE protons with the cosmic microwave background [1] was not observed. The Fly’s Eye air fluorescencetelescope also reported an event with 3 × 10 20 eV in 1994 [2].
High energy astronomical objects such as the active galactic nuclei and radio galaxies were searched as a possible origin
of such EHECRs, but none were found in the arrival directionof these events within 100 Mpc of our galaxy [3]. More distant origins may be considered, but only if a special mechanism to allow a longer propagation of EHECRs to take place,for example the violation of special relativity [4] or the EHE
neutrinos as the carrier of such energy [5].
It was therefore conceived that super-GZK (E > 10 20 eV)
cosmic rays may be generated by the decay of super-heavy
particles in the nearby universe. Energies beyond 10 20 eV are
easily attained if the mass of the particle is at the Grand Unification scale. A concentration of the particles in the galactic
hallo makes the non-observation of GZK-cutoff viable. Suchsuper-heavy particles may be surviving as a relic particle of19

Ground Array of ph-1 TA

Fig. 1. Detector Arrangement of ph-1 TA. The locations of the 507
surface detectors are indicated by filled green boxes for the deployed ones and filled purple boxes for the four undeployed ones
and the one to be moved. The three fluorescence telescope stations are marked by filled red circles. The three communication
towers are marked by filled yellow triangles. The central laser facility is marked by a red cross.

the Big Bang or presently generated by the decay of topological defects [6]. An abundant generation of EHE gamma rays
and neutrinos, in place of protons and nuclei, is expected in
the decay of such particles.

Overview of TA
The Telescope Array (TA) project was proposed in 2000
[7] to investigate the origin of super-GZK cosmic rays by employing a large array of fluorescence telescopes with ∼100
times larger acceptance than AGASA. The HiRes experiment,
however, presented an energy spectrum indicating the GZKcutoff in the 27th ICRC in Hamburg and the result was later
published in 2003 [8]. It was a monocular spectrum obtainedby the single telescope.
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. The construction of full TA is thus deferred, and we initiated constructing a composite detector withAGASA-like ground array and TA fluorescence telescopes [9]instead. We call it as phase-1 TA (ph-1 TA). We expect simultaneous measurement of the same EXECRs by the detectors of
two different types will sort out the systematics of two methods. It will guide us to a reliable determination of the primaryenergy 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 ∼1900 km 2 sr for zenith angles below 60◦ , which is approximately an order of magnitudelarger than that of AGASA. The fluorescence telescope will
have a stereoscopic aperture of ∼860 km 2 sr with 10% duty
factor at 1020 eV. The telescope will also supply informationon the primary particle species by measuring the longitudinal
shower profile. It is located in the West Desert of Utah, 140
miles south of Salt Lake City (lat. 39.3 ◦N, long. 112.9 ◦W, alt.
∼1400 m). The construction was completed in 2007, and TA
is fully operating from March 2008.

The ground detector array consists of 507 plastic scintillators on a grid of 1.2 km spacing. It covers the ground areaof ∼700 km 2 . Approximately 80% of them are on the Federal
land, ∼10% on the state trust land and the rest on privately
owned land. The detection (trigger) efficiency is ∼100% forcosmic rays with energies more than 10 19 eV with zenith angle less than 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 m 2 large and is read out by
104 wave length shifter fibers installed in grooves on the surface (see Fig.2). The fiber (Y-11(200)M; Kuraray Co., Ltd.)
has a diameter of 1 mm and a length of 5 m. Both ends of thefiber are bundled and optically connected to the photomultiplier (9124SA; Electron Tubes Ltd.). A passage of cosmic ray
muon gives ∼25 photo-electrons in average. Two layers areused for the coincidence measurement for the muon calibration trigger. There is a possibility for extending the dynamic
range by setting different PMT gains for two counters in the
future.
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, wave forms of
2.56μ s duration 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. The relative timing between remotely separated counters will be better than
±20 ns by the GPS, which is sufficient to supply good resolution for the determination of the arrival direction.
When one of the PMT signals exceeds a trigger threshold of three muons, the timing is recorded in a local trigger
list. The content of the list is transmitted to a branch DAQ
board by the wireless LAN at 1 Hz. The list contains lessthan 100 events for normal counters. To cover communication in the whole surface detector array, the array is divided
into three regions. The branch DAQ board is installed on acommunication tower built at the periphery of the array foreach region. Each surface detector is assigned to one of thethree branch DAQ boards on the tower. A colinear antenna
which is indirectional in azimuth is connected to each branch
DAQ board. Three communication towers about 12 m highwere built in September 2006. An air shower event is identified by the branch DAQ firmware by requiring clustered hits
(at least three adjacent counters) with a good coincidence timing (within 8μ sec). 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 with good coincidence timing (±32μ sec) respond by transmitting the wave form data to the branch DAQ
board. We employ a commercially produced wireless transmitter with the maximum speed of 11 Mbps 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 hightransmission speed together with a large buffering memory ateach counter. The data in a branch DAQ board on the tower
are transmitted to an industrial PC board inside a cabinet atthe tower site. The data taken in the PC board at the tower

20

Fig. 2. Scintillation Detector of TA. (left) scintillator plates with fiberson the surface. (right) PMTs with fiber bundles.

Fig. 4. Air Shower Event Observed with Surface Detectors. (a) an array of surface detectors which observed more than 1/3 of a muon
signal. The numbers near the circles indicate the numbers of particles that passed the detectors. The radius of the circle is proportional to logarithm of the number of particles. (b) wave form
distributions from the detectors. The numbers show the detector
locations.

2007. We chose about 50 clustered detectors as a subarray ineach branch to check on the stability of communication between the branch DAQ board and the detectors to establish
DAQ system. We adjusted the height of the antennas of all
the detectors in the three subarrays to minimize the effect ofradio wave reflected on the ground upon direct wave between
the detectors and a communication tower. Based on the debugging with these subarrays, we tuned all the remaining detectors in October 2007. We have 503 surface detectors in
the field after we deployed remaining counters in December
2007. We have been taking data for the whole ground arrayfrom March 2008. We plan to deploy remaining four countersin the autumn of 2008.
Fig. 3. Deployed Surface Detector.

sites are then transmitted via wireless long-distance communication network and stored in a mass storage at the Cosmic
Ray Center in DELTA. Fig.4 shows an air shower event takenwith surface detectors.
The total electrical power consumed by the PMT, ADC,
GPS and LAN is approximately 6 W and is locally generated
by the solar panel of ∼120 W capacity (KC-120J; Kyocera
Co., see Fig.3). Behind the panel is a heat-insulated enclosure
containing the backup battery (DCS100-L; 12V, ∼100 Ah anddeep cycle) and all the electronics. A communication antenna
is fixed to a mast 3.3 m tall. The planar-type antenna is used
for most of the surface detectors while the parabolic antenna
with higher gain is used for the detectors far from the tower.
The total weight of the counter is about half tons, such thatit can be easily deployed by helicopter without disturbing thewilderness environment.
We started the assembly of scintillator detectors in ICRR
in the spring of 2005 and completed the assembly in the autumn of 2006. We exported them to the Cosmic Ray Centerin Delta of Utah, USA, where we finally assembled scintillator detectors on the platforms together with other components. We started major deployment of the counters in October 2006. We deployed 485 counters by the end of Februay,

Fluorescence Telescope
The ph-1 TA has three fluorescence stations. The fluorescence station in the southeast is called the Black Rock Mesa
(BRM) site. The southwestern station is called Long Ridge(LR) site and the station in the north is called Middle Drum
(MD) site.
Twelve reflecting telescopes are installed at each of the
BRM and LR stations (see Fig.5) and cover the sky of 3 ◦ − 34◦
in elevation and 108 ◦ in azimuth looking toward the center ofthe ground array.
The field of view of each telescope (see Fig.6) is 18.0 ◦ inazimuth and 15.5 ◦ in elevation. A spherical dish of 6.8 m 2 iscomposed of 18 hexagonal mirrors with a radius of curvatureof 6067 mm. The direction of each mirror was individually
adjusted and a spot size of less than 20 mm in diameter wasachieved at the focal plane (2960 mm). The mirror is made by
10.5 mm thick high thermal resistivity glass (Schott Borofloat)
and is aluminum coated by vacuum deposition. The surfaceof the aluminum is protected by producing a ∼50 nm thickanodization layer.
The air shower image is detected by a mosaic PMT cameraon the focal plane (see Fig.7). 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 UV transmitting glass filter (Schott BG3, 4 mm thick) is attached in frontof each PMT for blocking the night sky background in the vis-

21

Fig. 5. Fluorescence Telescope Station at Black Rock Mesa.

Fig. 6. Fluorescence Telescopes of TA.

ible light range. The whole camera is assembled in a chassis
with a window made by a UV transparent plexiglass.
Negative high voltage is applied to the PMT by a bleeder
circuit using zener diodes to ensure a stable operation underhigh night sky background. The high voltage was individually
adjusted for all PMTs. With a PMT gain of ∼10 5, a linearityof up to 32 k photoelectrons in 100 ns was achieved.
A signal from the PMT is amplified by a factor of 50 by
the pre-amplifier and is sent to a Signal Digitizer and Finder(SDF) with a twisted pair cable about 25 m long. 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 of fluorescenceFig. 7. PMT Camera of TA fluorescence Telescope.

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 is estimated every
1 ms and is subtracted. The SDF is a 9U VME module and16 channels are mounted in one module. There are 16 SDF
modules in one VME crate for one camera.
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 andcollected to a storage PC by Ethernet during the daytime.
Fig.8 shows 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. 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 YAP generates ashort light pulse of ∼3000 photons around 370 nm and has an
excellent temperature stability. The calibration of the standard
PMT will be maintained by the YAP pulser.
For the calibration of the standard PMT, we developed
a light source using a Rayleigh scattering of nitrogen laser(337 nm) in the nitrogen atmosphere. The power of laser ismeasured pulse by pulse to an accuracy of 5% and the known

22

Fig. 8. Air Shower Event Observed by the Fluorescence Telescope.
(left) PMTs with signals are shown in the two-dimensinal configuration of the camera. (right top) wave forms of PMTs. (right bottom) time evolution of the sum of light output is shown for two
cameras. Red data correspond to those from the camera 8 andblack data correspond to the camera 9.

Fig. 9. TA Lidar at Black Rock Mesa.

cross section of Rayleigh scattering is applied to calculate theintensity of the scattered light.
The UV fluorescence light generated by the air shower
is scattered and lost along the path of transmission to thetelescope. The responsible processes are Rayleigh scattering by the air molecule and Mie scattering by the aerosol.
The Rayleigh scattering can be calculated with an accuracyof ∼5% from the known density and temperature distributionof the atmosphere. The amount of Mie scattering differs fromplace to place and changes with time reflecting the aerosol
distribution in the air. It has to be continuously monitored onsite.
A lidar system located at the Black Rock Mesa station isused for the atmospheric monitoring. 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 opticalaxis as shown in Fig.9. The laser can be shot to any direction
and the back-scattered light is received by the telescope to analyze the extinction coefficient along the path of the laser. We
had shown in Akeno that the change of the three-dimensional
distribution of extinction coefficient can be monitored within
10 km from each station [10].
We are also building a laser shooting facility in the middle of the array. The site is chosen such that a vertical shotof the laser from this station is equidistant to all fluorescencestations. The intensity of the laser shot is monitored to 5%

Fig. 10. Electron Linac. (left) the linac which was assembled in KEK.
(right) electron linac beam seen by the Fluorescence telescopes(simulation by GEANT).

accuracy and the Rayleigh scattering at high altitude can beconsidered as a “standard candle” observable at all stations.
The comparison of the received light gives a reliable information for the difference and the change of atmospheric conditions. For monitoring the cloud in the night sky, we installed
an infra-red CCD camera at the Black Rock Mesa station, andtake data of the night sky every hour during FD observation.
In order to confirm the absolute energy scale of the fluorescence detector in situ, we plan to deploy a compact electronlinear accelerator ∼ 100 m away from the fluorescence stationand inject an electron beam vertically up into the atmosphere.
The simulation of observed fluorescence signal by 40 MeV
electron beams is shown in Fig.10. A beam of 10 9 electrons
with a duration of 1 μ s well simulates a shower energy deposition of ∼4×10 16 eV 100 m away from the station, whichcorresponds to a shower of ∼4×10 20 eV 10 km away. The calibration is obtained by comparing the observed fluorescencesignal with the expected energy deposition calculated by the
GEANT simulation. The accelerator was designed with a collaboration of KEK accelerator physicists and was assembled
in KEK. We have been testing the basic performance of theaccelerator in KEK from February 2007. The main accelerator part will be installed in a 40-feet commercial container,
and we will be able to transport the accelerator system to Utah
in JFY 2008.
In March 2007, the telescope system at the BRM station
was nearly completed. In November, the telescope systemboth at the BRM and LR stations started regular operation.
The HiRes observatory was shut down in April 2006. The
Middle Drum fluorescence station has been constructed using refurbished equipment from the old HiRes-I observatory
at Dugway in Utah. Leveling of the site started in November 2006, and construction of the building was completed in
March 2007. The Middle Drum Observatory consists of sevenbays each about the size of a two car garage as shown in
Fig. 11. We started moving HiRes mirrors and installed toa new building in May as shown in Fig. 12 . MD Observatory was partially operated in July 2007, and started regularobservation with all the 14 telescopes from the beginning of

23

Fig. 11. The Middle Drum Observatory Building.

Fig. 12. Mirrors with cameras at the Middle Drum Observatory.

November 2007. HiRes mirrors are 20% smaller in area thanthe mirrors in the BRM and LR stations. The MD fluorescence detector will also observe at eleveation angles from 3 to
31 degrees.
Three fluorescence stations are fully operated from
November of 2007.

Prospects
The construction of the ph-1 TA was completed in 2007 by
the collaboration of Japanese, Korean, and American physicists. We started taking data and the ph-1 Ta is fully operated. The group consists of physicists who have been working
in AGASA, HiRes and other HEP experiments in US, Korea,
and Japan. The Japanese fund for ph-1 TA was approved in2003 by the Grants-in-Aid for Scientific Research (Kakenhi)
of Priority Areas. The US group has submitted a matching
proposal to NSF in 2005. The US proposal includes a construction of TALE, a Low Energy extension of TA down to1017 eV, to investigate the modulation of CR composition andspectrum expected by the galactic to extra-galactic transitionof CR origins. The infrastructure of TA and TALE in Utah
is also the responsibility of US group. The US fund is supported by the US National Science Foundation (NSF) throughawards PHY-0307098 and PHY-0601915 (University of Utah)

and PHY-0305516 (Rutgers University).
The Pierre Auger group is constructing a large hybrid experiment in Argentina with 1600 water tank detectors andfour fluorescence telescope stations. All the fluorescence telescopes are operated. The Auger group calibrated the groundarray energy estimator ρ (1000), the muon density 1000 m
away from the shower center, by the measurement of shower
energy from the fluorescence telescope. The extrapolation of
the calibration from the lower energy, where most of the hybrid events were collected, caused the major part of the systematic error.
Recently the Auger group and the HiRes group publishedthe results of energy spectrum, which are consistent withGZK cutoff [11, 12], although their energy scales are determined only 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 [13] while the HiRes group reported that no correlations, other than ramdom correlations,have been found [14].
The acceptance of Auger ground array is ∼4.5 times
larger than that of ph-1 TA assuming the same zenithal acceptance. The scintillator of TA counts the number of penetrating
charged particles and it is dominated by the electrons which
outnumber the muons by an order of magnitude. The watertank of Auger on the other hand is more sensitive to the penetrating high energy muons rather than the soft electrons whichstop near the surface of the water tank and do not generate as
many Cherenkov photons.
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 severely limited particularly for the EHE gamma
rays and neutrinos. It is our belief that the characteristic features of ph-1 TA, the sampling of electromagnetic shower energy, the unique calibration of fluorescence generation, usageof 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.

Bibliography[1] K.Greisen, Phys. Rev. Lett. 16, 748 (1966); T.Zatsepin
and V.A.Kuzmin, JETP Lett. 4, 178 (1966).
[2] D.J.Bird et al., Astrophys. J., 424, 491 (1994).
[3] Y.Uchihori et al., Astropart. Phys. 13, 151 (2000); G.Sigl
et al., Phys. Rev. D63, 081302 (2001).
[4] H.Sato and T.Tati, Prog. Theo. Phys. 47, 1788 (1972);
S.Coleman and S.L.Glashow, Phys.Rev. D59, 116008(1999).
[5] T.J.Weiler, Astropart.Phys. 3, 303 (1999).
[6] V.Kuzmin and I.Tkachev, JETP Lett. 68, 271 (1998);
V.Berezinsky, P.Blasi and A.Vilenkin, Phys.Rev. D58,
103515 (1998); K.Hamaguchi, I.Izawa, Y.Nomura
and T.Yanagida , Phys.Rev. D60, 125009 (1999);
V.Berezinsky, Nucl. Phys. Proc. Suppl. 81, 311 (2001).

24[7] The Telescope Array Project: Design Report, July, 2000.
[8] T.Abu-Zayyad et al., Phys. Rev. Lett. 92, 151101 (2004);
T.Abu-Zayyad et al., Astropart. Phys. 23, 157 (2005).

Tibet III Air Shower Array (2003)

36,900 m2[9] M.Fukushima et al., Proc. of 28th ICRC, Tsukuba, 2,1025 (2003); S.Kawakami et al., Proc. of 28th ICRC,
Tsukuba, 2, 1033 (2003); F.Kakimoto et al., Proc. of
28th ICRC, Tsukuba, 2, 1029 (2003); M.Fukushima,
Proc. of APPI2003 workshop, KEK Proceedings 20036.
[10] T.Yamamoto et al., Nucl. Instr. and Methods A488, 191(2002).
[11] R.U. Abbasi et al. (HiRes Collaboration), Phys. Rev.
Lett. 100, 101101 (2008).
[12] J. Abraham et al. (Pierre Auger Collaboration), Phys.
Rev. Lett. 101, 061101 (2008).
[13] J. Abraham et al. (Pierre Auger Collaboration), Astropart. Phys. 29 (2008); J. Abraham et al. (Pierre Auger
Collaboration), Science 318, 939 (2007);FT Detector (512)FT Detector w/ D−PMT(249)15 m

Density Detector (28)789 detectors[14] R.U. Abbasi et al. (HiRes Collaboration), astroph/0804.0382.

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 northen sky.
The Tibet I array was constructed in 1990 and it was gradually upgraded to the Tibet II by 1994 which consisted of
185 fast-timing (FT) scintillation counters placed on a 15 m
square grid covering 36,900 m 2 , and 36 density (D) countersaround the FT-counter array. Each counter has a plastic scintillator plate of 0.5 m 2 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 m 2 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 m 2 to 22,050 m 2 , and we call this array and further
upgraded one Tibet III. In 2002, all of the 36,900 m 2 area wasFig. 1. Schematic view of the Tibet III array.

covered 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 mapof cosmic rays around the Moon demonstrates the angular resolution to be around 0.9 ◦ at a few TeV for the Tibet III array.
The pointing error is estimated to be better than ∼0.01 ◦, bydisplacement of the shadow’s center from the apparent center in the north-south direction, as the east-west componentof the geomagnetic field is very small at the experimental site.
On the other hand, the shadow center displacement in the eastwest direction due to the geomagnetic field enables us to spectroscopically estimate the energy scale uncertainty at ±10 %level.
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:

25(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.

We will introduce a part of the results obtained in this fiscal year.
It is demonstrated [1] that the large-scale anisotropy of approximately 5 TeV galactic cosmic ray (GCR) intensity observed by Tibet Air Shower experiment can be reproduced by
the superposition of a bi-directional and uni-directional flows(UDF and BDF) of GCRs. The heliosphere is located inside
the local interstellar cloud (LIC) very close to the inner edgeof the LIC. If the GCR population is lower inside the LIC thanoutside, the BDF flow is expected from the parallel diffusionof GCRs into LIC along the local interstellar magnetic field(LISMF) connecting the heliosphere with the region outside
the LIC, where the GCR population is higher. A type of the
UDF, on the other hand, is expected from the B×∇n drift flux
driven by a gradient of GCR density (n) in the LISMF (B).
The LISMF orientation deduced from the best-fit direction of
the BDF is almost parallel to the galactic plane and more consistent with the suggestion of Frisch (1996) than that of Lallement et al. (2005). We note that the model, if holds, yields the
LISMF polarity together with its orientation.
We observed the shadowing of galactic cosmic rays in the
direction of the Moon, what we call the Moon’s shadow, by
the Tibet air shower array (Tibet-III) in operation at Yangbajing (4300 m a.s.l.) in Tibet, China since 1999. As almost all
the cosmic rays are positively charged, they are bent by thegeomagnetic field, thereby shifting the Moon’s shadow westward. Cosmic rays will also produce a shadow additionally inthe eastward direction of the Moon, if they contain negatively
charged particles, such as antiprotons, according to their fraction. We selected 1.5×10 10 air shower events with energy beyond 3 TeV approximately from the dataset accumulated by
the Tibet air shower array. With the dataset, we detected theMoon’s shadow at ∼40σ level. The center of the Moon wasin the direction away from its apparent center of the Moon by
0.23◦ to the west. Comparison between the Moon’s shadow
data and a full Monte Carlo simulation enables us to search
for the existence of the shadow produced by antiprotons at
multi-TeV energies. We found no evidence for the existenceof antiprotons in this energy region. As is shown in Fig. 3, we
set an upper limit of 7 % on the flux ratio of antiprotons toprotons at the 90 % confidence level in the multi-TeV energy
region.[3]Fig. 2. From [1]. The observed and reproduced sidereal anisotropyof GCR intensity. The intensity in 5x 5 pixel is represented in acolor-coded format as a function of the right ascension on the horizontal axis and the declination on the vertical axis, (a): observed
anisotropy, (b): reproduced anisotropy, (c): significance map of
the residual anisotropy. The dotted line in each panel shows thecelestial equator, while the white curve represents the Galactic
equator in the celestial coordinate. The star symbol in each panel
indicates the heliospheric nose direction (the upstream directionof the interstellar wind). The black pixels containing strong TeV
gamma ray sources indicated in (c) are excluded from the present
best-fit analysis,. For more detail, see [1].

Fig. 3. From [3]. The antiproton/proton ratio at the atmosphere. For
more detail, see [3].

26

tems.
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
Fig. 4. From [4]. The differential variation of relative CR intensity inthe local solar time. The solid lines are the sinusoidal curves best
fitted to the data. The error bars are statistical only. For moredetail, see [4].

Fig. 5. Observed yearly variation of the Sun’s shadow depth compared with our simulation assuming a Radial Field model.

We show[4] that the amplitude of the Compton-Getting(CG) anisotropy contains the power-law index of the cosmicray energy spectrum. Based on this relation and with the Tibet air-shower array data, we measure the cosmic-ray spectral index to be −3.03 ± 0.55 stat ± < 0.62syst between 6 TeV
and 40 TeV, consistent with −2.7 from direct energy spectrum measurements, as is shown in Fig. 4. Potentially, thisCG anisotropy analysis can be utilized to confirm the astrophysical origin of the “knee” against models for non-standard
hadronic interactions in the atmosphere.
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 2006
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 inassociation with the Solar Cycle 23. Additionally, we made acomparison between observation and Monte Carlo simulationof the Sun’s shadow depth using a Radial Field model, whichis in agreement with the observation, as is shown in Fig. 5

Other Activities
This group has developed and completed several automatic measuring systems that are powerful for analyzing cosmic ray tracks or air shower spots, that is, automatic microdensitometers, precise coordinate-measuring systems andimage scanners controlled by a computer. Enormous data
recorded on nuclear emulsion plates or X-ray films are rapidly
and precisely measured by the use of these measuring sys-(1) Gamma-ray astronomy in the 100 TeV region
We have a plan to construct a large (∼ 10, 000 m 2 ×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 m 2 ) 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. 6, 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 appratus 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 extragalacitic
origin may be an interesting target as well.
In fall, 2007, a prototype underground muon detector,
composed of two 52m 2 water pools, was successfully constructed in Tibet to demonstrate the technical feasibility, cost

27

Fig. 9. Illustration of YAC array.
Fig. 6. Tibet AS + MD (red curve) integral flux sensitivity (5σ or 10
events/1yr) for a point source.

Fig. 7. Prototype muon detector viewed from outside, just before being covered with soil.

estimate, validity of our Monte Carlo simulation, as is shownin Figs. 7 and 8.

Fig. 8. Prototype muon detector viewed from inside.

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

(2) Chemical composition of primary cosmic rays making the knee in the all-particel 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 nulei
than helium. The next step is to identify the chemical component making the knee in the all particle energy spectrum. We
have a plan to install an air shower core detector array (1000
to 5000 m 2 in area) around the center of Tibet III, as is illustrated in Fig. 9 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 10 shows the expected energy spectra of cosmic-ray ironnuclei depending on theoretical models. Tibet AS + YAC has
a strong model discrimination power.

28

Tibet ASγ collaboration
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of:Hirosaki Univ., Hirosaki, Japan; Saitama Univ., Urawa, Japan;
IHEP, Beijing, China; Yokohama National Univ., Yokohama,Japan; Hebei Normal Univ., Shijiazhuang, China; Tibet Univ.,
Lhasa, China; Shandong Univ., Jinan, China; South West
Jiaotong Univ. Chengdu, China; Yunnan Univ., Kunming,
China; Kanagawa Univ., Yokohama, Japan; Faculty of Education, Utsunomiya Univ., Utsunomiya, Japan; ICRR, Univ. 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; Tochigi Study Center, Univ. of the Air, Utsunomiya,
Japan; AMNC, Utsunomiya Univ., Utsunomiya, Japan; Tokyo
Metropolitan Coll. of Aeronautical Eng., Tokyo, Japan;
Shonan Inst. of Technology, Fujisawa, Japan; RIKEN, Wako,
Japan; School of General Education, Shinshu Univ. Matsumoto, Japan.

[7] “Spectral index of high-energy cosmic rays by theCompton-Getting effect at solar time frame with the Tibet air shower array”, M. Amenomori et al., Nuclear
Physics B (Proc. Suppl.) 175-176, 427–430, (2008).
[8] “Northern Sky Survey for Gamma-ray Point Sources in
100 TeV Region with the Tibet Air Shower Array”, M.
Amenomori et al., Nuclear Physics B (Proc. Suppl.) 175176, 431–434, (2008).
[9] “A large underground water Cherenkov muon detector
array with the Tibet air shower array for the Gamma-ray
astronomy in the 100 TeV region: Overview and physics
goal”, M. Amenomori et al., Nuclear Physics B (Proc.
Suppl.) 175-176, 476–479, (2008).
[10] “A large underground water Cherenkov muon detector
array with the Tibet air shower array for the Gamma-ray
astronomy in the 100 TeV region: detector design andsimulation”, M. Amenomori et al., Nuclear Physics B(Proc. Suppl.) 175-176, 480–483, (2008).

The Ashra Project
Bibliography
Papers in refereed journals[1] “Implication of the sidereal anisotropy of 5TeV cosmic
ray intensity observed with the Tibet III air shower array”, M. Amenomori et al., Proceedings in AIP Conf.
932 283–289, (2007).
[2] “Underground water Cherenkov muon detector arraywith the Tibet air shower array for gamma-ray astronomy in the 100 TeV region”, M. Amenomori et al., Astrophysics and Space Science 309 435–439, (2007).
[3] “Moon Shadow by Cosmic Rays under the Influenceof Geomagnetic Field and Search for Antiprotons at
Multi-TeV Energies”, M. Amenomori et al., Astroparticle Physics 28 137–142, (2007).
[4] “New Estimation of the Spectral Index of High-Energy
Cosmic Rays as Determined by the Compton-Getting
Anisotropy”, M. Amenomori et al., ApJ 672 L53–L56,(2008).
Papers in conference proceedings[5] “Cosmic ray data and their interpretation: about the Tibet Air Shower Array - Chemical Composition of Cosmic Rays at the Knee Viewed from the Tibet Air Shower
Experiment -”, M. Shibata for the Tibet ASγ experiment, Nuclear Physics B (Proc. Suppl.) 175-176, 267–
272, (2008).
[6] “The cosmic-ray energy spectrum around the knee measured by the Tibet-III air-shower array”, M. Amenomori
et al., Nuclear Physics B (Proc. Suppl.) 175-176, 318–
321, (2008).

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 80% 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 rays in the atmosphere. It can also be used to monitor
optical transients in the wide field of sky.
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:• 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.

29

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

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

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

EeV-CR
Fluorescence
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.

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 15 mag,for which we expect 3-σ signals (Fig. 1). The unique advantage is the on-time detection of the events without resorting
to usual satellite alerts. 10∼20 events per year are expectedin coincidence 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.

reconstruction is thus significantly improved and it is better
than one arcmin for the primary energy of EeV and higher [4].
This is useful to investigate events clustered around the galactic and/or extragalactic sources. This in turn would give us
information as to the strength and coherence properties of themagnetic 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 issummarized in Table 1.

Fig. 1. Early light curves (unfiltered, R and V ) for a set of GRBs with
detections within minutes of the gamma-ray event. All the measurements shown have been taken from GCN circulars (Guidorzi
et al. astro-ph/0511032). The limiting magnitude ( B) expectedwith Ashra (4s-exposure) is shown as a horizontal line. There are
no observations within 10 s after the GRB events.

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 2 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 comparable withthat of the High Resolution Fly’s Eye detector (HiRes). The
arcmin pixel resolution of Ashra provides finer images of longitudinal development profiles of EeV cosmic ray (EeV-CR)
air showers. The resolution of arrival direction with the stereo

Test Observation
We have constructed a 2/3-scale prototype Ashra detector and a 3m-diameter altazimuth Cherenkov telescope on
Haleakala to verify the optical and trigger performances.
From October 2004 to August 2005 at the observatory, We
made good observations for 844 hours out of 1,526 hours ofthe moonless nighttime. The efficiency is 55% of the moonless nighttime and 11% of entire time. This inefficiency is due
primarily to bad weather.
The fine resolution (arc-minutes) in the ultra wide field ofview (0.5 sr) has already been demonstrated using a 2/3-scalemodel. Fig. 2 shows an example of a 50-degree FOV image inwhich the constellations Taurus and Orion can be clearly identified with the 2/3-scale prototype. The inset, a two-degreesquare window, shows a close-up view of the Pleiades.
Our wide field observation covered the HETE-2 WXM
error box at the time of GRB041211. 2,000 images weretaken every 5 s with 4-s exposure from the time 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 of B∼11.5 magnitude[5]. This is compared with other observations in Fig. 3 [6] [7].
We also successfully performed two more observations coincident with Swift: GRB050502b [8] and GRB050504 [9].
A demonstration of air Cherenkov imaging of high-energy
gamma/cosmic ray is shown in Fig. 4 which was taken during observing Mkr501. Separately, we have confirmed the

30Fig. 2. Example of a 50-degree FOV image taken by the Ashra prototype. The solid lines are drawn to indicate the constellations
Taurus and Orion. The inset, a two-degree square window, showsa close-up view of the Pleiades.

Fig. 4. Self-triggered Cherenkov image of air shower detected by using the Ashra photoelectric image pipeline and a prototype trigger
sensor system. This image was taken during tracking Mkr501.

timum with star light images from the pilot observation.
In December 2005, we evaluated the night sky backgroundflux on Mauna Loa using the Ashra light collector installed
and aligned in a shelter. The result is fairly consistent withthe background in La Palma and Namibia by the HESS group
From the star light observations, our understanding of the lightcorrection efficiency to be accurate within 5% level.
The civil engineering construction of light collectors in shelters at the Mauna Loa site was completed in August 2007.
Figure 5 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
to enhance the scientific impacts.

Fig. 3. 3-sigma limiting magnitudes of the test observation with
the Ashra prototype and comparison with other observations for
GRB041211 as a function of time after GRB. Note that the horizontal axis unavoidably stands for time (s) in logarithmic scale after
the burst (positive) and in linear scale before the burst (negative).

alpha-parameter peak of TeV γ -rays from the Crab nebula to
be greater than 5 σ .
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 op-

Fig. 5. The Ashra main and sub stations at the Mauna Loa sites.

Observation
As a first step, we have started the observation of optical transients. During observation, Optical images were constantly collected every 6 s after 4-s exposure. Table 2 summarizes our observation statistics up to now. In the table, 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 0.1.

31

Season
S001
S002
S003
(on going)

PeriodMaximum Observable Time

Observable Time

Observed Time

Number of(astronomically allowed)(good weather rate)(operation efficiency)

99.5 hr93.2 hr(94 %)
115.0 hr
(93 %)
99.0 hr(100 %)

86.1 hr(92 %)
113.7 hr
(99 %)
98.1 hr(99 %)

Images
41000

6/28
–7/16
7/21
–8/14
8/19
–9/4

123.1 hr99.0 hr

64300
57100

Table 2. Summary of Ashra optical transients observation.

Apparently, we have made a good start in terms both of good
weather rate and operation efficiency. In particular, good
weather rate greater than 90 % is very impressive.
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
Section . We have prepared the optical and photoelectric image pipeline system in that light collector as shown in Fig. 6.
The installation of trigger and DAQ system is in progress now.
Pilot observation to confirm the detection principle of tau neutrino will be carried out soon.

[2] Sasaki, M., “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, 2003.
[3] Sasaki, M., et al., 2005. “Status of Ashra project,” Proc.
29th Int. Cosmic Ray Conf. Pune 8, 17-200.
[4] Sasaki,M., et al., “Design of UHECR telescope with 1
arcmin resolution and 50 ◦ field of view”, Nucl. Instrum.
Methods, vol. A492, pp. 49–56, Oct. 2002.
[5] Sasaki, M., et al., 2004. GCN Circ. 2846.
[6] Sasaki,M., et al., 2005. Proc. 29th Int. Cosmic Ray Conf.
Pune 8, 17-200.
[7] Sasaki, M., et al., 2005. “Observation of Optical transients with the Ashra Prototype,” Proc. 29th Int. Cosmic
Ray Conf. Pune 5, 319-322.
[8] Sasaki, M., et al., 2005. GCN Circ. 3499.
[9] Sasaki, M., Manago, N., Noda, K., Asaoka, Y., 2005.
“GRB050502b: Early Observation,” GCN Circ. 3421.

Fig. 6. The light collector towards Mauna Kea equipped with Photoelectric Image Pipeline.

Perspective
The full Ashra observatory (Ashra-2) will consist of threeexperimental sites separated by about 30 km on Mauna Loa(3,300 m), Camp Kilohana (2,014 m) on the side of MaunaKea, and Hualalai (2,320 m) on the island of Hawaii. The
full configuration emphasizes the stereoscopic observation
Cherenkov and fluorescence lights from air showers with twoor three stations at separated sites as well as the effective detection area for air showers. The parallax observation for optical transients with two or more stations is also useful forrejecting local background events.

Bibliography[1] http://www.icrr.u-tokyo.ac.jp/∼ashra

32

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
Introduction
A gravitational wave is a physical entity in space-time predicted by Einstein’s theory of general relativity. Its existence
was proven by the observation of PSR1913+16 by Taylor and
Hulse 2 , 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 stepof 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 afive-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 runsthat span from two to eight weeks, which ended in 2004. Since
2004, we were trying to attain its ultimate sensitivity as reported in the previous Annual reports (2004-2006). About
TAMA project, we present its development of Seismic Attenuation System (SAS) newly installed for four main mirrors.
In regard with CLIO project, the construction of which wasstarted in 2003 and ended in March, 2007, we have succeeded
to operate its sensitive laser interferometry at cryogenic temperature at first in the world. In addition to these R&Ds, we
conducted research on optical quality measurement, Resonant
Sideband Extraction scheme, practical suspension system by
crystal fibers, digital control system and so on.

Status of TAMA Project[Spokesperson : Kazuaki Kuroda] ICRR, Univ. of Tokyo,
Kashiwa, Chiba 277-8582
In collaboration with the members of: TAMA collaboration*2 J. H. Taylor and J. M. Weisberg, Astrophysical J., 345 (1989) 434.

NAOJ, Tokyo; KEK, Tsukuba; UEC, Tokyo; Osaka City
Univ., Osaka; Kyoto Univ., Kyoto; Osaka Univ., Osaka; Niigata Univ., Niigata
The achieved sensitivity of TAMA at the time of Data Taking Run 9 was reported in the previous Annual report (20052006).[1] We recognize that there is still a gap between theachieved sensitivity and the practically attainable one, at low
frequencies. However, we could demonstrate that the basic
techniques for the interferometer operation was acquired by
the fulfillment of the target noise curve at frequencies morethan 800 Hz, where the optical system properly worked andthe control system was appropriate. The noise spectrum atfrequencies lower than 30 Hz was disturbed by non-stationary
ground motion and the spectrum in a frequency range from
30 Hz to 300 Hz was determined by the actuator noise tostabilize 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 300 Hz to 800 Hz, we have finally finished the installation of Seismic Attenuation System (SAS) for four main
mirrors and improved the performance of anti-vibration at low
frequencies. One set of the new SAS is illustrated in Fig 1.

Fig. 1. One set of Seismic Attenuation System (SAS) newly installed
to TAMA. The previous mirror suspension system was modified
and the system was suspended through the monolithic geometrical anti-spring (Standard Filter) with the vertical pre-isolator (Filter
Zero) sit on the plate supported by three inverted pendulums thatwas electrically controlled to maintain its neutral position.

The previous mirror suspension system had been mounted
on an optical table supported by three sets of stack consisting of multilayer sandwiches of sealed rubber and massplate. The optical table was removed and the mirror sus-

33

CLIO Project

Old
Suspension

10[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

10

10

SAS
10
2008/01/28 SAS
2006/08/24 Old Suspension

10

10

10

PSD RMS(@0.05Hz)
1.3 Pm
1.4 Pm10

10

Fig. 2. Improved displacement noise at the test mass by newly installed SAS. Comparing with the old system, the displacement
noise is decreased by more than one order at 2 Hz. Improvementof the interferometer sensitivity is ongoing.

pension that was slightly modified was suspended throughthe monolithic geometrical anti-spring with the vertical preisolator sit on the top plate supported by three inverted pendulums electrically controlled to maintain its neutral position.
The resonant frequency of the inverted pendulum was set as
30 mHz by a feedback circuit utilizing outputs of accelerometers mounted on the top table. This mechanism serves as theanti-vibration system against low frequency horizontal seismic motion. Vertically, two sets of geometrical anti-springwere installed through the top plate. Each resonances wereset 0.5 Hz. The mirror suspension system was designed as
the previous one except the recoil mass to hold the parts ofactuators. The upper plate suspends four wires suspending
the second mass part that behaves as a passive damper. Thispassive damper suspends both the main mirror and the recoil
mass part. [2]Figure 2 shows the improvement of anti-vibration performance at low frequencies. Comparing with the old system,
the displacement noise was decreased by more than one orderat 2 Hz. Although the displacement amplitudes at frequencies
less than 0.2 Hz were larger than the old system due to widening the working frequency range, RMS amplitude has been
improved from 1.4μ m to 1.3μ m as in Fig.2. Preliminary experiment to achieve the ultimate sensitivity using SAS shows
apparent improvement of sensitivity at low frequencies.
In parallel with the improvement by mounting SAS, analog parts of the interferometer control system are being replaced by digital ones.[3] Optimizing filters and lock acquisition procedure are expected to be conducted rather shortertime scale than before, which naturally enhances the speed ofcommissioning.[4] We expect that noise sources of TAMA interferometer are identified by these improvements. In regard
with data analysis, we made reports with LIGO project at thetime when the sensitivity of TAMA300 had competitiveness[5, 6]. Without new observation, persistent activity on thedevelopment of data analysis was conducted using existing
TAMA 300 observation data.[7, 8]

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
[3]. 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).

Fig. 4. Overview of the CLIO interferometer.

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 −19 m/ Hz around 100 Hz,
which would be 10 −18 m/ Hz if cryogenics is not applied [1].
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.
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) [2].
The 57-hours observation data were taken at February
2007 and analyzed for continuous gravitational wave from

34

Fig. 3. Location of the CLIO interferometer.

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

the 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
corresponds to the upper limit on the ellipticity of the neutronstar, ε = 29 [6].
We have started preparing for cooling the mirrors just after the observation. High purity aluminum wires were used

Fig. 6. CLIO displacement noise spectrum: The red curve is the current best sensitivity. The dotted line is the target sensitivity at room
temperature.

as the mirror suspension wires and heat conductor for cooling the mirrors. We tried two configurations[7]. The first isthat only one mirror suspension was modified for the coolingand diameter of 1ṁm high purity aluminum wires are used
for the suspension wires. Figure 7 shows three displacement
noise spectrum those are the best sensitivity presented in Fig.
6, before and after cooling one mirror. This is the first demonstration of the noise suppression of cooling. The second is that
all the suspension wires for the sapphire mirrors are replaced
to the aluminum wires diameter of 0.5ṁm and we tried thecooling all the mirrors. The mirrors were cooled successfully

35

at 14K̇ which is satisfied with our design temperature of 20 K̇
and the mirrors temperature were maintained for 10 months
by refrigerators. Even the mirrors were cooled, operation andcontrol of the interferometer have been done without problem.
Figure 8 shows the displacement noise spectrum, when all themirrors were cooled.

[6] T. Akutsu, submitted for publication (2007)[7] K. Yamamoto, et al., 2008 J. Phys. Conf. Ser. 122 (2008)
012002.

LCGT Project[Spokesperson : Kazuaki Kuroda] ICRR, Univ. of Tokyo,

Fig. 7. CLIO displacement noise spectrum: The blue curve shows thecase that all the mirrors were the room temperature, but one suspension wires were replaced to thick aluminum wires for cooling.
The red curve shows that after one mirror was cooled at 14K̇. The
green curve shows the best sensitivity without cooling.

Kashiwa, Chiba 277-8582
In collaboration with the members of:
LCGT collaboration; National Astronomical Observatory(Japan), KEK, Physics Department (Univ. of Tokyo), Department of Advanced Material Science (Univ. of Tokyo), Earthquake Research Institute (Univ. of Tokyo), Department ofEarth Science and Astronomy (Univ. of Tokyo), Institute for
Laser Science (Univ. of Electro-Communications), Department of Physics (Osaka City Univ.), Department of Physics(Osaka Univ.), Physics Department (Kyoto Univ.), Yukawa
Institute (Kyoto Univ.), Advanced Research Institute for Sciences and Humanities (Nihon Univ.), Agency of Industrial
Science and Technology, National Institute of Information
and Communications Technology, Department of Astronomy(Beijing Normal Univ.), Center for Astrophysics (Univ. of
Science and Technology, China), Institute for High Energy
Physics (Chinese Academy of Science), Inter University Centre for Astronomy & Astrophysics (IUCAA), Physics Department of Physcis (University of Western Australia), Laboratoryof Laser Interferometry (Sternberg State Astronomical Institute, Moscow Univ.), Louisiana State University.

Objective of LCGT

Fig. 8. CLIO displacement noise spectrum: The red curve is the sensitivity with cryogenic cooled mirrors.The blue curve is the current
best sensitivity.

After the discovery of the highly relativistic binary neutron star system 3 , a new young binary pulsar has been detected 4 . The former discovery had increased the coalescence
rate from 10 −6 to 10−5 a year in a galaxy as big as our Galaxy
5 and the latter pushes up by another factor of six. Although
it is a good news for the detection of gravitational waves, we
still need to wait for long time to detect by the presently existing detectors. This is the reason why we have 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.

Bibliography

Status of LCGT Project[1] M. Ohashi, et al., Class. Quantum Grav. 20 (2003) S599.

The target sensitivity of LCGT is to observe binary neutron star coalescence events occurring at 180 Mpc with
S/N=10 in its optimum configuration. [9, 10] This is tentimes more sensitive than that of the LIGO (I), and by two[2] S. Sato, et al., Phys. Rev. D 69 (2004) 102005.
[3] S. Takemoto, et al., Journal of Geodynamics 41 (2006)
23.
[4] S. Miyoki, et al., Class. Quantum Grav. 23 (2006) S231.
[5] T. Uchiyama, et al., Journal of Physics 32 (2006) 259.

*3 M. Burgay, et al., Nature, 426 (2003) 531.
*4 D.R. Lorimer, et al., Astrophysical J. 640(2006) 428.
*5 C. Kim, V. Kalogera and D. R. Lorimer, Astrophysical J. 584 (2003) 985.

36
-15

10

Table 1. LCGT design parameters to detect binary neutron-star coalescence events in 180 Mpc.

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 780 kW
3 cm
Sapphire 30 kg, 20 K
Diameter 25 cm
Mechanical Q:10 8
Frequency: 1 Hz; Q:1 × 10 8
10 K
≤ 10 −7 Paorders more than that of TAMA at their most sensitive frequencies. This will be attained by an interferometers located underground, using a three-kilometer length baseline,
cooling mirrors at cryogenic temperature, and a high-power
laser source employing 150 W output. The optical configuration is a power recycled Fabry-Perot-Michelson interferometer with the resonant-sideband-extraction (RSE) scheme (inFig. 9). The detailed design of the control system is being
tested for the resonant sideband extraction scheme.[11] Table 1 lists the important parameters of LCGT, which were revised three times from the original design.[12] 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 shotnoise 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) islimited by the photon recoil force noise. This requires that
thermal noise is reduced both by decreasing the temperatureand by decreasing the internal mechanical loss (i.e., increasing
the mechanical Q of vibration modes). The source of thermal
noise comes from both mirror internal vibration, mechanicalloss of the optical coating and swing noise of the pendulum
suspending the mirror. The reduction of thermal noise is attained by cooling both the mirror, itself, and the suspension
system that suspends the mirror.
The large change of the design this year was that the number of interferometers was reduced to one in order to consider
the non-negligible increase of material prices, reflecting world
economy, which means that LCGT gave up some part of original data analysis, such as back ground radiation, early detection independent from other observations and so on. However,this does not mean that we gave up to firstly detect the event
but we do our best to keep the attitude of the first detection.
Figure 10 compares the sensitivity curve of LCGT withthose of TAMA, CLIO (a 100 m prototype cryogenic interferometer placed underground of Kmioka mine), LIGO (initial

Sensitivity [1/RHz]

Item
Baseline LengthInterferometer

-16

10

-17

10

-18

10

-19

10

-20

10

-21

10

-22

10

-23

10

-24

10

3

4

5

6

7 8 9

100

2

3

4

5

6

7 8 9

1000

2

3

Frequency [Hz]Fig. 10. LCGT sensitivity (dotted blue line) compared with those of
TAMA (red line), CLIO (a 100m prototype cryogenic interferometer placed underground of Kmioka mine, blue line), LIGO (initial
LIGO, green line) and the design of TAMA (red broken line). The
horizontal axis is frequency [Hz] and the vertical√ axis represents
sensitivity spectrum for gravitational waves [1/ Hz].

LIGO) and the design of TAMA. The sensitivity at low frequencies of LCGT is attained by SAS, which will be provenby the current SAS in TAMA. That of higher frequencies is attained by higher laser power, which has been basically shown
by TAMA. The mid-frequency region is improved by cryogenic mirror and suspension system, which will be proven by
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
put inside a common high-vacuum chamber.
To realize this concept, the following research subjects
were conducted and reported:
1. Removal of heat produced by high-power laser illumination (annual report 1997-1998 and also in references[13])
2. Holding the high Qs of the mirror internal modes andsuspension pendulum [14]3. Reducing the contamination of mirror surfaces (annual
report 2000-2001 and also in [15]).

37

Fig. 9. Optical design of LCGT. The optical configuration is a power recycled Fabry-Perot-Michelson interferometer with the resonant-sideband-extraction (RSE) scheme.

4. Estimating heat production by optical loss in the mirror[16].
5. Alignment control of mirrors in a cryogenic environment [17]6. Low mechanical loss of the optical coating (annual report 2003–2004 and also in reference [18])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.

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.
The most dangerous problem was pointed by Braginskii.
6 Large power density of Fabry-Perot cavity may cause so*6 Braginskii, et al., Physics Lett. A 305 (2002)111.

38

called 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[19].
All of the above R&D confirmed the feasibility of reducing the thermal noise of the interferometer in the middlefrequency region. This research underlines the basis of LCGT.
However, for a practical cryogenic detector, many practical
R&Ds are needed for the installation of cryogenic mirrors.
One of 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 thisKashiwa cryogenic interferometer, we learned the necessityof several practical R&D items and began to construct the
CLIO interferometer in Kamioka to establish techniques forthe cryogenic interferometer.
Practical R&Ds: Measurement of the optical qualities ofsapphire
Fig. 12. Birefringence measurement was applied to a large sapphire
piece weighing 30 kg, which was fixed on a measurement table
and its optical readout system was mounted on the scanning cradle without changing the previous measurement procedure.

−7

x 10

Y[mm]

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. Al 2 O3 monocrystal is selected as the cryogenic mirror substrate because
it has excellent mechanical and thermal properties. However,there are some optical problems to be solved. High opticalabsorption and in-homogeneity of refractivity are concernedwith rather difficult reproducibility of large ingots exceeding 20 cm. While some small-sized Al 2 O3 crystal substrates
have good absorption quality and better homogeneity enoughto satisfy the LCGT requirement (10cm in diameter, 6cm inlength), larger samples have less quality [20]. Moreover, weknow that the fabrication technology of Al 2 O3 crystal to dateis not mature enough to consistently produce large substrates
of adequate quality. In order to inspect optical homogeneity oflarge pieces of Al2 O3 crystal for the production of better quality, we developed a scanning technique of birefringence measurement with high sensitivity and reported the determinationof the optical axis of the uni-axial crystal and the measurement of the fluctuation of birefringence. This measurement
was compared with both the measurement of Rayleigh scattering (University of Western Australia) and the measurementof refractive index (LMA, Laboratoire des Matriaux Avances Universit Claude Bernard Lyon 1 - IN2P3 / CNRS) as reported
in the previous annual report (2004-2005) and confirmed its
sensitivity that makes possible to be used for evaluating optical quality required for LCGT specification.
We applied the measuring system to a large sapphire piece,
250mm in diameter, 100mm in length. This was lent by
the courtesy of LIGO project, which was used to comparewith synthesized silica for the advanced LIGO interferometer. Since it weighs 30 kg, the previous scanning mechanism
is not durable to hold with required precision. Without changing measuring procedure of the previous system, optical readout system was mounted on a revised scanning cradle and the

100

15

50

10
5

0

0
−50
−5
−100
−100

−50

0
X[mm]

50

100

Fig. 13. Result of birefringence measurement of a large sapphire
piece lent from LIGO project. The cylindrical axis coincides with
m-axis of the crystal.

piece was firmly fixed on the measurement table as shown in
Fig. 12.
The result is shown in Fig. 13, which shows un-negligible
defect in the center of the piece. Numerically, the standard deviation of the fluctuated birefringence (σ (δ n)) represents thegrade of homogeneity. The designed beam radius of LCGTat the front mirror is 35 mm and averaged homogeneity ofthis beam area is 2.5 × 10 −7, where the worst homogeneity39

is 5.0 × 10−7, and the best homogeneity is 1.6 × 10 −7. Evenin this small area, the required quality of LCGT is not satisfied. Since homogeneity of even the same grade piece is individually different by nearly three times according to previous
measurements, the fact that this large piece does not meet therequirement does not mean that a piece of higher quality cannot be produced. The important point in this R&D is that weestablish a tool to distinguish the quality required to pass the
specification of LCGT.
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 [22] 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.

Bibliography[10] K. Kuroda et.al., “Current status of LCGT”, Seventh
Edoardo Amaldi conference on gravitational waves,
Sydney, July 8-14, 2007.
[11] F. Kawazoe et al., presented at Amaldi 7 meeting,
Sydney, July 8-14, 2007.
[12] 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.
[13] T. Uchiyama, et.al., Phys. Lett. A 242 (1998) 211.
[14] T. Uchiyama, et.al., Phys. Lett. A 261 (1999) 5;ibid
A273(2000)310.
[15] S. Miyoki, et al., Cryogenics 40 (2000) 61: ibid 41(2001) 415.

[1] H. Tagoshi it et al., Phys. Rev. D 63(2001)062001-1-5.
[16] T. Tomaru, et al., Phys. Lett. A 283 (2001) 80.
[2] R. Takahashi et al., Class. Quantum Grav. 25 (2007)
114036.
[3] D. Tatsumi et al., “TAMA 300 interferometer development”, TAUP 2007, September 11-15, 2007, Sendai.
[4] K. Araiet al., “Recent Progress of TAMA 300”, TAUP
2007, September 11-15, 2007, Sendai; D. Tatsumi et al“Current status of Japanese detectors”, Class. Quantum
Grav. 24(2007)S399.
[5] B. Abbott et al., Phys. Rev. D 72 (2005) 122004.

[17] N. Sato, et al., Cryogenics 43 (2003) 425.
[18] K. Yamamoto, et al., Class. Quantum Grav. 21 (2004)
S1075.
[19] K. Yamamoto, et al., presented at Amaldi 7 meeting,
Sydney, July 8-14, 2007.
[20] M. Tokunari et al., J. Phys.: Conference Series 32 (2006)
432.
[21] Z. Yan, et al., Applied Optics 40(2006) 1.

[6] B. Abbott et al., gr-qc/0512078 (2005)[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.
[9] M. Ohashi et al. “Status of LCGT and CLIO”, TAUP
2007, September 11-15, 2007, Sendai.

[22] Seventh Edoardo Amaldi conference on gravitational
waves, Sydney, July 8-14, 2007.
[23] Seventh Edoardo Amaldi conference on gravitational
waves, Sydney, July 8-14, 2007.

40

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 opearations — SDSS-I — on 30 June 2005 after five years of operation. The goal initially set was to cover 10,000 square degrees of sky, but at the time the production survey began, theFive 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 thesouthern sky). The imaging carried out over 5 years has sustained the planned pace. At the end of the survey 97% of thebaseline 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 the south). This is due to unusually poor weather conditions in the spring 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 re-reduced for a number of times, which are now madepublic as The Data Release of the Sloan Digital Sky Survey I to
VI (DR1-DR6), the last one comprising 8,417 square degrees
of imaging and 6,860 square degrees of spectroscopic surveys
done to 30 June 2006. This database contains 230 million
objects including 1,163,520 objects with spectroscopic information. These numbers include 790,220 galaxies and 102,350
quasars obtained with the uniform selection criteria.
The SDSS has entered a new phase, SDSS-II, continuing
through June, 2008. SDSS-II will carry 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 origion 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. By the second quater of 2007, 100% of imaging and
91% of spectroscopy have been completed.
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. By the second quaterof 2007, 97% of imaging and 63% of spectroscopy have been
completed.
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 teaken at various telescopes
through collabaration 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.

41

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 Ω m = 0.29 ± 0.04, Ω Λ = 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 cosmologicalparameters obtained by combining 3-year WMAP data andSDSS LRG measurements are Ωm = 0.239 ± 0.018, Ω Λ =0.761 ± 0.018 and H 0 = 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, Ω Λ +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 Ω m = 0.256 ± 0.029 using the dependenceof rs on the matter density Ω m (Fig. 2). This value of the matter density is derived from the localtions of BAO in the galaxy
power spectrum and in the CMB. This is an extermely 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 comsmology 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

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).

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).

42

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

models is the so-called “missing satellite” problem. CDM
models predicts at least 1-2 orders of manitude more lowmass sub-halos at the present epoch compared to the observed
abundance of dwarf galaxies surrounding the Milky Way andM31. All-sky photographic surves cover most of the sky, but
are limited to surface brightnesses of ∼ 25.5 mag arcsec −2 .
The selection effects are also difficult to model with accuracy.
The SDSS makes it possible to carry out a systematic survey for satellite galaxis, 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. Graviational
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. Us-

-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.
Fugure is taken from Scranton et al. Astrophys., J. 633, 589(2005).

ing ∼ 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
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 Ω m = 0.26 ± 0.08,ΩΛ = 0.74 ± 0.17, consistent with the values dervied 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.

43

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 extented 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).

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
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 z r = 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 containing 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.

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).

Fig. 7. Bright-end slope of the Quasar Luminosity Function as a function of redshift detemined 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).

44

Theory Grouppotential, by which the electroweak rho parameter is unity at
Lepton Flavour Violating τ Decays in the the tree level. All possible two-body elastic-scattering channels are taken into account to evaluate the S-wave amplitude
Left-Right Symmetric Model[Spokesperson : M. Aoki]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of KEK and Taiwan, Natl.
Cheng Kung U..
The Left-Right symmetric extension of the Standard
Model with Higgs isospin triplets can provide neutrino masses
via a TeV scale seesaw mechanism. The doubly charged
Higgs bosons HL±± and HR±± induce lepton flavour violating
decays τ ± → lll at tree-level via a coupling which is related
to the Maki-Nakagawa-Sakata matrix (VMNS ). We study themagnitude and correlation of τ ± → lll and μ → eγ with specific assumptions for the origin of the large mixing in V MNS
while respecting the stringent bound for μ → eee. It is also
shown that an angular asymmetry for τ ± → lll is sensitive tothe relative strength of the H L±± and HR±± mediated contributions and provides a means of distinguishing models withdoubly charged Higgs bosons.

matrix, and then the condition of perturbative unitarity is imposed on the eigenvalues to obtain constraint on the Higgs parameters. Masses of all scalar bosons turn out to be boundedfrom above, some of which receive more strict upper bounds
as compared to that in the standard model (712 GeV). In particular, the upper bound of the lightest scalar boson, whatever
it would be, is about 270 GeV.

Bibliography[1] A. G. Akeroyd, M. Aoki and Y. Okada, Phys. Rev. D 76
(2007) 013004[2] A. G. Akeroyd, M. Aoki and H. Sugiyama, Phys. Rev. D
77 (2008) 075010[3] M. Aoki and S. Kanemura, Phys. Rev. D 77 (2008)
095009Neutralino Dark Matter in Light Higgs Boson Scenario

Probing Majorana Phases and Neutrino [Spokesperson : M. Senami]
Mass Spectrum in the Higgs Triplet Model Kyoto Univ., Kyoto 606-8501
at the LHC.
[Spokesperson : M. Aoki]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of KEK, Taiwan, Natl.
Cheng Kung U. and SISSA.
Doubly charged Higgs bosons (H ++ ) are a distinctive signature of the Higgs Triplet Model of neutrino mass generation. If H ++ is relatively light (mH ++ < 400GeV) it will
be produced copiously at the LHC, which could enable precise measurements of the branching ratios of the decay channels H ++ → li l j . Such branching ratios are determined solely
by the neutrino mass matrix which allows the model to betested at the LHC. We quantify the dependence of the leptonic branching ratios on the absolute neutrino mass and Majorana phases, and present the permitted values for the channels ee, eμ and μ μ . It is shown that precise measurements ofthese three branching ratios are sufficient to extract information on the neutrino mass spectrum and probe the presence ofCP violation from Majorana phases.

Unitarity bounds in the Higgs model including triplet fields with custodial symmetry[Spokesperson : M. Aoki]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of Toyama U..
We study bounds on Higgs boson masses from perturbative unitarity in the Georgi-Machacek model, whose Higgs
sector is composed of a scalar isospin doublet, a real and acomplex isospin triplet fields. This model can be compatible
with the electroweak precision data without fine tuning because of the imposed global SU(2) R symmetry in the Higgs

In collaboration with the members of KEK, Tohoku Univ., and
SISSA.
Phenomenology of neutralino dark matter in the minimal
supersymmetric model is discussed for a scenario where thelightest Higgs boson mass is lighter than 114.4 GeV. We showthat the scenario is consistent not only with many collider experiments but also with the observed relic abundance of dark
matter. The allowed region may be probed by experimentsof Bs to μ + μ − in near future. The scenario predicts a large
scattering cross section between the dark matter and ordinary
matter and thus it may be tested in present direct detection
experiments of dark matter.

Bibliography[1] M. Asano, S. Matsumoto, M. Senami and H. Sugiyama,
Phys. Lett. B 663 (2008) 330 arXiv:0711.3950 [hep-ph].

Relic abundance of dark matter in universal
extra dimension models with right-handed
neutrinos[Spokesperson : M. Senami]
Kyoto Univ., Kyoto 606-8501
In collaboration with the members of Saitama Univ. and Tohoku Univ..
Relic abundance of dark matter is investigated in theframework of universal extra dimension models with righthanded neutrinos. These models are free from the serious
Kaluza-Klein (KK) graviton problem that the original universal extra dimension model has. The first KK particle of theright-handed neutrino is a candidate for dark matter in this45

framework, and its relic abundance is determined by three processes, (1) the decay of the KK photon into the first KK righthanded neutrino in the late universe, (2) production of the first
KK right-handed neutrino from the thermal bath in the early
universe, and (3) the decay of higher KK right-handed neutrinos into the first KK right-handed neutrino in the late universe.
When ordinary neutrino masses are large enough such as thedegenerate mass spectrum case, the last process contribute to
the abundance significantly, even if the reheating temperature
is low. The scale of the extra dimension consistent with cosmological observations can be 500 GeV in the minimal setup
of universal extra dimension models with right-handed neutrinos.

Bibliography[1] S. Matsumoto, J. Sato, M. Senami and M. Yamanaka,
Phys. Rev. D 76 (2007) 043528 [arXiv:0705.0934 [hepph]].

Primordial Non-Gaussianity in Multi-Scalar
Slow-Roll Inflation.
[Spokesperson : T. Suyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of Kyoto University
We analyze the non-Gaussianity for primordial curvature perturbations generated in multi-scalar slow-roll inflation
model including the model with non-separable potential bymaking use of δ N formalism. Many authors have investigatedthe possibility of large non-Gaussianity for the models withseparable potential, and they have found that the non-linear
parameter, f NL , is suppressed by the slow-roll parameters. We
show that for the non-separable models f NL is given by the
product of a factor which is suppressed by the slow-roll parameters and a possible enhancement factor which is given by
exponentials of quantities of O(1).

Bibliography[1] S. Yokoyama, T. Suyama and T. Tanaka, JCAP 07, 013(2007) [arXiv:0705.3178 [astro-ph]].

Non-Gaussianity in the modulated reheating scenario.
[Spokesperson : T. Suyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of Aoyamagauin University
We investigate the non-Gaussianity of primordial curvature perturbation in the modulated reheating scenario where
the primordial perturbation is generated due to the spacial
fluctuation of the inflaton decay rate to radiation. We use theδ N formalism to evaluate the trispectrum of curvature perturbation as well as its bispectrum. We give expressions forthree non-linear parameters f NL , τNL and gNL in the modulated reheating scenario. If the intrinsic non-Gaussianity of
scalar field fluctuations and third derivative of the decay ratewith respect to scalar fields are negligibly small, g NL has atleast the same order of magnitude as f NL . We also give general inequality between f NL and τNL which is true for otherinflationary scenarios as long as primordial non-Gaussianity
comes from super-horizon evolution.

Bibliography[1] T. Suyama and M. Yamaguchi, Phys. Rev. D 77, 023505(2008) [arXiv:0709.2545 [astro-ph]].

Primordial Non-Gaussianity in Multi-Scalar
Inflation.
[Spokesperson : T. Suyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of Kyoto University
We give a concise formula for the non-Gaussianity of theprimordial curvature perturbation generated on super-horizon
scales in multi-scalar inflation model without assuming slowroll conditions. This is an extension of our previous work. Using this formula, we study the generation of non-Gaussianity
for the double inflation models in which the slow-roll conditions are temporarily violated after horizon exit, and we showthat the non-linear parameter f NL for such models is suppressed by the slow-roll parameters evaluated at the time ofhorizon exit.

Bibliography[1] S. Yokoyama, T. Suyama and T. Tanaka, Phys. Rev. D
77, 083511 (2008) [arXiv:0711.2920 [astro-ph]].

Non-Gaussianity, Spectral Index and Tensor Modes in Mixed Inflaton and Curvaton
Models.
[Spokesperson : T. Suyama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, Saga University
and Aoyamagakuin University
We study non-Gaussianity, the spectral index of primordial scalar fluctuations and tensor modes in models wherefluctuations from the inflaton and the curvaton can both contribute to the present cosmic density fluctuations. Even thoughsimple single-field inflation models generate only tiny nonGaussianity, if we consider such a mixed scenario, large nonGaussianity can be produced. Furthermore, we study the inflationary parameters such as the spectral index and the tensorto-scalar ratio in this kind of models and discuss in what cases
models predict the spectral index and tensor modes allowedby the current data while generating large non-Gaussianity,
which may have many implications for model-buildings of theinflationary universe.

Bibliography[1] K. Ichikawa, T. Suyama, T. Takahashi and M. Yamaguchi, arXiv:0802.4138 [astro-ph].

46"Flavored" Electric Dipole Moments in SuWe derive general constraints on the relic abundances of apersymmetric Theories
long-lived particle which mainly decays into a neutrino (and[Spokesperson : M. Nagai]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR and Valencia
Univ..
The Standard Model (SM) predictions for the hadronic
electric dipole moments (EDMs) are well far from the present
experimental resolutions, thus, the EDMs represent very clean
probes of New Physics (NP) effects. Especially, within an
MSSM framework with flavor-changing (but not necessarily
CP violating) soft terms, large and potentially visible effects
to the EDMs are typically expected. In this Letter we pointout that, beyond-leading-order (BLO) effects, so far neglectedin the literature, dominate over the leading-order (LO) effects
in large regions of the parameter space, hence, their inclusionin the evaluation of the hadronic EDMs is unavoidable.

Bibliography[1] J. Hisano, M. Nagai and P. Paradisi, arXiv:0712.1285[hep-ph].

Stability of Metastable Vacua in Gauge Mediated SUSY Breaking Models with Ultra
Light Gravitino[Spokesperson : M. Nagai]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR.
Recently Murayama and Nomura proposed a simple
scheme to construct the gauge mediation models, using mextastable supersymmetry breaking vacua. It has a possibility to
predict the ultra light gravitino mass with a mass less than 16eV, while such a light gravitino may destabilize the metastablevacua. We investigate stability of the metastable vacuum of
their model. The transition rate from the false vacuum totrue ones is evaluated by numerical calculation, including the
Coleman-Weinberg potential destabilizing the metastable vacuum. It is found that when the messenger sector is minimal,
stability of the metastable vacuum imposes an upperbound on
squark mass Msq for the ultra light gravitino as M sq <1800
GeV at most. Squarks with this mass may be found in the
LHC experiments.

Bibliography[1] J. Hisano, M. Nagai, M. Senami and S. Sugiyama, Phys.
Lett. B 659 (2008) 361 [arXiv:0708.3340 [hep-ph]].

Cosmological constraints on neutrino injection[Spokesperson : T. Kanzaki
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, Lancaster Univ.
and Tohoku Univ..

something else) at cosmological time scales. Such an exotic
particle may show up in various particle-physics models basedon physics beyond the standard model. The constraints are
obtained from big-bang nucleosynthesis, cosmic microwave
background and diffuse neutrino and photon fluxes, depending on the lifetime and the electromagnetic and hadronicbranching ratios.

Bibliography[1] T. Kanzaki, M. Kawasaki, K. Kohri and T. Moroi Phys.
Rev. D 76, 105017 (2007).

Affleck-Dine leptogenesis via multiscalarevolution
in a supersymmetric seesaw model[Spokesperson : T. Takayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the member of Kyoto Univ.
A leptogenesis scenario in a supersymmetric standard
model extended with introducing right-handed neutrinos is reconsidered. Lepton asymmetry is produced in the condensate
of a right-handed sneutrino via the Affleck-Dine mechanism.
The LHu direction develops large value due to a negative effective mass induced by the right-handed sneutrino condensate through the Yukawa coupling of the right-handed neutrino, even if the minimum during the inflation is fixed at theorigin. The lepton asymmetry is nonperturbatively transferedto the LHu direction by this Yukawa coupling.

Bibliography[1] M. Senami and T. Takayama, JCAP 0711 (2007) 015

Formation of IMBHs as PBHs in the inflationary cosmology with running spectral index[Spokesperson : T. Takayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, Aoyama Gakuin
Univ., RESCEU and IPMU.
Formation of primordial black holes (PBHs) on astrophysical mass scales is a natural consequence of inflationary cosmology if the primordial perturbation spectrum has a large
and negative running of the spectral index as observationallysuggested today, because double inflation is required to explain it and fluctuations on some astrophysical scales are enhanced in the field oscillation regime in between. It is argued
that PBHs thus produced can serve as intermediate-mass black
holes (IMBHs) which act as the observed ultraluminous X-ray
sources (ULXs) by choosing appropriate values of the model
parameters in their natural ranges. Our scenario can be observationally tested in near future because the mass of PBHs
is uniquely determined once we specify the values of the amplitude of the curvature perturbation, spectral index and its
running on large scales.

47

Bibliography[1] T. Kawaguchi, M. Kawasaki, T. Takayama, M. Yamaguchi and J. Yokoyama, arXiv:0711.3886 [astro-ph]Increasing effective number of neutrinos bydecaying particles[Spokesperson : K. Nakayama]

In mirage-mediation models there exists a modulus field
whose mass is O(1000) TeV and its late-decay may significantly change the standard thermal relic scenario of the dark
matter. We study nonthermal production of the dark matter directly from the modulus decay, and find that for some parameter regions non-thermally produced neutralinos can become
the dark matter.

ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR and DESY.
We present models of decaying particles for increasing theeffective number of neutrinos N ν after big bang nucleosynthesis but before the structure formation begins. We point out
that our scenario not only solves the discrepancy between theconstraints on Nν from these two epochs, but also provides
a possible answer to deeper inconsistency in the estimationof the matter power spectrum amplitude at small scales, represented by σ8 , between the WMAP and some small scalematter power measurements such as the Lyman-alpha forest
and weak lensing. We consider (a) saxion decay into twoaxions; (b) gravitino decay into axino and axion; (c) Diracright-handed sneutrino decay into gravitino and right-handed
neutrino.

Bibliography[1] K. Ichikawa, M. Kawasaki, K. Nakayama, M. Senami
and F. Takahashi, JCAP 0705 (2007) 008 [arXiv:hepph/0703034].

Baryon Asymmetry in Heavy Moduli Scenario[Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR.
In some models of supersymmetry breaking, modulus
fields are heavy enough to decay before BBN. But the large
entropy produced via moduli decay significantly dilutes thepreexisting baryon asymmetry of the universe. We study
whether Affleck-Dine mechanism can provide enough baryon
asymmetry which survives the dilution, and find several situations in which desirable amount of baryon number remains
after the dilution. The possibility of non-thermal dark matter is also discussed. This provides the realistic cosmologicalscenario with heavy moduli.

Bibliography[1] M. Kawasaki and K. Nakayama, Phys. Rev. D 76 (2007)
043502 [arXiv:0705.0079 [hep-ph]].

Nonthermal dark matter in mirage mediation[Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR.

Bibliography[1] M. Nagai and K. Nakayama, Phys. Rev. D 76 (2007)
123501 [arXiv:0709.3918 [hep-ph]].

Cosmological implications of supersymmetric axion models[Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR.
We derive general constraints on supersymmetric extension of axion models, in particular paying careful attention to
the cosmological effects of saxion. It is found that for every
mass range of the saxion from keV to TeV, severe constraints
on the energy density of the saxion are imposed. Together
with constraints from axino we obtain stringent upper bounds
on the reheating temperature. We also find that all the cosmological difficulties, including gravitino, axino overproduction
and axionic isocurvature fluctuation, can be avoided if the saxion field has large initial amplitude during inflation and decays
before big-bang nucleosynthesis.

Bibliography[1] M. Kawasaki, K. Nakayama and M. Senami, JCAP 0803
(2008) 009 [arXiv:0711.3083 [hep-ph]].
[2] M. Kawasaki and K. Nakayama, arXiv:0802.2487 [hepph], to be published in Phys. Rev. D.

Space laser interferometers can determine
the thermal history of the early Universe[Spokesperson : K. Nakayama]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR, Univ. of Tokyoand RESCEU.
It is shown that space-based gravitational wave detectors
such as DECIGO and/or Big Bang Observer (BBO) will provide us with invaluable information on the cosmic thermal
history after inflation and they will be able to determine thereheat temperature TR provided that it lies in the range preferred by the cosmological gravitino problem, T R ∼ 105−9
GeV. Therefore it is strongly desired that they will be put into
practice as soon as possible.

Bibliography[1] K. Nakayama, S. Saito, Y. Suwa and J. Yokoyama,
arXiv:0802.2452 [hep-ph], to be published in Phys. Rev.
D.

48

Cosmological Constraints on Isocurvature
and Tensor Perturbations[Spokesperson : T. Sekiguchi]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR.
We investigate cosmological constraints on primordial
isocurvature and tensor perturbations, using recent observations of the cosmic microwave background and the large scale
structure. We find that present observations are consistent
with purely adiabatic initial conditions for the structure formation under any priors on correlations of isocurvature modes,
and upper limits on the contribution of isocurvature and tensor
perturbations are presented. We also apply the obtained constraints to some specific theoretical models, axion isocurvature perturbation models and curvaton models, and give some
implications for theoretical models.

Primordial Helium Abundance from CMB: aconstraint from recent observations and aforecast[Spokesperson : T. Sekiguchi]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR and Saga Univ.
We study a constraint on the primordial helium abundance Yp from current and future observations of CMB. Using
the currently available data from WMAP, ACBAR, CBI and
BOOMERANG, we obtained the constraint as Y p = 0.25 ±0.10 at 1σ level. We also provide a forecast for Planck using the Markov Chain Monte Carlo approach. In addition toforecasting the constraint on Y p , we investigate how assumptions for Y p affect the constraints on the other cosmologicalparameters.

Probing the Effective Number of Neutrino Species with Cosmic Microwave Background[Spokesperson : T. Sekiguchi]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of ICRR and Saga Univ.
We discuss how much we can probe the effective number of neutrino species Nν with cosmic microwave background alone. Using the data of WMAP, ACBAR, CBI and
BOOMERANG experiments, we obtain a constraint on theeffective number of neutrino species as 0.23 < N ν < 5.54 at
95% C.L. for a power-law LCDM flat universe model. The
limit is improved to be 0.64 < N ν < 5.03 at 95% C.L. if
we assume that the baryon density, N ν and the helium abundance are related by the big bang nucleosynthesis theory. We
also provide a forecast for the PLANCK experiment using a
Markov chain Monte Carlo approach. In addition to constraining Nν , we investigate how the big bang nucleosynthesis relation affects the estimation for these parameters and the othercosmological parameters.

Bibliography[1] M. Kawasaki and T. Sekiguchi, arXiv:0705.2853.
[2] K. Ichikawa, T. Sekiguchi and T.
arXiv:0712.4327

Takahashi,[3] K. Ichikawa, T. Sekiguchi and T.
arXiv:0803.0889.

Takahashi,

49

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

Norikura Observatory
Location:
Telephone (Fax):
Telephone (satellite):Telephone (car):Nyukawa-mura, Ohno-gun, Gifu Prefecture 506-2100
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:

Akeno-mura, Kitakoma-gun, 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

50

Norikura Observatory[Director of Norikura Observatory : Masato Takita]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of:1.

which 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.

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 possiblities 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 of2.

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 m 2 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 obsevation network
point (WDC). The 5 years from 2000 corresponded to thesolar 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 acitivities 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 m 2 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]).

51

The Sun is the nearest site to the Earth capable of accelerating particles up to high energies. When the Sun becomes
active, flares are frequently observed on its surface. The flareaccelerates the proton and ion to high energy and they are detected on the Earth soon after the flare. Among the particles
generated by the flare, high energy neutrons provide the mostdirect information about the acceleration mechanism as theycome straight from the flare position to the Earth without deflected by the magnetic field.
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 Ob-

servatory 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 consecquence 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 m 2 ) 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 the-52sis (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.
Norikura.

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) Polluted air pumping effects over central Japanese Alps insummer(1) Tree line dynamics

Under 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

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 to

53

the temperature enhancement of about 0.8 ◦ C for air temper-

Silva, N. B. Trivedi, W. D. Gonzalez and N. J. Schuch,
Adv. Space Res., doi:10.1016/j.asr.2003.05.064, 2005, inpress.

ature and about 0.3 ◦ C for ground temperature, plant growth
rates and phenological changes showed notable differences
between inside and outside of the chambers. The responses towarming, however, were different by different plant species.
The results suggest[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.

[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.

Bibliography[10] “Effects of atmospheric electric fields on cosmic rays”,
Y. Muraki et al., Phys. Rev. D, 69, 123010–1-13 (2004).

[1] “Precursors of geomagnetic storms observed by themuon detector networ”, 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 heliospher”, 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.

[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).

54

AKENO Observatory
Observatory
The 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.
It was established in 1977 as a research center for air
shower studies in the very high energy region. The Observatory has been administered by the ICRR as a facility of jointuniversity-use. An important part of observatory’s scientificoutputs originates from the university collaborators.
Fig. 1. Aerial View of Akeno Observatory and 1 km2 Array Area

From 1 km2 Array to AGASAThe Akeno Air Shower Experiment started in 1979 withan array covering 1 km 2 area (1 km 2 array). The array wasenlarged to 20 km 2 in 1985 and was gradually expanded to
Akeno Giant Air Shower Array (AGASA) of approximately
100 km2 area by 1990. The observation by AGASA continued
for 13 years until the beginning of 2004.
One of the distinctive features of Akeno experiments isthat the measurement was made over five decades of energies
well covering 10 15 eV - 1020 eV by using both the surface detector (for electromagnetic component) and the shielded detector (for muon component). This feature is well demonstrated in Fig.2; the spectra from Akeno 1 km 2 for 1014.7 eV 1018.7 eV [1, 2] and AGASA for 10 18.6 eV - 1020.3 eV [3] areplotted by open squares and solid circles in red. The wide energy coverage was accomplished by the arrays of scintillation
detectors of various inter-detector spacings from 3 m to 1 km
and with different triggering conditions.
The analysis had been made with similar algorithm under
the same definition of single particle throughout the energy
range covered. A difference exists however for the conversion
method to the primary energy; the total number of electrons
Ne is used for 1 km 2 array and the local density at 600 m fromthe shower core S(600) is used for AGASA. A shift of ∼10%in energy is seen between AGASA and 1 km 2 array around1018.5 eV. This is due to the difference of energy conversion
methods employed by two experiments.
at the maximum of shower developThe parameter N maxement is well known as one of the best primary energy estimators which does not depend sensitively on the interaction
model or primary composition. The observed N e at Akeno
experimentally with the longitudinal
was converted to N maxeshower development curves determined with constant intensity cut method of integral N e spectra measured at Mt. Chacaltaya and at Akeno[1]. The result around the knee is consistent with all-particle spectra extrapolated from the direct
measurements and those of recent results from Tibet[4] andKASCADE[5].
However, as seen in Fig.2, there are large discrepancies
among experiments in the highest energy region. It should
be noted that the systematic deviation among experiments already starts at 1017 eV. New data coming from TA and Pierre
Auger will have to be understood in a consistent manner withexisting lower energy data.

Research and Development
Facilities of Akeno Observatory have been used for a variety of air shower studies, detector developments and associated researches. Activities of recent 6 years (2002 - 2007) arelisted below.
• Study of EHECRs by AGASA by M.Teshima a,b,
N.Hayashidaa and AGASA collaboration (2000-2005).
• Research and Development of Telescope Array Detectors by Y.Araic , M.Chikawad , M.Fukushima a,
K.Hashimotoe , K.Hondae , N.Inoue f, F.Kakimotog,
S.Ogiog,h ,H.Sagawaa,
M.Sasakia ,Y.Tanakai,jS.Yoshida and TA collaboration (2000-2007).
• Observation of UHECRs with Lead-Burger Detector by
K.Hondae et al. (2000-2003).
• Observation of Air Shower Core for E > 10 16 eV by
H.Sakuyamak and N.Suzuki k et al. (2000-2004).
• Test Measurement of HE Cosmic Rays using Wide Angle Refractive Optics by H.Shimizu l , S.Ebisuzakil and
EUSO collaboration (2001-2005).
• Energy Calibration of AGASA Event with Schmidt
Type Air Fluorescence Telescope (CRIS) by S.Yoshida j
et al. (2002).
• Measurement of Galactic Cosmic Ray Flux with Large
Muon Telescope by S.Kawakami h et al. (2000-2007).
• Study of Cosmic Evolution by Quick Observation of
GRBs by S.Kawaig et al. (2003-2007).
• On-line Observation of GRBs by Wide Angle Optical
Telescope by T.Tamagawa l et al. (2003-2006).
• Chemical Composition of Primary Cosmic Rays for1017 eV < E < 1018 eV by M.Nagano m et al. (2003).
• Research and Development for High Resolution All
Sky Cosmic Ray Telescope by Y.Arai c , M.Ieiric ,R.Ogawan , M.Sasakia , Y.Tanakai , Y.Watanabeg et al.
(2003-2005).

26

3

2

-2 -1

-1

log(FLUX * E in eV m s sr )

55

25.5

25

24.5

24

23.5

23
14

15

16

17

18

19

20

21

log(ENERGY in eV)
Fig. 2. Energy Spectra of Cosmic Rays between 1014 eV and 1020.3 eV. The data marked as “Auger 2005” and “HiRes Stereo 2005” were
presented in the 29th ICRC in 2005, Pune.

• Effect of Cloud for Cosmic Ray Observation fromSpace by M.Nagano m et al. (2005).
a: Institute for Cosmic Ray Research, University of Tokyob: Max Planck Institute for Physics, Muenchen
c: Institute of Particle and Nuclear Studies, KEK, Tsukuba
d: Kinki University, Osaka
e: Yamanashi University, Kofu
f: Saitama University, Saitama
g: Tokyo Institute of Technology, Tokyoh: Osaka City University, Osaka
i: Nagasaki Institute of Applied Science, Nagasaki
j: Chiba University, Chiba
k: Meisei University, Tokyol: Riken Institute of Physical and Chemical Research, Tokyo
m: Fukui University of Technology, Fukui
n: Toho University, Tokyo

This manuscript was prepared by M.Nagano and
M.Fukushima.

Bibliography[1] M. Nagano et al., J. Phys. G: Nucl. Phys. 10, 1295
(1984).
[2] M. Nagano et al., J. Phys. G: Nucl. Phys. 18, 423 (1992).
[3] M. Takeda et al., Astropart. Phys. 19, 447 (2003).
[4] M. Takita et al., ICRR Annual Report (2005) p.23.
[5] T. Antoni et al., Astropart. Phys. 24, 1 (2005)

56

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 summer in 2009.

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

57

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 is theorganization of neutrino-related meetings. On Sep. 30th andOct.1st,, 2007, we organized 3rd International Workshop on a
Far Detector in Korea for the J-PARC Neutrino Beam. This
meeting was supported by JSPS (Japan) and KOSEF (Korea),
and was held at the University of Tokyo. 47 participants discussed the potential physics of neutrinos by detecting neutrinos in Korea. In addition, members of this Center were the key
members on the organization of ”Workshop on Next Generation Nucleon Decay and Neutrino Detectors 2007 (NNN07)”,
which was held at Hamamatsu on Oct.2nd to 5th. The meeting
was successful. On Nov. 2nd, 2007, we hosted one domestic
neutrino workshop on ”Recent neutrino oscillation data andthe implications of the large-mixing angles”. About 35 physicists participated in 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 FY2007, the public lecture washeld on April 7 (Sat) at Kashiwa. Two active scientists related to neutrino physics lectured on various aspects of neutrino physics. About 200 people heard the lectures.
This Center, together with the computer committee of
ICRR, is in charge of operating the central computer system
in ICRR. In FY2007, the computer system was upgraded byabout a factor of 5 to 10 in the performance relative to theprevious one.
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. 1. Public lecture held in Kashiwa in April 7, 2007.

Fig. 2. New computer facility that have started its operation in FY2007.

58

APPENDICES

A. ICRR International Workshops
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) Executive Committee(c) Advisory Committee

H. List of Personnel

59

A. ICRR International Workshops
Workshop on Next Generation Nucleon Decay and Neutrino Detector 2007
Date: October 2-5, 2007
Place: Hamamatsu, Japan(ICRR and KEK, and sponsored in part by Inoue Foundation for Science and HPK.)

OutlineThis series of workshops is organized to discuss about- Nucleon decay searches- Accelerator-based neutrino oscillation experiments- Neutrinos from supernovae, atmosphere, and Sun- Large detector technology- Photosensors... and others

NNN07 Program Advisory Committee
E. W.Beier (Pennsylvania U.), V. Berger (Wisconsin U.), J.-E. Campagne (LAL Orsay), J. Ellis (CERN), F. von Feilitzsch(TU Munchen), D. Finley (Ferimilab), B. Kayser (Columbia U. and Ferimilab), M. Lindner (MPI Heidelberg), N. K. Mondal(TIFR Mumbai), L. Mosca (CEA Saclay), K. Nishikawa (KEK), A. Rubbia (ETH Zurich), K. Sato (U. of Tokyo), H. Sobel(UC Irvine), A. Suzuki (KEK), Y. Suzuki (ICRR), Y. Totsuka (KEK), J. Wilkes (U. of Washington), T. Yanagida (U. of Tokyo).

NNN Steering Committee
C. K. Jung (Stony Brook U.), S. Katsanevas (IN2P3), K. Nakamura (KEK) .

NNN07 Local Organization Committee
H. Aihara (U. of Tokyo), K. Hagiwara (KEK), Y. Hayato (ICRR), J. Hisano (ICRR), T. Kajita (co-chair, ICRR), K. Kaneyuki(scientific-secretary, ICRR), M. Nakahata (ICRR), K. Nakamura (co-chair, KEK), K. Okumura (ICRR), C. Saji (KEK), M.
Shiozawa (ICRR).

Participants
40 from Japan, 48 from USA, 5 from Germany, 3 from Italy, 2 from Korea, 1 from Canada, 1 from Switzerland, 1 from
Russia, 1 from Poland.

B. ICRR Seminars
Date

LecturerTitle

Apr 13, 2007

Shigeki Matsumoto“ Hunting for the Top Partner in the Littlest Higgs Model with T-parity
at the LHC ”(Tohoku University)

Apr 19, 2007

Mayumi Aoki

“ Lepton Flavor Violating Tau Decay in the Left-Right Symmetric
Model ”(ICRR, University of Tokyo)

Apr 19, 2007

Sergey Petcov(SISSA/INFN, Itary and INRNE, Bulgaria)“ Low-Energy Leptonic CP-Violation and Leptogenesis ”

60

Apr 26, 2007

Teruaki Suyama“ Primordial Non-Gaussianity in Multi-Scalar Slow-Roll Inflation ”(ICRR, University of Tokyo)

May 22, 2007

Jennifer Raaf

“ First Oscillation Results from MiniBooNE ”(Boston University)

May 24, 2007

Kin-ya Oda“ Possibility of black hole production at LHC ”(RIKEN)Jun 1, 2007

Edwin L. Turner“ An Astrophysicist’s View of the Origin of Life Problem ”(Princeton University)

Aug 1, 2007

Alexander Dolgov“ Antimatter in the Galaxy ”(University of Ferrara, Italy /ITEP, Moscow, Russia / ICRR)

Aug 2, 2007

Kendall Mahn

“ Recent results and future plans for the Booster Neutrino Beamline ”(Columbia Univ)

Sep 10, 2007

Hiroaki Yamamoto“ From Initial LIGO to Advanced LIGO ”(LIGO, Caltech)Sep 10, 2007

Carsten Rott

“ Latest Results from the IceCube Experiment ”(Pennsylvania State University)

Oct 19, 2007

Hansjoerg Dittus“ Gravitational Physics on the Post-Newtonian Level with Satellites ”(ZARM, University of Bremen)

Oct 24, 2007

Rennan Barkana“ Cosmology with 21-cm Radio Observations ”(ICRR; University of Tel Aviv)

Oct 25, 2007

Toshio Namba“ Tabletop experiments –QED, axion, and so on– ”(ICEPP, University of Tokyo)

Nov 1, 2007

Kiyotomo Ichiki“ Creation of Magnetic Field and Gravitational Waves from Cosmological Density Perturbations, and their Ovservational Implications ”(University of Tokyo)

Nov 29, 2007

Tokonatsu Yamamoto“ Observation of Highest Energy Cosmic Ray by the Pierre Auger Observatory: status and prospective ”(Konan University)

Jan 8, 2008

Jozsef Kota

“ Acceleration of Energetic Particles at the Solar-wind Termination
Shock: Lessons from Voyager 1 and 2 ”(Lunar and Planetary Laboratory, University of Arizona,
Tucson, USA / ICRR)Jan 22, 2008

Peter Wessels“ High power lasers for gravitational wave detection ”(LZH, Germany)

Mar 6, 2008

Hidekazu Tanaka“ The SciBooNE neutrino experiment at Fermilab ”(Columbia University)

Mar 14, 2008

Johannes Bluemer(Karlsruhe Institute of Technology KIT / University andForschungszentrum Karlsruhe)“ The Pierre Auger Observatory: results on ultra-high energy cosmic
particles ”

61

C. List of Publications — 2007 fiscal year(a) Papers Published in Journals
1. “Solar Neutrino Measurements in Super–Kamiokande–II”, Super-Kamiokande Collaboration, Submitted to Phys. Rev.
D, arXiv:0803.4312[hep-ex]. Additional information in http://www-sk.icrr.u-tokyo.ac.jp/sk/lowe/sk2 data/
2. “Search for Supernova Neutrino Bursts at Super-Kamiokande”, Super-Kamiokande Collaboration, Astrophys J. 669(2007) 519, arxiv:0706.2283[astro-ph].
3. “A measurement of atmospheric neutrino flux consistent with tau neutrino appearance”, Super-Kamiokande Collaboration, Submitted to Phys. Rev. Lett., hep-ex/0607059.
4. “Search for Matter-Dependent Atmospheric Neutrino Oscillations in Super-Kamiokande”, Super-Kamiokande Collaboration, Phys. Rev. D 77 (2008) 052001.
5. “Experimental study of the atmospheric neutrino backgrounds for proton decay to positron and neutral pion searches inwater Cherenkov detectors”, K2K Collaboration, Phys. Rev. D., 77, 032003, 2008.
6. “CANGAROO-III Search for Gamma Rays from Centaurus A and the Ω Centauri Region”, S. Kabuki et al., Astrophys.
J. 668, 968 (2007).
7. “CANGAROO-III Search for Gamma Rays from SN 1987A and the Surrounding Field”, R. Enomoto et al., Astrophys.
J. 671, 1939 (2007).
8. “CANGAROO-III Observations of the 2006 Outburst of PKS2155-304”, Y. Sakamoto et al., Astrophys. J. 676, 113(2008).
9. “Observation of an extended VHE gamma-ray emission from MSH 15−52 with CANGAROO-III”, T. Nakamori et al.,Astron. Astrophys. 677, 297 (2008).
10. “Observation of Very High Energy gamma rays from HESS J1804−216 with CANGAROO-III Telescopes”, Y. Higashi
et al., Astrophys. J. 683, 957 (2008).
11. “CANGAROO-III Search for Gamma Rays from Kepler’s Supernova Remnant”, R. Enomoto et al., Astrophys. J. 683,
383 (2008).
12. “Very high energy gamma-ray observations of the Galactic Plane with the CANGAROO-III telescopes”, M. Ohishi etal., Astropart. Phys. 30, 47 (2008).
13. “CANGAROO-III Search for TeV Gamma-Rays from Two Clusters of Galaxies”, R. Kiuchi et al., submitted for publication (2008).
14. “Study on Machining of Large Acrylic Lens,” Katsuta,T., Yokomizo,S., Sasaki, M., Journal of the Japan Society ofPrecision Engineering, 73, No.2, 215-219 (Feb., 2007).
15. “All-sky Survey High Resolution Air-Shower Detector (Ashra),” Sasaki,M., Proceeding of International Workshop on
Energy Budget in the High Energy Universe (ICRR, Kashiwa), edit. by Sato, K. and Hisano, J., 197-204 (March, 2007).
16. “Implication of the sidereal anisotropy of 5TeV cosmic ray intensity observed with the Tibet III air shower array”, M.
Amenomori et al., Proceedings in AIP Conf. 932 283–289, (2007).
17. “Underground water Cherenkov muon detector array with the Tibet air shower array for gamma-ray astronomy in the
100 TeV region”, M. Amenomori et al., Astrophysics and Space Science 309 435–439, (2007).
18. “Moon Shadow by Cosmic Rays under the Influence of Geomagnetic Field and Search for Antiprotons at Multi-TeV
Energies”, M. Amenomori et al., Astroparticle Physics 28 137–142, (2007).
19. “New Estimation of the Spectral Index of High-Energy Cosmic Rays as Determined by the Compton-Getting
Anisotropy”, M. Amenomori et al., ApJ 672 L53–L56, (2008).
20. “Current status of Japanese detectors”, D. Tatsumi et al, Class. Quantum Grav. 24(2007)S399.
21. “Multi-Slit Imaging Spectroscopy Technique: Catalog of Intracluster Planetary Nebulae in the Coma Cluster”, Arnaboldi, M., et al., PASJ, 59, 419-425 (2007)

62

22. “The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations”, Phillips, M. M., et al., PASP, 119,360-387 (2007)
23. “The kinematics of intracluster planetary nebulae and the on-going subcluster merger in the Coma cluster core”, Gerhard,O., et al., A&A, 468, 815-822 (2007)
24. “Rest-Frame R-band Light Curve of a z ∼ 1.3 Supernova Obtained with Keck Laser Adaptive Optics”, Melbourne, J., etal., AJ, 133, 2709-2715 (2007)
25. “The Sloan Digital Sky Survey Quasar Catalog. IV. Fifth Data Release”, Schneider, D. P., et al., AJ, 134, 102-117 (2007)
26. “Quantitative comparison between type Ia supernova spectra at low and high redshifts: a case study”, Garavini, G., etal., A&A, 470, 411-424 (2007)
27. “A Catalog of Morphologically Classified Galaxies from the Sloan Digital Sky Survey: North Equatorial Region”,
Fukugita, M., et al., AJ, 134, 579-593 (2007)
28. “Spatial Variations of Galaxy Number Counts in the Sloan Digital Sky Survey. II. Test of Galactic Extinction in HighExtinction Regions”, Yasuda, N., et al., AJ, 134, 698-705 (2007)
29. “Wide-Field Survey around Local Group Dwarf Spheroidal Galaxy Leo II: Spatial Distribution of Stellar Content”,
Komiyama, Y., et al., AJ, 134, 835-845 (2007)
30. “Sloan Digital Sky Survey Standard Star Catalog for Stripe 82: The Dawn of Industrial Optical Photometry”, Ivezić, Ž.,et al., AJ, 134, 973-998 (2007)
31. “The Fifth Data Release of the Sloan Digital Sky Survey”, Adelman-McCarthy, J. K., et al., ApJS, 172, 634-644 (2007)
32. “Life Products of Stars”, Serenelli, A. M., Fukugita, M., ApJS, 172, 649-662 (2007)
33. “Exploring the Variable Sky with the Sloan Digital Sky Survey”, Sesar, B., et al., AJ, 134, 2236-2251 (2007)
34. “Supernovae in the Subaru Deep Field: an initial sample and Type Ia rate out to redshift 1.6”, Poznanski, D., et al.,MNRAS, 382, 1169-1186 (2007)
35. “The Sloan Digital Sky Survey-II Supernova Survey: Technical Summary”, Frieman, J. A., et al., AJ, 135, 338-347(2008)
36. “The Sloan Digital Sky Survey-II Supernova Survey: Search Algorithm and Follow-Up Observations”, Sako, M., et al.,AJ, 135, 348-373 (2008)
37. “The Sloan Digital Sky Survey Quasar Lens Search. III. Constraints on Dark Energy from the Third Data Release Quasar
Lens Catalog”, Oguri, M., et al., AJ, 135, 512-519 (2008)
38. “The Milky Way Tomography with SDSS. I. Stellar Number Density Distribution”, Jurić, M., et al., ApJ, 673, 864-914(2008)
39. “A New Determination of the High-Redshift Type Ia Supernova Rates with the Hubble Space Telescope Advanced
Camera for Surveys”, Kuznetsova, N., et al., ApJ, 673, 981-998 (2008)
40. “The Subaru/XMM-Newton Deep Survey (SXDS). VI. Properties of Active Galactic Nuclei Selected by Optical Variability”, Morokuma, T., et al., ApJ, 676, 121-130 (2008)
41. “The Subaru/XMM-Newton Deep Survey (SXDS). V. Optically Faint Variable Object Survey’2”, Morokuma, T., et al.,ApJ, 676, 163-183 (2008)
42. “Lepton Flavour Violating tau Decays in the Left-Right Symmetric Model”, A. G. Akeroyd, M. Aoki and Y. Okada,Phys. Rev. D 76 (2007) 013004
43. “Probing Majorana Phases and Neutrino Mass Spectrum in the Higgs Triplet Model at the LHC”, A. G. Akeroyd, M. Aoki
and H. Sugiyama, Phys. Rev. D 77 (2008) 075010
44. “Unitarity bounds in the Higgs model including triplet fields with custodial symmetry”, M. Aoki and S. Kanemura, Phys.
Rev. D 77 (2008) 095009
45. “Relic abundance of dark matter in universal extra dimension models with right-handed neutrinos,” S. Matsumoto,J. Sato, M. Senami and M. Yamanaka, Phys. Rev. D 76 (2007) 043528 [arXiv:0705.0934 [hep-ph]].

63

46. “Neutralino Dark Matter in Light Higgs Boson Scenario,” M. Asano, S. Matsumoto, M. Senami and H. Sugiyama, Phys.
Lett. B 663 (2008) 330 arXiv:0711.3950 [hep-ph].
47. “Primordial Non-Gaussianity in Multi-Scalar Slow-Roll Inflation ”, S. Yokoyama, T. Suyama and T. Tanaka, JCAP 07,
013 (2007) [arXiv:0705.3178 [astro-ph]].
48. “Non-Gaussianity in the modulated reheating scenario”, T. Suyama and M. Yamaguchi, Phys. Rev. D 77, 023505 (2008)[arXiv:0709.2545 [astro-ph]].
49. “Primordial non-Gaussianity in multiscalar inflation,, S. Yokoyama, T. Suyama and T. Tanaka, Phys. Rev. D 77, 083511(2008) [arXiv:0711.2920 [astro-ph]].
50. “Non-Gaussianity, Spectral Index and Tensor Modes in Mixed Inflaton and Curvaton Models”, K. Ichikawa, T. Suyama,
T. Takahashi and M. Yamaguchi, To appear in PRD. (arXiv:0802.4138 [astro-ph]).
51. “Revisiting Signature of Minimal Gauge Mediation”, J. Hisano and Yasuhiro Shimizu, Phys. Lett. B 655 (2007) 269-279.
52. “’Flavored’ Electric Dipole Moments in Supersymmetric Theories”, J. Hisano, M. Nagai and P. Paradisi,
arXiv:0712.1285 [hep-ph].
53. “Nonthermal dark matter in mirage mediation”, M. Nagai and K. Nakayama, Phys. Rev. D 76 (2007) 123501.
54. “Stability of Metastable Vacua in Gauge Mediated SUSY Breaking Models with Ultra Light Gravitino”, J. Hisano,
M. Nagai, M. Senami and S. Sugiyama, Phys. Lett. B 659 (2008) 361.
55. “Cosmological constraints on neutrino injection”, T. Kanzaki, M. Kawasaki, K. Kohri and T. Moroi, Phys. Rev. D 76,
105017 (2007).
56. “Affleck-Dine leptogenesis via multiscalar evolution in a supersymmetric seesaw model”, M. Senami and T. Takayama,
JCAP 0711 (2007) 015
57. “Formation of intermediate-mass black holes as primordial black holes in the inflationary cosmology with running spectral index”, T. Kawaguchi, M. Kawasaki, T. Takayama, M. Yamaguchi and J. Yokoyama, arXiv:0711.3886 [astro-ph].
58. “Increasing effective number of neutrinos by decaying particles,” K. Ichikawa, M. Kawasaki, K. Nakayama, M. Senami
and F. Takahashi, JCAP 0705 (2007) 008.
59. “Baryon Asymmetry in Heavy Moduli Scenario,” M. Kawasaki and K. Nakayama, Phys. Rev. D 76 (2007) 043502.
60. “Nonthermal dark matter in mirage mediation,” M. Nagai and K. Nakayama, Phys. Rev. D 76 (2007) 123501.
61. “Cosmological implications of supersymmetric axion models,” M. Kawasaki, K. Nakayama and M. Senami, JCAP 0803
(2008) 009.
62. “Space laser interferometers can determine the thermal history of the early Universe,” K. Nakayama, S. Saito, Y. Suwa
and J. Yokoyama, arXiv:0802.2452 [hep-ph], to be published in Phys. Rev. D.
63. “Solving Cosmological Problems of Supersymmetric Axion Models in Inflationary Universe,” M. Kawasaki and
K. Nakayama, arXiv:0802.2487 [hep-ph], to be published in Phys. Rev. D.
64. “Introducing neutrino mass into universal extra dimension models and solving cosmological problem”, S. Matsumoto,J. Sato, M. Yamanaka and M. Senami, Int. J. Mod. Phys. E 16 (2007) 1571.
65. “The neutrino masses and the change of allowed parameter region in universal extra dimension models,” S. Matsumoto,J. Sato, M. Senami and M. Yamanaka, arXiv:0711.2600 [hep-ph].

(b) Conference Papers
1. Y. Takenaga, “Search for neutral Q-balls in Super-Kamiokande II”, Workshop on Exotic Physics with Neutrino Telescopes, Uppsala, Sweden, Sep 20-22,2006,ISBN 978-91-506-1913-3 astro-ph/0701333 (2007)
2. Y. Obayashi, “SUPER-KAMIOKANDE: The Status of Neutrino Oscillations”, in Conference Proceedings Vol. 93“Frontier Objects in Astrophysics and Particle Physics” (Vulcano, Italy, May 22-27, 2006), F. Giovannelli & G. Mannocchi (eds.), SIF, Bologna 2007, ISBN 978-88-7438-034-3, p571-582

64

3. T. Kajita “Future neutrino oscillation physics in Japan”, Proceedings of the Neutrino Osicllation Workshop (Nucl. Phys.
B (Proc. Suppl.) 168, 155-160 (2007).)
4. T. Kajita “Updating the Future Long Baseline Experiment with the Kamioka-Korea two Detector Setup” Proceedings of
Twelfth International Workshop on Neutrino Telescopes (2007), pp211-221.
5. M. Fukushima, “AGASA Results and the Status of Telescope Array”, International Workshop on Energy Budget in theHigh Energy Universe, Feb. 22-34, 2006, Kashiwa, Japan.
6. M. Takeda, “The Telescope Array Experiment”, Forty Years of the GZK Problem (GZK40), the 3rd International Workshop on the Highest Energy Cosmic Rays and Their Sources, May 16-18, 2006, Moscow.
7. H. Sagawa, “Status of the Telescope Array”, 4th Korean Workshop on Origin, Propagation and Interaction of Energetic
Particles, May 17-19, Daejon, Korea.
8. S. Yoshida, “The Present Status of the Telescope Array Project”, Ultra-High Energy Cosmic Rays: Status and Perspectives (CRIS2006), May 29-June 2, Catania, Italy.
9. N. Sakurai, “Telescope Array Experiment”, 14th International Conference on Supersymmetry and the Unification of
Fundamental Interactions (SUSY06), June 12-17, Irvine, California.
10. M. Fukushima, “The Status of the Telescope Array”, International Workshop ”The UHE Universe; a vision for the next
decade”, June 19-21, Monteporzio Catone (Rome).
11. S. Ogio, “The Telescope Array Experiment”, 14th International Symposium on Very High Energy Cosmic Ray Interactions, Weihai, China, August 15-22 2006.
12. K. Kasahara, “Measurement of Photons and Neutrons in the Very Forward Region at the LHC”, 14th International
Symposium on Very High Energy Cosmic Ray Interactions, Weihai, China, August 15-22 2006.
13. M. Fukushima, “Status of Telescope Array (TA)”, International Workshop for Cosmic Ray and High Energy Universe,
March 5-6, Aoyama, Tokyo.
14. K. Kasahara. “LHCf: Measuring Zero Degree Photons and Neutrons at LHC for Cosmic Ray Physics”, International
Workshop for Cosmic Ray and High Energy Universe, March 5-6, Aoyama, Tokyo.
15. S. Ozawa, “The Telescope Array experiment”, International Symposium on Astronomy and Astrophysics of Extreme
Universe, March 22-23, Riken.
16. M. Amenomori et al., “A large underground water Cherenkov muon detector array with the Tibet air shower array for
the Gamma-ray astronomy in the 100 TeV region: detector design and simulation”, Nuclear Physics B (Proc. Suppl.),175-176, 480–483, (2008)
17. M. Amenomori et al., “A large underground water Cherenkov muon detector array with the Tibet air shower array for theGamma-ray astronomy in the 100 TeV region: Overview and physics goal”, Nuclear Physics B (Proc. Suppl.), 175-176,
476–479, (2008)
18. M. Amenomori et al., “Northern Sky Survey for Gamma-ray Point Sources in 100 TeV Region with the Tibet Air Shower
Array”, Nuclear Physics B (Proc. Suppl.), 175-176, 431–434, (2008)
19. M. Amenomori et al., “Spectral index of high-energy cosmic rays by the Compton-Getting effect at solar time framewith the Tibet air shower array”, Nuclear Physics B (Proc. Suppl.), 175-176, 427–430, (2008)
20. “The cosmic-ray energy spectrum around the knee measured by theM. Amenomori et al., Tibet-III air-shower array”,
Nuclear Physics B (Proc. Suppl.), 175-176, 318–321, (2008)
21. M. Shibata for the Tibet ASγ experiment”, “Cosmic ray data and their interpretation: about the Tibet Air Shower Array- Chemical Composition of Cosmic Rays at the Knee Viewed from the Tibet Air Shower Experiment -, Nuclear Physics
B (Proc. Suppl.), 175-176, 267–272, (2008)
22. D. Tatsumi et al., “TAMA 300 interferometer development”, TAUP 2007, September 11-15, 2007, Sendai.
23. K. Arai et al., “Recent Progress of TAMA 300”, TAUP 2007, September 11-15, 2007, Sendai; D. Tatsumi et al “Current
status of Japanese detectors”, Class. Quantum Grav. 24(2007)S399.
24. H. Tagoshi et al., “Results of Searches for inspiraling compact star binaries from TAMA 300fs observation in 20042004”, TAUP 2007, September 11-15, 2007, Sendai.

65

25. N. Kanda et al., “Short gravitational wave signal searches in TAMA 300 data: stellar collapse and black hole”, TAUP
2007, September 11-15, 2007, Sendai.
26. M. Ohashi et al. “Status of LCGT and CLIO”, TAUP 2007, September 11-15, 2007, Sendai.
27. K. Kuroda et.al., “Current status of LCGT”, Seventh Edoardo Amaldi conference on gravitational waves, Sydney, July
8-14, 2007.
28. S. Matsumoto, J. Sato, M. Senami and M. Yamanaka, “The neutrino masses and the change of allowed parameter regionin universal extra dimension models,” arXiv:0711.2600 [hep-ph].
29. J. Hisano, S. Matsumoto, M. Nagai, O. Saito and M. Senami, “Non-perturbative effect on thermal relic abundance ofdark matter,” AIP Conf. Proc. 957 (2007) 401.
30. J. Hisano, M. Nagai, M. Senami, S. Matsumoto and O. Saito, “Detection possibilities of thermally produced wino dark
matter”, 14th International Conference on Supersymmetry and the Unification of Fundamental Interactions, (SUSY06),(12-17 Jun 2006, Irvine, California), AIP Conf. Proc. 903 (2007) 575.
31. M. Nagai, “New two-loop contributions to hadronic EDMs in the MSSM”, 13th International Symposium on Particles,
Strings and Cosmology (PASCOS 07), (2-7 Jul 2007, London, England), AIP Conf. Proc. 957 (2007) 245.
32. J. Hisano, S. Matsumoto, M. Nagai, O. Saito and M. Senami, 13th International Symposium on Particles, Strings andCosmology (PASCOS 07), (2-7 Jul 2007, London, England), “Non-perturbative effect on thermal relic abundance ofdark matter”, AIP Conf. Proc. 957 (2007) 401.
33. K. Ichikawa, M. Kawasaki, K. Nakayama, M. Senami and F. Takahashi, “Increasing the effective number of neutrinos
with decaying particles,” 13th International Symposium on Particles, Strings and Cosmology (PASCOS 07), AIP Conf.
Proc. 957 (2007) 413.

(c) ICRR Report
1. ICRR-Report-525-2007-1iFebruary 15, 2008j “Atmospheric neutrino oscillation analysis with solar terms in SuperKamiokande” Yumiko Takenaga

66

D. Doctoral Theses
1. “Atmospheric neutrino oscillation analysis with solar terms in Super-Kamiokande”,
Yumiko Takenaga, Ph.D. Thesis, RCCN, Mar. 2008.
2. “Search for TeV Gamma-ray Emission from Clusters of Galaxies with CANGAROO-III Imaging Atmospheric
Cherenkov Telescopes”,
Ryuta Kiuchi, Ph.D. Thesis, CANGAROO, Mar. 2008.
3. “Study of optical properties of Al 2 O3 crystal for a gravitational wave telescope”,
Masao Tokunari, Ph.D. Thesis, Gravitational Wave, Mar. 2008.
4. “Search for continuous gravitational waves from PST J0835-4510”,
Tomomi Akutsu, Ph.D. Thesis, Gravitational Wave, Mar. 2008.

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
K.Okumura and M.Ohashi. 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 2007 fiscal year were :No.63 (Nov 30, 2007)• Report on the Current Status of the Telescope Array (TA) Experiment, Hiroyuki Sagawa.
• Report on the 30th International Cosmic Ray Conference
1. Ultra High Energy Cosmic Rays, Toshiyuki Nonaka.
2. Ultra High Energy Gamma Rays, Kyoji Nishijima.
3. Neutrino, Makoto Miura, Itaru Higuchi.
4. High Energy Phenomena, .Masato Takita.
5. SH, Yasushi Muraki.
• ICRR seminars.
• Self-introduction.
• Notice of Call for ICRR inter-University Researches in JFY2008.

67

No.64 (Jan 31, 2008)• Inflation and Initial Fluctuation of the Universe. Teruaki Suyama.
• Report on the ICRR Open House in JFY2007. Makoto Sasaki.
• Report on the Activity of the ICRR Public Relations Office at the Kashiwa Campus Open House in JFY2007 and the
Exhibition Related to Neutrino in Nara Women’s University, Hideo Itoh.
• Self-introduciton.
• Staff reassignment.

No.65 (March 31, 2008)• Didn’t the Kepler’s Supernova Remnant Produce Cosmic Rays Even If 400 Years passed after its Explosion?. Ryoji
Enomoto, Tatsuo Yoshida.
• Recent Report on Tibet Experiment. Masato Takita.
• Report on the Meeting for Presenting the Results of Inter-University Researches in JFY2007. Yoshinari Hayato.
• ICRR-Seminar.
• ICRR-report.

(b) Public Lectures• “Public Lecture on Neutrino”,
April 7 2007, Kashiwa, Chiba,“Evolution of the Universe, Supernova neutrinos and the chemical elements”, Toshitaka Kajino (National Astronomical
Observatory of Japan, University of Tokyo).
“Guft from the cosmos: Cosmic rays and atmospheric neutrinos”, Takaaki Kajita (ICRR, University of Tokyo).

(c) Visitors
KAMIOKA Observatory (Total: 114 groups, 2081 people)• Yumeno Tamago Jyuku (Science camp for Junior High School Students)• Yumeno Tamago Jyuku (Hida academy for High School Students)• MEXT Super Science High School (SSH) project: total 2 schools

68

F.

Inter-University Researches

Researcher Numbers

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

Application
Numbers

Adoption
Numbers

Researchers
Numbers

39
10
4
2
6

39
10
4
2
6

554
73
96
19
35

4
16
18

4
16
18

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

35
45
9

502
516
167

10

10

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 neucleon 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

69

17. Search for proton decay via e + π 0 mode
18. R&D of a 1 Mton 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 emmission 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 obsercation 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

70

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

71

88. Evaluation of a fiber-coupled laser stabilizatino 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 2 6Al 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 Calro Simulation Data Generation for the IceCube experiment
99. Neutrino workshop

72

G. List of Committee Members(a) Board of Councillors
SUZUKI, Yoichiro
KURODA, Kazuaki
KAJITA, Takaaki
FUKUSHIMA, Masaki
YAMAMOTO, Masayuki
OKAMURA, Sadanori
TAKASAKI, Tadafumi
EGUCHI, Toru
MIYAMA, Shoken
SATO, Fumitaka
EJIRI, Hiroyasu
MURAKI, Yasushi
OHTA, Itaru
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
Kounan University
Osaka University
Kounan University
The Open University of Japan
Institute of Space and Astronautical Science
ICEPP, University of Tokyo(b) Advisory Committee
SUZUKI, Yoichiro
TORII, Shoji
MURAKI, Yasushi
TANIMORI, Toru
KAWAKAMI, Saburo
YANAGIDA, Tsutomu
NAGAE, Tomohumi
NISHIKAWA Koichiro
NAKAMURA, Takashi
MINOWA, Makoto
KURODA, Kazuaki
FUKUGITA, Masataka
FUKUSHIMA, Masaki
MORI, Masaki
NAKAHATA, Masayuki
TAKITA, Masato

ICRR, University of Tokyo
Waseda University
Kounan University
Kyoto University
Osaka City University
University of Tokyo
Kyoto University
KEK
Kyoto University
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

73

H. List of Personnel
Director

SUZUKI Yoichiro

Vice-Director

KURODA Kazuaki

Kamioka Observatory(Neutrino and Astroparticle Division)
Scientific Staff
SUZUKI Yoichiro,
NAKAHATA Masayuki,
TAKEUCHI Yasuo,
SHIOZAWA Masato,
MIURA Makoto,
OBAYASHI Yoshihisa,
KAMEDA Jun,
TAKEDA Atsushi,
SEKIYA Hiroyuki,
YAMADA Satoru,
ITOH Yoshitaka,
KOBAYASHI Takashi,
Chief Secretary
AKIMOTO Masatoshi,
Technical Staff
MIZUHATA Minoru,
KANBE Tomio,
NAKAJIMA Tetsue,
Research Fellows
OGAWA Hiroshi,
WATANABE Hideki,
Secretary
OKURA Youko,
MAEDA Yukari,
Research Center for Cosmic Neutrinos(Neutrino and Astroparticle Division)
Scientific Staff
KAJITA Takaaki,
KANEYUKI Kenji,
SAKURAI Yoshihisa,
TSUKAMOTO Toshifumi,
Technical Staff
SHINOHARA Masanobu,
Research Fellows
HIGUCHI Itaru,
Secretary
FUKUDA Yoko,
KITSUGI Atsuko,
High Energy Cosmic Ray Division
Scientific Staff
FUKUSHIMA Masaki,
ENOMOTO Ryoji,
SASAKI Makoto,
OHISHI Michiko,
ASAOKA Yoichi,
Technical Staff
AOKI Toshifumi,
Research Fellows
OZAWA Shunsuke,
SHIBATA Tatsunobu
KONDO Yoshimi,
WANG Xiao,
YAN Zhitao,
Secretary
SAWANO Sumiko,
TATSUMI Fusako,

MORI Masaki,
YOSHIKOSHI Takanori,
TAKEDA Masahiro,
OHNISHI Munehiro,
SAKURAI Nobuyuki,
KOBAYASHI Takahide,
UDO Shigeharu,
SHIOMI Atsushi,
KAWATA Kazumasa,
NONAKA Toshiyuki,
FABRICE Cohen,
KOKUBUN Yayoi,

AKENO Observatory(High Energy Cosmic Ray Division)
Scientific Staff
SAGAWA Hiroyuki,
Technical Staff
TORII Reiko,
OHOKA Hideyuki,
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 Fellows
YAMAMOTO Kazuhiro,
SENAMI Masato,
Secretary
SAKAI Akiko,

MORIYAMA Shigetaka,
HAYATO Yoshinari
KOSHIO Yusuke,
ABE Ko,NAKAYAMA Shoei,

KUMAMARU Seiichi,

OKADA Eri,

OKUMURA Kimihiro,

TAKITA Masato,
HAYASHIDA Naoaki,

TOKUNOU Hisao,
HUANG Jing,YAMAKAWA Toshie,

KAWAGUCHI Masami,

AGEMATSU Yoshiaki,
SHIMODAIRA Hideaki,

USHIMARU Tsukasa,

KURODA Kazuaki,
YASUDA Naoki,
UCHIYAMA Takashi,
OKADA Atsushi,
SUYAMA Teruaki,

KAWASAKI Masahiro,HISANO Junji,
ICHIKAWA Kazuhide,
AOKI Mayumi,

74

Graduate
Students (Doctor)

Graduate
Students (Master)

Administration
Division Staff

IKEDA Daisuke,

KIDO Eiji,

TAKETA Akimichi,

KIUCHI Ryuta,
AITA Yuichi,
CHONAN Tsutomu,
MINAMINO Akihiro,
IIDA Takashi,
ISHIHARA Chizue,
TOKUNARI Masao,
AGATSUMA Kazuhiro,
NAGAI Minoru,
KONYA Kenichiro,
KONISHI Kohki(M2),YUKAWA Yohei,
OKUMURA Akira,SAKO Takashi,
NODA Koji,

TAKENAGA Yumiko,
MITSUKA Gaku,
IKEDA Ittoku
AKUTSU, Tomomi,

UESHIMA Kota,
NISHINO Haruki,

KANZAKI Toru,
SEKIGUCHI Toyokazu,

TAKAYAMA Tsutomu,
NAKAYAMA Kazunori,

KUNISAWA Toshiki,
EGUCHI Makoto,
UENO Koh,
SAITOH Takanori,
IMAI Yuta,
OKADA Takashi,

RYOKI Shinichi,
HIGASHI Yuhei,
NAKAJIMA Yuha,
MORIOKA Tomoko,
SUGIYAMA Shohei,
KAWAKAMI Etsuko,

NAGAI Yuichiro,

NAGANEO Nobuyoshi,
IIDA Nobuyuki
TASHIRO Megumi,
MATSUMOTO Kenichi
MARUMORI Yasuko

SASADA Noriaki,
AKIMOTO Mari,AKIYAMA Makiko,
KITA Aiko,

NAKAGAWA Noriyasu,

YAMAKAWA Yuichi,

HAZAMA Shunsuke,
ARASHIBA Soichi,

YAMAMOTO Tetsuya,
IRIE Makoto,
SAITO Akiko,
KATO Yasuhiro,