1

INSTITUTEFOR

COSMIC RAY RESEARCH
UNIVERSITY OF TOKYOANNUAL REPORT(APRIL 2001 – MARCH 2002)

2

Editorial Board
TAKITA, Masato
KOSHIO, Yusuke

ISSN 0919-8296cInstitutefor Cosmic Ray Research, University of Tokyo
5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8582 Japan
Phone : (81)4-71363100 (Director),
3101–3114 (Administration Oﬃce),
5114 (µ-ν), 5128 (Emulsion),
3176 (Air Shower), 5111 (Kamioka),
5124 (Primary), 5104 (Neutorino Center)
Telex :
Telefax : (81)4-7136-3115(81)4-7136-3118
Cable :

Printed by
Universal Academy Press, Inc.
Postal Address: C.P.O. Box 235, Tokyo 100-91, JAPAN
Address for Visitors: BR-Hongo-5 Bldg., 6-16-2, Hongo,
Bunkyo-ku, Tokyo 113, JAPAN
Telephone: + 81 3 3813 7232
Facsimile: + 81 3 3813 5932
E-Mail: general@uap.co.jp
WWW URL: http://www.uap.co.jp

3

TABLE OF CONTENTS
Preface........................................................................................

Research Divisions

1

Kamiokaµ-ν (+ Primary Cosmic Ray )Air Shower
Emulsion
Neutrino Center
Observatories and Stations...............................................................................

33

Norikura Observatory
Akeno Observatory.............................................................

41...........................................................................

42.......................................................................

43

Appendix A.

ICRR International Workshop

Appendix B.

Seminar in 2001

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

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

46

Appendix E.

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

46...............................................................

47..........................................................................

48

ICRR News
Appendix F.

List of Committee Members(a) Board of Councillors(b) Executive Committee(c) Advisory Committee

Appendix G.

List of Personnel

4

PREFACEIt is a pleasure to bring to you our annual report for the ﬁscal year 2001,
describing various activities of Institute for Cosmic Ray Research (ICRR), theUniversity of Tokyo.
ICRR is an institute closely associated with Japanese universities. ICRR thus
hosts or co-hosts several experimental facilities which are jointly used by about
350 researchers and graduate students of universities. Major experiments done incollaboration are Super-Kamiokande at Kamioka Observatory, AGASA at Akeno
Observatory, CANGAROO at Woomera in Australia, Tibet-AS-Gamma in Tibet,
and TAMA 300 at National Astronomical Observatory. These experiments arequite unique compared with other competing experiments in the world and someof them have already produced very important results which are described in thisvolume.
Cosmic ray physics today presents major challanges to probe physics beyond
the standard theory of the micro-world: discovery and reﬁnement of neutrino
oscillation via the atmospheric neutrino observation is the most important step
towards further uniﬁcation beyond what we ﬁrmly established in the standard
model. Besides the neutrino beam which nature gave us fortuitously there now
exists the man-made beam directed to Super-K from KEK at Tsukuba. Anintermediate result of this K2K experiment so far presented is compatible withresult obtained from the atmospheric neutrino oscillation at Super-K. In anotherfrontier TeV gamma rays observed by CANGAROO shed new light on the originof high energy cosmic ray. Despite of the ﬁrm conﬁdence that underlines theexistence of the GZK cutoﬀ highest energy comic rays beyond this cutoﬀ are kept
observed by AGASA. This is perhaps a subject to be examined in more detail by
the next generation of detectors such as AUGER and Telescope Array.
We hope to continue to make major contribution to cosmic ray physics in theworld in coming years.

Motohiko Yoshimura, Director of ICRR

5

Organization
Board of Councillors

Research Division
Kamioka Division

Directorµ−ν+Division
Primary Cosmic Ray
Air Shower Division

Faculty Council

Emulsion Division
Facilities
Norikura Observatory

Advisory Committee

Akeno Observatory
Kamioka Observatory
Neutrino Center

User’s Committee

Administration Division

Number of Staﬀ Members in 2001

Director
Kamiokaµ–ν + Primary
Air Shower
Emulsion
Neutrino Center
Guest
Norikura
Administration
Total

Scientiﬁc
Staﬀ
1
10
5
9
4
3
4

Technical
Staﬀ

Research
Fellows

Administrators
and Secretaries

2
3
5
10
1

3

2
4
2
1

1
1

3
36

12

21

7
12

81

FY 1996–2001 Budget
Personnel
expenses
Nonpersonnel
expenses
Total

1996

1997

1998

1999

2000

2001

476 072572 318536 510569 050589 879

418 475

1 259 435

1 278 788

1 680 983

1 411 063

1 423 789

1 518 584

1 735 507

1 851 106

2 217 493

1 980 113

2 013 668

1 937 059

(in 1 000 yen)1

KAMIOKA DIVISION

Cosmic ray interactions in the atmosphere produce
neutrinos. The prediction of the absolute ﬂux has an
uncertainty of at least ± 20%. However, the ﬂavor ratio of the atmospheric neutrino ﬂux, (νµ + ν̄µ )/(νe + ν̄e ),has been calculated to an accuracy of better than 5% in a
broad energy range from 0.1 GeV to higher than 10 GeV.
The ﬂuxes of upward and downward going neutrinos are
expected to be nearly equal for Eν > (a few GeV).
SK observed 11,872 fully-contained (FC) events and913 partially-contained (PC) events during 1489 days ofdata taking. 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 outerdetector. The neutrino interaction vertex was required tohave been reconstructed within the 22.5 kiloton ﬁducial
volume, deﬁned to be > 2 m from the PMT wall.
The FC events were classifed into “sub-GeV” (Evis <1330 MeV) and “multi-GeV” (Evis > 1330 MeV) samples. The numbers of observed and predicted events for
sub- and multi-GeV energy regions in SK are summarizedin Table 1. Among FC events, single-ring events are identiﬁed as e-like or µ-like based on a Cherenkov ring pattern. All the PC events were assigned to be multi-GeVµ-like. Using the number of e-like and µ-like events, theratio of (µ/e) was obtained and it is signiﬁcantly smaller

cosθ

500
400
300
200
100
0

1

-1

-0.5

0

cosθ

0.5

1

350 Multi-GeV µ-like + PC

Multi-GeV e-like

140

300

120

250

100

200

80

150

60

100

40

50

20
0

Sub-GeV µ-like

Number of Events

450 Sub-GeV e-like
400
350
300
250
200
150
100
50
0
-1
-0.5
0
0.5

Number of Events

Atmospheric neutrinos

Data
MC
Sub-GeV
e-like3266 3081.0µ-like3181 4703.9
R = 0.638 ± 0.016 ± 0.050
Multi-GeV
e-like772
707.8µ-like(FC+PC) 1577 2198.2
R = 0.658+0.030−0.028 ± 0.078

Number of Events

Super-Kamiokande (SK) is a large water Cherenkov
detector, located 1000 m underground in Kamioka mine,
Japan. 50 kton of pure water is contained in a stainless steel tank of 39.3 meters in diameter and 41.4 m inheight. The main purpose of the SK detector is the detection of atmospheric neutrinos, solar neutrinos, supernova
neutrinos, and search for nucleon decays. Sk had been
taking data from April 1996 to July 2001 using 11,146
20-inch photomultipliers (PMTs) for inner detector and1,885 8-inch PMTs for outer detector. In 2001, several
hundred bad PMTs were replaced. While ﬁlling pure water into the SK tank after the PMT replacement, large
number of PMTs were destroyed on November 12, 2001.
The detector was reconstructed in 2002 using about 5200
20-inch PMTs. Pure water was ﬁlled from October toDecember in 2002 and data taking with full water wasstarted from December 2002.
During the ﬁrst ﬁve years of data taking, SK has established neutrino oscillations in atmospheric neutrinos andsolar neutrinos. Furthermore, the long baseline accelerator neutrino experiment (K2K), which has been runningsince 1999, conﬁrmed the νµ oscillations.
In this report, those results obtained by SK and K2K
are described.

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

Number of Events

Super-Kamiokande
Overview

-1

-0.5

0

cosθ

0.5

1

0

-1

-0.5

0

cosθ

0.5

1

Fig. 1. Zenith angle distributions for sub-GeV e-like, sub-GeV µ-like,
multi-GeV e-like and multi-GeV (FC+PC) µ-like events. Cos Θ= 1 means down-going particles. The solid histograms show theMC prediction for the no neutrino oscillation case. The dotted histograms show the Monte Carlo prediction for νµ ↔ ντ oscillations
with sin2 2θ = 1 and ∆m2 = 2.5 × 10−3 eV2 .

than the expectation as shown in the table.
The zenith angle distributions for the sub- and multiGeV samples are shown in Fig. 1. The µ-like data fromSK exhibited 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 thebest-ﬁt expectation for νµ ↔ ντ oscillations. The oscillated Monte Carlo well reproduced the zenith angle distributions of the data. Some fraction of the multi-ring
event are also subdivided into e-like and µ-like events using the event pattern of the most energetic Cherenkov
ring in each event. Figure 2 shows the zenith angle distribution of multi-ring events and they also agree wellwith the expectations from neutrino oscillations.

2

80

2

60
40
20
0

10 -2
-1

-0.5

0

cosθ

0.5

1

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

1.4 Upward Stopping µ1.2
1

10 -40 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

0.8

2

0.6

sin 2θ

0.4-1-0.8 -0.6 -0.4 -0.2

cosθ

0

Fig. 3. Zenith angle distributions of upward through-going muons(left) and upward stopping muons (right). The solid histogramshows the expected flux for the null neutrino oscillation case. The
dashed histogram shows the expected flux for the νµ ↔ ντ oscillation with sin2 2θ = 1.0 and ∆m2 = 2.5 × 10−3 eV2 .

Energetic atmospheric νµ ’s passing through the Earthinteract with rock surrounding the detector and produce
muons via charged current interactions. These neutrino
events are observed as upward going muons. Upward
going muons are classiﬁed into two types. One is “upward through-going muons” which have passed throughthe detector, and the other is “upward stopping muons”
which come into the detector and stop inside the detector. The mean neutrino energy of upward throughgoing muons and upward stopping muons are ∼ 100 GeV
and ∼ 10 GeV, respectively. SK has observed 1878
upward through-going muons and 456 upward stoppingmuons during 1678 and 1657 days’ live time, respectively.
Fig. 3 shows the zenith-angle distributions of those upward muons. They agree with the expectations with neutrino oscillations.
We carried out a neutrino oscillation analysis using
all the SK atmospheric neutrino data. Fig. 4 shows theallowed neutrino oscillation parameter region for νµ ↔
ντ oscillations obtained by this analysis. The best ﬁt
oscillation parameters are sin2 2θ = 1.0 and ∆m2 = 2.5×
10−3 eV2 . The allowed oscillation parameter range is
obtained to be sin2 2θ > 0.92 and ∆m2 = (1.6 − 3.9) ×
10−3 eV2 at 90% C.L.
The neutrino oscillation analysis described above assumed νµ ↔ ντ oscillations. The possibility of νµ ↔ νs(sterile neutrinos) oscillation was investigated using two
methods, one using the MSW eﬀect for oscillations andanother using a neutral current (NC) enriched sample.
The forward scattering amplitude of νµ and ντ are same,but that of νs is diﬀerent. The diﬀerence in the ampli-

Fig. 4. Allowed region of νµ → ντ neutrino oscillation parameters
obtained by SK by using contained atmospheric neutrino eventsand the upward-going muon events.

80

4

70

3.5

60

3

20
10

0.5

50
40
30

250

number of events

0

-1

0.2

flux(×10 cm s Sr )

-1
-2 -1

10 -3

number of events

cosθ

-13

4 Upward Through Going µ
3.5
3
2.5
2
1.5
1
0.5
0
-1 -0.8 -0.6 -0.4 -0.2 0

Flux(10 cm s sr )

-13

-2 -1

-1

Flux(10 cm s sr )Fig. 2. Zenith angle distributions for multi-ring sub-GeV µ-like (left)
and multi-ring multi-GeV µ-like samples. The solid and dashedhistograms show expectations without and with neutrino oscillations, respectively.

-2 -1

1

νµ - ντ

10 -1

-13

cosθ

Multi-GeV Multi-ring µ−like100∆m (eV )50 Sub-GeV Multi-ring µ−like
45
40
35
30
25
20
15
10
5
0
-1
-0.5
0
0.5

Number of Events

Number of Events

2

2.5
2

1.5

200

150

100

1
50

0
-1

0
cosΘ

1

0
-1

-0.8

-0.6cosΘ-0.4

-0.2

0

0
-1

0

cosΘ

1

Fig. 5.
Zenith angle distribution of higher energy PC events(left), upward-going muons (middle) and NC enriched sample(right). The solid and dashed histograms show expectationsfor νµ ↔ ντ and νµ ↔ νs oscillations, respectively, assuming∆m2 = 3 × 10−3 eV2 and sin2 2θ = 1.

tude causes suppression of neutrino oscillations for higher
energy neutrinos. Figure 5 (left) shows zenith angle distribution of high energy PC events (E > 5 GeV, < E >= ∼ 25 GeV) together with expected distributions forνµ ↔ ντ and νµ ↔ νs oscillations assuming ∆m2 = 3 ×
10−3 eV2 and sin2 2θ = 1.
The same ﬁgure for upward-through-going muons isshown in Fig. 5 (middle). The second method to discriminate νµ ↔ ντ and νµ ↔ νs oscillations is using
NC events. In case of νµ ↔ ντ oscillations, the event
rate of NC interaction should be same as null oscillations. On the other hand, the NC event rate is smallerfor νµ ↔ νs . A NC enriched sample was made requiring
multi-ring event pattern and the most energetic ring tobe e-like. The estimated fraction of NC event is 29% in
the sample. The observed zenith angle distribution of
the sample is shown in Fig. 5 (right). Those distributions show that the pure νµ ↔ ντ hypothesis ﬁts better
than the pure νµ ↔ νs hypothesis. Scanning all possible∆m2 and sin2 2θ ranges, pure νµ ↔ νs oscillations are
disfavored with more than 99% C.L.
We have also performed a search for the appearance ofEvent/day/bin

35-20 MeV
2

1

0
-1.0

-0.5

0.0

0.5

1.0
cos θSunντ events. The charaged current interaction of ντ produces τ . The signatures of τ -decays are (1) larger multiplicity of Cherenkov rings, (2) larger number of decay
electrons, and (3) relatively spherical event pattern, andso on. A likelihood of τ -like events are made based on
those signatures. Fig. 6 shows zenith angle distributionof the events which give larger τ likelihood. Excess of
events above the expectations without τ indicates the appearance of τ events. The excess number of τ -like events
is 145 ± 44 (stat.)+11−16 (sys.). It is consistent with the
expectation of 86 events for the oscillation parameters
obtained above.

Solar neutrinos
The observed ﬂux by the solar neutrino experiments(Homestake, Kamiokande, Super-Kamiokande, Gallium
experiments, and SNO charged current) were lower thanthe expectations from the Standard Solar Model (SSM),
which has been known as “solar neutrino problem”. The
precise measurement of solar neutrinos by SK and SNO
established that the solar neutrino problem is due to neutrino oscillations.
SK detects 8 B solar neutrinos through neutrinoelectron scattering, ν + e → ν + e. The electron energy,
direction and the time of the events are measured. Theν + e → ν + e method of the solar neutrino detection issensitive not only to νe but also to νµ and ντ . The crosssection of νµ + e and ντ + e scatterings are about 17 ofthat of νe + e.
In order to perform precise solar neutrino measurement, the energy scale, the energy resolution, the angular resolution and the vertex position resolution wereprecisely calibrated using LINAC system and 16 N events
generated by a DT neutron generator. The absolute energy scale was calibrated with an accuracy of ∼ 0.6%.
Figure 7 shows the angular distribution to the direction of the sun. SK has observed about 22,000 solar
neutrino events above 5 MeV during 1496 days of live

2

8
7

6

Fig. 6. Zenith angle distribution of τ -like events. The solid and dashedhistograms show expectations with and without τ appearance.

νµ+ντ flux (10 /cm /sec)

Fig. 7. Angular distribution to the direction of the sun.

6

SNO CC

SK

3σ
2σ
1σ

5
4

SNO NC32

SSM ±1σ

1
0

0

1

2

3
4
5
6
6
2
νe flux (10 /cm /sec)

Fig. 8. νe flux and νµ + ντ flux contour obtained by SK and SNO
data.

time. This number corresponds to the 8 B solar ν ﬂux
of 2.35 ± 0.02 (stat.) ± 0.08 (sys.) × 106 cm−2 s−1 ,which is 46.5 ± 0.5 (stat.)+1.6−1.5 (sys.)% of the SSM prediction. Recently, Sudbury Neutrino Observatory (SNO)
presented their results of the charged current (CC), neutral current (NC), and electron scattering (ES) ﬂuxes.
SNO is a Charenkov detector using 1000 ton heavy water. Their CC ﬂux, to which only νe contributes, was6−2 −1
1.76+0.06
s . The−0.05 (stat.) ± 0.09 (sys.) × 10 cm
4.2 σ higher ﬂux in SK shows the existence of the νµand/or ντ in solar neutrinos observed at earth. It is the
direct evidence for solar neutrino oscillations. Figure 7
shows ﬂux of νe and νµ + ντ obtained by SK ﬂux, SNO
CC ﬂux and SNO NC ﬂux. The total neutrino ﬂux obtained by those measurement is consistent with the SSM
prediction as shown in the ﬁgure.
Combining the ﬂux measurements by SK, SNO, Homestake, and gallium experiments, several allowed regions(ﬂux global solutions) remain as shown in Fig. 8. The
precise measurement of energy spectrum and day/nightvariation by SK enable us to discuss the oscillation parameters. Figure 9 shows the recoil electron spectrum
normalized by SSM prediction. Expectations from eachﬂux global solutions are shown in the ﬁgure. The Small
Mixing Angle (SMA) and just-so solutions expect distortion of the energy spectrum. However, the SK energy

1
2

SK-I 1496day 5.0-20MeV 22.5kt∆m in eV

0.8

2

SMA

0.6

Just-so
LMA

10

10
10
10

2

10
10
10

0.45

10
10
10

0.4

10

Night

10

Day
Night

10

All

Just-so

-11

-12

10

2

0.5

-1

-10

Zenith Spectrum νe→νµ/τ (95%C.L.)
-4

10

-3

10

-2

10

-1

1

10
10
2
tan (Θ)2

Fig. 11. Exclusion area for νe ↔ νµ /ντ from (flux-independent)
zenith-spectrum analysis at 95% confidence level. The separate
regions with the names are allowed regions based on the absolute
fluxes measured by solar neutrino experiments.

SK-I 1496day 5.0-20MeV 22.5kt

Day

-9

10

12
14 20
Energy(MeV)

0

1
cosθz

Fig. 10. Day/night variation data. The day and night time data are
sub-divided as a function of the zenith angle of the sun.

spectrum is nearly ﬂat. Figure 10 shows the day/nightvariation. The day/night diﬀerence is expressed as:
N ight − Day= 0.021 ± 0.020+0.013−0.012 .
1
(Day
+
N
ight)
2
The measured energy spectrum and day/night diﬀerence
are used to constrain neutrino oscillation parameters.
The energy range of the solar neutrino spectrum is divided into 8 energy bins and day/night is divided into
one bin for day and 6 bins for night according to thezenith angle of the sun. Fig. 11 shows the excluded region by the SK zenith-spectrum analysis overlaied withthe allowed regions obtained by the ﬂux global analysis.
SMA, just-so, and LOW solutions are disfavored withmore than 95% C.L. The absolute ﬂux is a free parameter in this analysis. By constraining the total ﬂux of 8 B
neutrinos either using the SSM prediction or SNO NC

10

-3
2

8

LOW
-8

10

2

6

SMA

-7

10

∆m in eV

Data/SSM-6

10

Fig. 9. Recoil electron energy spectrum of solar neutrinos. Ratio of
the observed spectrum to the expected spectrum is shown. The
solid, dashed and dotted histograms show typical large mixing
angle (LMA), small mixing angle (SMA), and just-so solutions.
νe ↔ νµ (ντ ) oscillations are assumed.

0.35

-5

10

0.2

0.55

LMA
-4

10
10

0.4

0

-3

10

10

∆m in eV

Data/SSM

4

(a)
-4

-5

10

-6

10

-7

10

-8

10

-9

10

-10

10

-11

-12

10

10
Zenith Spectrum νe→νµ/τ (95%C.L.)
-4

10

-3

10

-2

10

-1

1

10
10
2
tan (Θ)

2

10

-3

(b)
-4

-5

-6

-7

-8

-9

-10

-11

-12

10

Zenith Spectrum νe→νµ/τ (95%C.L.)
-4

10

-3

10

-2

10

-1

1

10
10
2
tan (Θ)2

Fig. 12. Allowed regions of neutrino oscillation parameters from SK
zenith spectrum. The flux is constrained by (a) the SSM predictionand (b) SNO CC and NC flux measurements.

and CC ﬂux measurements, allowed regions of oscillation parameters are obtained using SK zenith-spectrum
as shown in Fig. 12. Only large mixing angle solutions
are allowed.
Combining the results of SK measurement, SNO ﬂux
measurements, and radiochemical experiments (Homestake, GALLEX and SAGE), a single allowed region ofoscillation parameters is obtained as shown in Fig. 13.
The conﬁdence level of other solutions are less than 2%.
The obtained solution is only LMA solution and it is thesensitive region of KamLAND experiment.

Search for nucleon decay
One of the most unique predictions of Grand Uniﬁed
Theories (GUTs) is baryon number violation. In many2

∆m in eV

2

5

10
10
10
10
10
10
10
10
10
10

at 90% C.L.
Analyses of other nucleon decay modes and the improvements of the analysis in for these two modes are in
progress.

-3

-4

-5

List of Publications-6

The number of citations before January 2003 is shown.

-7[1] Fukuda, Y. et al. 1998, Measurement of a small
atmospheric νµ /νe ratio, Phys. Lett. B, 433, 9–18.
The number of citations: 534-8[2] Fukuda, Y. et al. 1998a, Study of the atmospheric
neutrino ﬂux in the multi-GeV energy range, Phys.
Lett. B, 436, 33–41.
The number of citations: 525

-9

-10

-11

-12

10

Ga+Cl+SK+SNO Rates
95%C.L.
8and SK Zen Sp νe→νµ/τ ( B, hep free)
-4

10

-3

10

-2

10

-1

1

10
10
2
tan (Θ)2

Fig. 13. Allowed region obtained by combining SK zenith spectrum,
SNO CC and NC measurements, and radoichemical experiments.

GUT models, either p → e+ π 0 or p → ν̄K + is the dominant decay modes.
p → e+ π 0 : This decay mode has a characteristic event
signature, in which the electromagnetic shower caused by
the positron is balanced against the two showers causedby the gamma rays from the decay of the π 0 .
We searched for proton decay events in the fullycontained atmospheric neutrino sample. The essential selection criteria are: 800 < total invariant mass
< 1050 MeV/c2 and total momentum < 250 MeV/cn inaddition to requirements on the number of rings, particle
type, π 0 mass and µ → e decay. The detection eﬃciency
is estimated to be 40%. The expected number of background events was 0.3. No candidate event was observed.
The lower limit on the partial lifetime for p → e+ π 0 was
obtained to be τ /Bp→e+ π0 > 5.4 × 1033 years at 90%
C.L.
p → ν̄K + : The momentum of the K + from p → ν̄K +is 340 MeV/c and is below the threshold momentum forproducing Cherenkov light in water. Candidate events
for this decay mode are therefore identiﬁed through the
decay products of the K + : K + → µ+ ν and K + → π + π 0 .
Two separate decay methods were used to search for
K + → µ+ ν. The ﬁrst method searched for the monoenergetic muons from the stopped K + . The signal canbe found as an excess of single-ring µ-like events at
236 MeV/c above the continuous background due to atmospheric neutrino interactions. In the second method,a coincidence of a γ (from 16 N ∗ and a delayed µ (fromK + ) was required.
By combining all the three results, no evidence forp → ν̄K + was observed and the lower limit of the partial
lifetime for this mode was obtained to be 2.2 × 1033 yr[3] Fukuda, Y. et al. 1998b, Measurements of the solar neutrino ﬂux from Super-Kamiokande’s ﬁrst
300 days, Phys. Rev. Lett., 81, 1158–1162.
The number of citations: 385[4] Shiozawa, M. et al. 1998, Search for proton decay
via p → e+ π 0 in a large water Cherenkov detector,
Phys. Rev. Lett., 81, 3319–3323.
The number of citations: 54[5] Fukuda, Y. et al. 1998c, Evidence for oscillationof atmospheric neutrinos, Phys. Rev. Lett., 81,
1562–1567.
The number of citations: 1599
[6] Nakahata, M. et al. 1999, Calibration of SuperKamiokande using an electron LINAC, Nucl. Inst.
Meth. A, 421, 113–129.
The number of citations: 40[7] Fukuda, Y. et al. 1999, Constraints on neutrino oscillation parameters from the measurement of daynight solar neutrino ﬂuxes at Super-Kamiokande,Phys. Rev. Lett., 82, 1810–1814.
The number of citations: 293[8] Fukuda, Y. et al. 1999a, Measurements of the solar
neutrino energy spectrum using neutrino-electron
scattering, Phys. Rev. Lett., 82, 2430–2434.
The number of citations: 274[9] Fukuda, Y. et al. 1999b, Measurements of the ﬂux
and zenith-angle distribution of upward throughgoing muons by Super-Kamiokande, Phys. Rev.
Lett., 82, 2644–2648.
The number of citations: 379[10] Fukuda, Y. et al. 1999c, Neutrino induced upward
stopping muons in Super-Kamiokande Phys. Lett.,
B467, 185–193.
The number of citations: 138[11] Futagami, T. et al. 1999, Observation of the eastwest anisotropy of the atmospheric neutrino ﬂux,
Phys. Rev. Lett., 82, 5194–5197.
The number of citations: 49

6[12] Takeuchi, Y. et al. 1999, Measurements of Radon
concentrations at Super-Kamiokande, Phys. Lett.
B, 452, 418–424.
The number of citations: 4[13] Hayato, Y. et al. 1999, Search for proton decay
through p → ν̄K + in a large water Cherenkov detector, Phys. Rev. Lett., 83, 1529–1533.
The number of citations: 46[14] Blaufess, E. et al. 2001, N-16 as a calibration source
for Super-Kamiokande, Nucl. Inst. Meth. A, 458,
638–649.
The number of citations: 2[15] Fukuda, S. et al. 2000, Tau neutrinos favored oversterile neutrinos in atmospheric muon-neutrino oscillations. Phys. Rev. Lett., 85, 3999–4003.
The number of citations: 330[16] Fukuda, S. et al. 2001, Solar B-8 and hep neutrino measurements from 1258 days of SuperKamiokande data.
Phys.
Rev.
Lett., 86,
5651–5655.
The number of citations: 340[17] Fukuda, S. et al. 2001a, Constraints on neutrino oscillations using 1258 days of Super-Kamiokande solar neutrino data. Phys. Rev. Lett., 86, 5656–5660.
The number of citations: 282[18] Fukuda, S. et al. 2002, Search for neutrinos fromgamma-ray bursts using Super-Kamiokande. Ap.
J., 578.
[19] Fukuda, S. et al. 2002a, Determination of solar
neutrino oscillation parameters using 1496 daysof Super-Kamiokande data. Phys. Lett. B, 539,
179–187.
The number of citations: 70

Collaboration
Institute
ICRR, Univ. of Tokyo
Boston Univ.
BNL
Univ. of California, Irvine
Caliﬁrnia State Univ.
George Mason Univ.
Gifu Univ.
Univ. of Hawaii
KEK
Kobe Univ.
kyoto Univ.
LANLLouisiana State Univ.
Univ. of Maryland
MIT
Univ. of Minnesota
State Univ. of New York, Stony
Brook
Niigata Univ.
Osaka Univ.
Seoul National Univ.
Shizuoka Seika College
Tohoku Univ.
Univ. of Tokyo
Tokai Univ.
Tokyo Institute of Technology
Warsaw Univ.
Univ. of Washington

Country
Japan
USA
USA
USA
USA
USA
Japan
USA
Japan
Japan
Japan
USA
USA
USA
USA
USA
USA

(∗ )
22
7
1
9
3
1
1
4
9
2
5
1
3
6
1
1
10

Japan
Japan
Korea
Japan
Japan
Japan
Japan
Japan
Poland
USA

4
3
3
1
7
1
4
4
1
4

(∗ ) Number of participants.

K2K
Overview
The ﬁrst long baseline neutrino oscillation experiment was
conducted. The neutrino beam produced at the KEK-PS
was directed to the Super-Kamiokande detector, 250 km awayfrom the neutrino production target. The experiment is sensitive to the neutrino oscillation for ∆m2 ≥ 3 × 10−3 eV2with large mixing angles. The observation of the atmospheric
neutrino oscillation by Super-Kamiokande will be tested experimentally and the precise oscillation parameters would bedetermined. About 4.8 × 1019 protons on target were used
to produce neutrinos from April 1999 to July 2001. A totalof 56 neutrinos from KEK have been identiﬁed in the SuperKamiokande detector, while the expected number of eventsin the absence of neutrino oscillation was 80.1+6.2−5.4 . Distortion of neutrino energy spectrum reconstructed from 29 fullycontained single ring events was also observed. Thus, theprobability that the observed ﬂux at Super-Kamiokande is
explained by statistical ﬂuctuation without neutrino oscillations is less than 1%. Allowed region of ∆m2 at 90% C.L.
is 1.5 ∼ 3.9 × 10−3 eV2 at the maximal mixing. K2K experiment has resumed its data taking since Dec, 2003 andwill continue until early 2005. By that time, the number ofneutrino events should be twice larger than at present.

The Long Baseline Neutrino Oscillation Experiment
The discovery of the neutrino oscillation by SuperKamiokande in 1998, has lead to the conclusion that neutrino
has a ﬁnite mass. The discovery implies the existence of new

7

DATA

3500

MC
3000

CCQE (MC)

2500
2000
1500
1000
500

Fig. 14. The arrangement of the near detectors.

physics beyond the standard model of the elementary particles with a huge energy scale. Since the observed neutrinomass diﬀerence of ∆m2 ∼ 3 × 10−3 eV2 suggests the oscillation length is about a few hundred km for one GeV neutrinos,
this observation can be experimentally tested by using the artiﬁcially created neutrino beam with the detector placed at a
few hundred km from the neutrino production point.
The k2k experiment was planned to detect such oscillationeﬀect and to determine the oscillation parameters precisely.
The neutrino beam created at KEK has a mean energy of 1.3
GeV and was sent to the Super-Kamiokande detector, 250 km
west of KEK, every 2.2 seconds with the duration of 1.1 µ second. In the site of KEK, at the distance of 300 m from thetarget, we have prepared near detectors which mainly consist of 1kt water Cherenkov detector, ﬁne grained scintillation
ﬁber detector (FGD) and the muon ranger. The supplemental detectors are also placed. The arrangement of the front
detectors is shown in Fig. 14.
There are several beam monitors, proton proﬁle monitors,
the muon monitor and the pion monitor, placed along the neutrino beam line. The decay length is about 200 m, therefore
the beam is not scaled exactly by 1/r2 law. The ﬂux ratio of
the near to the far detector was obtained by the beam Monte
Carlo calculation by taking account of the spread and emittance of the beam at the target, the production of the pions,the focusing eﬀect by the HORN and the decay of pions toneutrinos. The beam calculation was validated by the pion
monitor which measured the produced pion directions andmomentum.
The beam ﬂux and the spectrum were measured by thefront detectors. ICRR group has a responsibility of providing
the Super-Kamiokande data and the construction of the 1kt
front detector and the analysis of the data from those detector
components. The coverage of PMT in the 1kt front detector
is same as the Super-Kamiokande detector with the 40% of
the total inner detector surface. The 1kt detector provides
information of the absolute neutrino ﬂux and the spectrumof the neutrino beam. Figure 15 shows the muon momentum
spectrum obtained by using the single ring fully contained
events at 1kt detector. The observed spectrum is well reproduced by the Monte Carlo simulation in which beam energy
spectrum and neutrino interaction in water are taken into account. Combining the 1kt data and FGD data together withconstraint of the pion monitor measurement, the expected00

200 400 600 800 1000 1200 1400 1600 1800 2000
Pµ (MeV/c)

Fig. 15. The muon momentum spectrum obtained by using single
ring fully contained events at the 1kt detector. The box shows thecorresponding Monte Carlo simulation. The hatched histogramshows CC quasi-elastic component in MC.

Fig. 16. The timing distribution of fully contained event observed at
Super-Kamiokande with respect to the beam injection timing.

neutrino energy spectrum was obtained for the far detector.
All the systematic errors due to detector bias or uncertainty ofneutrino interactions were carefully taken into account. The
neutrino beam was delivered about 6 months per year from1999. We have accumulated 4.8 × 1019 protons from April
1999 to July 2001.
The synchronization of the timing between KEK 12 GeV
Proton Synchrotron and Super-Kamiokande detector was performed using a GPS system. Figure 16 shows the timing
distribution of the fully contained events observed at SuperKamiokande with respect to the proton beam injection timing. The time of ﬂight of neutrinos from KEK to SuperKamiokande (∼ 830 µsec) is corrected in the ﬁgure.
Neutrino events were clearly observed near ∆T = 0 andthe spread in the timing was consistent with the duration of beam injection at KEK 12 GeV PS. In total, 56
events were identiﬁed as K2K beam induced events at SuperKamiokande. Using the large number of observed neutrino
events at front detectors, expected number of neutrino eventsat Super-Kamiokande was calculated to be 80.1+6.2−5.4 assuming
no-oscillation.
29 µ-like single ring events were observed and the neutrinoenergy spectrum obtained from the energy and scattering angle of the observed muons is shown in Fig. 17. From the deﬁcit

8

Eventsoscillations will be possible.

12

List of Publications

10[1] Ahn, S. H. et al. 2001, Detection of accelerator produced neutrinos at a distance of 250 km. Phys. Lett.
B, 511, 178–184.
The number of citations: 87

8[2] Ahn, M. H. et al. 2002, Indication of neutrino oscillation
in a 250 km long baseline experiment. to be publishedin Phys. Rev. Lett.

6
4

Collaboration

2
0

0

1

2

3

4

5
Eνrec

2

2

∆m (eV )Fig. 17. The reconstructed Eν distribution from single ring fully
contained events at SK. Points with error bars are data. Box
histogram is expected spectrum without oscillations, where theheight of the box is the systematic error. The solid line is the best
fit spectrum. These histograms are normalized by the number of
events observed. In addition, the dashed line shows the expectation with no oscillations normalized to the expected number of
events.

-2

10

-3

10

-4

10

0

0.2

0.4

0.6

0.8
1
2
sin 2θ

Fig. 18. Allowed regions of oscillation parameters. Dashed, solidand dot-dashed lines are 68.4%, 90% and 99% C.L. contours,
respectively. The best fit point is indicated by the star.

of observed number of events together with the shape distortion of neutrino energy spectrum, we have concluded thatprobability of null oscillation is less than 1%. The allowed
region of ∆m2 and sin2 2θ is shown in Fig. 18. The obtained
result for neutrino oscillation parameters are consistent withthat from atmospheric neutrino oscillations.
K2K is expected to continue accumulating data throughearly 2005. By that time, the number of neutrinos observedin Super-Kamiokande should be twice larger than at present,
and statistically signiﬁcant, detailed analysis of the neutrino

Institute
ICRR, Univ. of Tokyo
KEK, High Energy Accelerator Research Organization
Kobe University
Kyoto University
Niigata University
Okayama University
Tokyo University of Science
Tohoku University
Chonnam University
Dongshin University
Korea University
Seoul National University
Boston University
University of California at Irvine
University of Hawaii at Manoa
Massachusetts Institute of Technology
State University of New York at
Stony Brook
University of Washington at Seattle
University of Warsaw(∗ ) Number of participants.

Country
Japan
Japan

(∗ )
23
12

Japan
Japan
Japan
Japan
Japan
Japan
Korea
Korea
Korea
Korea
USA
USA
USA
USA

6
8
2
3
1
1
5
1
1
6
4
5
3
1

USA

6

USA
Poland329µ-ν (Gravitational Wave)
Overview• Gravitational wave experiment
Gravitational waves are physical entities in spacetime
predicted by Einstein’s theory of general relativity. Theirexistence was indirectly proven by the observation of
PSR1913+16 by Taylor and Hulse1 who won the Nobel
prize in 1993. However, nobody has succeeded in directly
detecting gravitational waves.
Theory of gravitation is tested by the detection of gravitational waves. A gravitational wave detector is the lasteye of mankind to inspect the universe.
In order to directly observe gravitational waves, wehave been developing a large scale interferometric gravitational wave detector. We succeeded in operating
TAMA for more than 1000 hours with a sensitivity which
would make observation of the coalescence of double neutron stars occurring within a range of 30 kpc with a signal
to noise ratio of 10. After this long term observation, we
installed a power recycling mirror to improve its sensitivity towards its ﬁnal goal.
However, it is diﬃcult to observe such gravitational
wave events because statistical studies show that thebirth rate of the coalescence of double neutron stars is10−6 a year in a galaxy as big as our Galaxy.2 Thismeans that we need to wait for long time to detect thegravitational wave from the coalescence of binary neutron stars by the present detector. This is the reason
why we have to construct LCGT (Large-scale Cryogenic
Gravitational wave Telescope).3
There are many other possible gravitational wave
sources in the universe other than the coalescence of binary neutron stars. However, the coalescence of binary
neutron stars diﬀers completely from other sources in thesense that its wave form is precisely determined and its
existence is certainly conﬁrmed.
LCGT adopts cryogenic mirrors with a 3 km baseline
and will be mounted in tunnels in the Kamioka mine. We
are conducting R&Ds for cryogenic mirrors and planing
to buid a 100 m cryogenic laser interferometer (CLIO) at
the Kamioka site, which is promised to be ﬁnanced for
2002–2006.

TAMA project[Spokesperson : Kazuaki Kuroda]µ-ν Div., ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
12

3

J.H. Taylor and J.M. Weisberg, Further experimental tests ofrelativistic gravity using the binary pulsar PSR 1913+16, Astrophysical J., 345 (1989) 434.
E.S. Phinney, The rate of neutron star binary merges in theuniverse: minimal predictions for gravity wave detectors, Astrophysical J. 380 (1991) L17.
K. Kuroda, et al., Large-scale cryogenic gravitational wave telescope, Int. J. Mod. Phys. D8 (1999) 557.

Table 1. TAMA data taking runs.

Run
DT1
DT2
DT3
DT4
DT5
DT6

Term
6-Aug → 7-Aug
17-Sept → 20-Sept
20-Apr → 23-Apr
21-Aug → 4-Sept2-Mar → 8-Mar
15-Aug → 20-Sept

Year
1999
1999
2000
2000
2001
2001

Length (Hour)
7
31
13
161
111
1038

In collaboration with members of :TAMA collaboration (NAOJ, Tokyo; KEK, Tsukuba;
UEC, Tokyo; Osaka City Univ., Osaka; Kyoto Univ., Kyoto; Osaka Univ., Osaka; Niigata Univ., Niigata)
TAMA is a gravitational wave project to construct a
300 m baseline laser interferometer at the Mitaka campus of the National Astronomical Observatory of Japan(NAOJ) and to conduct observations. TAMA is a ﬁve
year project started in April, 1995 and is organized byresearchers belonging to universities and national laboratories. We regard the TAMA interferometer as a step
towards the ﬁnal scale interferometer in the sense of technology and the construction budget. We have achieved
so far six data taking runs that spans from two to fourweeks (Table 1). In the former half runs, its sensitivity
improvemnet was the ﬁrst priority. Nonetheless, bothstability and reliability needed to be improved to checkthe sensitivity itself. In the latter half runs, the operation became easier by the installation of an automatic
control system.
During the course of this project, we have established techniques necessary for constructing large-scaleand highly sensitive interferometers. We are conﬁdent
that the TAMA project is successful and that the several
techniques developed so far will be useful for LCGT in
the future.
The data taken at DT6 is under study. No traces ofgravitational waves have been detected. Previous result
was published and its stable operation was reported.4
The sensitivity of each run is shown in Fig. 1 (the dates
do not exactly correspond to those of data taking runs).
The sensitivity has been steadly improved and is close to
the goal of the ﬁrst phase (the ﬁrst phase means the interferometer optical system without a recycling mirror).
At the time of DT6, we analyzed several noise sourcesthat governed the sensitivity curve and almost all sources
4

H. Tagoshi, et al., First search for gravitational waves frominspiraling compact binaries using TAMA300 data, Phys. Rev.
D63 (2001) 062001-1; M. Ando, et al., Stable operation of a
300-m Laser Interferometer with Suﬃcient Sensitivity to Detect Gravitational-Wave Events within Our Galaxy, Phys. Rev.
Lett. 86 (2001) 3950.

10

Fig. 1. TAMA sensitivity is steadly improved. It is close to the goal
sensitivity of the first phase.

were identiﬁed except the noise that limits the sensitivity
around at 600 Hz.
After DT6, TAMA entered a Phase II stage, where a
power recycling mirror was installed to reduce the shotnoise. The recycling mirror was installed between the
beam splitter and the mode cleaner (in Fig. 2). At thisstage, the power recycling gain was set three, that will be
ﬁnally set 10. The sensitivity was not recovered to thelevel of DT6 in this ﬁnancial year, mainly due to a total
rearrangement of optical pieces.
We could observe the coalescence of neutron star binaries occurring within 30 kpc with a signal to noise ratioof 10 at the time of DT6. The range depends on themass of the target as shown in Fig. 3. As far as the coalescence of the binary neutron stars with the nominal
mass of 1.4 M is concerned, the distance range does
not become larger by improving the sensitivity at lower
frequency such as 100 Hz. Low frequency improvement iseﬀective for the detection of coalescences involving heavier compact star like black holes. Roughly speaking, theﬁnal goal would be attained by raising the sensitivity byten. This can be performed by increasing internal light
power by applying the power recycling.

R&D for LCGT
[Spokesperson : Kazuaki Kuroda]µ-ν Div., ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with members of :LCGT collaboration (NAOJ, Tokyo; KEK, Tsukuba;
UEC, Tokyo; Osaka City Univ., Osaka; Kyoto Univ., Kyoto; Osaka Univ., Osaka; Niigata Univ., Niigata)
The target sensitivity of LCGT is to observe binary
neutron star coalescence events occurring at 200 Mpc
with S/N=10. This is ten times more sensitive thanthat of the ﬁrst LIGO and two orders more than thatof TAMA at their most sensitive frequencies. This will

be attained by using a three-kilometer baseline locatedunderground, cooling mirrors at cryogenic temperature,and high-power laser source employing a 100 W output
with higher recycling gain. The optical conﬁguration succeeds that of TAMA, which is a Fabry- Perot-Michelsoninterferometer with techniques of the frontal modulation,
wave-front sensing, and power recycling.
The Table 2 lists the important parameters of LCGT.
The ultimate sensitivity of a laser interferometer is determined by seismic noise at low frequency (10–30 Hz)(which is reduced by improving the vibrational isolation
system), and it is limited by photon shot noise at high frequency (more than 300 Hz), which can be improved only
by increasing the light power in the main cavities. The
sensitivity of middle frequencies (30–300 Hz) is limitedby thermal noise and this is reduced both by decreasing
the temperature and by decreasing the internal mechanical loss (i.e., increasing the mechanical Q of vibrationalmodes). The source of thermal noise comes from bothmirror internal vibration and swing noise of the pendulum supporting the mirror. Reduction of thermal noise
is attained by cooling down the temperature of both themirror itself and the suspension system that suspends themirror.
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 most straight forward solutions for the improvementof sensitivity.
A conceptual design of the cryogenic mirror system isshown in Fig. 4, where only part of the end-mirror chamber is focused. The mirror is suspended by one or twoloops of sapphire ﬁbers connected to an alignment control
platform that has a heat link to the heat anchor (4 K)
inside the vacuum located just above the platform. This
platform is suspended with a G-10 (thermal insulator)
rod connected through the center holes of the radiation
shields to an isolation table suspended by a low frequency
vibration isolator, which is at room temperature. All ofthese cryogenic system and the vibration isolator are put
inside the common high vacuum. The support of thevibration isolator needs to be ﬁxed on the ground independently of the chamber supports (Figure 4 diﬀerently
shows).
To realize this concept, the following research subjects
were considered:
1. removal of the heat produced by high power laser
illumination
2. maintainance of the high Qs of mirror internal
modes and suspension pendulum
3. prevention of contamination of mirror surfaces
4. estimation of heat production by optical loss in the
mirror
5. control of the alignment of mirrors in cryogenic environment

11Fig. 2. Optical configuration of TAMA300 at the time of DT6. After DT6 the recycling mirror was installed between the beam splitter andthe mode cleaner.

Table 2. LCGT design parameters

Item
Baseline Length
Laser Power
Input power at BS
Finesse of main cavity
Beam radius at End
Main Mirror
Mechanical Q
Suspension pendulum
Anti-vibration
Fig. 3. Expected signal to noise (SN) ratio for each mass of detectablebinary system at 10 kpc. The sensitivity at 100 Hz was better at
the time of DT6 than in June, 2001. This improved SN ratio forheavier mass of the member star of binaries. The improvement at
the mass of the neutron star binary (1.4 M ) was relatively small.

We had already ﬁnished the ﬁrst two subjects and hadreported in the previous annual report (1997–1998). 5
In regard to the third and fourth items, the results
were reported in the last annual report (2000–2001) andpublished in papers.6
5

6

T. Uchiyama, et al., Cryogenic cooling of a sapphire mirrorsuspension for interferometric gravitational wave detectors,
Phys. Lett. A242 (1998) 211; T. Uchiyama, et al., Mechanicalquality factor of a cryogenic sapphire test mass for gravitational
wave detectors, Phys. Lett. A261 (1999) 5; T. Uchiyama, etal., Mechanical quality factor of a sapphire ﬁber at cryogenic
temperatures, Phys. Lett. A273 (2000) 310.
S. Miyoki, et al., Cryogenic contamination of an ultra-low loss

Parameter
3 km
100 W
1 kW
1250
3 cm
Sapphire 51 kg, 30 K
108
1 Hz, Q=2 × 108 , 10 K
10−3 at 1 Hz

As for the last item, we conﬁrmed that a superconducting ﬁlm can be used for the receptor of magnetic force inplace of permanent bar magnets that are normally usedin the existing detectors. The ﬁlm can be easily sputtered on the mirror surface wihtout harmly degrading
the mechanical Q of the mirror.
All the above R&Ds conﬁrmed the feasibility of the reduction of thermal noise of the interferometer. We evaluated that these researches underline the basis of LCGT.
However, a practical cryogenic detector need many pracmirror for cryogenic laser interferometeric gravitational wave
detector, Cryogenics 40 (2000) 61: S. Miyoki, et al., Cryogenic
contamination speed for cryogenic laser interferometric gravitational wave detector, Cryogenics 41 (2001) 415: T. Tomaru,etal., Cryogenic measurement of the optical absorption coeﬃcientin sapphire crystals at 1.064 µm for the large-scale cryogenic
gravitational wave telscope, Phys. Lett. A283 (2001) 80.

12
5#5QTUKOKNCTU[UVGOFig. 5. Thermal conductivity of sapphire fiber was found to be proportional to its cubic of the diameter for thin fibers.

Fig. 4. Overview of the cryogenic suspension system. The mirror issuspended by sapphire fibers connected to a platform that has aheat link to a 4 K heat anchor inside the vacuum. The platform issuspended with a G-10 rod connected through the center holes ofradiation shields to an isolation table suspended by low frequency
anti-vibration system at room temperature in the common highvacuum.

tical R&Ds for the installation of cryogenic mirrors.
Therefore, we started to do researches for this application. The next section describes one of such R&Ds.

A dependence of thermal conductivity on thicknessof fiber
The mirror is cooled by sapphire crystaline ﬁbers. The
conductivity test had been done using 250 µm diameter
sapphire ﬁbers. The diameter of the ﬁber was chosen
by the consideration of the bending curvature that could
tightly wrap the cylindrical surface of the mirror, 10 cm
in diameter. Since the mirror size is increased up to
20–30 cm for LCGT, we can adopt thicker ﬁbers. Although the suspension thermal noise limits the thicknessof the ﬁber at room temperature, the sapphire suspension becomes free from this limit at cryogenic temperature mainly due to a decreasing thermal expansion rate
towards lower temperatures. Therefore, thicker ﬁber canbe used to satisfy the sole requirement of heat ﬂow fromthe mirror to the heat anchor point. If the diameterof the ﬁbers are increased, thermal conductivity at cryogenic temperature supposedly increase more rapidly than
the square of the diameter because of the ease of phonon
scattering at the inner surface of the ﬁber so long as thediameter is shorter than the mean free path of phonons
at the temperature.
Experiment to check this point was done by measuringconductivities of three kinds of diameter and the depen-

dence was found to be proportional to the cubic of thediameter (Fig. 5). This result reduces the load of sapphire ﬁbers in consideration of the heat ﬂow.
In regard to the last question of the actuation at
cryogenic temperature, we are developing an actuation
method that utilizes Meissner eﬀect in a thin super conducting ﬁlm on the surface of the mirror. This magnetic
actuator has wider dynamic range compared with electrostatic actuation method. A practical design must be
pursued for LCGT.

R&D research in Kashiwa
To show the feasibility of cryogenic mirrors for moresensitive detectors, a cryogenic interferometer needs tobe established. For this purpose we are developing a
one-arm cryogenic interferometer. A vacuum cryostat
system with a beam duct was made and set in Kashiwa
campus. It has two identical vacuum cryostats and a 6 mlong vacuum tube with radiation shield (40 K) inside. In
this cryostat, the cylindrical axis of radiation shields andalso that of the vacuum chamber are placed horizontally.
We can access the experimental inner space by horizontally opening the vacuum lids. Cryogenic temperatures
are maintained by a Giﬀord-McMahon refrigerator withthermal conductor from the head of the refrigerator to
the inner radiation shield. Since the refrigerator is a vibration noise source, it is designed to be mounted far
from the cryostat itself.
Cooling speed and mechanical vibration were measured and compared with their design values as reported
in the previous annual report. For the cooling speed,since the design was done for steady state in cryogenic
temperature, the low thermal conductivity of the thermal conductor in higher temperature caused a fairly longcooling time, roughly one week. However, this long cooling time is compensated by ease of use of the cryostat
system. Because this system does not need liquid nitro-13
1/2
15.25M
EOM

PBS

WB
EOM

ISO

Nd: YAG
Laser

CCD

1/2

VaccumTank

Heat Link
Wires
1/2

1/4
CCD

PD
1/2

1/4
PD

4 K Shield
90 K ShieldFig. 6. Experiment for Cryogenic mirror suspension system in Kashiwa
campus. One arm Fabry-Perot cavity consists of two cryogenic
mirrors housed in cryostats connecting 6 m long vacuum tube
with inner radiation shield. Optical system needs to be put inside
the vacuum to reduce sound noise.
Fig. 8. 20 m intereferometer in Kamioka Mineline.

Kamioka 20 m prototype detector for possible
coalescence of binary MACHO[Spokesperson : Masatake Ohashi]µ-ν Div., ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582

Fig. 7. Disturbance of the refrigerator vibration at the suspended
mirrors of the cryogenic Fabry-Perot interferometer.

gen nor liquid helium.
An optical layout of the experiment is shown in Fig. 6.
The eﬀect of the vibration of the refrigerators was low
enough to be isolated by conventional anti-vibration technique as designed. The measured displacement noise isshown in Fig. 7. The excitation around 50 Hz in thisﬁgure was thought to be produced by the mechanicalresonances of the radiation shield plates, which can be
reduced by appropriate support stems inside the cryostat chamber in the next experiment.
In conclusion, we have succeeded to present the feasibility of using cryogenic mirrors for LCGT by the above
basic experiments in the past years. The next step in
R&D for cryogenic mirrors is to show the reduction ofnoise amplitude itself, which needs more realistic interferometer other than the prototype with a shorter base-

In collaboration with members of :NAOJ, Tokyo; NIAIST, Tsukuba
The prototype 20 m interferometer (LISM) was operated underground of the Kamioka Mine. The sitenear the Super-Kamiokande detector is a planned siteof LCGT. The LISM has shown a long term stability of
the interferometer and produced a high-quality data by
taking advantage of both the low seismic noise and thehigh temperature stability in the Kamioka undergroundspace.
We developed the 20 m prototype interferometer at
NAOJ since 1991. When the ﬁnal experiment for R&D of
TAMA project (a high-gain recycling7 ) was ﬁnished, we
decided to move the 20 m interferometer from TAMA site
into the Kamioka Mine to catch possible GW events fromthe coalescence of binary MACHO-BHs in our Galaxy8 .
LISM interferometer consists of three parts; a lightsource with a mode cleaner, a primary cavity as a frequency reference and a secondary cavity to sense GW. A
laser is a commercial NPRO with wavelength of 1064 nm
and output power of 700 mW. Two cavity are formed
by a pair of high quality mirrors with a ﬁnesse of about
25000 and length of 20 m. The optical layout is called as
Locked Fabry-Perot conﬁguration (shown in Fig. 9). The
main part of LISM is housed in vacuum chambers and thepressure is kept at 10−6 torr by two ion pumps. Dataaquisition system has eight channnels with 20 kHz sampling and another eight channels with slow sampling formonitoring the interferometer and environment. Time
information is obtained from GPS signals. We started
78

S. Sato, et al., Applied Optics, 39 (2000) 4616–4620.
T. Nakamura, et al., ApJ 487 (1997), L139.

14
GW Signal

Secondary
Cavity

40MHz

NPRO
LASER

Mode
CleanerPrimary
Cavity18MHzFrequency
stabilization
control

Fig. 9. Optical layout of LISM interferometer

Fig. 10. Lock Status Summary of TAMA300 and LISM

observations early in 2000. The operation of LISM isvery stable owing to the advantage of quiet undergroundsite.
After several improvements, mainly frequency stabilization of the laser, the strain sensitivity of LISM
reached hrms = 6.0 × 10−20 around 800 Hz. This sensitivity makes it possible to catch the event of binary
neutron star inspirals up to 1kpc with SN=10. A coincidence run with TAMA300 is highly important. We
synchronized LISM observation with DT6 of TAMA300(Fig. 10). Over 700 hours data were recorded and theanalysis is now underway. This is a ﬁrst coincidence analysis of actual two interferometers in the world.

15

SDSS
SLOAN DIGITAL SKY SURVEY
The Sloan Digital Sky Survey (SDSS) achieved the
Photometric First Lightin May 1998. It began to takecommissioning data from the fall of the same year. During the time the construction of the two double spectrographs was completed and the ﬁrst observation wasmade in May 1999. Since then both hard and software
have been tuned and the quality of the data have beenbrought into nearly the survey grade. While we are stillin the beginning of the survey and we still need to understand some systematics, as well as to improve the calibration, the data we obtained by now greatly surpass thestandard of currently available wide ﬁeld surveys in both
quality and quantity, but also in the photometric precision. As for the quantity, it would be enoug to mention
that imaging over 150 square degrees is carried out with
ﬁve colours in one night, which is compared to a typical‘wide ﬁled survey’ that comprises a few square degrees
with one, or at most, two colours. Photometric surveys
which are comparable to SDSS in the sky coverage alluse photographic plates. A typical example is AngloAustralian project 2dF, whose photometric accuracy is
no better than 30%, which is compared to 2–3% accuracy of the SDSS. This achievement is clearly by virtueof the huge CCD camera we have built. We select target
objects for spectroscopy based on the photometric survey,
so that the photometric accuracy limits the fundamental
accuracy of all follow-up observations and analyses. The
SDSS also enjoys an enormous spectroscopic capability.
We are able to obtain over 6000 spectra per night if wespend a full night for spectroscopy. Our operations are
not yet at the full scale, since we still need many veriﬁcations. By the spring of 2001, however, 6% of the sky(2,400 square degrees) have been imaged and 3% of thesky (150,000 spectra) are spectroscopically studied. (Ourgoal is to survey over 1/4 the entirte sky).
These data have been used to produce early science results. By the time of the end of FY2000, 25 papers havebeen written for research journals and 14 have alreadybeen published; these numbers are rapidly growing at thetime of writing this report. The topics cover wide subjects of astronomy, stellar science, galaxy science, active
galactic nuclei, and cosmology. Speciﬁcally, enormous
multi-colour imaging capability has greatly pushed forward high redshift quasar studies. This is demonstrated
by the number of high redshift quasars we have found:
40 years of quasar searches have given 105 quasars with
redshifts (z) higher than 4; From 10 nights of imaging
SDSS found 132 quasars with z > 4. For z > 5 10 out
of 11 are SDSS quasars. The highest redshift record wasrenewed 4 times, and now it is z = 6.3. It is interestingthat these quasars show normal spectra, indicating thepresence of the normal heavy element abundance. Our
study has enabled to delineate the evolution of quasars

when galaxies were forming. We have also discovered astrange ‘quasar’ which does not show any emission lines.
We have found a number of low temperature stars,
which are beyond M type and classiﬁed as L and T types.
T stars are dominated by methane absorption bands,
quite similar to the Jupiter spectrum. It was shownthat L and T stars form a continuous class in spite ofan apparent discontinuity observed in the optical colour
bands. These observations have alredy promoted studies of the atmosphere of low temperature stars where thedust forms. From the observed number density of these
low temperature stars we can conclude that low mass
stars do not dominate the stellar mass of galaxies, as wasonce conjectured to solve the dark matter problem. Studies of stars are interesting not only from their own right,
but also in that they would shed light on the structure of
Milky Way. An analysis of the colour-magnitude diagram
for millions of stars we imaged has revealed that the thin
Galactic disc (to which the sun belongs to) is surrounded
by a thick disc of the scale height twice the thin disc.
These thick disc stars are clearly distinguished from halostars. The presence of the thick disc has been suggested
for a decade but it has been a matter of debate: theSDSS established its presence unambiguously. We havealso assembled a large number of RR Lyrae, from which
we could show that halo stars are distributed as r−2.7
out to 60 kpc from the Galactic centre, but their distribution sharply declines beyond this distance: the Milky
Way has a sharp edge. This study at the same time revealed a conspicuous clump of stars at 50 kpc from the
Galactic centre. A further study of the spatial distribution of A stars showed that this clump is interpreted asdebris from the collision of the Sagitarius dwarf galaxy
with the Milky Way. These are all important aspects tounderstand how galaxies formed and evolved.
Galaxy science needed more time to produce results,
as we had to ﬁrst verify the quality of catalogues. For
this purpose we have inspected more than 100,000 objects by eyes and checked against catalogues producedby the photometric pipeline. This eﬀort has clariﬁed thestatistical accuracy of the galaxy catalogue, but also it
has been used to tune the software. One of the mostelementary analyses for galaxy science is galaxy counts
as a function of magnitude. We have derived the counts
from one million galaxies for a range over 10 magnitudes,from 12 to 22 mag, much wider in the dynamic range
than any other single surveys to date could explore. This
study showed that the counts behave as expected in a homogeneous universe, excluding a few indications for thecontrary made in the past. At the same time, however,
we have detected a small variation of the galaxy distribution over a very large scale (which aﬀects up to 150 Mpc).
An accurate determination of the luminosity function ofgalaxies in ﬁve colour bands have also a great impact on

16logue. We note, however, that the catalogue in the stateof the art is not quite complete, and the users are advised
to verify it appropriately before their use.

Fig. 1. ‘Pie diagram’: a section of the three dimensional distributionof galaxies in the (2.5 deg wide) equatorial strip. The data contains about 40,000 galaxies obtained in 4 nights of imaging and10 nights of spectroscopic follow-up. The black points stand fornormal galaxies to r  = 17.8 mag, and red points are luminous red
galaxies to r  = 18.8 mag in order to sample a deeper sky. Notethat the limit of the celebrated Harvard Center for Astrophysics
survey is about 150 Mpc.

galaxy science, since it is the most fundamental statisticthat is used for any statistical analyses of galaxies, yet
has suﬀered from uncertainties by a factor of two in thenormalisation. This uncertainty has hampered accurate
understanding of evolution of galaxies.
SDSS is among a few groups which detected the gravitational lensing shear ﬁled caused by galaxies at the ﬁrst
time. The shear from individual galaxies is very small
and this detection needed a large ststistical smaple. Taking the advantage that lensing galaxies of the SDSS sample are given redshift measurements we could determine
the mass to light ratio of galaxies, which is about 150 insolar units out to a large radius (∼ 260h−1 kpc).
The quantitative understanding of large-scale structure of the universe is one of the advertised goals of the
SDSS project. We have just started studies for largescale clustering of galaxies. Our current aim is to clarify
systematic eﬀects, to establish the robust strategy to derive the power spectrum of density perturbations, and to
estimate the realistic error of the analysis. We have employed several independent methods to derive the power
spectrum, and veriﬁed that all methods give a convergent
answer where they ought to do if proper treatments are
made for the data.
There are many more to write about science from
SDSS, but we should quit here. Many objects foundby SDSS have already been taken as excellent targets ofobservations for more detailed studies with the Subaru
Telescope from its beginning phase. We ﬁnally advertise that our data taken at the equatorial strips (for both
north and south, 2.5 deg wide) are already open to the
public (from June 2000). The data are 5% of the goal,but many millions of objects are registered in the cata-

17

AIR SHOWER DIVISION
Overview

1. Introduction

Two major research activities of the Air Shower division are the study of extremely high energy cosmic raysby the AGASA/TA group and very high energy gamma
rays by the CANGAROO group.
At the Akeno observatory, a series of air shower arrays of increasing geometrical sizes have been constructed
and operated to observe ultra high energy cosmic rays.
The AGASA (Akeno Giant Air Shower Array) is thenewest and the largest, which started the operation in1991 and presently covers the ground area of 100 km2 as
the world largest air shower array. In 10 years of operation, AGASA observed a handful of cosmic rays exceeding the theoretical energy end point of the extra-galactic
cosmic rays (GZK cutoﬀ) at 1020 eV. The Telescope Array (TA), an array of air ﬂuorescence telescopes to bebuilt in Utah, USA, is to succeed the AGASA with 30
times larger aperture and the particle identiﬁcation capability. It intends to unveil the origin of super-GZK
cosmic rays discovered by the AGASA.
The CANGAROO project (Collaboration of Australia
and Nippon for a GAmma-Ray Observatory in the Outback) is a set of large imaging Cherenkov telescopes tomake 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 purpose of this project is to explore the violent, non-thermal universe and to reveal theorigin of cosmic-rays. We have detected several gammaray sources in the southern sky and detailed study ofthese sources are now ongoing.

AGASA [1, 2] is the Akeno Giant Air Shower Arraycovering over 100 km2 area in operation at Akeno village
about 130 km west of Tokyo, in order to study extremely
high energy cosmic rays (EHECR) above 1019 eV. In thisenergy region, distinctive features in the energy spectrum
and arrival direction distribution are expected.
If the cosmic rays are of extragalactic origin, photopion production between cosmic rays and primordial
microwave background photons becomes important atenergies above 6 × 1019 eV with a mean free path ofabout 6 Mpc. Therefore a cutoﬀ in the spectrum are
expected around several times 1019 eV. This is called
as the Greisen-Zatsepin-Kuzmin (GZK) cutoﬀ [3]. Since
the cosmic rays exceding this cutoﬀ energy must be originated at nearby sources within 50 Mpc. In this senario,
the expected arrival direction distribution of EHECR isrelatively isotropic and should have some correlation withthe material distribution around our galaxy; super galactic plane or clusters of galaxies.
On the other hand, if they are galactic origin, theirarrival direction distribution should have strong correlation with the galactic structure, since the gyroradiusof protons of energy above 1019 eV are comparable withthe galactic scale. Therefore a study of correlations of
EHECR with the galactic structure and/or with the large
scale structure of galaxies is important.
As accerleration mechanism of these EHECR, the diffusive shock acceleration is most widely accepted andshocks at radio lobes of relativistic jets from Active
Galactic Neuclei, termination shocks in local group ofgalaxies, etc. are discussed to be possible sites [4]. The
acceleration above 1020 eV in dissipative wind models of
cosmological gamma-ray burst is also proposed [5]. Sincevarious diﬃculties are still anticipated in accelerating cosmic rays up to the highest observed energies, it is also
discussed that these cosmic rays are possiblly the decay
products of some massive particles produced at the collapse and/or annihilation of cosmic topological defects
which could have been formed in a symmetry-breaking
phase transiton in the early universe [6].
The details of the AGASA are described in Chiba et
al. [1] and Ohoka et al. [2]. The array is operational
since 1991 and the exposure is about 1500 km2 sr year
till the end of 2000. Extensive air showers, observed till
July 2001, with zenith angles smaller than 45◦ and withcore locations inside the array area were used. In theenergy range above 1019 eV, we only used such events
that passed through an eye scan to conﬁrm their core
positions and energies.

Study of the Most Energetic Cosmic Rays
with AGASA — AGASA Collaboration[Spokesperson : M. Teshima]
Air Shower Div. ICRR, Univ. of Tokyo, Kashiwa, Chiba 2778582
In collaboration with the members of:Hirosaki University, Hirosaki; Saitama University,
Urawa; Tokyo Institute of Technology, Tokyo; Nishina
Memorial Foundation, Tokyo; Yamanashi University,
Kofu; Nagoya University, Nagoya; Ehime University,
Matsuyama; Osaka City University, Osaka; Fukui
University of Technology, Fukui; National Institute ofRadiological Sciences, Chiba; RIKEN, Saitama.

18

2. Energy Spectrum

The details of determination of arrival directions andS(600) are described in Takeda et al. [10].
The diﬀerential primary energy spectra above
1018.5 eV are shown in Fig. 1 [10]. The bars represent
statistical errors only and the error in the energy determination is about 30% above 1019 eV, which is estimatedfrom analyzing the artiﬁcial showers simulated considering shower development ﬂuctuation and experimental
errors in each detector [10].
The energy spectrum extends beyond 1020 eV and we
observed 8 events above GZK cutoﬀ energy. If the realenergy spectrum is that shown in Fig. 1 as the dashedcurve, the expected number of events above 1020 eV isless than one, taking account of the energy resolution.
The energy spectrum is therefore more likely to extend
beyond 1020 eV without the GZK cutoﬀ.

10

26

J(E) E 3 [m -2 sec-1 sr -1 eV 2 ]

AGASA

10

AGASA + A20
o

+60

Dec
o

+30

24

h

h

RA

12

0

h

Galactic Plane

-30
-60

o

o

Supergalactic Plane
Fig. 2. The arrival direction of the highest energy cosmic rays above
1020 eV on the galactic coordinate.

Density [arbitrary unit]

In order to estimate the primary energy of giant air
showers observed by the AGASA, the particle density at
a distance of 600 m from the shower axis (S(600)) is used
as an energy estimator, which is known to be a goodparameter [7]. The conversion factor from S(600) [perm2 ] to primary energy E0 [eV] is derived by simulation[8] as
E 0 = 2.0 × 1017 × S(600)1.0 .
(1)

25

1
3

6

4
2

10

24

23

10

19

0

20

40

Separation Angle [deg]Fig. 3. The space angle distribution between two events above
4 ×1019 eV. We can see a clear peak below three degrees.

Uniform sources

10

0

20

10

Energy [eV]Fig. 1. The energy spectrum observed with AGASA. The verticalaxis is multipled by E3 . Error bars represent the Poisson upperand lower limits at 68% and arrows are 90% C.L. upper limits.
Numbers attached to points show the number of events in eachenergy bin. The dashed curve represents the spectrum expected forextragalactic sources distributed uniformly in the Universe, taking
account of the energy determination error.

3. Arrival Direction
3.1 Above GZK energy
The arrival direction of the highest energy cosmic rays
above 4 × 1019 eV is shown in Fig. 2 in the equatorial

coordinate. Small dots and squares show events between
4 × 1019 eV and 1020 eV, respectively. They appear to
be distributed uniformly over the observable sky. We
have carried out several tests for global anisotropy but
could not ﬁnd any large scale structures in this distribution. However, we found one triplet and ﬁve doublets ofevents clustering within an angular resolution (2.5◦ ) as
indicated by shadowed circles. The chance probability forthis clustering eﬀect was evaluated as low as Pch ∼ 10−3 .
No outstanding astronomical objects have been found in
the directions of these clusters within 50 Mpc.
In Fig. 3, we have shown the space angle distribution
between events (some kind of auto-correlation). We cansee clear peak at small angles (le3 degrees). This peak
distribution could be explained by the angular resolutionof AGASA. This result strongly suggests the existence ofpoint like sources (compact sources) and weak magnetic

Declination[degree]

19verse, caused by the spontaneous breaking of symmetries,
have been proposed as a candidate for production of ex4 tremely high energy cosmic rays. Such TD’s are magnetic
3 monopoles, cosmic strings, domain walls, superconducting strings etc. The remarkable result from this scenario
2is that bulk of cosmic rays above 1020 eV may be gamma1 rays rather than protons and the energy spectrum is ex25
0 pected to extend up to the GUT scale ∼ 10 eV witha hard exponent such as 1.35 [12], which is based on the-1
exponent of hadronization in QCD.

90

30

-30

anti G.C.

G.C.

-2
-90

-3
300

200
100
Right Ascention[degree]

0

Fig. 4. The statistical signiﬁcance of the deviations of the arrival
direction distribution of the cosmic rays above 1018 eV on theequatorial coorinate.

ﬁeld in the intergalactic spaces of ≤ nG order, if they arecharged particles.

References[1] N. Chiba et al., Nucl. Instrum. Methods A 311,
388 (1992).
[2] H. Ohoka et al., Nucl. Instrum. Methods A A372,
527 (1997).
[3] K. Greisen, Phys. Rev. Lett. 16, 748 (1966); G.T.
Zatsepin and V.A. Kuzmin, Pisma Zh. Eksp. Teor.
Fiz. 4, 144 (1966).
[4] Various acceleration models are discussed in Astrophysical Aspects of the Most Energetic Cosmic
Rays, ed. M. Nagano and F. Takahara (World Scientiﬁc, Singapore, 1990) pp. 252–334.
[5] E. Waxman, Phys. Rev. Lett. 75, 386 (1995); M.
Vietri, Ap. J. 453, 883 (1995); M. Milgrom and V.
Usov, Ap. J. 449, L37 (1995);[6] Recent summary and references are described in P.
Bhattacharjee, Proc. of ICRR Symp. on ExtremelyHigh Energy Cosmic Rays : Astrophysics and Future Observatories ed. M. Nagano, (Inst. of Cosmic
Ray Research, University of Tokyo., 1997) p. 125.
[7] A.M. Hillas et al, Proc. 12th ICRC, Hobart 3, 1001
(1971).
[8] H.Y. Dai et al., J. Phys. G: Nucl. Part. Phys. 14,793 (1988).
[9] S. Yoshida et al., J. Phys. G: Nucl. Part. Phys.
20, 651 (1994).
[10] M. Takeda et al., Phys. Rev. Lett. 81, 1163 (1998).
[11] N. Hayashida et al., Astroparticle Phys. 10, 303(1999).
[12] P. Bhattacharjee, C.T. Hill and D.N. Schramm,
Phys. Rev. Lett. 69, 567 (1992).

3.2 Anisotropy around 1018 eV
The harmonic analysis in the right ascension was carried out using the comsic rays about 216,000 events observed by AGASA [11]. k ∼ 14 at 1018 eV can be seenin the ﬁrst harmonic. The phase of maximum amplitude
corresponds to 15 hr in right ascension. The statisticalsigniﬁcance is high, corresponding to a chance probability of 10−6 .
In Fig. 4 the arrival direction distributions in equatorial coordinates are shown. They show the statisticalsigniﬁcance of the deviations from the expectation. Here,the energy region of 1018 eV ∼ 1018.4 eV is selected which
maximize the harmonic analysis k-value. We can not observe events with declination less than −25◦ , as long as
we use showers with zenith angles less than 60◦ . In thisﬁgure, we have chosen a circle of 20◦ radius to evaluate the excess. In the siginicance map, a 4.5 σ excess(obs./exp. = 506/413.6) near the Galactice enter region
can be seen. In contrast, newar the direction of antiGalactic Center we can see a deﬁcit in the cosmic rayintensity (−4.0 σ). An event excess from the direction of
the Cygnus region is also seen with 3.9 σ (obs./exp. =
3401/3148).

Telescope Array Project

4. The highest energy events[Spokesperson: M. Fukushima]

There are eight events whose energies exceed considerably the GZK cut-oﬀ energy. Their sources can’t bevery far and must be within a few tens of Mpc. However,there are no candidate astronomical objects within a few
tens of Mpc in the direction of the highest energy events
which may be able to accelerate particles to more than
1020 eV.
These observations have led to suggestions that particles may be directly produced by decay from objects
produced in phenomenon occurring on a higher energy
scale [6, 12]. For example, topological defects (TD’s)left over from the phase transitions in the early uni-

Air Shower Div. ICRR, Univ. of Tokyo, Kashiwa, 277-8582
Chiba
In Collaborattion with the members of:
ICRR, Univ. of Tokyo, Tokyo, Japan; KEK, High Energy Accelerator Organization, Tsukuba, Japan; University of California at Los Angeles, Los Angeles, California, USA; Montana State University, Bozeman MT,
USA; Columbia University, Navis Laboratories, Irvington, New York, USA; University of Utah, Salt Lake City,
Utah, USA; Kinki University, Osaka, Japan; University of Adelaide, Adelaide, South Australia, Australia;

20

University of New Mexico, Albuquerque, New Mexico,
USA; University of Alabama in Huntsville, Alabama,
USA; Yamanashi Univ., Kofu, Japan; Saitama Univ.,
Urawa, Japan; Konan University, Kobe, Japan; Tokyo
Institute of Technology, Tokyo, Japan; Osaka City Univ.,
Osaka, Japan; Nagasaki Institute of Applied Science, Nagasaki, Japan

Extremely High Energy Cosmic Rays
The origin of the extremely high energy (EHE) cosmic rays is an enigma. Ten events observed by AGASA
clearly demonstrate the existence of particles above
1020 eV in the universe. As predicted by Greisen Zatsepin and Kuzmin (GZK), such particles collide with themicrowave background and quickly loses its energy by thepion photoproduction. The universe is no longer transparent for EHE particles, and we have to look for theorigin of such particles within 50 Mpc (= GZK limit) of
our galaxy.
Powerful extragalactic objects such as the active galactic nuclei, radio galaxies and the gamma ray bursts may
be suspected as the acceleration site of EHE proton or
nucleus. The search for the astronomical origin in thearrival direction of the AGASA events, however, failed
to ﬁnd such objects within 100 Mpc of our galaxy. The
origins beyond this limit may be tolerated, but only if
we assume special mechanism to allow a longer propagation beyond the GZK cutoﬀ, such as the violation of
special relativity or the EHE neutrinos as the carrier ofsuch energy. In addition, it is generally perceived thatthe astronomical acceleration above 1020 eV is diﬃcult
to achieve.
It is fascinating to imagine that the EHE cosmic ray is
generated by the decay of super-heavy elementary particles in the present universe. The energies above 1020 eVare easily obtained if the particle mass is at the GrandUniﬁcation scale of 1015 GeV. Such particles may beeither surviving as a relic particle of the Big Bang orpresently generated by the decay of topological defects.
An abundant generation of EHE gamma rays and neutrinos, in place of protons and nuclei, is expected in sucha decay.

Fig. 1. Proposed station deployment of TA.

Overview of Experiment
The Telescope Array (TA) experiment is proposed to
draw a decisive conclusion on the mysterious origin of
EHE cosmic rays[1][2]. It is a giant array of air ﬂuorescence detectors, which measures the UV ﬂuorescenceof molecular nitrogen generated by the air shower particles. The observation of the whole shower development
process enables an unbiased determination of the energy
and arrival direction of incoming cosmic rays. The particle species are determined by measuring the depth of theshower maximum (Xmax ) in the atmosphere. This is the
key feature of the experiment.
The eﬀective aperture of TA is more than 30 times
larger than that of AGASA. It is approximately the same
size as the future ground array experiment, the southern

Fig. 2. An artist’s view of a TA station.

hemisphere Pierre Auger Laboratory, to be constructedin Argentina.
The Telescope Array consists of 10 measurement stations deployed in the West Desert of USA, near Salt Lake
City, Utah. Each station is separated by ∼40 km and is
distributed as shown in Fig. 1. Smaller versions of air
ﬂuorescence detectors, Fly’s Eye and HiRes, have been
operating in the vicinity.
Each TA station is equipped with two rings of 20 imaging telescopes arranged in a circle of 30 m diameter (see21Fig. 2). The upper ring covers the elevation angle of3◦ –19◦ and the lower ring covers 19◦ –34◦. A total of
40 telescopes covers 360◦ in azimuth and is sensitive tothe cosmic rays above 1020 eV falling within 50 km of
the station. Most of the cosmic rays will be measured
simultaneously by 2 or more stations. This stereo measurement removes an ambiguity of the reconstruction andenables a precise determination of the shower geometry.
The development of the shower in the air is recorded by
the imaging camera composed of a matrix of photomultipliers (PMTs).
A steerable laser is placed at the center of each station.
It will be used to determine the extinction coeﬃcient of
the ﬂuorescence light along the transmission path to thetelescope.

TelescopeFig. 4. Prototype PMT camera.

Images50y

The telescope is composed of a spherical mirror andan imaging camera placed on the focal plane. Eighteen hexagonal segment mirrors form a reﬂection surface
equivalent to a circle of 3 m φ with a curvature of radius
6 m. A prototype mirror is shown in Fig. 3. The segment
mirror is formed with a 10 mm thick Pyrex glass and analuminum coating is made by the vacuum deposition. A
layer of aluminum oxide is formed by the anodization
technique for the protection of the mirror surface.
A set of 256 PMTs with a hexagonal window is arranged in 16 × 16 array and forms an imaging plane of
the camera (see Fig. 4). A single telescope covers the skyof 18◦ in azimuth and 15.6◦ in elevation with a pixel ac-

0

-50
-50

0

50

x

light intensity

30

20

10

0
-50

0

50

x

Fig. 5. Optical performance of the telescope. Images formed byparallel lights at diﬀerent injection angles are shown.

Fig. 3. Prototype mirror.

ceptance of 1.1◦ × 1.0◦ for one PMT. The image obtainedby this optics was simulated by ray tracing and the resultis shown in Fig. 5. The average spot size is small enoughcompared with the size of the PMT photocathode.
The phototube (Hamamatsu R6234 or equivalent) has

22

P x km x km

10 2

Horizontal
10

Vertical10Electronics
A nearby vertical shower produces a PMT signal withshort (∼ 1 µs) duration but with a high pulse height. A
distant shower with a running away conﬁguration produces a long (up to 20 µs) and weak signal over the nightsky background.
The electronics of TA copes with this problem by the
combination of custom developed LSI chip (CSI: charge
sampling integrator) and a pipeline ADC. It achieves 12bit resolution, 200 ns sampling time with 16-bit dynamic
range by H/L AD conversion scheme. Each readout channel is equipped with a digital signal processor (DSP),
which executes a baseline subtraction and signal ﬁnding algorithm every 10 µs. The result is sent to a VME
trigger processor by the optical network. The prototype
electronics is shown in Fig. 6.
The trigger processor searches for an air shower trackin 3-dimensional space XYT; X and Y being the Cartesian coordinates of the imaging camera and T for thetime coordinate. The decision is made within 30 µs of theelapsed time and is distributed to each DSP. The DSP
makes a data sparciﬁcation upon receipt of the trigger,

10

10 2

P x km x km

a bialkali photocathode. A light reﬂector is placed in the
gap between PMTs such that the ﬂuorescence light impinging on the gap is reﬂected and guided to the central
region of the photocathode. This minimizes the insensitive area between PMTs and improves the uniformity of
the imaging plane. A UV transparent ﬁlter is placed in
front of the PMT array to block the night sky backgroundin the visible light region.
An important way of calibrating and monitoring the
PMT gain is realized by a small light pulser made bya Cerium activated YAlO3 scintillator (YAP). An alphaparticle from 241 Am painted on the scintillator generates∼ 104 photons around 370 nm, the mount of which canbe absolutely calibrated elsewhere. The YAP pulser ismounted on a computer controlled x-y stage in front of
the imaging camera. The YAP will scan the PMT imaging plane and the pulse height spectrum of each PMT
will be recorded for calibration.
Individual PMTs will be driven by the negative highvoltage controlled with an accuracy of 0.1 V. It facilitates the online adjustment of each PMT gain by YAP
and opens the possibility of taking data under high background when the Moon is in the sky.

5

DISTANCE [km]Fig. 6. A prototype ADC-DSP board.

10

1
0

5

10

DISTANCE [km]Fig. 7. Attenuation of back scattered light with the distance of transmission for vertical and horizontal laser shots. A good weather(above) and a bad weather (below) examples are shown.

and transport all the data around the discovered shower
track for further event building. The ADC and the trigger processor are now installed on the Akeno observatorysite together with the prototype telescope, and the integrated system is being tested for the observation of the
air shower event.

Atmospheric Monitoring
The ﬂuorescence light undergoes the scattering and absorption before reaching the telescope. The major contribution comes from the molecular (Rayleigh) scattering and the aerosol (Mie) scattering. The strength ofRayleigh scattering can be calculated by using the density proﬁle of the atmosphere. The Mie scattering however depends on the amount and type of the aerosol andits distribution in the atmosphere, which may vary withthe place and time.
We plan to install a steerable YAG UV laser systemat each station and shoot a laser pulse along the online
reconstructed shower track for each event. We measure
the side and back scattered laser lights at each station,and derive the extinction coeﬃcient for each event.
We performed such experiments on the HiRes site in
Utah and at Akeno observatory in Japan. In the Akeno
experiment the laser was shot 256 times at a ﬁxed direction and its back scattered light was measured at thesame location (a lidar method)[3]. The strength of thedetected signal is shown as a function of the distanceto the scattered point in Fig. 7. A similar experiment
performed on the HiRes site shows that the attenuation

Number of Events

23

50

Number of Events

0

-50

0
50
100
Energy Resolution [ %]Construction

20

0

Number of Events-100

proton with this condition is 64,000 km2 sr. We expect
to collect more than 30 events of EHE cosmic rays above
1020 eV every year with a duty factor of 10%.
The target volume for the EHE neutrino with
E=1020 eV is 1.1 × 1011 ton sr without considering theduty factor. The detection of HE neutrino is possible by
the monocular measurement. The acceptance is 2 × 1010
ton sr for E=1017 eV neutrino.
The distributions of the reconstructed energy, Xmax
and arrival direction are shown in Fig. 8 for 1020 eV protons. The shape of the reconstructed distribution is wellcontrolled and has no long tails from the average value.

-200

-100

0
100
200
2
Xmax Resolution [ g/cm ]25

The Telescope Array will be built by the collaborationof Japanese, American and Australian physicists. The
group consists of cosmic ray physicists who have beenworking in AGASA and HiRes experiments, and highenergy physicists who worked in the accelerator experiments in US and Japan.
The development of the mirror, camera and electronics
system will be completed in 2002. A prototype telescope
will be installed near the planned site in 2003 and its
performance will be thoroughly checked.

Bibliography
0

0

1

2
3
4
5
Angular Resolution [ degree]

Fig. 8. Reconstruction of energy, Xmax and arrival direction for1020 eV proton. The resolution of reconstruction is 6%, 25 gr/cm2
and 0.6◦ respectively.

length by the Mie scattering could reach 25 km and is signiﬁcantly better than the standard atmospheric model of
the western US desert [4]. The R/D eﬀort is continuingin Akeno and Utah to obtain a most reliable way of atmospheric correction.
The acceptance of the TA will be reduced by the thecloud obscuring the ﬁeld of view. We will install a scanning infra-red camera at each station and regularly takea picture of the night sky. The obscuration will also be
identiﬁed by shooting the laser along the online reconstructed track and observing a large backward scattering.

Performance
The performance of TA for the EHE cosmic rays wasestimated by the Monte Carlo study. The longitudinal
proﬁle of the air shower was generated by the CORSIKA shower simulation code. The generation, transmission and detection of the ﬂuorescence light was fully
simulated. The event was reconstructed from the digitized data by searching for the best arrival direction andshower parameters to ﬁt the observed PMT response including the time proﬁle.
In order to guarantee a reliable stereo reconstruction,
we require at least 2 stations have a track extending morethan 5◦ in the ﬁeld of view. The aperture of the 10 20 eV[1] The Telescope Array Project: Design Report. July,
2000, available by the web http://www-ta.icrr.utokyo.ac.jp/index.html.
[2] T. Aoki et al., Proc. of 27th International Cosmic
Ray Conference, 915 (2001).
[3] T. Yamamoto et al., Proc. of 27th International
Cosmic Ray Conference, 663 (2001).
[4] M. Sasano et al., Proc. of 27th International Cosmic Ray Conference, 653 (2001).

Very High Energy Gamma Ray Observation
with Imaging Cherenkov Telescope in Australia: CANGAROO experiment[Spokesperson : M. Mori]
Air Shower Div., ICRR, Univ. of Tokyo, Kashiwa, Chiba
277-8582
In collaboration with the members of:
Ibaraki Prefectural University, Ami, Ibaraki;
Ibaraki University, Mito, Ibaraki;
Institute of Space and Astronautical Science, Sagamihara, Kanagawa;
Konan University, Kobe, Hyogo;
Kyoto University, Kyoto, Kyoto;
MSSSO, Australian National University, ACT 2611, Australia;
National Astronomical Observatory, Mitaka, Tokyo;
Osaka City University, Osaka, Osaka;
Shinshu University, Nagano, Nagano;
STE Laboratory, Nagoya University, Nagoya, Aichi;
Tokai University, Hiratsuka, Kanagawa;Tokyo Institute for Technology, Meguro-ku, Tokyo;

24

University of Adelaide, Adelaide, SA 5005, Australia;
Yamanashi Gakuin University, Kofu, Yamanashi;
Yamagata University, Yamagata, Yamagata.

PSR 1706-44 and SN1006
These sources are extensively studied by Kyoto University group. The preliminary results are obtained and presented at 27th ICRC in Aug. 2001 [5, 6, 7]. Both sourceswere re-conﬁrmed to be there. The ﬂuxes are consistent
with the previous measurement with CANGAROO-I. For
detail, one can see the above references.

RX J1713.7-3946: one of cosmic ray origin?
With the 10-m telescope, we have conﬁrmed RX
J1713.7-3946 as a TeV source [8, 9]. The image orientation angle (α) is plotted in Fig. 10 (the inserted
graph). The α distribution is broad as if it is a diﬀuse

10
10

-8

0

α (degrees)

20 40 60 80

1400
1200
1000
800
600
400
200
0

-9

-2

-1

-1

Differential Flux (cm sec TeV )Fig. 9. The second 10-m telescope completed in March 2002. The
ﬁrst telescope can be seen in the background.

10
10
10
10
10
10

-10
-11
-12
-13
-14

Number of Events / 5 degrees

Very high energy (VHE) gamma-rays at TeV energies
are searched for in the southern sky by the CANGAROO
Collaboration as an international collaboration with Australian universities. The new imaging Cherenkov telescope (CANGAROO-II), ﬁrst built with a 7-m diameter
reﬂector in 1999, was expanded to have a 10-m reﬂector,
in February 2000 in Woomera, South Australia, (136◦ 47
E, 31◦ 06 S). and has been in operation on moonless,clear nights. The optical reﬂector is composed of 114
spherical mirrors of 80 cm in diameter made of composite material (mainly CFRP) arranged to form a parabolic
surface and has a focal length of 8 m [1]. A multi-pixel
photomultiplier-tube camera is set at the focal plane, giving a ﬁeld of view of 2.76◦ × 2.76◦ . Each pixel of photomultiplier tube views 0.115◦ × 0.115◦. The outputsof the photomultiplier tubes are digitized and used toreconstruct the image of Cherenkov light emitted fromair shower particles created by very high energy γ-rays(sub-TeV in energy) in the upper atmosphere. The arrival direction of γ-rays is determined with an accuracyof ∼ 0.2◦ as well as to distinguish from Cherenkov lightimages of cosmic-ray background events.
With the 10-m telescope, we have observed various objects which includes gamma-ray sources we have detectedwith the 3.8-m telescope, CANGAROO-I: the Crab pulsar/nebula, the pulsar PSR 1706–44, supernova remnants SN1006 and RX J1713.7–3946, and the pulsar PSR
1509–58. We also observed other candidate objects suchas active galactic nuclei (AGN). The results are summarized in the following sections.
Now we are constructing an array of four 10-m
Cherenkov telescopes, called CANGAROO-III, which
will be completed by 2003 [2]. With its stereoscopic
imaging capability of Cherenkov light, we will explore
the high energy universe with excellent sensitivities [3].
In March 2002 the second 10-m telescope was constructed
100-m west of the ﬁrst telescope (Fig. 9). It is equippedwith an improved multi-pixel camera which has a wider
ﬁeld-of-view of 4 degrees [4], reﬁned mirrors and fasterelectronics. This telescope is under tuning to commencestereoscopic observation of Cherenkov light which enables
us to detect gamma-rays with higher resolution.

-15

10

-1

1

10

10

2

Energy (TeV)

Fig. 10. Diﬀerential ﬂux of RX J1713.7-3946 obtained by CANGAROO-II. The white circles are obtained by the 10-m telescope,
black squares are by the 7-m, and white squares are by the 3.8-m.
The inserted graphs are image orientation angle α for ON- (points
with error bars) and OFF-source run (histogram).

source, consistent with the previously published result[10]. The statistical signiﬁcance of the α-peak is 8.7 σ.
Also the diﬀerential ﬂux is obtained as shown in Fig. 10,
consistent with ref. [10]. The power law spectrum is observed even in the sub-TeV region which is extended toless than 400 GeV, whose behavior is hard to understandif the emission is produced by by high-energy electrons
via inverse Compton or bremsstrahlung processes. Instead, the emission is consistent with gamma-rays produced via decay of neutral pions emitted in collisionsof high-energy protons with surrounding matter of thisSNR. This can be an evidence that this SNR is one ofbirth places of cosmic-ray protons and cast a prospect of
the long-standing problem of cosmic-ray origin [11].

Southern AGNs
The analysis of southern nearby AGNs are carried out

-9

10

10

Whipple 2001
HEGRA-CT 2001 (scaled)

CANGAROO-II
2001
-11

10

2

10

-10

10

10

radio
-5

10

-12

Number of events-2 -1

E dN/dE (erg cm s )

10

1
0

-1

2

EGRET

2

-2

CANGAROO

ASCA-1

E dF/dE or E F(>E) (eV cm s )

25

10

2

10
1

10

10

0

5

10

10

10

2

Energy (TeV)1010Photon energy, E (eV)Fig. 11.
Multiwavelength spectrum of RX J1713.7-3946 andemission models. Lines show model calculations: synchrotron
emission (solid line), inverse Compton emission (dotted lines),
bremsstrahlung (dashed lines) and emission from neutral pion
decay (short-long dashed line). Inverse Compton emission andbremsstrahlung are plotted for two cases: 3 µG (upper curves)and 10 µG (lower curves). See ref. [9] for details.

by Tokai University group. The preliminary results basedon observations of PKS 2155–304 and PKS 2005–489 in
2000 were presented at 27th ICRC [12]. We could notsee gamma-ray signals from both sources and obtained
upper limits which are lower than some of theoreticalpredictions. We are promising that we can carry out asystematic study on the mechanism of cosmic-ray emission from AGN jets.

Mrk 421 observed at large zenith angles: question
on cosmology
We observed Mrk421, a nearby AGN and an established TeV gamma-ray source in the northern hemisphere, in Jan. to Feb. 2001 when it was in high state.
The zenith angles for this observation was around 70 degrees. The trial for such a large zenith angle observation
was a challenge to the atmospheric Cherenkov method.
Due to the slant depth of atmosphere, the energy threshold becomes as high as 10 TeV, but the detection area
becomes wider and we have sensitivities to low gammaray ﬂuxes. Analysis of the data shows a gamma-ray signal of which signiﬁcance is greater than 5 σ [13, 14].
TeV photons collide with infrared photons and produce
electron-positron pairs. The mean free path of this absorption becomes important for cosmological distances.
In the case of Mrk421 (z = 0.03), previous estimate ofintergalactic infrared background ﬂux predicts a cut-oﬀ
in energy spectrum of around several TeV. The detectionof over 10 TeV photons is not compatible with such estimate and may require reacessment of background photon
ﬂux in the Universe.

NGC 253: completely new window
NGC 253 is one of the closest starburst galaxies. Highstar formation rate means copious supernova remnants
and could be a new category of TeV gamma-ray sources.

1

10

Energy (TeV)

Fig. 12. The observed gamma-ray (main panel) and the energy spectrum of gamma-ray events (inserted panel). In the inserted panel,data are represented by circles with error bars, with a 2 σ upper
limit plotted at the highest energy. Best-ﬁt spectra for a power-law(E −4.0 ; dot-dashed line) and a cut-oﬀ (E −1.9 exp(−E/4 TeV);
dotted line) are shown. See ref. [14] for details.

It can be seen from the southern hemisphere with a goodcondition, i.e., it culminates near zenith. The observation
was carried out in Oct. 2000 and Oct. 2001. Gammaray signals were detected in both the data obtained in2000 and 2001. The ﬂux is very faint, such as several
times weaker than the Crab nebula. Ibaraki university
and ICRR group have completed the analysis and a paper
has been submitted for publication [15].

Other targets
A supernova remnant RCW 86 and a pulsar PSR
1259–63 have been observed in Mar. 2001. The analyses are underway by Kyoto group (RCW 86) and ICRR
(PSR 1259–63). Other targets, such as the Galactic center, SS443, and RX J0852–4622 were oberved in 2001 andanalyses are underway.

Near future prospect
The tuning of the second 10-m telescope will be completed in November 2002 and stereoscopic observation of
Cherenkov images will begin with two 10-m telescopes.
The complete array of four telescopes will be completed
by 2003. Even considering the schedule of the HESS
project in Namibia, we are still ahead. The eﬀorts in theﬁrst one or two year are very important to us.

SummaryThis year has been very productive, we think, andmany interesting results are coming out as describedabove. With improved sensitivity of stereo imaging technique, we hope our understanding of the high-energy universe will be put forward.

26

Bibliography[1] A. Kawachi et al., Astropart. Phys., 14, 261–269(2001).
[2] M. Mori et al., AIP Conference Proceedings 587,
pp. 927–931 (2001); Proc. 27th ICRC (2001) Vol.5,
pp. 2831–2834.
[3] R. Enomoto et al., Astropart. Phys., 16, 235–244(2002).
[4] S. Kabuki et al., Nucl. Inst. Meth. Phys. Res. A(in press).
[5] J. Kushida et al., Proc. 27th ICRC (2001) Vol.6,
pp. 2424–2427.
[6] T. Tanimori et al., Proc. 27th ICRC (2001) Vol.6,
pp. 2465–2468.
[7] S. Hara et al., Proc. 27th ICRC (2001) Vol.5,
pp. 2455–58.
[8] R. Enomoto et al., Proc. 27th ICRC (2001) Vol.5,
pp. 2477–2480 .
[9] R. Enomoto et al., Nature, 416, 823–826 (2002).
[10] H. Muraishi et al., Astron. Astrophys., 354,
L57–61 (2000).
[11] F. Aharonian, Nature, 416, 797–798 (2002).
[12] K. Nishijima et al., Proc. 27th ICRC (2001) Vol.5,
pp. 2626–2629.
[13] K. Okumura et al., Proc. 27th ICRC (2001) Vol.5,
pp. 2679–2682.
[14] K. Okumura et al., Astrophys. J. Lett. (in press).
[15] C. Itoh et al., submitted for publication.

27

EMULSION DIVISION
Overview
The Naming of the Emulsion Division was historicallyby the group activities of the early days, the present division covers the ﬁelds of research activities much wider
than the name may suggest. It consists of two maingroups, one is the experiment group and the other is thetheory group. The former aims to clarify high-energy
cosmic ray interactions and primary cosmic ray composition in high-energy region, mainly by means of emulsion
or related technique. The latter carries out the theoretical research of astro-particle physics in general.
A large-area emulsion-chamber experiment started in
the early 197’s, being succesively carried out at the topof Mt. Fuji (at 3 750 m a.s.l.) in order to study theproperties of high-energy hadron interactions as well as
the chemical composition of cosmic rays around 1015 –1017 eV, came to an end with a great success in 1994.
Emulsion chambers were often taken on board balloons
at the Sanriku Balloon Center of ISAS in order to obtain direct information on cosmic ray composition as wellas high energy heavy-ion interactions at energies around1013 –1014 eV. New results on the heavy primary spectrum from ∼ 100 GeV/particle to ∼ 100 TeV/particle
were obtained by the Hirosaki-Aoyama Gakuin group.
The chamber uses a multi-layered sandwich of X-ray ﬁlms
(SXF), nuclear emulsion plates and target layers. An
auto-scanning system was developed to identify interaction vertices for this experiment.
International collaboration plays an important role in
the activities of this division. A large-scale emulsion
chamber project was carried out with Chinese physicists at Mt. Kanbala (5 500 m a.s.l.) in Tibet during
the period from 1980 through 1990, with fruitful results.
The same project, however, is still being conducted with
Brazilian physicists at Mt. Chacaltaya (5 200 m a.s.l.)in Bolivia. These large-scale emulsion chambers can directly observe the phenomena induced by primary cosmic
rays of 1015 –1017 eV. Some interesting results are brieﬂyreported below.
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.) andhas been successful. An extension of the air shower array was completed 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. The Tibet air shower array has a good angularresolution better than 1 degress for air showers even at
multi-TeV energy region, with the result that the solar
magnetic ﬁeld eﬀect on the cosmic ray shadow by the sun
was for the ﬁrst time observed in 1992. From this experiment with better statistics, new information is expected
to be obtained on the large-scale structure of the solar
and interplanetary magnetic ﬁeld and its time variation

due to the solar activity cycle.
Balloon borne emulsion-chamber experiments havebeen carried out with US physicists at Texas in the U. S.
or in the Southan Hemisphere from Australia to Brazil
in order to achieve a long-duration exposure ﬂight. In
December of 1993 the antarctic balloon loaded emulsion
chambers were launched from MucMuro base (78◦ S) andsuccessfully recovered after 200 hours. The energy spectra of protons, helium nuclei and others have been obtained up to about 1014 eV, and helium nuclei show aslightly ﬂatter spectrum than protons at high energies.
The JANZOS (Japan Australia New Zealand Observation of Supernova) project, being successfully carriedout at Black Birch Range since 1987, was completely ﬁnished in March of 1995. The results obtained by this experiment have already been published in many scietiﬁcjournals.
A theory group has been added to this division since1979. The group is working on astro-particle physics, including cosmology, super-symmetry phenomenology, andbaryo-genesis. Though the group is small, it has been active and published about 60 papers in refereed journals
during last 5 years.
The development of various detectors for new experiment is being made by introducing new technology suchas scintillating ﬁber, super-conducting magnet etc. A
superconducting solenoid spectrometer was completed in
1993 to use for cosmic-ray balloon experiments in 1995.
A scintillating ﬁber calorimeter has been developed touse for the observation of GeV gamma rays on board
satellites in future.
This division has developed and completed several automatic measuring systems that are powerful for analyzing cosmic ray tracks or shower spots, that is,
automatic microdensitometers and precise coordinatemeasuring systems controlled by a computer. Enormous
data recorded on nuclear emulsion plates or X-ray ﬁlms
are rapidly and precisely measured by the use of thesemeasuring systems. At present ﬁve workstations are introduced to improve data-processing capacity.
The divison’s emulsion-pouring facilities can meet thedemands for making any kind of nuclear emulsion plates
which are used for cosmic ray or accelerator experiments.
The thermostatic processing facilities are favorably operated in order to develop nuclear emulsion plates or X-rayﬁlms. Using these facilities, it is also possible to makeand develop emulsion pelicles of 600 micron thickness
each. In this way these facilities are made available to all
qualiﬁed scientists who want to carry out joint research
successfully.

28

Search for Celestial Gamma-Ray Point
Sources and Study of Cosmic-Ray Composition at the “Knee” Energy Region in the
Tibetan Highlands (The Tibet ASγ Collaboration)[Spokesperson : Masato Takita]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of:Hirosaki Univ., Hirosaki; Utsunomiya Univ., Utsunomiya; Saitama Univ., Urawa; Kanagawa Univ.,
Yokohama; Yokohama National Univ., Yokohama;
Shonan Inst. of Technology, Fujisawa ; Tokyo Metropolitan Coll. of Aeronautical Eng., Tokyo ; NACSIS, Monbusho, Tokyo ; Konan Univ., Kobe, Waseda Univ.,
Tokyo, Shibaura Inst. of Technology, Tokyo, Nagoya
Univ.; China
Since 1990 the Tibet air shower array has been successively operated at Yangbajing (4 300 m above sea level) inTibet. Some results obtained from this experiment havebeen reported elsewhere. The air shower array (Tibet-I)
was updated in late 1994 by increasing the number ofscintillation detectors from 65 to 221, and then this newarray (called as Tibet-II) has been fully operating. The
Tibet-II array consists of 185 ﬁrst-timing (FT) detectorsof 0.5 m2 each. For the FT detectors, plastic scintillatorsof 3 cm thickness each are used and 2 φ PMTs (HPK
H1161) are equipped. They are placed in a grid of a
15 m spacing, as the previous array. Among these, eachof 52 FT detectors also contains a 1.5 φ PMT (HPK
H3178) for a wide-range particle density measurement.
The FT array is also surrounded by 32 density detectors of 0.5 m2 each to obtain a good core location for
individual shower event. The eﬀective area for detecting
the contained events is about 8 times as large as the oldone, and shower events has been accumulated at a rate ofabout 150 Hz to eﬃciently detect showers with energies
around 10 TeV. In 1996, a dense array was constructednear the center of the Tibet-II array. This array (HDarray) consists of 110 scintillation detectors each being
placed at a grid of 7.5 m spacing and was sensitive to
air showers with energies around 3 TeV. A trigger rateof this array has been set to about 150 Hz. Using thisHD array, in 1999, we succeced in observing γ-ray signals
from the Crab Nebula at 5.5 σ conﬁdence level. This was
the ﬁrst detection of multi-TeV γ-ray signals by a conventional air shower array. Following it, we also detected
multi-TeV γ-rays successfully at 3.7 σ level from Mrk501
which was in a highly ﬂaring state between March 1997
and August 1997.
In the late fall of 1999, the area of the HD array wasenlarged up to 22000 m2 (Tibet-III )as shown in Fig. 1.
It is equipped with 533 scintillation counters (497 FT +36 density PMTs) in total. The trigger rate is 680 Hz.
The performance of the array has been well examinedby observing the Moon’s shadow, and the deﬁcit mapof cosmic rays around the Moon gives an angular reso-

Fig. 1. Tibet-III array operating at Yangbajing.

Fig. 2. Moon shadow observed by Tibet-III.

lution of the array to be arround 1.0◦ for the Tibet-III
array, as is shown in Fig. 2. Multi-TeV gamma-ray signal
was successfully detected at sim5σ level from the Crab(the standard candle in gamma-ray astronomy) by the
Tibet-III array, as shown in Fig. 3. We also succeededin observing multi-TeV gamma-ray ﬂares at sim7σ levelfrom Markarian 421 which was in a very active phase during the year 2000 and 2001, shown in Fig. 4. We are now
accumulating Tibet-III data to obtain a standard TeV
γ-ray ﬂux and to search for unknown constant/transient
TeV γ-ray sources.
A hybrid experiment of emulsion chamber (EC) andair shower array started in 1996 to obtain the proton
ﬂux around the knee of the primary cosmic ray spectrum. The total area of EC each having the size of 40 cm
× 50 cm is 80 m2 and the total thickness of lead plates is
14 r.l.. High sensitive X-ray ﬁlms are inserted at every 2r.l. to detect gamma-ray families. Just under the emulsion chambers, the burst detectors with the same area as
EC were set up to locate the shower cores of family events
to be observed in the emulsion chambers. This detector
complex is set up near the center of the Tibet-II arrayto get on the information about accompanying air showers. The ﬁrst EC exposure was terminated in August

29

Fig. 5. Yearly variation of the Sun’s shadow observed by the Tibet-I(1991, 1992), Tibet-II (1996, 1997, 1 998, 1999) and Tibet-III(2000, 2001) arrays, respectively. Mode energies are 10 TeV.

Fig. 3. Energy spectrum of gamma rays from the Crab observed by
Tibet-III.

Fig. 4. Gamma-ray signal around Mrk421 in its flaring phase in theyear 2000 and 2001 observed by Tibet-III.

of 1997 and X-ray ﬁlms inserted in EC were developed
for analysis. Many gamma-ray families were detected in
the EC and a correspondence between these families andtheir accompanied air showers is now in progress by using
the data from burst detectors, emulsion chambers andair shower array. A high-energy family event of about
500 TeV was observed in this exposure and its primaryenergy is estimated to be about 1016 eV from the sizeof accompanying AS. This hybrid experiment continued
until 1999. Using the burst + air shower array data, we
obtained the energy spectrum of primary protons (820
proton-induced events during 690-day detector live time)with its primary energies 200–1000 TeV by a neural network method. The diﬀerential energy spectrum obtainedin this energy range can be ﬁt by a power law with thespectral index of −2.97±0.06, which is steeper than thatobtained by direct measurements at lower energies. We
also obtained the energy spectrum of helium nuclei. Allof the features of burst events are wholly compatible theheavy enriched composition in the knee region. The pri-mary proton spectrum including the EC data around theknee region, being inaccessible by any direct observations, are being analyzed. Roughly one third of the EC
data has been analyzed. Automatic analysis programs
are under development.
As discussed elsewhere, this array will be very powerful to get new information on the relation between atime variation of the large structure of the solar and interplanetary magnetic ﬁelds and the solar activity, since
suﬃcient data taken from this array can follow the movement of the sun shadow at every one-two months. The
sun’s shadow was observed in the direction signiﬁcantly
away from the apparent sun’s position during the period from 1990 through 1993. Note that this period almost corresponds to the solar cycle near the maximum
or at the decreasing phase (Cycle 22). In 1996 and 1997,
however, we found that the sun’s shadow was observed
almost at the same position as the Sun, since the solar cycle is now in a quiet phase. Since 1998, the sun’s
shadow began to be obscure shown in Fig. 5, as the solar
activities restarted. We expect that the Sun’ shadow willchange again its position according to the solar activity
as the next solar cycle (Cycle 23) goes toward its maximum around the year of 2001. Thus, the results willconsiderably contribute to the study of solar terrestrial
physics.

Exotic Phenomena Observed by Mountain
Emulsion Chamber (Chacaltaya Collaboration)[Spokesperson: Akinori Ohsawa]
ICRR, Univ. of Tokyo, Kashiwa, Chiba 277-8582
In collaboration with the members of: Waseda Univ.,
Tokyo; Aoyama Gakuin Univ., Tokyo; Yamanashi Univ.,
Kofu; Saitama Univ., Urawa; Kochi Univ., Kochi; Kinki
Univ., Osaka; USSR; Brazil
A series of emulsion chamber exposures have been continuously carried out at Mt. Chacaltaya (5 300 m) since1963. Several interesting events including Centauro-type
events have been observed in the emulsion chambers withcarbon target layer so far exposed at the Chacaltaya Observatory by Chacaltaya group of Brazil-Japan Collab-

30

oration and Pamir-type chamber exposed at the Pamir
station (4 300 m) in collaboration with the Pamir group.
Details of these events were already published elsewhere.
An over-all interpretation of exotic cosmic-ray phenomena is under study. A possible scenario is examined
under the hypothesis of the existence of quark matter.
The core of a compact star can be made of quark matter with u,d and s quarks, which is more stable , under high pressure than ordinary nuclear matter. Violent
stellar activity has a chance of emitting the core material into outer space, and a small globule of the quark
matter would be positively charged and accelerated tothe cosmic-ray energy region. When such quark-matter
globule comes into the atmosphere, it undergoes nuclear
interactions with characteristics that are diﬀerent fromthe common nuclear interactions. The incoming globule
is made of a small dense core with high baryon number
and the surrounding pion cloud. A core collision resultsin multiple baryon production, like the Centauro-type,and fragmentation of the quark-matter globule. Here,one expects emission of an excited quark-globule, which
can then transition into a bundle of hadrons and electromagnetic particles.
A new project (OMEGA) is worked out to study
hadronic interactions at energies around 1015 –1017 eV
by constructing a large-scale emulsion chamber combinedwith an air shower array at Mt. Chacaltaya. The
air shower array provides information on the primarycosmic-ray energy and the stage of air shower development at the observation level. A clue to solving theanomalous behavior of families mentioned above is expected to be given by such hybrid experiment. A smallscale experiment has been continued at Mt. Chacaltaya
and some results were reported elsewhere.

Theory Group
Time Evolution of Tunneling Phenomena[Spokesperson at ICRR: M. Yoshimura]
ICRR, Kashiwa 277-8582
Collaboration with the members of ICRR
Matsumoto and Yoshimura studied time evolution oftunneling phenomena occurring in thermal medium. The
time-dependent tunneling rate and the survival probability were derived by using the real-time formalism. The
eﬀect of environment, especially its inﬂuence on the time
evolution was clariﬁed in this work. It was found that anonlinear resonance eﬀect enhances the tunneling rate at
ﬁnite times of order 2/η, with η the friction coeﬃcient. In
the linear approximation this eﬀect has relevance to theparametric resonance. This eﬀect is expected to enhance
the possibility of early termination of the cosmologicalphase transition much prior to the typical Hubble time.

References[1] Sh. Matsumoto, Soryushiron Kenkyu (Kyoto) 104(2002), B21.

Primordial magnetic field generation in cosmological phase transitions[Spokesperson at ICRR: T. Uesugi]
ICRR, Kashiwa 277-8582
The existence of coherent magnetic ﬁelds over various
astrophysical scales has been established up to thepresent. To explain the observed magnetic ﬁeld ingalaxies, clusters, and interclusters, we studied a generation of the seeds of primordial magnetic ﬁelds duringcosmological phase transitions. In the previous study,
we estimated the primordial magnetic ﬁeld generated bygauged Q-balls during the electroweak phase transition.
At the electroweak scale, however, coherent scale of thegenerated magnetic ﬁeld cannot become larger thangalactic scales. To explain the large scale magnetic
ﬁeld, we are considering the generation mechanism due
to a non-equilibrium process during inﬂationary universe.

Delocalization Transition and Localization Lengthof Random Mass Fermions in an Imaginary Vector
Potential[Spokesperson at ICRR: K. Takeda ]ICRR, Kashiwa 277-8582
Collaboration with the member of Nagoya Institute of Technology
It is believed that almost all states tend to localize
in disorder systems in two and lower dimensions. However, it was shown by the recent studies that some speciﬁc states remain extended in the presence of correlateddisorder. We studied one-dimensional system of Diracfermions with a random-varying mass by the transfermatrix method which we developed recently [1]. We
investigated the eﬀects of nonlocal correlation of thespatial-varying Dirac mass on the delocalization transition. In particular, we calculated both “typical” and“mean” localization lengths as functions of energy, using imaginary vector potential. The results of numerical
study are in good agreement with the ones of analytical
calculations. We also obtained the relation between thelocalization length of states and the correlation length of
the random mass.

References[1] K. Takeda and I. Ichinose, J. Phys. Soc. Jpn. 70
p3623 (2001).

Study on AdS/CFT and dS/CFT Correspondence[Spokesperson at ICRR: N. Yokoi ]ICRR, Kashiwa 277-8582
Collaboration with the members of Osaka Univ., Ibaraki
Univ., and KEK
The AdS/CFT correspondence is the correspondence
between supergravity or superstring theory on the Antide Sitter (AdS) space-time and the superconformal ﬁeld

31

theory (CFT) on its boundary. We studied the quantum corrections for the supergravity on the AdS background and an extension of the holographic renormalization group in order to investigate the AdS/CFT correspondence at the sub-leading order of 1/N expansion of
the CFT [1]. We also studied the quantum aspects ofthe three-dimensional gravity with a positive cosmological constant from the perspective of the dS/CFT correspondence, which is the correspondence between quantum gravity on de Sitter space-time and a certain CFT[2].

References[1] T. Kubota, T. Ueno and N. Yokoi, in preparation.
[2] H. Umetsu and N. Yokoi, in preparation.

List of Other Inter-University Research Programs
Code No.: 6
Title: Study of primary cosmic rays by RUNJOB
Spokesperson: T. Shibata (Aoyama Gakuin University)
Participating Institutions: Aoyama Gakuin Univ., Hirosaki Univ. andShonan Institute for Technology, Gifu Univ.
Code No.: 7
Title: Observation of High-Energy Electrons andGamma Rays with a Balloon-borne Instrument
Spokesperson: Shouji Torii (Kanagawa University)
Participating Institutions: Kanagawa Univ., ISAS,
Rikkyou Univ.,
ICRR Univ. of Tokyo, and Shibaura Inst. of Technology.
Code No.: 8Title: Obsevation of high-energy primary electrons andatmospheric gamma rays by emulsion chambers.
Spokesperson: T. Kobayashi (Aoyama Gakuin University)
Participating Institutions: Utsunomiya Univ., Kanagawa Univ., ICRR Univ. of Tokyo, Univ. of Tokyo,
Kanagawa Prefectural College of Nursing and Medical
Technology.
Code No.: 9Title: Sidereal daily variation of 10 TeV-region galactic
cosmic-ray intensity observed by the Tibet air shower
array .
Spokesperson: K. Munakata (Shinshu University)
Participating Institutions: Shinshu Univ.

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RESEARCH CENTER FOR COSMIC NEUTRINOS
Research Center for Cosmic Neutrinos was establishedin April 1999. The main objective of this center is to
study neutrinos based on data from various observations
and experiments. In order to promote the studies of neutrino physics, it is important to provide the place fordiscussions on theoretical ideas and experimental resultson neutrino physics. Therefore, one of the most important, practical jobs of this center is the organization ofneutrino related meetings.
In the ﬁscal year 2001, we organized three local neutrino meetings. Two of them were held in ICRR, and one
in Tokyo Metropolitan University. In these meetings, wehave discussed topics such as, atmospheric neutrinos, solar neutrinos, supernova neutrinos, accelerator neutrino
experiments, reactor neutrino experiments, double beta
decay, phenomenology of neutrino oscillations, CP violation in neutrino sector, models of neutrino mass, anduniﬁed theories. In each meeting, we had about 50 participants.
Atmospheric neutrino data from Super-Kamiokande
give the most precise information on neutrino oscillations. With the increased data, it is more important tohave better predictions of the neutrino ﬂux. Therefore,
we work on the prediction of the atmospheric neutrino ﬂux. In order to predict the ﬂux accurately, it isimportant to know the details of the data on the measurements of primary and secondary cosmic ray ﬂuxes.
For this reason, we have a close collaboration with researchers working in the cosmic ray ﬂux measurements.
The preliminary results from the new detailed calculationshows about 10% smaller absolute ﬂux than the previously used ﬂux. Also, the new ﬂux, which is calculated
including the accurate three dimensional geometry of the
Earth and the interaction, shows an enhancement of theﬂux in the horizontal direction for sub-GeV neutrinos.
It is important that the general public knows theachievements of the present science. Because of this reason, we had a public lecture at Kashiwa, the city our
new campus is located. Three active scientists related toneutrino physics lectured on various aspects of neutrino
physics.
Finally, scientiﬁc staﬀs in this center are actively working in the Super-Kamiokande and K2K experiments.

33

OBSERVATORIESandSTATIONS
Location of the Institute and the Observatories in Japan34

OBSERVATORIES and STATIONSNorikura 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 Underground Observatory
Location:
Telephone:
Fax:

Higashi-mozumi456, Kamioka-cho, Yoshiki-gun, Gifu Prefecture 506-1205
N 36◦ 25 26 , E 137◦19 11 , 357.5 m a.s.l.
+578-5-2116+578-5-2121

See Kamioka Division for the research activities.

35

NORIKURA OBSERVATORY
Norikura Observatory (36.10◦N and 137.55◦E) was
founded in 1953 and attached to ICRR in 1976. It is
located at 2770 m above sea level, and is the highest altitude manned laboratory in Japan maintained all theyear. Experimental facilities of the laboratory are madeavailable to all the qualiﬁed scientists in the ﬁeld of cosmic 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 accessed easily by the car in summer (JuneOctober) but an aid of snowmobile is necessary in wintertime.

ﬂare particles in association with a large ﬂare occurredon the 29th of September, 1989. The data suggested
that protons could be accelerated at least up to 50 GeV
in a large solar ﬂare considering the geomagnetic cut-oﬀ
rigidity of the proton is estimated to be 11.5 GeV at Mt.
Norikura. The high altitude of the observatory is essential for detecting the ﬂare particles without signiﬁcantattenuation.
In 1990, Nagoya group constructed a solar neutrontelescope consisting of scintillators and lead plates, whichmeasures the kinetic energies of incoming neutrons up
to several hundred MeV. This telescope observed highenergy neutrons associated with a large ﬂare occurredon the 4th of June, 1991. The same event was simultaneously detected by the neutron monitor and the highcounting meson telescope of the Norikura observatory.
This is the most clear observation of solar neutrons at
the ground level in almost ten years since the ﬁrst observation at Jungfraujoch in 1982.
A new type of large solar neutron telescope (64 m2 sensitive area) was constructed by Nagoya group in 1996. It
consists of scintillators, proportional counters and woodabsorbers piled up alternately. This takes a pivotal role
among a worldwide network of ground based solar neutron telescopes of the same type in Yangbajing in Tibet,
Aragatz in Armenia, Gornergrat in Switzerland, Chacaltaya in Bolivia and Mauna Kea in Hawaii. The Sun isbeing watched for 24 hours using this network.

Fig. 1. Norikura Observatory.

Present academic interests of the laboratory is focusedon the modulation of high energy cosmic rays in the interplanetary space associated with the solar activity andthe generation of energetic particles by the solar ﬂares.
For the modulation study, two small experiments havebeen operated continuously for a long time. One is aneutron monitor operated to study the correlation of solar activity and the cosmic ray ﬂux. The other is a highcounting meson telescope consisting of 36 m2 scintillation
counters to study the time variation of cosmic rays withenergies of 10–100 TeV.
The Sun is the nearest site to the Earth capable of accelerating particles up to high energies. When the Sun
becomes active, ﬂares are frequently observed on its surface. The ﬂare accelerates the proton and ion to highenergy and they are detected on the Earth soon after
the ﬂare. Among the particles generated by the ﬂare,high energy neutrons provide the most direct information
about the acceleration mechanism as they come straightfrom the ﬂare position to the Earth without being affected by the magnetic ﬁeld.
The detection of solar ﬂare particles has been very active in the Norikura observatory for the last 10 years. The
muon telescope of the observatory successfully detected

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

The Sun is reaching the maximum activity in 2001 andthe active phase will continue for next few years. All
the telescopes in the Norikura observatory, neutron, meson and muon telescopes, will be operated continuously
through this solar cycle (Cycle 23) in order to obtaincomprehensive information on the solar ﬂare phenomena. Important hints for understanding the mechanismof cosmic ray acceleration will be obtained by this measurement.

36

In addition to the long-term cosmic-ray observations
mentioned above, various kinds of short-dated experiments are carried out every year taking an advantage ofthe high altitude of the observatory. As a few examples,
following experiments have been performed; a search forsuper heavy particles with plastic plates, a precise measurement of atmospheric gamma rays and muons, collection of cosmic dusts contained in the snow and theperformance study of the balloon borne cosmic ray experiments. A part of the facility has been open for theenvironmental study at high altitude such as the aerosol
removal mechanism in the atmosphere.

37

AKENO OBSERVATORYThe Akeno Observatory has evolved into a complex
scientiﬁc center for studying ultra-high-energy cosmic
rays through extensive air showers in the energy range
1015 eV ∼ 1020 eV, and is being used by many universities. The Observatory is in Akeno village, located about
20 km west of Kofu-city and about 130 km west of central Tokyo. Its altitude is 900 m above sea level, and thelocation is at longitude 138.5◦E and latitude 35.5◦N. An
areal view of the 1 km2 array area is shown in Fig. 1.

The following seven experiments were performed withthe arrays described in the reports of the Air Shower
Division.
Giant Air Shower (GAS)a) Observation of ultra-high-energy cosmic rays (M.
Teshima, ICRR)b) Prototype detector for Telescope Array (M. Sasaki,
ICRR)

Fig. 1. Aerial view of the Akeno 1 km2 array area.

C: Central laboratory
S: Sub-electronics stations

D: Dormitory
M: Muon detectors (1 GeV)

ME: Muon detectors (0.5 GeV)

Cal: Calorimeter

38

Fig. 2. One of the detector stations of Akeno Giant Air Shower Array (AGASA) ((a) outside, (b) inside)c) Arrival-time distribution of electrons of GAS at far
from the core (K. Honda, Yamanashi Univ.)d) The observation of electron and muon components
with lead-burger detector (S. Kawakami, Osaka
City Univ.)e) Prototype detector for Pierre Auger project (J. W.
Cronin, Univ. of Chicago)f) Study of EAS above 1016 eV (H. Sakuyama, Meisei
Univ.)g) Preliminary study of detemination of chemicalcomposition of cosmic rays above knee region (F.
Kakimoto, Tokyo Tech.)Fig. 3. View of a prototype water Čerenkov detector and a tent for a
3 m dish telescope.

39

AppendicesA. ICRR International Workshop
B. Seminar in 2001
C. List of Publications(a) Papers Published in Journals(b) Conference Papers(c) ICCR-Report

D. Doctoral Theses
E. Public Relations
ICCR News

F. List of Committee Members(a) Board of Councillors(b) Executive Committee(c) Advisory Committee

G. List of Personnel

41

A. ICRR International Workshop

The 2nd TAMA symposium
Date 2002/02/06–08
Sanjo Kaikan (7-3-1, Hongo, Bunkyo, Tokyo, Japan)(Cooperate with Tokyo university)

International Workshop on Technique and Application of Xenon Detectors
On December 3 and 4, 2001, we will have a two-day workshop concentrated on experiments using Xenon. The
workshop will be held at Kashiwa-campus of the Institute for Cosmic Ray Research, Univ. of Tokyo, Japan. The
purpose of this workshop is to discuss all aspects of experiments using Xenon, including problems and techniques.
One of the rare gases, Xenon, is very promising material of detectors for particle and astrophysics. This is owing
to special properties of Xenon: (1) large scintillation output, (2) large atomic number, (3) fast timing response,(4) long life for ionized electrons, (5) particle identiﬁcation power, (6) large density of liquid, (7) no long-life radio
isotope, and so on. Those prominent properties makes many physicist interested in detectors using Xenon. Recently,
we have many kinds of future plans for large-scale Xenon detectors around the world. In particular, some of themwill use several tons of Xenon. Although their goals are diﬀerent, we are frequently required to solve same kindsof problem. Because of such situation, we feel that it is a reasonable time to organize an international technicalworkshop concentrated on this subject. We hope our workshop exhaustively covers all applications using Xenon.
Purpose of the Workshop Xenon is used and planning for gamma ray detectors, double beta decay experiments,
dark matter search experiments, solar neutrino experiments, and so on. The purpose of this technical workshop
is to form a new strong community in which information and techniques of Xenon are intensively studied andshared, and to exchange our knowledge and status of planning detectors. The subjects which will be covered are: 1)
various detector technologies, 2) puriﬁcation of Xenon, 3) PMT development, 4) Xenon production, 5) enrichment,
6) calibration, 7) low background environment, 8) applications for various physics, etc.
This workshop is supported by the Grants-in-Aid for Scientiﬁc Research on Priority Areas A, “Neutrino Oscillations and Their Origin,” from the Ministry of Education, Culture, Sports, Science, and Technology, Japan.

Participants
41 from Japan, 8 from USA, 3 from Germany, 2 from Italy, 2 from UK, 1 from Ruccia, 1 from Ukraine, 1 from
Portugal

The 3rd Workshop on “Neutrino Oscillations and Their Origin”
The 3rd International Workshop on Neutrino Oscillations and their Origin (NOON2001) will be held at Kashiwacampus of the Institute for Cosmic Ray Research, University of Tokyo, Japan, December 5th through December 8thof 2001.
Initiated by the discovery of neutrino oscillations in atmospheric neutrinos in Super-Kamiokande, the series of theworkshop entitled “Neutrino Oscillations and their Origin” has been held since 2000 in Japan. In this year, anotherevidence for neutrino oscillations has been found in solar neutrinos, combining the results of Super-Kamiokande and
SNO results. These discoveries carry the investigation of neutrino oscillations a step further and give us hints to search
for the origin of neutrino masses. In the workshop, we will discuss latest experimental results, phenomenologicaltheoretical analysis, and theoretical implications which predicts neutrino oscillations. Topics in the workshop areatmospheric neutrinos (experimental results and ﬂux predictions), solar neutrinos (experimental results, solar models
and nuclear cross sections), phenomenology of the neutrino oscillations, theoretical origin of neutrino oscillations(GUTs etc.), and lepton ﬂavor violation processes. As a 3rd workshop, we have a stress on the following subjects:

421) precisions of the determination of the mixing and mass matrices in near future; 2) theoretical implications of thediﬀerent solar neutrino solutions, MSW-LMA, LOW or quasi-Vacuum; 3) constraints on the sterile neutrinos fromthe experimental data; 4) constraint on neutrino masses from supernovae, 5) relation between neutrino oscillations
and double beta decay, and so on.
In this workshop, we bring experimentalists and theorists together and discuss about those subjects.
This workshop is supported by the Grants-in-Aid for Scientiﬁc Research on Priority Areas A, “Neutrino Oscillations and Their Origin,” from the Ministry of Education, Culture, Sports, Science, and Technology, Japan.

Participants
68 from Japan, 9 from USA, 4 from Italy, 3 from Germany, 2 from Switzerland, 2 from UK, 1 from Ruccia, 1from Ukraine, 1 from Portugal

B. Seminar in 2001
Date

Title

Lecturer

6 June 2001

Developments of Superstring theory andnonperturbative ﬁeld theory
Trajectory tracing in empiricalgeomagnetospheric models: Suggestion forplasma transport to the magnetotail
Observational cosmology
BESS experiment
B phsics from Lattice NRQCD
Quantum Computing and Biophysics
Domain Walls in Cosmology:
Old Problems and New Solutions
The Alpha Magnetic Spectrometer,
an experiment to search for dark matterand antimatter on the ISS
Gamma ray emission from AGN and pulsars
Present Status of Auger Project in Argentine
Measurement of the Charged Current 8 B
Solar Neutrino Flux with the Sudbury
Neutrino Observatory
How much can intervening magnetic ﬁelds
aﬀect our under standing of the nature of
Ultra High Energy Cosmic Ray?
The K2K Participation in the Harp Experiment
The theory of physical combination
The Origin of the Hubble Sequence ofGalaxy Types
The recent topics about ultra high energy
air shower
Hard X-ray emission from the galactic disk
and spectrum of subrelativistic cosmic rays
New Results from K2K
Cosmic Ray Propagation and
the Cosmic Ray Source Spectrum
The study of jet activity by multi-wavelength
observation of Blazars
Dark matter search by LiF bolometerin deep underground
Horizontal Showers from Haverah Park andAuger observatory
From Big Crunch to Big Bang

T. Eguchi

12 June 2001

28 June 2001
4 July 2001
5 July 2001
6 July 2001
16 July 2001
26 July 2001

17 September 2001
27 September 2001
28 September 2001

22 October 2001

26 October 2001
31 October 2001
27 November 2001
29 November 2001
20 December 2001
21 December 2001
24 January 2002
13 February 2002
15 February 2002
18 February 2002
4 March 2002

K. SekiN. Sugiyama
Y. Asaoka
J. Shigemitsu
A. D. Patel
Y. V. Dumin
R. Battiston

Q. LuoR. BiralF. Duncan

G. M. Tnaco

J. HillT. Miwa
R. Ellis
M. Teshima
V. A. Dogiel
J. HillR. Clay
C. Tanihata
K. Miuchi
R. Vazquez
J. Maharana

43

18 March 2002
19 March 2002

SciFi detector in K2K experiments andthe current results
Baksan Neutrino experiments:
data and analysis

T. Iwashita
A. V. Butkevich

C. List of Publications — 2001 fiscal year(a) Papers Published in Journals
1. “Eﬀect of Multiple Scattering in the Lidar Measurement of Tropospheric Aerosol Extinction Proﬁles,” W.
Widada, H. Kinjo, H. Kuze, N. Takeuchi and M. Sasaki, OPTICAL REVIEW Vol. 8, No. 5 382–387 (2001)
2. “The Optical Reﬂector System for the CANGAROO-II Imaging Atmospheric Cherenkov Telescope,” Astropart.
Phys. 14 261 (2001)
3. “Phenomenological approach of multiple particle production at high energies: Energy distribution of produced
particles by data of direct observation,” Physical Review D64 054004 (2001)
4. “Cryogenic contamination speed of an ultra-low loss mirror for the cryogenic laser interferometer,” S. Miyoki
et al., Cryogenics 41 415 (2001).
5. “Cryogenic measurement of the optical absorption coeﬃcient in sapphire crystals at 1.064 µm for the large-scale
cryogenic gravitational wave telescope,” T. Tomaru et al., Physics Letter A 283, 80 (2001)
6. “Stable operation of a 300-m laser interfereometer with suﬃceint sensitivity to detect gravitational-wave events
within our galaxy,” M. Ando, et al., Phys. Rev. Lett. 86, 3950–3954 (2001).
7. “First search for gravitational waves from inspiraling compact binaries using TAMA300 data,” H. Tagoshi, etal., Phys. Rev. D 63, 062001 (2001).
8. “8 B and hep Neutrino Measurements from 1258 Days of Super-Kamiokande Data,” The Super-Kamiokande
Collaboration, Phys. Rev. Lett. 86, 5651–5655 (2001)
9. “Constraints on Neutrino Oscillations Using 1258 Days of Super-Kamiokande Solar Neutrino Data,” The
Super-Kamiokande Collaboration, Phys. Rev. Lett. 86, 5656–5660 (2001)
10. “16 N as a calibration source for Super-Kamiokande,” The Super-Kamiokande Collaboration, Nucl. Instr. &Meth. A 458, 636–647 (2001)
11. “Comparison of three-dimensional and one-dimensional schemes in the calculation of atmospheric neutrinos,”M. Honda et al., Phys. Rev. D, 64 (2001) 053011.
12. “Observation of atmospheric neutrinos,” T. Kajita and Y. Totsuka, Rev. Mod. Phys. 73 (2001) 85.
13. “Oscillations of atmospheric neutrinos,” C. K. Jung et al., Ann. Rev. Nucl. Part. Sci, 51 (2001) 451.
14. “Method for determination of —Ue3— in neutrino oscillation appearance experiments,” T. Kajita, H. Minakata
and H. Nunokawa, Phys. Lett. B, 528 (2002) 245.

(b) Conference Papers
1. “Energy estimation of AGASA events,” N. Sakaki for the AGASA Collaboration Proc. of 27th ICRC, Hamburg,
2001, Vol. 1, 329 (2001)
2. “Cosmic Ray Energy spectrum above 3 × 1018 eV,” N. Sakaki for the AGASA Collaboration Proc. of 27th
ICRC, Hamburg, 2001, Vol. 1, 333 (2001)
3. “Anisotropy of cosmic-ray arrival direction at 1018 eV observed by AGASA,” M. Teshima for the AGASA
Collaboration Proc. of 27th ICRC, Hamburg, 2001, Vol. 1, 337 (2001)
4. “Clusters of Cosmic Rays above 1019 eV observed with AGASA,” M. Takeda for the AGASA Collaboration
Proc. of 27th ICRC, Hamburg, 2001, Vol. 1, 341 (2001)

44

5. “Muon component in giant air showers with energies greater than 1018.5 eV observed by AGASA,” N. Inouefor the AGASA Collaboration Proc. of 27th ICRC, Hamburg, 2001, Vol. 1 345 (2001)
6. “Properties of EHE gamma-ray initiated air showers and their search by AGASA,” (89 kB) K. Shinozaki for
the AGASA Collaboration Proc. of 27th ICRC, Hamburg, 2001, Vol. 1 346 (2001)
7. “A search for horizontal air showers induced by extremely high energy cosmic neutrinos observed by Akeno
Giant Air Shower Array,” S. Yoshida for the AGASA Collaboration Proc. of 27th ICRC, Hamburg, Vol. 3 1142
(2001)
8. “Likelihood Analysis of sub-TeV Gamma-rays from RXJ1713-39 with CANGAROO-II,” R. Enomoto et al.
Proc. of 27th ICRC, Hamburg, 2001, Vol. 5, 2477–2480 (2001)
9. “Observation of TeV Gamma-rays from NE-rim of SN1006 with CANGAROO-II 10 m Telescope,” S. Hara etal. Proc. of 27th ICRC, Hamburg, 2001, Vol. 5, 2455–58 (2001)
10. “Development of Light Guides for the Camera of CANGAROO-III Telescope,”— F. Kajino et al. Proc. of 27th
ICRC, Hamburg, 2001, Vol. 5, p. 2909 (2001)
11. “Data Acquisition System of the CANGAROO-III Telescope,” H. Kubo et al. Proc. of 27th ICRC, Hamburg,
2001, Vol. 5, pp. 2900–2903 (2001)
12. “Observations of PSR1706-44 with CANGAROO-II Telescope,” J. Kushida et al. Proc. of 27th ICRC, Hamburg,
2001, Vol. 6, 2424–2427 (2001)
13. “The CANGAROO-III Project: Status Report,”—M. Mori et al. Proc. of 27th ICRC, Hamburg, 2001, Vol. 5,
2831–2834 (2001)
14. “Very High Energy Gamma-ray Observation of Southern AGNs with CANGAROO-II Telescope,” K. Nishijima
et al. Proc. of 27th ICRC, Hamburg, 2001, Vol. 5, 2626–2629 (2001)
15. “Search for Gamma-rays above 10 TeV from Markarian 421 in a High State with the CANGAROO-II Telescope,” K. Okumura et al. Proc. of 27th ICRC, Hamburg, 2001, Vol. 5, 2679–2682 (2001)
16. “Study of the TeV Gamma-ray Spectrum of SN 1006 around the NE Rim,” T. Tanimori et al. Proc. of 27th
ICRC, Hamburg, 2001, Vol. 6, 2465–2468 (2001)
17. “Multi-TeV gamma-ray emission from the Crab Nebula observed with the new Tibet-III air shower array,” M.
Amenomori et al., Proc. of 27th ICRC, Hamburg, 2001, Vol. 6, 2395–2398 (2001).
18. “Multi-TeV gamma-ray observation of several strong outbursts of Mrk421 during 2000 and 2001 with the
Tibet-III air-shower array,” M. Amenomori, et al., Proc. of 27th ICRC, Hamburg, 2001, Vol. 6, 2661–2664(2001).
19. “Performance of the Tibet-III air-shower array,” M. Amenomori et al., Proc. of 27th ICRC, Hamburg, 2001,
Vol. 2, 572–576 (2001).
20. “Search for TeV burst-like events coincident with the BATSE bursts using the Tibet air shower array,” M.
Amenomori et al., Proc. of 27th ICRC, Hamburg, 2001, Vol. 7, 2753–2756 (2001)
21. “Primary proton ﬂux around the “knee” region deduced from the observation of airshowers accompanied by
gamma-ray families,” M. Amenomori et al., Proc. of 27th ICRC, Hamburg, 2001, Vol. 1, 18–21 (2001)
22. “Upper limit of diﬀuse gamma rays from galactic plane using the data with Tibet and HD array,” M.
Amenomori et al., Proc. of 27th ICRC, Hamburg, 2001, Vol. 6, 2344–2347 (2001)
23. “Sun’s shadow in a high state of solar activity detected with the Tibet air shower array,” M. Amenomori etal., Proc. of 27th ICRC, Hamburg, 2001, Vol. 1, 18–21 (2001)
24. “A wide sky survey to search for TeV gamma-ray sources by the Tibet air shower array,” M. Amenomori etal., Proc. of 27th ICRC, Hamburg, 2001, Vol. 6, 2544–2547 (2001)
25. “The ﬂux and spectrum of solar neutrinos at Super-Kamiokande,” E. Blaufuss for the Super-Kamiokande
Collaboration, Proc. of 27th ICRC, Hamburg, 2001, Vol. 7, 3005 (2001)
26. “Recent results from Super-Kamiokande on atmospheric neutrinos,” J. Kameda for the Super-Kamiokande
Collaboration, Proc. of 27th ICRC, Hamburg, 2001, Vol. 3, 1057 (2001)

45

27. “A search for astronomical neutrino sources with the Super-Kamiokande detector,” S. Matsuno for the SuperKamiokande Collaboration, Proc. of 27th ICRC, Hamburg, 2001, Vol. 3, 1065 (2001)
28. “Discriminating between νµ ντ and νµ νsterile in atmospheric νµ oscillations with the Super-Kamiokande detector,” A. Habig for the Super-Kamiokande Collaboration, Proc. of 27th ICRC, Hamburg, 2001, Vol. 3, 1061
(2001)
29. “Search for nucleon decay in Super-Kamiokande,” K. Kobayashi for the Super-Kamiokande Collaboration,
Proc. of 27th ICRC, Hamburg, 2001, Vol. 4, 1459 (2001)
30. “Very High Energy Gamma Rays from Active Galactic Nuclei,” T. Kifune, Proc. of AGN Variability Acrossthe Electromagnetic Spectrum Sydney, Australia, (June 25–29, 2001), Publ. Astron. Soc. Australia, Vol. 19,
No. 1 1–4 (2002)
31. “Very High Energy Gamma-Ray Observations of AGNs with CANGAROO,” K. Nishijima, Proc. of AGN
Variability Across the Electromagnetic Spectrum Sydney, Australia, (June 25–29, 2001), Publ. Astron. Soc.
Australia, Vol. 19, No. 1 26–28 (2002)
32. “CANGAROO-II and CANGAROO-III,” M. Mori, Proc. of Gamma-Ray Astrophyiscs 2001 Baltimore, USA(April 4–6, 2001), AIP Conference Proceedings 587, 927–931
33. “The Telescope Array Project,” M. Sasaki et al., Proceeding of EHECR 2001, International Workshop on
Extremely High Energy Cosmic Rays(c) ICRR-Report
1. ICRR-Report-473-2001-3“Doctor Thesis: Lepton T-and CP-violation search with neutrino factory”
Masafumi Koike
2. ICRR-Report-476-2001-6“Muon anomalous magnetic moment, lepton ﬂavor violation, and ﬂavor changing neutral current processes in
SUSY GUT with right handed neutrino”
Seungwon Baek, Toru Goto, Yasuhiro Okada, and Ken-ichi Okumura
3. ICRR-Report-478-2001-8“Contributions to the 27th International Cosmic Ray Conference, Hamburg, Germany, August 7–15, 2001”
CANGAROO collaboration
4. ICRR-Report-479-2001-9“Study of high energy cosmic ray interactions and primary composition at energies 1015 –1017 eV using mountainbased detectors”
V. Kopenkin, Y. Fujimoto, A. Ohsawa, C. E. Navia, C. R. A. Augusto and H. Semba
5. ICRR-Report-480-2001-10“Contributions to 27th International Cosmic Ray Conference (07–15 Aug. 2001, Hamburg) from Cosmic Ray
Collaboration at Mt. Chacaltaya”
A. Ohsawa
6. ICRR-Report-481-2001-11“The Telescope Array Project: To appear in the Proceedings of the EHECR2001, International Workshop on
Extremely High Energy Cosmic Rays (ICRR Kashiwa, Japan, 22–23 March 2001)”
Makoto Sasaki
7. ICRR-Report-482-2001-12“Dissertation: Constraints of the neutrino oscillation parameters from 1117 day observation of solar neutrino
day and night spectra in Super-Kamiokande”
Nobuyuki Sakurai

46

D. Doctor Thesis
S. HaraTitle: Observation of TeV Gamma-Rays from the Supernova Remnant SN1006 with CANGAROO-II Telescope
Cource: Doctor (Tokyo Institute of Technology)
S. Nagano
Title: A Study of Frequency and Intensity Stabilization System with a High-power Laser for the TAMA300
Gravitational-wave Detector
Cource: Doctor (University of Tokyo)
O. Miyakawa
Title: Development of a Variable-Bandwidth Laser Interferometer Gravitational Wave Detector
Cource: Doctor (University of Tokyo)
Andrew L. Stachyra
Title: A Search for Astrophysical Point Sources of Neutrinos with Super-Kamiokande
Cource: Doctor (University of Washington)

E. Public Relations
ICRR NewsICRR News is a newspaper published quaterly in Japanese to inform the Institute’s activities. This year’s
editors were M. Sasaki and M. Ohnishi. 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. anouncements,
7. and other items of relevance.

The main topics in the issues in 2001 ﬁscal year were :No. 45 (May 31, 2001)• The statement from the old and new director (M. Yoshimura and Y. Totsuka)
No. 46 (August 31, 2001)• The current status of CANGAROO (M. Mori)• TAMA300 and LCGT (K. Kuroda)• The report of Kashiwa clerk oﬃce (I. Hada)

47

No. 47 (December 31, 2001)• Report of Super-Kamiokande accident (M. Yoshimura)• Origin of the barion number in univerce, dark matter and Q ball (M. Kawasaki)• Report of 27th international cosmic ray conference (T. Kajita, K. Okumura, M. Takita, M. Fukushima)• Report of the inspection of the Minister of Education, Science and Culture in Super-Kamiokande (Y. Suzuki)• Report of the open house in ICRR (M. Takita)

F. List of Committee Members(a) Board of Councillors
YOSIMURA, Motohiko
SUZUKI, Yoichiro
KURODA, Kazuaki
FUKUSHIMA, Masami
SATO, Katsuhiko
KAJINO, Shinithi
YAMADA, Sakue
MASKAWA, Toshihide
KAIFU, Norio
SATO, Humitaka
EJIRI, Hiroyasu
NAGASHIMA, Yorikiyo
OHTA, Itaru
NISHIDA, Tokuhiro
ITO, Nobuo

ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
University of Tokyo
University of Tokyo
KEK
Kyoto University
National Astronomical Observatory
Kounan University
Osaka University
Osaka University
Utsunomiya University
Japan Society for the Promotion of Science
Osaka City University(b) Executive Committee
YOSHIMURA, Motohiko
AIHARA, Hiroaki
KOYAMA, Katsuji
NISHIKAWA, Koichiro
MATSUOKA, Masaru
OHTA, Itaru
MURAKI, Yasushi
SAKATA, Michinori
YANAGIDA, Tsutomu
MOTOBAYASHI, Toru
KURODA, Kazuaki
SUZUKI, Yoichiro
FUKUSHIMA, Masami
TAKITA, Masato

ICRR, University of Tokyo
University of Tokyo
Kyoto University
Kyoto University
National Space Development Agency of Japan
Utsunomiya University
Nagoya University
Konan University
University of Tokyo
Rikkyo University
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo(c) Advisory Committee
MURAKI, Yasushi
TAKITA, Masato
MATSUBARA, Yutaka
YANAGITA, Shohei
KAJINO, Fumiyoshi
NISHIJIMA, Kyoshi
TORII, Shoji
MUNAKATA, Kazuki
MIZUTANI, Kohei
SAKURAI, Takahisa

Nagoya University
ICRR, University of Tokyo
Nagoya University
Ibaraki University
Konan University
Tokai University
Kanagawa University
Sinshu University
Saitama University
Yamagata University

48

KANEYUKI, Kenji
SASAKI, Makoto
MORI, Masaki
OHASHI, Masataka
SEKIGUCHI, Masaki

ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo
ICRR, University of Tokyo

G. List of Personnel
Director
Kamioka group
Scientiﬁc Staﬀ

Cheif Secretary
Technical Staﬀ
Research Fellows
Secretary
Research Center for Cosimic
Neutrinos
Scientiﬁc Staﬀ
Technical Staﬀ
Visiting Scientist
Research Fellows
Secretary
CANGAROO group
Scientiﬁc Staﬀ
Research Fellows
TA/AGASA group
Scientiﬁc Staﬀ
Techinical Staﬀ
Research Fellows
Emulsion Division
Scientiﬁc Staﬀ
Technical Staﬀ
Research Fellows
Theory group
Scientiﬁc Staﬀ
Research Fellows
Mu Nu Division(Gravitational Wave group)
Scientiﬁc Staﬀ
Technical Staﬀ
Research Fellows(SDSS group)
Scientiﬁc Staﬀ
Research Fellows
NorikuraTechnical Staﬀ

YOSHIMURA, Motohiko
TOTSUKA, Yoji, SUZUKI, Yoichiro,
NAKAHATA, Masayuki, ITOH, Yoshitaka,
FUKUDA, Yoshiyuki, MIURA, Makoto, TAKEUCHI, Yasuo,
SHIOZAWA, Masato, KOSHIO, Yusuke,
MORIYAMA, Shigetaka, OBAYASHI, Yoshihisa
GOTO, Shohachiro
YOKOKAWA, Keiji, FURUTA, Noboru
NAMBA, Toshio, KAMEDA, Jun
OHTSUBO, Junko, MORITA, Yasuko, TAJIKA, Sonoko

KAJITA, Takaaki, KANEYUKI, Kenji, OKADA, Atsushi
SHINOHARA, Masanobu
BUTKEVICH, A. V., HILL, James E.
HONDA, Morihiro
FUKUDA, Yoko
ENOMOTO, Ryoji, MORI, Masaki,
HATANO, Yoshikazu, KAWACHI, Akiko
OKUMURA, Kimihiro, KSENOFONTOV, L.
FUKUSHIMA, Masami, TESHIMA, Masahiro,
SASAKI, Makoto, HAYASHIDA, Naoaki
TORII, Reiko, OHOKA, Hideyuki,
SHIMODAIRA, Hideaki, AOKI, Toshifumi
TAKEDA, Masahiro, YAMAMOTO, Tokonatsu
WIENCKE, L., CHA, M., SAKURAI, Nobuyuki
TAKITA, Masato, OHSAWA, Akinori, OHNISHI, Munehiro
TOYODA, Setsuko, KOBAYASHI, Takahide
KOPENKIN, Vladimir, Xu Xianwu,
SHIOMI, Atsushi, TSUCHIYA, Harufumi, OUCHI, Tatsumi
YOSHIMURA, Motohiko, HISANO, Junji
TAKEDA, Koujin, MATSUMOTO, Shigeki,
YOKOI, Naoto, UESUGI, Tomoko

KURODA, Kazuaki, OHASHI, Masatake, MIYOKI, Shinji
ISHIZUKA, Hideki, YAMAMOTO, Kuniyuki
TAYLOR, Colin T. YAMAMOTO, Kazuhiro
FUKUGITA, Masataka, SEKIGUCHI, Masaki
NAKAMURA, Osamu
AGEMATSU, Yoshiaki, USHIMARU, Tsukasa

49

Post Graduate Students
KOBAYASHI, Kazuyosi (D3), NAKAYAMA, Shoei (D3),
YAMADA, Shuei (D3), OSONE, Satoko (D3),IZU, Kouhei (D3), MIYAKAWA, Osamu (D3),SUZUKI, Rieko (D2), KIMURA, Masahiko (D2),ISHITSUKA, Masaki (D1), KATAGIRI, Hideaki (D1),
TSUCHIYA, Ken-ichi (D1), MASE, Keiichi (D1),
MANAGO, Naohiro (D1), OKUTOMI, Akira (D1),KASAHARA, Kunihiko (D1), GOTO, Tomotsugu (D1),
INADA, Naohisa (D1), OHISHI, Michiko (M2),KABUKI, Shigeto (M2), TSUNOO, Hajime (M2),
TSUJIKAWA, Yoshihiro (M2), JOBASHI, Masashi (M2),
MASUDA, Masataka (M2), HAYASHI, Maoto (M2),
TSUJI, Isao (M2), KONDO, Kazuhiro (M2),
TOKUNARI, Masao (M2), OOYABU, Takato (M1),UCHIDA,Tadashi (M1), KURASAWA, Katsumi (M1)
Administration Division
Staﬀ

Technical Staﬀ

HADA, Isao, IGARASHI, Tsutomu, NAKAMURA, Hiroshi,
FURUKAWA, Toshiko, SHIZUKAI, Saori,
WATANABE, Hiroko, TASHIRO, Megumi, KOKUBUN, Yayoi,
IINUMA, Yuri, ASANO, Kouji, HIRUKAWA, Seiji,
MARUMORI, Yasuko, AKIYAMA Makiko, TANAKA, Sae,
MOTOIKE, Wakana, TAKAHASHI, Akiko
KOBAYASHI, Masanobu