International Symposium in Honor of Professor Nambu
for the 10th Anniversary of his Nobel Prize in Physics
Dec. 12, 2018

Cosmic Ray Research in Japanand Osaka City University
Takaaki Kajita
Institute for Cosmic Ray Research, The University of Tokyo

Outline• Introduction• Present cosmic ray research: 1) Neutrinos
Appendix: Neutrino oscillations• Present cosmic ray research: 2) Very high energy cosmic rays
• Present cosmic ray research: 3) Gravitational waves• Summary
Many thanks to Prof. Kanda for providing me a report on“Cosmic Ray Institute” of the Osaka City University.
2Introduction

3

History of 2 “Cosmic Ray Institutes” in Japan after World War IIyear
1949“Norikura Cosmic Ray Observatory” at the Norikura Mountain by Prof. Y. Watase(Osaka City Univ., OCU)
1950
“Asahi Hut” at the Norikura Mountain supported by Asahi Academic Grant (ofAsahi News Paper)
1950“Underground cosmic ray observatory” at Yaizu (OCU)
1952“Cosmic Ray Institute” at OCU
1953“Cosmic Ray Observatory (Norikura Observatory)” of the Univ. of Tokyo (UToyko)
1956 “Norikura Cosmic Ray Observatory” of OCU was closed
1956
Cosmic Ray Division of the Institute for Nuclear Studies (INS, UTokyo)
1961“Underground cosmic ray observatory” moved to Mitsuishi from Yaizu (OCU)
1976“Institute for Cosmic Ray Research” of UTokyo (based on Norikura Observatory
and Cosmic Ray Division of INS)
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Norikura Observatory
Norikura Observatory (ICRR) (in the 1950’s?)“Asahi Hut” (around 1950, from a book onProf. Minagawa)5Cosmic Ray Research in OCU and Prof. Nambu
An article in Japanese science magazine “自然” by Minoru Oda (Nov. 1978):……. 実験のグループには理論家が横にいなければ、という強い信念を（渡瀬譲は）もっていた。
批判者としての理論家、少なくとも理論的雰囲気がないと型にはまった技術万能主義になったり、頑固にいつまでもつづけるしかしようがない実験になってしまう、というのである。…….
こういうことから、素粒子論グループをつくることを小竹（理工学部長）に説いて実現している。…...
早川幸男（当時気象研）、山口嘉夫、西島和彦（東大理学部）、阪大から中野薫夫を採ることにし、その上に教授として南部陽一郎（東大理学部）を置くことにした。……

……, (Yuzuru Watase, leader of the cosmic ray group OCU) had a strong belief that there
should be theorists next to the groups of experimentalists. Theorists are required as critics.
At least, without a theoretical atmosphere, the groups might become too technology
oriented, or might continue experiments without any reasons.
Therefore, Y. Watase persuaded Kotake (Dean) to form a group of theoretical particle
physics. …. He decided to hire Sachio Hayakawa, Yoshio Yamaguchi, Kazuhiko Nishijima andTadao Nakano. Finally, he decided to hire Yoichiro Nambu as the professor of this group. ….
6

Present cosmic ray research in Japan• Present cosmic ray research: 1) Neutrinos
Appendix: neutrino oscillations• Present cosmic ray research: 2) Very high energy cosmic rays
• Present cosmic ray research: 3) Gravitational waves

7

Present cosmic ray research: 1) Neutrinos

8Discovery of atmospheric neutrinos (1965)
In 1965, atmospheric
neutrinos were observed
for the first time bydetectors located very
deep underground.
In South Africa
F. Reines et al., PRL 15, 429 (1965)

 In India
C.V. Achar et al., PL 18, 196 (1965)

OCU (Hinotani and Miyake)
Photo by H.Sbel

Photo by N. Mondal
9Kamioka Nucleon Decay Experiment (Kamiokande) In the 1970’s, Grand Unified Theories were proposed. These theories predicted that protons
and neutrons (i.e., nucleons) should decay with the lifetime of about 1030 years.
 Several proton decay experiments began in the early 1980’s. One of them was the KGF
experiment lead by Prof. Saburo Miyake and people in OCU. The other was Kamiokande.

Kamiokande(3000 ton water
Cherenkov detector)
Electronics/computer
Water system

Detector
wall

Cherenkov
light

Photodetectors

Charged particle

10Kamiokande construction team (Spring 1983)
M. Takita

TK
M. Nakahata

Y. Totsuka

A. Suzuki T.Suda

K. Arisaka

M. Koshiba(2002 Nobel Prize)

T. Kifune
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Kamiokande
The experiment began in July 1983.

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Message from Prof. Nambu
On Nov. 16, 1984, Professor Nambu visited Kamiokande. Unfortunately, we haveno photo of him…. However, in Kamiokande, we ask visitors to leave a message.

So we shouldobserve a proton
decay before
2084…
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Supernova SN1987A
BeforeAfterFeb. 1987
（LMC, 160,000
light-years)
14

Birth of neutrino astronomy
Total 24 neutrino events observed by 3 detectors
on Feb. 23, 1987;

Kamiokande-II Understood the basic
mechanism of thesupernova explosion!

(11 events)

IMB-3(8 events)

Baksan(5 events)

Prof. M. Koshiba(Cultural Medal 1997,Nobel prize 2002)
15

Birth of neutrino astronomy
Fax from Prof. Nambu to Prof. Koshiba,
when Prof Koshiba received the Cultural
Medal in 1997.

“Wanted to be a physicist”

16The present neutrino detector: Super-Kamiokande (50,500 ton)17Exploring the history of Supernova explosion
timetoday

Super-K
Birth of theUniverse

Super-Kamiokande collab. would like to observe neutrinos
produced by the Supernova explosion in the past Universe!

Credit: NASA/WMAP Science Team18

Detecting Supernova relic neutrinos
νe(M. Ikeda, neutrino 2018)+ p  e+ + n ,n + Gd  Gd + γ’s (total E of γ’s ~8MeV)
100[%]
Capture on gadolinium [%]100

Expected spectrum in SK-GD

Gd capture eff.

SRN flux: Horiuchi, Beacom and Dwek,PRD, 79, 083013 (2009)9080

σ: 10 years with SK-Gd

0.2% Gd2(SO4)3 （~100t for SK）
gives 90% neutron capture

80
70

6060

Total BG

50

4040

30

2.5σ4.3σ

2020

2.1σ

10000000.002

0.02
0.02

0.2
0.2

Gadolinium
sulfateconcentration[%]concentration [%]Gadolinium
sulfate10 1214 16 18

20 22 24 26 28

Position Energy (MeV)
19

Status and plans

July 2018
End of Aug., 2018
Super-K will resume the data taking in Jan. 2019.
Probably, Super-K-Gd with Gd (0.02%) will begin in late 2019 (or early 2020).
Super-K-Gd with Gd (0.2%) will begin in 202X.
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Appendix: Neutrino oscillations

21

Atmospheric neutrinos
Cosmic ray

Incoming cosmicrays

Air nucleus
PionMuon

The Kamiokande and IMB experiments observed thedeficit of atmospheric neutrinos in the late 1980’s toearly 1990’s. No one understood why.

Electron2 muonneutrinos 1 electronneutrino© David Fierstein, originally published in Scientific American, August 199922

Evidence for neutrino oscillations (Neutrino Conference in 1998)
Y. Fukuda et al., PRL 81 (1998) 1562µ-neutrino
τ-neutrino

Super-Kamiokande

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Solar neutrino oscillation (2001-2002)
SNO
νe flux
Super-K ES(νe +νµ +ντflux)

SK, PRL 86 (2001) 5651
SNO PRL 89 (2002) 011301
SNO PRC 72, 055502 (2005)

νeDe-pp
νµ +ντ flux !!

νeνeSNO
νe +νµ +ντflux

νDνpnFlux (106/cm2/sec)

1000 ton of heavy water (D2O)+ Accelerator based long baseline neutrino oscillation experiments (K2K and T2K).

Nakaya-san.

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Hyper-K as a natural extension of water Ch. detectors
Kamiokande & IMB

Neutrinos from SN1987A
Atmospheric neutrino deficit
Solar neutrino (Kam)Super-K

Atmospheric neutrino oscillation
Solar neutrino oscillation with SNO
Far detector for K2K and T2K

Hyper-K25

Present cosmic ray research: 2) Very highenergy cosmic rays

26

Cosmic-ray flux

Cosmic ray flux
102
10-1
10-4
10-7
10-10
10-13
10-16
10-19
10-22
10-25
10-28

How cosmic rays of 1020 eV aregenerated?
orWhat are the most powerfulaccelerators generating cosmic rays of1020 eV?

Highest-energy
cosmic rays
~1020eV 1020 eV cosmic rays do not come fromthe very far Universe (~< 50Mpc), due
to the interaction of cosmic ray andcosmic microwave backgroundradiation.
 1020 eV cosmic rays are not bentmuch by the galactic and inter109 1010 1011 1012 1013 1014 1015 1016 1017 1018 1019 1020 1021
galactic magnetic fields.
Energy (electron volt, eV)
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How can we detect 1020 eV cosmic rays?
Fluorescence detector
detects air fluorescence
Light from air shower

Surface detector
Simulation of avery high energy
cosmic ray in theatmospheredirectly observes penetrating
secondary particles at thesurface

28Telescope Array (TA) experiment (Utah, USA)

Fluorescence
Detectors (FD)
3 stations

Main
institutions inJapan: OCUand ICRR.
Main persons in OCU: Profs.
Ogio (photo) and Tsunesada

Surface Detectors (SD)507 plastic scintillator SDs
1.2 km spacing~700 km2

29

Telescope Array (TA) site

TA surface detector30

Cosmic ray arrival direction
With 25° oversampling,Maximum pre-trial
significance: ~5σat RA=144.3o,Dec=+40.3oObserved: 34
Expected : 13.5
Post-trial significance : 3σ

The data show an interesting excess at a particular direction!
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The next stage…
Telescope Array needs more data.
 x4 improvement in the surface area
(3000 km2, the “TAx4” project)
We really look forward to seeing new
results from Telescope Array!

32

Present cosmic ray research: 3) Gravitational
waves

33

Introduction
LIGO Scientific Collaboration and Virgo Collaboration,
PRL, 116, 061102 (2016)

Press Conference at NSF on Feb. 11, 2016

Congratulations to LIGO and Virgo!

And many subsequent observations.
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Common goals of ground based GW detectors

Merger of binary neutronstars
 We want to understandthe origin of the heavy
metals in the Universe(more accurately).
…

Merger of binaryblackholes How the blackholes
were created?
…

Supernova explosion
 How the heavy stars
finish their life?
 ….
35

global map of GW detectors
LIGO
KAGRA
Virgo
LIGO-India

In operation

Under Construction

Project approved

The world GW community works together to know the details (e.g., sources) of GWs.
36

KAGRA gravitational wave detector

Maininstitutions inJapan: OCU
NAOJ, KEK,and ICRR.
Main persons in OCU: Profs.
Kanda (photo) and Itoh37

KAGRA 3km x 3km arms

Connection and the leak tests of 3km
X 3km beam tubes have been finishedin Feb. 2015.

38

Toward the detection of GWs in KAGRA

Preparation of cryogenic mirror at
the University of Toyama.
（22cm (diameter), 15cm (thick), 23kg）
 To the KAGRA site

Installation of the first cryogenic mirror（Nov.30, 2017）

KAGRA plans the first operation in late 2019.
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Summary• The field of cosmic rays had significant progresses. Groups in OCU
and various institutions in Japan have been playing very importantroles in these progresses.
• We are in the era of “multi-messenger astronomy”: neutrinos,
cosmic rays and gravitational waves play very important roles.
• Please stay tuned.

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