スーパーカミオカンデにおけるスーパーカミオカンデにおける天体ニュートリノの観測天体ニュートリノの観測

　東海大学理学部　東海大学理学部 西嶋恭司西嶋恭司

SuperSuper--KamiokandeKamiokandeの紹介の紹介

太陽ニュートリノ問題の解決と太陽ニュートリノ問題の解決と

　ニュートリノ振動　ニュートリノ振動

超新星ニュートリノ超新星ニュートリノ

その他天体ニュートリノその他天体ニュートリノ

小柴昌俊氏小柴昌俊氏ノーベル物理学賞受賞ノーベル物理学賞受賞(2002)(2002)

ニュートリノの主な発生源ニュートリノの主な発生源

太陽 核融合反応

超新星 重力エネルギーの放出

高エネルギー天体　宇宙線とガスの衝突

大気 宇宙線と大気との衝突

ビッグバン　熱平衡の名残り

原子炉 核分裂

加速器 素粒子反応

ニュートリノ研究の歴史ニュートリノ研究の歴史●１９３０：W.パウリ　ニュートリノの存在を予言。●１９５６：F.ライネスとC.コーワンが反電子ニュートリノを発見。●１９６２：L.レーダマンら人工ニュートリノビームによりミューニュートリノを発見。●１９６２：牧二郎・中川昌美・坂田昌一がニュートリノ振動の理論を提唱。

●１９８７：小柴昌俊らカミオカンデ研究グループが超新星爆発により発生したニュートリノを世界で初めて観測。

●１９９１：ＣＥＲＮのＬＥＰ実験で軽いニュートリノが３世代しか存在しないことを証明。

●１９９８：スーパーカミオカンデ研究グループが大気ニュートリノの観測からニュートリノ振動を発見。

●２０００：米国フェルミ研究所の実験でタウニュートリノの存在を確認。

●２００１：カナダのSNO研究グループと日本のスーパーカミオカンデ研究グループが太陽ニュートリノ観測でもニュートリノ振動の存在を証明。

●２００２：KamLAND研究グループが原子炉ニュートリノを用いて、ニュートリノ振動の存在を独立に証明。

SuperSuper--KamiokandeKamiokandeCollaborationCollaboration

ICRR, U. TokyoBoston U.BNLU.C. IrvineC.S.U. Dominguez HillsGeorge Mason U.Gifu U.U. HawaiiKEKKobe U.Kyoto U. LANLL.S.U.

U. Maryland, College ParkU. MinnesotaSUNY Stony BrookNiigata U.Osaka U. Seoul National U.Shizuoka U.Shizuoka Seika CollegeTohoku U.Tokai U.Tokyo Institute of TechnologyWarsaw U. U. Washington

SuperSuper--Kamiokande Kamiokande DetectorDetector

Large imaging water Cherenkov detector50,000 ton of pure water

1 km (2,700m.w.e.)

39.3m

41.4

m

SK

Inner Detector (32,000 t)11,146 PMTs (50cm φ)

Outer Detector (18,000 t)1,867 PMTs (20cm φ)

建設中

Basic Reaction Basic Reaction for Detectionfor DetectionElectron scattering

νe + e- → νe + e-

Quasi elastic scatteringνl + N → l + N’

Other reactionsνlN → νlN, νlN → lN’h, νlN → νlNh, νlN → lN’mπ,

νlN → νlNmπ, νl

16O → l±π±16O, νl

16O → νlπ016O and deep inelastic scattering

Solar neutrino

Atmospheric neutrino

Atmospheric neutrino

12.5 MeV electron

603 MeV/c muon

492 MeV/c electron

νµ + N → µ + N’

νe + N → e + N’

Physics Objectives of the Physics Objectives of the SuperSuper--KamiokandeKamiokande

Study of neutrino mass and mixingSolar neutrinos and atmospheric neutrinos

Study of deep interior of astrophysical objects

The Sun, supernovae, ⋯⋯Search for possible point sources in the sky

Active galactic nuclei, gamma-ray bursts, ⋯⋯Search for proton decay

Solar neutrinosSolar neutrinos

http://www.sns.ias.edu/~jnb/

P + P → ２H＋e++νｅ P + e－+ P → 　２H +νｅ2H + p → 3He + γ

３He+ ３He →α+ 2p ３He +α → 7Be +γ ３He + p → 4He + e++νｅ

7Be + e－ → 7Li + νｅ 7Be + p → 8B + γ

7Li + p → 2α　 8B → 8Be* + e＋+νｅ8Be* → 2α

99.75% 0.25%

86% 14%

99.85% 0.15%

Solar neutrino fluxSolar neutrino fluxMay 31, 1996 – July.15, 2001Live time : 1,496 daysEe = 5.0 MeV – 20 MeV

( )126 scm10

0.08(sys.))0.02(stat.2.35−−×

±±=B8φ

230(stat.)22,385N ±=ν

COSθsun

νe-

θsun

(syst.).)0.005(stat0.465SSM

DATA0.0150.016

BP2000−+±=

Solar Neutrino ProblemSolar Neutrino Problem

M.Smy @ Neutrino2002

Electron scatteringElectron scatteringνe ν

νee-

e-

Wν

e-Z

e-

σ(νee- )/σ(νµ(τ)e- ) = 6 ~ 7νµ(τ) e-

Total cross section for 8B neutrinos

5 10 15Energy threshold(MeV)

10-4

6cm

2 νee-

Charged Current & Neutral CurrentCharged Current & Neutral Current

Charged currentνe e-

Wpn

pDeuteriump

Neutral currentνe , νµ , ντνe , νµ , ντ

Z0

nnpDeuterium

p

φES = φe +0.15 φµ,τSK φES = 2.35±0.09

(cf. φSSM = 5.05+1.01/-0.81)

[x106/cm2/s]φCC = φeSNO φCC = 1.76±0.11

SNO φNC = 5.09±0.64 φNC = φe + φµ+ φτ

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6νe flux (106 /cm2/sec)

ν µ+ντ flu

x (10

6 /cm2 /se

c)

1σ2σ3σ

SSM ±1σ

SK SNO CC

SNO NC

Obtained total flux: φexp = 5.3±0.7

Combined flux analysis of SK, Combined flux analysis of SK, SNO CC and NCSNO CC and NC

Oscillation Analysis without SK Oscillation Analysis without SK data (Chlorine, Gallium, SNO CC) data (Chlorine, Gallium, SNO CC)

Global fit

SMALMA

LOW

VAC

M.Smy @ Neutrino2002

Oscillation probability for each solutionOscillation probability for each solution

Small Mixingsloped spectrum

Large Mixingalmost flat, and slight day/night differenceLOWslightly sloped spectrum

Just-sostrong distortion

DayNight

Eν (MeV)

Spectral shape and Day/night analysis

Model independent test of ν oscillation

Solar neutrino spectrum(SSM)

P(ν e→

ν e)

Expected Energy Spectrum Expected Energy Spectrum from from ν ν Oscillation Oscillation

(preliminary)

0

0.2

0.4

0.6

0.8

1

6 8 10 12 14Energy(MeV)

Dat

a/S

SM

20

SK-I 1496day 5.0-20MeV 22.5kt

SMA

Just-so

LMA

Consistent with flat.

Day/Night AsymmetryDay/Night Asymmetry(preliminary)

Seasonal VariationSeasonal Variation

Sunspot #Sunspot #χ2 for eccentricity: 4.7 / 7 d.o.f. (69% C.L.)

(χ2 for flat: 10.3 / 7 d.o.f. (17% C.L.) )

Oscillation analysis (combined fit)Oscillation analysis (combined fit)

allowed(Ga+Cl+SNO CCRates)

νe→νµ/τ (95%C.L.)

tan2(Θ)

∆m2 in

eV2

10-12

10-11

10-10

10 -9

10 -8

10 -7

10 -6

10 -5

10 -4

10 -3

10-4 10-3 10-2 10-1 1 10 10 2

allowed(Ga+Cl+SNO CCRates)

νe→νµ/τ (95%C.L.)

tan2(Θ)

∆m2 in

eV2

10-12

10-11

10-10

10 -9

10 -8

10 -7

10 -6

10 -5

10 -4

10 -3

10-4 10-3 10-2 10-1 1 10 10 2

excluded(rate notconstrained)

SK 1496 Days

Zenith spectrum with flux Zenith spectrum with flux constraintconstraint

allowed(rate con-strained tosolar model)

SK 1496 Days

Zenith Spectrum νe→νµ/τ (95%C.L.)

tan2(Θ)

∆m2 in

eV2

10-12

10-11

10-10

10 -9

10 -8

10 -7

10 -6

10 -5

10 -4

10 -3

10-4 10-3 10-2 10-1 1 10 10 2

Global fit using results from all Global fit using results from all experimentsexperiments

Comparison with Comparison with KamLANDKamLAND datadata

0.1%

0.32%

1%

3.2%

10%

νe→νµ/τ (95%C.L.)

tan2(Θ)

∆m2 in

eV

2

10 -5

10 -4

10 -3

10-1 1

D/N asymmetry contour in SK

KamLAND allowed region

Precise measurement of D/N asymmetry is important for defining oscillation parameter

Supernova NeutrinosSupernova Neutrinos

Evolution of massive starsformation of iron corephoto disintegration of irongravitational collapse

Core-collapse supernova explosion

Released gravitational energy:1053erg

９９％ is in the form of neutrinos

Totani, Sato, Dalhed, Wilson，１９９８

SNSN１９８７１９８７AAFebruary 23, 1987

Detection of Neutrino Burst at Detection of Neutrino Burst at KAMIOKANDEKAMIOKANDE

KAMIOKANDE11個／13秒3×1053erg

⇒　ノーベル物理学賞IMB

8個／6秒2×1053erg

理論的にしか語ることのできなかった、超新星爆発の理論を観測的に実証。ニュートリノで宇宙を観測し、天体の進化、宇宙の進化を明らかにするニュートリノ天文学を創始した。

Search for Supernova Search for Supernova Neutrino Burst in SKNeutrino Burst in SK--II

Prompt explosion modelH.Suzuki(1988)

Prompt events can be used for neutrino burst candidate search

3 events/0.5 sec or4 events/2.0 sec or8 events/10 sec

Detection Efficiency for Detection Efficiency for supernova neutrino burstssupernova neutrino bursts

Distance from the Earth(kpc)

Det

ectio

n Ef

ficie

ncy

Assuming supernova with 12 M◎,full detection efficiency keeps up to～80kpc

Results of Supernova Burst Results of Supernova Burst SearchSearch

DataLive-time : 1703.9 days　Energy threshold : 6.5 MeV

There is no clear evidence of neutrino burst from Supernova90% C.L. upper limits for SN explosion

For our galaxy: <0.26 SN/yr (including 4.26yr Kamiokande)

For extra galaxy (D～80kpc): <0.49 SN/yr

Supernova Relic Neutrinos(Supernova Relic Neutrinos(SRNsSRNs))

Diffuse background of SN relic ν(SRN)should exist!All six types of ν emitted, but only νesearched for at SK via inverse β decay

νe + p → e+ + n

Flux predictionsFSRN = 2-54 νe cm-2s-1

Window for Window for SRNsSRNs

Solar 8B

Solar hep

Atmospheric νe

SRN predictions

Models:Population synthesis

(Totani et al., 1996)Constant SN rate

(Totani et al., 1996)Cosmic gas infall

(Mataney, 1997)Cosmic chemical evolution

(Hartmann et al., 1997) Heavy metal abundance

(Kaplinghat et al., 2000)LMA ν oscillation

(Ando et al., 2002)

Background SourcesBackground Sources

We cannot tag SRN events!Reducible B.G.

muon induced spallationatmospheric νµ

Solar νIrreducible B.G.

atmospheric νe

atm. νµ → µ → decay einvisible

Energy Spectrum of SRN Energy Spectrum of SRN CandidatesCandidates

Atmospheric νe

Decay electrons

Total background

Total B.G. + 90% C.L. SRN limit

Fitting the Final DataFitting the Final Data

∑= +

−⋅+⋅+⋅=

16

122

22 ])()()[(

l sysstat

llll NCBAσσ

γβαχ

Nl : the # of events in the lth binAl : the fraction of the SRN spectrumBl : the fraction of the decay electron spectrumCl : the fraction of the atmospheric νe spectrumα : fitting parameter for the # of SRN eventsβ : fitting parameter for the # of decay electronsγ : fitting parameter for the # of atmospheric νe events

Flux CalculationFlux CalculationUse 90% upper limit on α to get full spectrum flux limits:

whereNp=# of free protons in SK(1.5×1033)τ =detector live time(1496 days)f(Eν)=normalized SRN spectrum shapeσ (Eν) =cross section for the inverse β decay (9.52×10-44 Ee pe)ε (Eν) =signal detection efficiency

∫∞

×=

MeVp dEEEEfNF

3.19)()()( νννν εστ

α

SRN Search ResultsSRN Search Results

Summary of SRN Search Summary of SRN Search

SRN signal would manifest as distortion of Michel spectrumNo distortion ⇒ flux limits90% C.L. limits at SK are 1-2 orders of magnitude better than previous limitsSome SRN models can be constrained or rejected. However an increase in sensitivity of a factor～6 is needed to probe all models

Search for Neutrinos from Search for Neutrinos from GammaGamma--Ray BurstsRay Bursts

A time correlation analysis between GRBs and Super-Kamiokande events (spectrum-independent)SK data

LE: Eν=7∼80MeVHE: Eν=200MeV∼200GeVupmu: Eν=2GeV∼100TeV

GRB dataBATSE online catalog + the non-triggered supplement to the BATSE catalog(Kommers et al.2001)1371 GRBs(May 31, 1996∼May, 2000)

GRBGRB--Neutrino Correlation AnalysisNeutrino Correlation AnalysisGRB Search with LE and HE neutrinos

±10s:arriving simultaneously with the onset of the GRB±100s:90% of the GRBs have T90≤100s±1000s:>99.9% of the GRBs have T90≤1000s1hr:scan the 24hr period before each GRB(SN-like)1hr:scan the 24hr period after each GRB(AG)

GRB Search with upward-going muons±1000s; ≤15°1hr:scan the 24hr period before each GRB(SN-like)1hr:scan the 24hr period after each GRB(AG)

AssumptionNegligible neutrino flight time delay (due to mass)Constant background

Distributions of the Number of GRB Distributions of the Number of GRB Neutrino Signal Candidate EventsNeutrino Signal Candidate Events

±100s window

the 1 hr window between 4 and 5 hr after the GRB time

90% C.L. Upper Limit on 90% C.L. Upper Limit on Number of SK Events per GRBNumber of SK Events per GRB

Sample GRBs Search Windows Tot.Bgd. Tot.Sig. N90[cm-2]

LE 1081 ±100s 173 177 24.1×10-3

HE e-like 1111 ±100s 12.3 16 9.5×10-3

HE µ-like 1111 ±100s 9.7 14 9.6×10-3

upmu 1454 ±1000s, ≤15° 0.67 1 2.35×10-3

GRB Neutrino Total GRB Neutrino Total Fluence Fluence Upper Limits(90% C.L.)Upper Limits(90% C.L.)

Assuming an E-2 neutrino spectrum

Eν range Fνe[cm-2] Fνe[cm-2] Fνµ[cm-2] Fνµ [cm-2] Prediction [cm-2]

7MeV – 80MeV 4.44×107 9.52×105 2.65×108 2.65×108 1.4

0.2GeV – 200GeV 1.66×102 2.97×102 1.39×102 3.00×102 1.7×10-2

2GeV – 100 TeV 3.83×10-2 4.96×10-2 1.1×10-3

Summary of GRB Neutrino Summary of GRB Neutrino SearchSearch

Time and direction correlation search was done.No signal in excess of the expected background fluctuations was found.Our limits are at least a factor 30 higher than our rough estimate of GRB neutrino emission and are consistent with most model predictions.Sensitivity to GRB neutrinos is still too law.

A Search for Astronomical A Search for Astronomical Neutrino SourceNeutrino Source

Upward going muons(UGM's)1264 live days1416 through going & 345 stopping UGM'sAcceptance area:

∼1200 m2

UGM Acceptance UGM Acceptance aginstaginst DeclinationDeclination

Declination below -54° always visibleDeclination above 54° not accessiblewith SK UGM data

Poisson Probability Sky MapPoisson Probability Sky Map

count UGM's that come within 4° cone drawn at the center of each bin (=n)get average noise using bootstrapmethod (=µ)calculate cumulative Poisson probability as,

∑−

=

−−=1

0 !1)|(

n

i

i

ei

nprob µµµ

Poisson Probability Sky Map of Poisson Probability Sky Map of UpwardUpward--going going MuonsMuons

Preliminary

Distribution of the number of UGMDistribution of the number of UGM

the distribution of the number of UGM's in 4° half angle cone.average noise distribution obtained from 1000 fake noise sky maps genarated by bootstrap method.

UM Flux Limit for Possible UM Flux Limit for Possible Neutrino SourcesNeutrino Sources

Summary of a Search for Summary of a Search for Astronomical Neutrino SourceAstronomical Neutrino Source

Super-Kamiokande upward-going muon data is used to serach for astronomical neutrino sourceCumulative Poisson probability sky map and UGM number distribution show no statistically significant excessPossible neutrino sources chosen did not show significant number of excess UGM from them and UGM flux limits are obtained

SumarrySumarry

Solar neutrinos:evidence for neutrino oscillationSupernova neutrino bursts:upper limitSupernova relic neutrinos:upper limitGamma-ray burst neutrinos:upper limitAstronomical high energy neutrino source:upper limit

PMT交換作業

爆縮事故（１）

爆縮事故（２）

再建（１）

再建（２）

Super-Kamiokande has been restarted

Pure water filling: Oct.-Dec.

Tank was full on December10, 2002. (13 months after the accident.)

Charge(pe) >26.723.3-26.720.2-23.317.3-20.214.7-17.312.2-14.710.0-12.2 8.0-10.0 6.2- 8.0 4.7- 6.2 3.3- 4.7 2.2- 3.3 1.3- 2.2 0.7- 1.3 0.2- 0.7 < 0.2

Super-KamiokandeRun 20941 Event 2717102 -12 -11 :01 :49 :47

Inne r: 340 5 hi ts, 27 823 pE

Oute r: 1 58 hi ts, 306 pE (in-time)

Tri gg er ID: 0 x0b

D wall : 1 690 .0 cm

Full y-Co nt aine d

0 500 1000 1500 20000

142

284

426

568

710

Times (ns)

Typical cosmic ray muon in SK-II

Total number of PMTs in SK-II: ~5200 PMTs ~47% of SK-I(cf. 11146 PMTs in SK-I)