1

Super-Kamiokande Results(Neutrino Oscillations)

Outline of the talk:Outline of the talk:• Brief introduction/history• What we have learnt

– Atmospheric neutrinos– Solar Neutrinos– （K2K）

• Future Prospects

Neutrino Heliograph

Super-Kamiokande

Y.SuzukiKamioka ObservatoryICRR, Univ. of Tokyo2004-08-19 @ Nobel Symposium

2

42m

39m

ν

C Scientific American

Super-Kamiokande

250km

J-PARC

KEK-PS

• 50,000 tons (22,500 ton fid.) Water Cherenkov Detector• 1,000 m underground• Inner-Detector (ID) : 11,146 50cm photomultiplier tubes

(40% photocathode-coverage) for SK-I (May-96 ~ July-2001)

• Outer-Detector (OD) : 1,885 20cm PMTs

3

SK-Collaboration

• Number of Institutions: 36– 17 Japan– 15 US– 1 Poland– 3 Korea

• 76 Japanese• 62 Foreigners

4

Brief History1991-04 Construction started as a 5yr project1992-10 US Group joined1996-04 Experiment started1998-06 Discovery of (Atmospheric) Neutrino Oscillation2000-06 Indication of Large Mixing for solar neutrino

oscillation2001-06 SNO+SK: evidence of solar ν oscillation2001-11 Accident (lost 6,777 PMTs)2002-12 Experiment re-started (SK-II: w/ 47% of PMTs)

2004-02 Evidence for the oscillatory behavior2004-06 Confirmation of atmospheric neutrino

oscillation by K2K (@99.99%C.L)

2005-11~2006-06 Full reconstruction work2006-07 Experiment will resume (SK-III)

Acrylic + FRP vessel

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Atmospheric neutrinos

Talks today:• Two flavor analysis (SK-I final): full paper < 1 month

– Determination of the oscillation parameters• L/E analysis: accepted in June-04

– First Oscillatory Evidence• Three flavor analysis: preliminary

Papers in preparationExotic scenarios (non-standard int., decay, LxE, etc)Sterile admixtureCPT violation

Understudyντ appearance (statistical methods)

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Characteristics and Event Classification

Wide range of path-length (3 orders)and energy (5 orders)

L: ~10~13,000 kmE: ~0.1~10,000 GeVFl

ight

pat

h-le

ngth

(km

)

zenith angle (cosθ)

Eν in GeV

Up Down

Even

ts/1

000d

ays

Parent neutrino energyFully Contained (Eν ~1GeV)

UpwardThrough-going µ (Eν ~100GeV)

UpwardStopping µ (Eν ~10GeV)

Partially Contained (Eν ~10GeV)

subGeV: Evis>1.33GeVMulti-GeV: < 1.33GeV

Zenith angle distribution

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νµ - ντ

0

20

40

60

80

100

120

140

160

180

200

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

Multi-GeV µ-like+P.C.Multi-GeV µ-like+P.C.Multi-GeV µ-like+P.C.cosθ

nu

mb

er o

f ev

ents Super Kamiokande Preliminary

( 1.0, 2.2×10-3 )

Super-Kamiokande, 1998

Up-going Down-going

10

10 2

10 3

-1 -0.5 0 0.5 1cosΘ

0.3-0.5 GeV

0.9-1.5 GeV

3.0-5.0 GeV

νe+ν–

e

-1 -0.5 0 0.5 1cosΘ

0.3-0.5 GeV

0.9-1.5 GeV

3.0-5.0 GeV

νµ+ν–

µ

2:1

Up-Down Symmetry at High EnergyMixture of νe, νe, νµ and νµ

Uncertainty in Up/Down: ~1~2% Eν <1GeV~1% in a few GeV region

Hol./Vert (upmu reion): ~2% (from π/K ratio)

~

Key distribution: Uniformity of the Pr. Cosmic ray + beyond the geomagnetic cut off

Discovery of neutrino oscillation

Event SummaryMay`96 ~ July`01(SK-I)1489days (Contained)1678days (Up-muons)~14,000 events

Rsub-GeV=0.658±0.016(stat)±0.032(syst)

Rmulti-GeV=0.702 (stat)±0.099(syst)+0.032

−0.03010-5 10-4 10-3 10-2 10-1 1

∆m2(eV2)

(<1.33GeV)

(>1.33GeV)

R=(µ/e)data/(µ/e)MCUncertainty in R (flux)

3% @ 5GeV15% @100GeV

8

9

Super-Kamiokande1489d (Contained)+ 1678d (Up-µ) (revised)

Zenith Angle Distribution

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Oscillation Contour

1.5x10-3eV2 < ∆m2 < 3.4x10-3 eV2

sin22θ > 0.92 (@90%C.L.)Best fit: sin22θ =1.02, ∆m2=2.1x10-3 eV2

χ2=174.9/177dof, χ2=465/179dof for null oscill∆χ2=290.1Rather flat

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L/E Analysis

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 10 102

103

104

L/E (km/GeV)

Dat

a/P

red

icti

on

(n

ull

osc

illat

ion

)

All the data1489.2days

Aim of the L/E analysis (λ=4πE/∆m2)• To observe oscillation pattern

direct oscillatory evidence • Strong constraint on ∆m2

• Distinguish other exotic hypotheses in L/E

Select events only with good L/E resolution

0

0.2

0.4

0.6

0.8

1

1 10 102

103

104

L/E (km/GeV)

Pro

b.(νµ

νµ

)

decoherence

decay

Dip for oscillation

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1 10 102

103

104

L/E (km/GeV)

Osc

illat

ion

/Nu

ll o

scill

atio

n (

MC

)

100 yr MCw/ selection

Guide line

Aspects of the analysis

12

• Need statistics& need to contain muons

expand fiducial vol. (26.4kt)• Categorize PC by chargeOD

different cuts make the L/E resolution better

Eν Eobserved

Reconstructed from observed energy using relations based on MC simulation

Flight length (L) Zenith angle

Estimated from the zenith angle of the particle direction (vector sum)0

20

40

60

80

100

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

Num

ber

of e

vent

s

observed charge / expectation from through-going

OD stopping

OD through-going

OD through-going MC

OD stopping MC

Preliminary

FC single-ring

Eν /Eobserved Energy0

0.5

1

1.5

2

2.5

1 10log10(Eobserved)

Eν/

Eo

bse

rved

10 2

10 3

10 4

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

Zenith angle (cosΘ)

Flig

ht le

ngth

(km

)

Direction

Reconstruction of E and L

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L/E resolution cut

Select events with ∆(L/E) < 70%

horizontally going events: due to large dL/dcosθ

low energy events: due to large scattering

angle

Fist dip

1/2 oscillation

Reasons for the rejected events

2726 events (3726 ev. expected)~ 1 /5 of total dataCut for OD stopping

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Result of L/E analysis• The first dip has been

observed at ~500km/GeV

• This provide a strong confirmation of neutrino oscillation

• The first dip observed cannot be explained by other hypotheses

3.4 σ to decay3.8 σ to decoherence

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1 10 102

103

104

L/E (km/GeV)

Da

ta/P

red

icti

on

Preliminary

Oscillation

DecayDecoherence

1489.2 days FC+PC

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Constraint on the neutrino oscillation parameters from L/E analysis

Best Fit:∆m2=2.4x10-3,sin22θ=1.00χ2min=37.8/40 d.o.f.(sin22θ=1.02, χ2min=37.7/40 d.o.f)

Allowed region (@90%C.L.)1.9x10-3 < ∆m2< 3.0x10-3 eV2

0.90 < sin22θ

Consistent with the standard zenith angle analysis

Stronger constraint on ∆m2

even with fewer data sample

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3 flavor analysisRemarks:• Matter effect (νµ<->νe)

– Effect through θ13– Mass heirarchy

• sign of ∆m132

• Effect through ∆m12(larger than what we thought before)– Interference

• Assumed ∆m12=0 (this analysis)– will be included

InverseNormal

mν2

mν3mν2mν1

mν3 mν1Parameters

Δm132, θ23, θ13

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Effect of ∆msol2 on the atmospheric oscillation

|Ue3|=0.2∆m12

2=7x10-5eV2

Interference

0.9

0.925

0.95

0.975

1

1.025

1.05

1.075

1.1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosΘ

Eff

ect

Sub-GeV: Eν < 400 MeV

0.9

0.95

1

1.05

1.1

1.15

1.2

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosΘ

Eff

ect

Multi--GeV

Interference Interference

θ13

Current assumption, ∆m12=0 is marginally OK.

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Allowed region for active 3-flavor oscillations

sin2θ13 < 0.16 @∆m2=2x10-3eV2

Nor

mal

Inve

rted

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Solar neutrinos8B solar-ν measurement (Ee > 5MeV) by ν+e-→ν+e-

DirectionalityReal time measurementEnergy measurement (Calibration by LINAC and 16N)Sensitive to νe, νµ, ντ: σ(νµ(τ)+e-) ~0.15×σ(νe+e-)

High statistics ~15ev./day

• Original Aim of Super-K Solar Neutrinodetect flux independent evidence• Day/night flux difference, spectrum distortion, seasonal variationexcluded SMA and showed the solution is large mixingin 2000.

• The evidence was obtained by the comparison of SK (ES) & SNO (CC) flux in 2001.

And we still have not seen such flux independent evidence yet.

SK data in 2000

NOW2000/Neutrino2000

• Excluded Small Mixing Angle Solutions

• Only large mixing solutions are allowed

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21

SuperSuper--KamiokandeKamiokande--I solar neutrino data I solar neutrino data

BP2004 (~15% diff.)5.82(1±0.23) x 10-6 / cm2 / s

Bp2000:5.05(1 ) x 10-6 / cm2 / s

May 31, 1996 – July 13, 2001 (1496 days )

8B flux : 2.35 ± 0.02 ± 0.08 [x 106 /cm2/sec]

Data/SSMBP2004= 0.406 +0.014-0.013±0.004

( Data/SSMBP2000 = 0.465 ±0.005 +0.016/-0.015 )

22385±230 solar ν events(14.5 events/day)

+0.20−0.16

16,700: e-type solar neutrinos (from SNO)

About 5,700 µ/τ type solar neutrinos in Super-K

This is the way the first evidence for the flavor conversion was shown in 2001

Seasonal Seasonal variationvariation

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Consistent with the expectation from the earth’s eccentricity

χ2 = 4.7 / 7dof (eccentricity) ;

χ2 = 10.7 / 7dof (flat)

0.4

0.5

0.6

JAN

FE

B

MA

R

AP

R

MA

Y

JUN

JUL

AU

G

SE

P

OC

T

NO

V

DE

C

Dat

a/S

SM

SK-I 1496day 5.0-20MeV 22.5kt(Preliminary)

χ2 for eccentricity = 4.7 C.L. = 69%χ2 for flat = 10.3 C.L. = 17%(8-1 d.o.f.) (with sys. err.)

Energy spectrum of SK-I

∆m2=6.3x10-5eV2

tan2θ=0.55

∆m2=7.2x10-5eV2

tan2θ=0.38

Energy correlated systematic error

χ2(flat)=20.2/20 (44.3% C.L.)23

SK-I day/night difference

(Day-Night)ADN=(Day+Night)/2

24

φ(8B)day = 2.32 ± 0.03 ±0.080.07 φ(8B)night = 2.37 ± 0.03 ± 0.08

D-N= -(0.021 ± 0.020 ± )(D+N)/2

0.0130.012

Day-Night Flux difference

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Zenith ‘seasonal’ spectrum likelihood (new)# Backgrounds# Backgroundsin each energy bins

# Signal# SignalEvents

EventEnergy

Event“Time”

Likelihood for solar neutrino extraction Eventsin each energy bins

( ) ( )∏∏= 1=

+−×⋅+⋅∑=

bin ii i

N

i

n

iiiiSB tzEcpSmcuBe

1

)(),()(ν

ννννL

∑=

j j

iim

MCMC

Solar Signal ShapeSolar Signal Shape

Background ShapeBackground Shape

21 Energy bins21 Energy bins

cosθsun All the time informationIs added (un-binned)Including seasonal inf.

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Oscillation analysis

( ) ( )SSMSSM8

22osc

SSMSSM8

22osc8

Btan, ,

Btan,B

ii

ii

ii

ii hep

mhephhep

mb+

∆=

+∆

=θθ

i

iii

ii

i

fhb

hepηβρ +

=+

= ,B

Datad SSMSSM8i

( )timevar2

2

2

2

2

2

12

22 log2 L∆−+++

−= ∑

= R

R

S

S

B

BN

i i

iibin d

σδ

σδ

σδ

σρχ

Spectrum

( ) ( ) ( ) ( )RR

iSS

iB

iRSi ffff δδδδδδ ××= ΒΒ ,,

Energy correlated systematic error Time variation

8B spec. shape

energy scale

energy resolution

Function for energy correlated systematic errors

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Results of Super-Kamiokande

SK only (68, 95% C.L.)SK only (68, 95% C.L.)SSM SSM 88B B ν ν FluxFluxConstrained to BP2000Constrained to BP2000

SK only (68, 95% C.L.)SK only (68, 95% C.L.)SSM SSM 88B B ν ν FluxFluxConstrained to BP2004Constrained to BP2004

LMA-best(tan2θ=0.55, ∆m2=6.3x10-5eV2)

LMA-best(tan2θ=0.48, ∆m2=6.3x10-5eV2)

SK only (95% C.L.)SK only (95% C.L.)SSM SSM ν ν Flux IndependentFlux Independent

SK only (95% C.L.)SK only (95% C.L.)SSM SSM ν ν Flux IndependentFlux Independent

BP2000 BP2004

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SK and SNO only,SK and SNO only,SSM SSM νν Flux IndependentFlux Independent68% and 95% C.L.68% and 95% C.L.SK+SNO best(tan2θ=0.38, ∆m2=6.0x10-5eV2)

KEK PS

250 km

SK

K2K Long base line neutrino oscillation experiment

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Observation Experiment(Atmospheric ν)Experiment started in April, 1999

)27.1(sin2sin.2

22

ν

θE

Lmprob ∆⋅= L=250km (fixed), <Eν> ~ 1.3GeV

∆m2 = 2.5x 10-3 eV2, sin22θ=1~ 0.3

Expect ~70% disappearance

4

6

8

10

12

14

16

18

Eνrec

0

2

Entries 56

even

ts/0

.2[G

eV]

Disappearance of νµ 2.92.9σσDistortion of Eν spectrum 2.52.5σσ∆∆mm22<(1.7~3.5)<(1.7~3.5)××1010--33 eVeV22 @sin@sin2222θθ=1.0 =1.0 (90%C.L.)(90%C.L.)

Spectrum8.9×1019 POT

• NSKobs=108

151 for no oscillation• NSK

exp (best fit)=104.8

Best FitKS prob.=52%

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5[GeV]

K2K has confirmed neutrino oscillations at K2K has confirmed neutrino oscillations at 3.93.9σσ

SK-II Atmospheric neutrinos

• Detector performance is OK– e/µ-Id, energy scale look good.

• Data is consistent with SK-I results– FC: 8.22±0.16 ev/day (8.17 SK-I)– PC: 0.51±0.04 ev/day (0.61 SK-I)

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31

SK-II solar neutrinos

Flux= 2.38 ± 0.09 (stat.)x106/cm2/s

8 – 20 MeV

Dec.24,2002 – March 25, 2004

Solar ν signal = 2161 (stat.) events

325 days

(Systematic error under study)(cf. SK-I result: 2.35 ± 0.02(stat.) ± 0.08(sys.))

+82- 80

• Detector performance is OK• Data is consistent with SK-I results

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SuperSuper--Kamiokande Kamiokande IIIIII1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

11,146 Number of ID PMTs 5,18240% Photocathod coverage 19% 40%

~6 p.e./MeV Cherenkov light yield ~2.8 p.e./MeV ~6 p.e./MeVAcrylic+FRP cases

SK-IIIaccident

SK full reconstruction

SK-I SK-II

11,146

Nov May

Data takingJune-2006

Ready for T2K experiment starting in 2009

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Future Prospects (Atm-ν)(Sensitivity to non-zero θ13)

MM-e 2.5 - 5.0 GeV0

50

100

150

200

250

300

350

400

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

s213=0.05s213=0.00null oscillation

e appearance

1+multi-ring, e-like, 2.5 - 5 GeVSk 20yr (450ktonyr)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1sin2θ23

sin

2 θ13

X

∆m2=0.0025eV2

s2θ23 = 0.50s2θ13 = 0.025

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

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1sin2θ23

sin

2 θ13

X

∆m2=0.0025eV2

s2θ23 = 0.65s2θ13 = 0.025

99%C.L.

s22θ23=0.91

90%C.L.

0

5

10

15

20

25

30

35

40

0 0.02 0.04 0.06 0.08sin2θ13

∆χ2 (s

in2 θ 13

- (

no

θ13

))

0

5

10

15

20

25

30

35

40

0 0.02 0.04 0.06 0.08sin2θ13

∆χ2 (s

in2 θ 13

- (

no

θ13

))

0

5

10

15

20

25

30

35

40

0 0.02 0.04 0.06 0.08sin2θ13

∆χ2 (s

in2 θ 13

- (

no

θ13

))

3σ 3σ 3σ

(∆χ2 ∝～ exposure)

34

0.35

0.4

0.45

0.5

0.55

5 7.5 10 12.5 20Energy(MeV)

Dat

a/SS

M(B

P200

4)

P(ν e→

ν e)

Future Prospects (Sol-ν)(Sensitivity to the spectrum distortion)

νe survival probability Recoil electron spectrum

~10% upturn should be seen

Live time (years)

Sig

nific

ance

( σ

)

3σ level

Assumptions:Correlated systematic error: x 0.54.0-5.5MeV background: x 0.3(same BG as SK-I above 5.5MeV)

Solar+KamLAND best fit

tan2(θ)0.280.380.380.380.55

∆m2 (eV2)7.2 x 10-5

10 x 10-5

7.2 x 10-5

4.8 x 10-5

6.3 x 10-5

Better Energy scale calibration (~±0.4%) is needed.Better 8B spectrum shape from nuclear physics is needed.

Lowering threshold

Remaining B.G. for lower energygamma from the rockradio isotope (e.g. Rn)

Possibility to lower the threshouldDown to 4.0 MeV0.12

0.13

0.14

0.15

0.16

0.17

0.18

0.19

0.2

0.21

0.22

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cosθsun

Eve

nt/

day

/kto

n

SK-I 511days20.5kton (Preliminary)

4.5-5.0MeV

In SK-I, after install the 2nd level trigger system, the efficiency above 4.5MeV became ~100% (Sep. 2000~)

Acrylic cover againt RnFrom PMT (for SK-III)

35

36

Summary• The observation of the direct oscillatory

behavior makes the atmospheric neutrino oscillation more and more solid.

• K2K has confirmed the atmospheric neutrino oscillation at 99.99% C.L. in 2004.

• Although the evidence of the solar ν oscillation has been first shown by SNO(CC) and Super-K(ES) and gets more stronger now, the characteristic behavior of the day-night flux difference and the low energy spectrum upturn have not yet been observed.