Solar neutrino measurement at Super Kamiokande

ICHEP'04ICRRK.Ishiharafor SK collaboration

Super Kamiokande detectorResult from SK-IStatus of SK-IIFuture plan

Super Kamiokande detector

50 k ton water Cherenkov Detector located at 1000 m underground.

41.4

m

39.3m

E e 9.87 MeV

cos sun 0.915

Feature of solar neutrino observation

8B neutrino measurement by + e- → + e- Strong directionalityReal time measurement.Sensitive to ee-

=~0.15×ee- High statistics ~15ev./day with Ee > 5MeV Studies on energy spectrum.

Precise energy calibration by LINAC and 16N.

Solar neutrino observation at SK I

B8e flux 2.35 0.02 0.08 106 cm2 s

0.406 0.004 0.0140.013

SSM BP2004

Sun sun

e

May/31/96 – Jul/13/01 22400 events (14.5 ev/day)

Event/

day/k

ton/

bin

Direction to the Sun

Solar neutrino events

SK-I day/night difference

Cos

Flu

x in

10^

6/cm

^3

SK-I (1496 days) 5.0-20. MeV 22.5 kton

day nightADNDay Night

Day Night 20.021 0.020 0.012

0.013

Z

mantle

core

SK Day

z

Un-bined day/night analysisEnergy and zenith angle dependence of event rate variatoin.

(Δm2 = 6.3×10-5 eV2, tan2θ = 0.55)

L e iBi S

i 1

N bin

1

ni

Bi U i c mi S p c , E z c , E

#B.G. in eachenergy bin

#SignalEvents

Event“Time"

BackgroundShape

Solar signalshape

ADN 0.018 0.016 0.0120.013

cf. old method 0.02 0.021 0.0120.013

j j

i

MC

MC

Energy spectrum of SK-I

m2=6.3x10-5eV2, tan2=0.55

m2=7.2x10-5eV2, tan2=0.38

Best fit 8B flux: 4.84 x 106 /cm2/sec

Energy correlated systematic error

Best fit 8B flux: 5.21 x 106 /cm2/sec

SK only (BP 2000 flux)

No distortion

Our data is consistent with no distortionOur data is consistent with no distortion..Consistent with LMA within 1 Consistent with LMA within 1 ..

SSMSSM8

22osc

SSMSSM8

22osc8

B

tan, ,

B

tan,B

ii

ii

ii

ii hep

mheph

hep

mb

i

iii

ii

i

f

hb

hep

,

B

Datad

SSMSSM8i

timevar2

2

2

2

2

2

12

22 log2 L

R

R

S

S

B

BN

i i

iibin d

Oscillation analysis

Spectrum

RR

iSS

iB

iRSi ffff ,,

Energy correlated systematic error

Time variation

Function for energy correlated systematic errors

8B spec. shape

energy scale

energy resolution

Michael Smy, UC Irvine

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

SK onlySK only(68% C.L.)(68% C.L.)

SSM SSM FluxFluxIndependentIndependent

SK only (68% C.L.)SK only (68% C.L.)SSM SSM 88B B Flux (BP2004)Flux (BP2004)

SK only (95% C.L.)SK only (95% C.L.)SSM SSM 88B B Flux(BP2004)Flux(BP2004)

Michael Smy, UC Irvine

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

SK onlySK only(68% C.L.)(68% C.L.)

SSM SSM FluxFluxIndependentIndependent

SK only (68% C.L.)SK only (68% C.L.)88B B Flux ConstrainedFlux Constrainedto BP2004 & SNO NCto BP2004 & SNO NC

SK only (95% C.L.)SK only (95% C.L.)88B B Flux ConstrainedFlux Constrainedto BP2004 & SNO NCto BP2004 & SNO NC

Michael Smy, UC Irvine

KamLAND

SK/SNO

KamLAND from hep-ph/0406035(KamLAND Collaboration)

sin2 is determined by SK/SNO

Result form SK/SNO is consistent withResult form SK/SNO is consistent with that from KamLAND!that from KamLAND!

Dose this difference indicate new physics ?Dose this difference indicate new physics ?

Status of SK-II

Period '96-'01 accident '03-'05#PMTs 11,146 5,182Photo Coverage 40 % 19 %Light yield ~6 p.e./MeV ~2.8 p.e/MeV Energy threshold 5.0 MeV 8.0 MeV

SK-I SK-II

SK-II 325 days (22.5 kton)8.0-20.0 MeVSignal =

SK-II preliminary result

Flux = 2.38±0.09(stat.) × 106/cm2/scf. SK-I 2.35±0.02(stat.) ± 0.08(sys.)

Event rate at SK-II is consistent with SK-I!Event rate at SK-II is consistent with SK-I!

Solar neutrino events

Dec.24,2002 – March 25, 2004

Direction to the Sun

Systematic error is under study

82802161

Day

Night

Day NightDay Night 2

0.025 0.075 stat.Average of SK-I

Day/Night Asymmetry and Energy Spectrum Day/Night Asymmetry and Energy Spectrum at SK-II are also consistent with SK-I!at SK-II are also consistent with SK-I!

SK-II works well !SK-II works well !

Physics motivation in future

Find evidence of matter effect.(Find smoking gun of LMA.)

How to do ?

Energy spectrum distortionRecoil electron

spectrum

reduce sys. error

reduce stat. error

Lower threshold

~10% upturn should be seen

tan2()0.550.380.380.380.28

m2 (eV2)6.3 x 10-5

4.8 x 10-5 7.2 x 10-5

10.0 x 10-5

7.2 x 10-5

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

Significance of shectrum distortion

Sig

nifi

canc

e ()

Live time (year)

3σ

Reject Background(~50% Radon, ~50% Gamma)

➢ Acrylic cover prevents radon from emitting from PMTs.

➢ Improve vertex fitter to reduce contamination of gamma events.Dependent on CPU power !

Reduce systematic ErrorWater transparency measurement with 7 laser calibrations.

SK tankLasers for w.t. measurements

Analysis of lower energy region in SK-I

629 +128 -126(sta.) signals68016+-262 bg events

4.5 – 5.0 MeV dataFlux: 3.13±0.63(sta.)±0.16(sys.) /cm2/sec

Direction to the sun

1496 days

466 days

Solar neutrino energy spectrum

4.5-5.0 MeV data is consistent with data with E>5.0 MeV.

We've already successed to lower EWe've already successed to lower Ethth to 4.5 MeV ! to 4.5 MeV !

summary

Day/night asymmetry is obtainedby un-binned methodADN= -1.8±1.6 +1.3/-1.2 %.

Preliminary results from SK-II are consistent with SK-I.

Hope to see definite energy spectrum distortion in SK-III, if it should be there.If not, it indicates new physics

13, CPT violation ...