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 ...