Solar neutrino measurement at Super Kamiokande

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Solar neutrino measurement at Super Kamiokande
ICHEP'04 ICRR K.Ishihara for SK collaboration

• Super Kamiokande detector
• Result from SK-I
• Status of SK-II
• Future plan

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Super Kamiokande detector

• Feature of solar neutrino observation
• 8B neutrino measurement by ?? e- ? ?? e-
• Strong directionality
• Real time measurement.
• Sensitive to ?e????????? ????????e-??0.15???
  e?e-??
• High statistics 15ev./day with Ee gt 5MeV
• Studies on energy spectrum.
• Precise energy calibration by LINAC and 16N.

41.4m
39.3m
50 k ton water Cherenkov Detector located at 1000
m underground.
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Solar neutrino observation at SK I
May/31/96 Jul/13/01 22400 events (14.5 ev/day)
Direction to the Sun
Solar neutrino events
Event/day/kton/bin
e
Sun
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SK-I day/night difference
SK-I (1496 days) 5.0-20. MeV 22.5 kton
Flux in 106/cm3
day
night
Cos q
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Un-bined day/night analysis
Energy and zenith angle dependence of event rate
variatoin.
(?m2 6.310-5 eV2, tan2? 0.55)
B.G. in each energy bin
Signal Events
Event Time"
Solar signal shape
Background Shape
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Energy spectrum of SK-I
No distortion
?m27.2x10-5eV2, tan2?0.38
Best fit 8B flux 5.21 x 106 /cm2/sec
?m26.3x10-5eV2, tan2?0.55
SK only (BP 2000 flux)
Best fit 8B flux 4.84 x 106 /cm2/sec
Our data is consistent with no distortion. Consist
ent with LMA within 1 s.
Energy correlated systematic error
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Oscillation analysis
Energy correlated systematic error
Spectrum
Time variation
8B spec. shape
energy scale
energy resolution
Function for energy correlated systematic errors
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SK only (68 C.L.) SSM ??Flux Independent
SK only (68 C.L.) SSM 8B ??Flux (BP2004)
SK only (95 C.L.) SSM 8B ??Flux(BP2004)
SK only (95 C.L.) SSM ??Flux Independent
Michael Smy, UC Irvine
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SK only (68 C.L.) SSM ??Flux Independent
SK only (68 C.L.) 8B ??Flux Constrained to
BP2004 SNO NC
SK only (95 C.L.) 8B ??Flux Constrained to
BP2004 SNO NC
SK only (95 C.L.) SSM ??Flux Independent
Michael Smy, UC Irvine
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sin2q is determined by SK/SNO
Result form SK/SNO is consistent with that from
KamLAND!
KamLAND
SK/SNO
KamLAND from hep-ph/0406035 (KamLAND
Collaboration)
Michael Smy, UC Irvine
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Status of SK-II
SK-I
SK-II
Period '96-'01 accident '03-'05 PMTs 11,146
5,182 Photo Coverage 40 19 Light
yield 6 p.e./MeV 2.8 p.e/MeV Energy
threshold 5.0 MeV 8.0 MeV
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SK-II preliminary result
Dec.24,2002 March 25, 2004
SK-II 325 days (22.5 kton) 8.0-20.0 MeV Signal

Solar neutrino events
Flux 2.380.09(stat.) 106/cm2/s cf. SK-I
2.350.02(stat.) 0.08(sys.)
Systematic error is under study
Direction to the Sun
Event rate at SK-II is consistent with SK-I!
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Day/Night Asymmetry and Energy Spectrum at SK-II
are also consistent with SK-I! SK-II works well
!
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Physics motivation in future

• Find evidence of matter effect.(Find smoking gun
  of LMA.)
• How to do ?

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Energy spectrum distortion
Recoil electron spectrum
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• 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.

Lasers for w.t. measurements
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Analysis of lower energy region in SK-I
Direction to the sun
Solar neutrino energy spectrum
1496 days
We've already successed to lower Eth to 4.5 MeV
!
629 128 -126(sta.) signals 68016-262 bg events
466 days

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summary

• Day/night asymmetry is obtainedby un-binned
  methodADN -1.81.6 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 q13, CPT violation ...