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Solar neutrino measurement at Super Kamiokande

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. Super Kamiokande detector. Feature of solar neutrino observation 8 B neutrino measurement by  + e - →  + e -

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Solar neutrino measurement at Super Kamiokande

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  1. 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

  2. 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 > 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.

  3. 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

  4. SK-I day/night difference SK-I (1496 days) 5.0-20. MeV 22.5 kton Flux in 10^6/cm^3 day night Cos q

  5. Z Day SK core mantle z Un-bined day/night analysis Energy and zenith angle dependence of event rate variatoin. (Δm2 = 6.3×10-5 eV2, tan2θ = 0.55) #B.G. in each energy bin #Signal Events Event “Time" Solar signal shape Background Shape

  6. Energy spectrum of SK-I No distortion m2=7.2x10-5eV2, tan2=0.38 Best fit 8B flux: 5.21 x 106 /cm2/sec m2=6.3x10-5eV2, 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. Consistent with LMA within 1 s. Energy correlated systematic error

  7. Oscillation analysis Energy correlated systematic error Spectrum Time variation 8B spec. shape energy scale energy resolution Function for energy correlated systematic errors

  8. 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

  9. 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

  10. Dose this difference indicate new physics ? 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

  11. 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

  12. 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 = 2.38±0.09(stat.) × 106/cm2/s cf. SK-I 2.35±0.02(stat.) ± 0.08(sys.) Systematic error is under study Direction to the Sun Event rate at SK-II is consistent with SK-I!

  13. Day Night Average of SK-I Day/Night Asymmetry and Energy Spectrum at SK-II are also consistent with SK-I! SK-II works well !

  14. Physics motivation in future • Find evidence of matter effect.(Find smoking gun of LMA.) How to do ?

  15. Significance of shectrum distortion 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 tan2() 0.55 0.38 0.38 0.38 0.28 Lower threshold Significance (s) reduce stat. error reduce sys. error ~10% upturn should be seen 3σ Live time (year) Assumptions: Correlated systematic error: x 0.5 4.0-5.5MeV background: x 0.3 (same BG as SK-I above 5.5MeV) Energy spectrum distortion Recoil electron spectrum

  16. SK tank • 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

  17. Analysis of lower energy region in SK-I 4.5 – 5.0 MeV data Flux: 3.13±0.63(sta.)±0.16(sys.) /cm2/sec 4.5-5.0 MeV data is consistent with data with E>5.0 MeV. 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

  18. 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 physicsq13, CPT violation ...

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