2. 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

3. Super Kamiokande detector 50 k ton water Cherenkov Detector located at 1000 m underground. 41.4m 39.3m Feature of solar neutrino observation  8 B neutrino measurement by  + e - →  + e - Strong directionality Real time measurement. Sensitive to e        e -  =~0.15×  e  e -   High statistics ~15ev./day with E e > 5MeV  Studies on energy spectrum. Precise energy calibration by LINAC and 16 N.

4. Solar neutrino observation at SK I Sun e May/31/96 – Jul/13/01 22400 events (14.5 ev/day) Event/day/kton/bin Direction to the Sun Solar neutrino events

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

6. Z mantle core SK Day zz Un-bined day/night analysis Energy and zenith angle dependence of event rate variatoin. (Δm 2 = 6.3×10-5 eV 2, tan 2 θ = 0.55) #B.G. in each energy bin #Signal Events Event “Time" Background Shape Solar signal shape

7. Energy spectrum of SK-I  m 2 =6.3x10 -5 eV 2, tan 2  =0.55  m 2 =7.2x10 -5 eV 2, tan 2  =0.38 Best fit 8 B flux: 4.84 x 10 6 /cm 2 /sec Energy correlated systematic error Best fit 8 B flux: 5.21 x 10 6 /cm 2 /sec SK only (BP 2000 flux) No distortion Our data is consistent with no distortion. Consistent with LMA within 1 .

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

9. Michael Smy, UC Irvine SK only (95% C.L.) SSM  Flux Independent SK only (68% C.L.) SSM  Flux Independent SK only (68% C.L.) SSM 8 B  Flux (BP2004) SK only (95% C.L.) SSM 8 B  Flux(BP2004)

10. Michael Smy, UC Irvine SK only (95% C.L.) SSM  Flux Independent SK only (68% C.L.) SSM  Flux Independent SK only (68% C.L.) 8 B  Flux Constrained to BP2004 & SNO NC SK only (95% C.L.) 8 B  Flux Constrained to BP2004 & SNO NC

11. Michael Smy, UC Irvine KamLAND SK/SNO KamLAND from hep-ph/0406035 (KamLAND Collaboration) sin 2  is determined by SK/SNO Result form SK/SNO is consistent with that from KamLAND! that from KamLAND! Dose this difference indicate new physics ?

12. Status of SK-II Period'96-'01accident'03-'05 #PMTs11,1465,182 Photo Coverage 40 %19 % Light yield~6 p.e./MeV~2.8 p.e/MeV Energy threshold5.0 MeV8.0 MeV SK-I SK-II

13. SK-II 325 days (22.5 kton) 8.0-20.0 MeV Signal = SK-II preliminary result Flux = 2.38±0.09(stat.) × 10 6 /cm 2 /s cf. SK-I 2.35±0.02(stat.) ± 0.08(sys.) 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

14. 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 !

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

16. Energy spectrum distortion Recoil electron spectrum reduce sys. error reduce stat. error Lower threshold ~10% upturn should be seen tan 2 (  ) 0.55 0.38 0.28  m 2 (eV 2 ) 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 0.5 4.0-5.5MeV background: x 0.3 (same BG as SK-I above 5.5MeV) Significance of shectrum distortion Significance (  ) Live time (year) 3σ

17.  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 Error Water transparency measurement with 7 laser calibrations. SK tank Lasers for w.t. measurements

18. Analysis of lower energy region in SK-I 629 +128 -126(sta.) signals 68016+-262 bg events 4.5 – 5.0 MeV data Flux: 3.13±0.63(sta.)±0.16(sys.) /cm 2 /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 E th to 4.5 MeV !

19. summary Day/night asymmetry is obtained by un-binned method A DN = -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...