Solar and atmospheric neutrino oscillations in SuperKamiokande

Abstract

The recent results of solar and atmospheric neutrino oscillations in Super-Kamiokande (SK) are presented. SK has four phases (SK-I to IV) since starting the operation in 1996. In this time update, the 2365 and 2520 days of data for SK-IV was used for solar and atmospheric neutrino analysis, respectively. In solar neutrino analysis, the lowering energy threshold (3.5MeV) has achieved in SK-IV thanks to the background reduction. More than 84,000 signals were totally observed in 5200 days through all the phases, and no long term flux time variation was seen. The night flux was 3.3¥% higher than day flux which caused by the neutrino oscillation of the matter effect of the earth at 3 sigma level. No significant distortion of the energy spectrum was seen. The obtained global neutrino oscillation parameters were determined as $\Delta m^2_{21} = 7.49 \times 10^{-5} eV^2$ and $\sin^2\theta_{12} = 0.308$. In atmospheric neutrinos, 0.33 MegatonYears of data were accumulated, and the analysis were carried out. The best fit of the neutrino oscillation parameters are $\Delta m^2_{32}=2.5 \times 10^{-3}, \sin^2\theta_{23}=0.587, \delta_{CP}=4.189$ for normal hierarchy case. The normal hierarchy is preferred with significance $\Delta \chi^2 = \chi^2(NH)-\chi^2(IH)=-4.3$. The tau neutrino appearance by atmospheric neutrino oscillation was confirmed at $4.6\sigma$ level.