Precise measurement of the solar neutrino day-night and seasonal variation in Super-Kamiokande-I

Abstract

The time variation of the elastic scattering rate of solar neutrinos with electrons in Super-Kamiokande-I was fit to the variations expected from active two-neutrino oscillations. The best fit in the large mixing angle solution has a mixing angle of ${\mathrm{tan}}^{2}\ensuremath{\theta}=0.55$ and a mass squared difference of $\ensuremath{\Delta}{m}^{2}=6.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}{\mathrm{eV}}^{2}$ between the two neutrino mass eigenstates. The fitted day-night asymmetry of $\ensuremath{-}1.8\ifmmode\pm\else\textpm\fi{}1.6(\mathrm{stat}{)}_{\ensuremath{-}1.2}^{+1.3}(\mathrm{syst})%$ has improved statistical precision over previous measurements and agrees well with the expected asymmetry of $\ensuremath{-}2.1%.$