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 tan(2)theta=0.55 and a mass squared difference of Deltam(2)=6.3x10(-5) eV(2) between the two neutrino mass eigenstates. The fitted day-night asymmetry of -1.8+/-1.6(stat)(-1.2)(+1.3)(syst)% has improved statistical precision over previous measurements and agrees well with the expected asymmetry of -2.1%.