Precise Measurement of the Solar Neutrino Day/Night and Seasonal Variation in Super-Kamiokande-I

TL;DR

This paper reports precise measurements of solar neutrino variations in Super-Kamiokande-I, confirming neutrino oscillations with improved statistical accuracy and consistent day/night asymmetry results.

Contribution

It provides the most precise measurement to date of solar neutrino day/night and seasonal variations, supporting the active two-neutrino oscillation model.

Findings

Best fit oscillation parameters: tan^2θ=0.55, Δm^2=6.3×10^-5 eV^2

Fitted day/night asymmetry: -1.8% with improved precision

Results agree with theoretical expectations of -2.1% asymmetry

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^2theta=0.55 and a mass squared difference of Deltam^2=6.3times10^-5eV^2 between the two neutrino mass eigenstates. The fitted day/night asymmetry of -1.8+-1.6(stat)+1.3-1.2(syst)% has improved statistical precision over previous measurements and agrees well with the expected asymmetry of -2.1%.