The Solar Neutrino Day/Night Effect in Super-Kamiokande

TL;DR

This paper reports on the measurement of the solar neutrino day/night effect in Super-Kamiokande, providing precise neutrino oscillation parameters and confirming the expected asymmetry with improved statistical accuracy.

Contribution

It presents the first detailed measurement of the solar neutrino day/night effect in Super-Kamiokande, refining neutrino oscillation parameters with enhanced statistical precision.

Findings

Measured day/night asymmetry of -1.7% with statistical and systematic uncertainties.

Determined neutrino mixing angle as sin^2θ=0.276+0.033-0.026.

Estimated mass squared difference as Δm^2=7.1+0.6-0.5×10^-5 eV^2.

Abstract

The time variation of the elastic scattering rate of solar neutrinos with electrons in Super-Kamiokande-I was fit to the day/night variations expected from active two-neutrino oscillations in the Large Mixing Angle region. Combining Super-Kamiokande measurements with other solar and reactor neutrino data, the mixing angle is determined as sin^2theta=0.276+0.033-0.026 and the mass squared difference between the two neutrino mass eigenstates as Delta m^2=7.1+0.6-0.5x10^-5eV^2. For the best fit parameters, a day/night asymmetry of -1.7+-1.6(stat)+1.3-1.2(syst)% was determined from the Super-Kamiokande data, which has improved statistical precision over previous measurements and is in excellent agreement with the expected value of -1.6%.