Comprehensive Study of the Possibility of Day - Night Effect Enhancement

Abstract

A set of quantitative predictions for the day-night asymmetry in the Super - Kamiokande detector is presented. For these predictions, neutrino events are collected in ``samples'' defined by the trajectories in the Earth of the corresponding solar neutrinos. The more important samples considered here are: the full sample of neutrinos detected at night, the sample of night neutrinos which cross the Earth core and the sample of night neutrinos which does not cross the Earth core. For energy integrated event rates, the day-night asymmetry for core crossing neutrinos is up to six times bigger than the day-night asymmetry for the full sample of night neutrinos. When the reduction in statistics is considered, an effective enhancement up to a factor $\approx 2.3$ is obtained. The selection of core crossing neutrinos may be relevant for the recoil - $e^-$ spectra too. From these results it is reasonable to expect the Super Kamiokande detector be able to constrain the small mixing angle solution of the solar neutrino problem ($\sin^2 2 θ_v \leq 0.01$) through the day-night effect. Furthermore, it is proposed that the day-night effect may limits the total flux of 8B neutrino produced in the Sun. At last, the sensitivity of these predictions to the Earth model uncertainties is quantitatively discussed.