Day - Night Effect Predictions for the SNO Detector

Abstract

Detailed predictions for the day-night (D-N) asymmetry in the energy-integrated one year signals in the SNO detector in the case of the MSW $ν_e \to ν_{μ(τ)}$ and/or $ν_e \to ν_s$ transition solutions of the solar neutrino problem are presented. The asymmetries in the charged current (CC) and $ν- e^{-}$ elastic scattering (ES) event rates are calculated for both MSW solutions; in the case of the $ν_e \to ν_s$ transition solution the D-N asymmetry in the neutral current (NC) event rate are derived as well. The asymmetries are calculated for three night samples of events which are produced by the solar neutrinos crossing i) the Earth mantle only (Mantle), ii) the Earth core (Core) and iii) the Earth core and/or the mantle (Night). The effects of the uncertainties, e.g., in the values of the cross-sections of the CC and NC neutrino-induced reactions on deuterium on the corresponding D-N asymmetry predictions are analyzed. It is shown, in particular, that that due to the strong enhancement of the transitions of the solar neutrinos crossing the Earth core, at $\sin^22θ_V \leq 0.01$ the corresponding one year average D-N asymmetry in the Core sample of CC events in the case of the $ν_e \to ν_{μ(τ)}$ solution can be larger by a factor of up to $\sim 8$ than the asymmetry in the Night sample. Iso - (D-N) asymmetry contours in the $Δm^2 - \sin^22θ_V$ plane for the SNO detector are derived in the region $\sin^22θ_V \gsim 10^{-4}$ for the Core and Night samples of the CC, ES and NC events.