A Study of the Day - Night Effect for the Super-Kamiokande Detector: II. Electron Spectrum Deformations and Day - Night Asymmetries

Abstract

Using the results of a high precision calculation of the solar neutrino survival probability for Earth crossing neutrinos in the case of MSW ${\nu }_e\to {\nu }_{\mu (\tau )}$ transition solution of the solar neutrino problem, performed in an earlier study, we derive predictions for the one-year averaged day-night (D-N) asymmetry in the deformations of the $e^{-}$ - spectrum to be measured with the Super - Kamiokande detector, and for the D-N asymmetry in the energy- integrated one year signal in this detector. The asymmetries are calculated for solar ${\nu }_e$ crossing the Earth mantle only, the core and the (mantle + core) for a large representative set of values of the MSW transition parameters $\Delta m^2$ and ${\sin }^{2}2{\theta }_v$ from the ``conservative'' MSW solution region obtained by taking into account possible uncertainties in the values of the ${}^8$B and ${}^7$Be neutrino fluxes. The effect of the uncertainties in the value of the bulk matter density and in the chemical composition of the core, on the D-N asymmetry predictions is discussed. It is shown, in particular, that for ${\sin }^{2}2{\theta }_v\le 0.013$ the one year average D-N asymmetry for neutrinos crossing the Earth core can be larger than the asymmetry for (only mantle crossing + core crossing) neutrinos by a factor of up to six. Iso - (D-N) asymmetry contours in the $\Delta m^2-{\sin }^{2}2{\theta }_v$ plane for the Super - Kamiokande detector are derived in the region ${\sin }^{2}2{\theta }_v\text{gsim}10^{-4}$ for only mantle crossing, core crossing and (only mantle crossing + core crossing) neutrinos. Our results indicate that the Super - Kamiokande experiment might be able to test the ${\sin }^{2}2{\theta }_v\le 0.01$ region of the MSW solution of the solar neutrino problem by performing selective D-N asymmetry measurements.

Comments: LaTeX, 18 pages, 3 Tables, 16 Figures in 7 postscript files