Bounds on the Solar Antineutrino total Flux and Energy spectrum from the SK experiment

Abstract

A search for inverse beta decay electron antineutrinos has been carried out using the 825 days sample of solar data obtained at SK. The absence of a significant signal, that is, contributions to the total SK background and their angular variations has set upper bounds on a) the absolute flux of solar antineutrinos originated from ${}^{8}B$ neutrinos ${\Phi }_{\bar{\nu }}({}^{8}B)=<1.8\times 10^{5}c{m}^{-2}{s}^{-1}$ which is equivalent to an averaged conversion probability bound of P<3.5% (SSM-BP98 model) and b) their differential energy spectrum, the conversion probability is smaller than 8% for all $E_{e,vis}>6.5$ MeV going down the 5% level above $E_{e,vis}\approx 10$ MeV. It is shown that an antineutrino flux would have the net effect of enhancing the SK signal at {\em hep} neutrino energies. The magnitude of this enhancement would highly depend on the, otherwise rather uncertain, steepness of the solar neutrino spectrum at these energies.

Comments: 5 pages, 3 ps figures