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 Φ ν ( 8 B)⩽1.8×10 5 cm −2 s −1 which is equivalent to an averaged conversion probability bound of P 6.5 MeV going down the 5% level above Ee,vis≈10 MeV. It is shown that an antineutrino flux would have the net effect of enhancing the SK signal at hep neutrino energies. The magnitude of this enhancement would highly depend on the, otherwise rather uncertain at this moment, steepness of the solar neutrino spectrum at these energies.