Superkamiokande and solar antineutrinos

We propose to exploit the angular distribution of the positrons emitted in the reaction νe + p → n + e+ to extract a possible antineutrino signal from the Superkamiokande background. From the statistics collected in just 101.9 days one obtains a model independent upper bound on the antineutrino flux Φν-(Eν-> 8.3 MeV) < 9 · 104 cm−2s−1 at the 95% C.L. By assuming the same energy spectrum as for the 8B neutrinos, the 95% C.L. bound is Φν-(Eν-> 8.3 MeV) < 6 · 104 cm−2s−1. Within three years of data taking, the sensitivity to νe → νe transition probability will reach the 1% level, thus providing a stringent test of hybrid oscillation models.