Signature of supernova neutrino flavor mixing in water Čerenkov detectors

It is shown that the characteristic count rates and angular distributions from supernova neutrino-induced events can depend sensitively on the degree of neutrinos flavor mixing.

Abstract

We study supernova neutrino burst signals in large water \ifmmode \check{C}\else \v{C}\fi{}erenkov detectors, examining the effects of mixing between ${\ensuremath{\nu}}_{e}$ and either ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ or ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ and taking account of charged current ${\ensuremath{\nu}}_{e}$ capture on oxygen in the detector. We show that the characteristic count rates and angular distributions from supernova neutrino-induced events can depend sensitively on the degree of neutrino flavor mixing. This sensitivity results from the different average energies expected in supernova models for ${\ensuremath{\nu}}_{e}$ on the one hand and ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ and ${\ensuremath{\nu}}_{\ensuremath{\tau}}$ on the other, the steep increase in the $^{16}\mathrm{O}({\ensuremath{\nu}}_{e},{e}^{\ensuremath{-}})^{16}\mathrm{F}$ cross section with neutrino energy, and the backward-peaked nature of the exit channel electron in this reaction. Neutrino flavor-mixing effects would be identifiable in the super Kamiokande detector for the neutrino burst of a galactic supernova.