Signature of supernova neutrino flavor mixing in water Čerenkov detectors

We study supernova neutrino burst signals in large water Čerenkov detectors, examining the effects of mixing between ${\nu }_e$ and either ${\nu }_{\mu }$ or ${\nu }_{\tau }$ and taking account of charged current ${\nu }_e$ 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 ${\nu }_e$ on the one hand and ${\nu }_{\mu }$ and ${\nu }_{\tau }$ on the other, the steep increase in the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({\nu }_e,e^{-}){}_{}{}^{16}{}_{}{}^{}\mathrm{F}$ 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.