OSCILLATION EFFECTS ON NEUTRINOS FROM THE EARLY PHASE OF A NEARBY SUPERNOVA

Abstract

Recent observations of atmospheric and solar neutrinos strongly support the phenomenon of neutrino oscillations — a manifestation of a nonzero and nondegenerate mass spectrum. Neutrinos emitted during stellar core collapse leading to a supernova are of the electron neutrino type at source — as for solar and reactor (anti-)neutrinos — and provide another useful tool in the search for flavor oscillations. Their propagation to an earth-bound detector involves length scales that can uniquely probe very small neutrino mass differences hitherto unobservable. Although the number of neutrinos emitted during the collapse phase is much smaller than that emitted in the post-bounce epoch (in which all flavors of neutrinos are emitted), a nearby supernova event may nevertheless register a substantial number of detections from the collapse phase at SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO). The measurement of the fluence of these neutrinos at SNO and the distortion of the spectrum detected at SK can yield valuable information about neutrino mass difference and mixing which are illustrated here in terms of two- and three-flavor oscillation models. In particular, we find that R SNO , the ratio of the calorimetric detection of the neutrino fluence via the neutral current channel to the total energy integrated fluence observed via the charged current channel at SNO, is a sensitive probe for oscillations. We also find that αn, the ratio of the nth central moments of the distributions seen at SK and SNO (charged current), can be a useful tool (especially for n=3) to look for neutrino oscillations.