Identifying neutrino mass hierarchy at extremely small theta(13) through Earth matter effects in a supernova signal

Abstract

Collective neutrino flavor transformations deep inside a supernova are sensitive to the neutrino mass hierarchy even at extremely small values of theta(13). Exploiting this effect, we show that comparison of the antineutrino signals from a galactic supernova in two megaton class water Cherenkov detectors, one of which is shadowed by the Earth, will enable us to distinguish between the hierarchies if sin^2 theta(13) < 10^{-5}. On the other hand, the observation of Earth effects in the inverted hierarchy for sin^2 theta(13) > 10^{-3} will provide a robust observable signature of collective oscillations occurring deep inside the supernova.