Identifying Neutrino Mass Hierarchy at Extremely Small θ13 through Earth Matter Effects in a Supernova Signal

Collective neutrino flavor transformations deep inside a supernova are sensitive to the neutrino mass hierarchy even at extremely small values of θ13. 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 Earth, will enable us to distinguish between the hierarchies if sin2θ13 < or approx. 10-5, where long baseline neutrino experiments would be ineffectual