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

TL;DR

This paper demonstrates that analyzing Earth matter effects on supernova neutrino signals can determine the neutrino mass hierarchy even at very small theta(13) values, using large water Cherenkov detectors.

Contribution

It introduces a method to identify neutrino mass hierarchy through supernova neutrino signals affected by Earth matter effects at extremely small theta(13).

Findings

Earth effects distinguish hierarchies if sin^2 theta(13) < 10^{-5}.

Observation of Earth effects indicates collective oscillations inside supernova.

Method applicable with two megaton water Cherenkov detectors, one shadowed by Earth.

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.