Mass Hierarchy Determination via future Atmospheric Neutrino Detectors

TL;DR

This study evaluates how future atmospheric neutrino detectors can determine the neutrino mass hierarchy by analyzing survival rates and matter effects, using detailed simulations and statistical methods.

Contribution

It compares the effectiveness of water Cherenkov and magnetized iron detectors in identifying the neutrino mass hierarchy through comprehensive simulations.

Findings

Both detector types show significant sensitivity to the hierarchy.

Matter effects enhance the ability to distinguish the hierarchy.

Detector performance depends on energy and path-length measurements.

Abstract

We study the problem of determination of the sign of Delta m^2_{31}, or the neutrino mass hierarchy, through observations of atmospheric neutrinos in future detectors. We consider two proposed detector types : (a) Megaton sized water Cerenkov detectors, which can measure the survival rates of nu_\mu + \bar{\nu}_\mu and nu_e + \bar{\nu}_e and (b) 100 kton sized magnetized iron detectors, which can measure the survival rates of \nu_\mu and \bar{\nu}_\mu. For energies and path-lengths relevant to atmospheric neutrinos, these rates obtain significant matter contributions from P_{\mu e}, P_{\mu \mu} and P_{ee}, leading to an appreciable sensitivity to the hierarchy. We do a binned \chi^2 analysis of simulated data in these two types of detectors which includes the effect of smearing in neutrino energy and direction and incorporates detector efficiencies and relevant statistical, theoretical and systematic errors. We also marginalize the \chi^2 over the allowed ranges of neutrino parameters in order to accurately account for their uncertainties. Finally, we compare the performance of both types of detectors vis a vis the hierarchy determination.