The Neutrino Mass Hierarchy from Nuclear Reactor Experiments

TL;DR

This study uses extensive simulations to evaluate how reactor neutrino experiments can determine the neutrino mass hierarchy, considering various factors like analysis methods, parameters, and baselines, and proposes solutions to analysis issues.

Contribution

It provides a comprehensive simulation-based analysis of reactor neutrino experiments, identifying optimal configurations and addressing analysis biases for hierarchy determination.

Findings

Weighted Fourier transform removes spectral analysis bias.

Optimal baselines and detector locations are identified.

Reactor experiments can confidently determine the hierarchy despite degeneracies.

Abstract

10 years from now reactor neutrino experiments will attempt to determine which neutrino mass eigenstate is the most massive. In this letter we present the results of more than seven million detailed simulations of such experiments, studying the dependence of the probability of successfully determining the mass hierarchy upon the analysis method, the neutrino mass matrix parameters, reactor flux models, geoneutrinos and, in particular, combinations of baselines. We show that a recently reported spurious dependence of the data analysis upon the high energy tail of the reactor spectrum can be removed by using a weighted Fourier transform. We determine the optimal baselines and corresponding detector locations. For most values of the CP-violating, leptonic Dirac phase delta, a degeneracy prevents NOvA and T2K from determining either delta or the hierarchy. We determine the confidence with which a reactor experiment can determine the hierarchy, breaking the degeneracy.