Determination of the mass hierarchy with medium-baseline reactor-neutrino experiments

TL;DR

Future medium-baseline reactor antineutrino experiments can determine the neutrino mass hierarchy with high confidence if optimized for baseline length and energy resolution, achieving significant sensitivity after several years.

Contribution

This study analyzes how baseline length and energy resolution affect the sensitivity of reactor experiments in determining the neutrino mass hierarchy, providing optimal parameters for future setups.

Findings

Optimal baseline length is 40-55 km.

High confidence in hierarchy determination after 5-15 years.

Can measure mixing parameters with ~0.5% accuracy.

Abstract

I discuss the sensitivity of future medium baseline reactor antineutrino experiments on the neutrino mass hierarchy. By using the standard chi^2 analysis, we find that the sensitivity depends strongly on the baseline length L and the energy resolution (delta E/E)^2 = (a/ E/MeV)^2 + b^2, where a and b parameterize the statistical and systematic uncertainties, respectively. The optimal length is found to be L ~ 40-55 km, the larger resolution the shorter optimal L. For a 5 kton detector (with 12% weight fraction of free proton) placed at L ~ 50 km away from a 20 GW_th reactor, an experiment would determine the mass hierarchy with (Delta chi^2)_min ~ 9 on average after 5 (15) or more years of running with the (a, b) = (2, 0.5)% ((3, 0.5)%) energy resolution. This type of experiment can also measure the relevant mixing parameters with the accuracy of ~ 0.5%.