The High Energy Neutrino Nuisance at a Medium Baseline Reactor Experiment

TL;DR

Medium baseline reactor experiments aiming to determine the neutrino mass hierarchy face challenges from high-energy tail effects, but applying an energy-dependent weight in Fourier analysis can mitigate this issue and improve accuracy.

Contribution

The paper identifies a spurious dependence in Fourier-based hierarchy determination and proposes an energy-dependent weighting method to eliminate it and enhance results.

Findings

Spurious dependence on high-energy tail affects hierarchy determination.

Energy-dependent weighting reduces this dependence.

Improved accuracy in neutrino mass hierarchy identification.

Abstract

10 years from now medium baseline reactor experiments will attempt to determine the neutrino mass hierarchy from the differences (RL+PV) between the extrema of the Fourier transformed neutrino spectra. Recently Qian et al. have claimed that this goal may be impeded by the strong dependence of the difference parameter RL+PV on the reactor neutrino flux and on slight variations of Delta M^2_32. We demonstrate that this effect results from a spurious dependence of the difference parameter on the very high energy (8+ MeV) tail of the reactor neutrino spectrum. This dependence is spurious because the high energy tail depends upon decays of exotic isotopes and is insensitive to the mass hierarchy. An energy-dependent weight in the Fourier transform not only eliminates this spurious dependence but in fact increases the chance of correctly determining the hierarchy.