The High Energy Neutrino Nuisance at a Medium Baseline Reactor Experiment

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.