A Combined Analysis of the Reactor Antineutrino Anomaly Experiments in Search of a Sterile Neutrino

Abstract

The Reactor Antineutrino Anomaly refers to a collection of short baseline reactor experiments ($d<100\text{m}$) used in a 2011 analysis searching for oscillations into a sterile neutrino, which found a deficit in the overall antineutrino yields with 98.6\% confidence. While later analyses of these experiments exist, none have fully included the spectral information from all experiments that have it. Here, an analysis was performed of the original reactor anomaly experiments incorporating all the spectral information, using modern fluxes and an updated cross section. The fluxes tested were the 2012 Huber-Mueller flux, the 2017 Daya Bay flux (modifying the Huber-Mueller flux with a 7.8\% reduction for $^{235}$U), and the 2019 Estienne flux. Each flux was also tested with the addition of a Gaussian bump near $E_{\nu}\approx5\text{ MeV}$ to the $^{235}$U flux, which various experiments have indicated exists. Statistical assumptions were made such that the significance levels given would be upper bounds. Without the bump, a possible sterile neutrino was indicated at a significance level of up to $3.29\sigma$, though the highest significance came with the oldest flux (Huber-Mueller). A consistent deep minimum in the $\chi^{2}$ is present at $\Delta_{}m^{2}=2.35\text{ eV}^{2}$, being the deepest minimum for the Daya Bay and Estienne fluxes. With the 5 MeV bump the highest significance was $4.35\sigma$ with the Estienne flux, and the deepest $\chi^{2}$ minimum is located at $\Delta_{}m^{2}\approx0.42\text{ eV}^{2}$ for all fluxes, but the $\chi^{2}$ goodness of fit was generally worse.