Interpreting Reactor Antineutrino Anomalies

Abstract

The experimental and theoretical research on the physics of massive neutrinos is based on the standard paradigm of three-neutrino mixing, which describes the oscillations of neutrino flavors measured in solar, atmospheric, and long-baseline experiments. However, several anomalies, corresponding to an $L/E$ of 1m/MeV, could be interpreted by involving sterile neutrinos, as in the Reactor Antineutrino Anomaly (RAA) and Gallium anomaly. STEREO was designed to investigate this conjecture, which could potentially extend the Standard Model (SM). The detector provides a comprehensive study of anomalies for a pure $^{235}\text{U} $ antineutrino spectrum, using a Highly Enriched Uranium (HEU) core. We describe an analysis of the full set of data generated by STEREO and an accurate prediction of reactor antineutrinos. The measured antineutrino energy spectrum suggests that the anomalies originate from biases in nuclear experimental data used for predictions, while rejecting the hypothesis of a light sterile neutrino. Our result supports the neutrino content of the SM and establishes a new reference for the $^{235}\text{U}$ antineutrino energy spectrum.