The antineutrino energy structure in reactor experiments

TL;DR

Recent reactor experiments have observed an unexpected energy structure in the antineutrino spectrum, likely due to inaccuracies in flux predictions, prompting analysis of experimental data and models to understand this anomaly.

Contribution

This work reviews the observed antineutrino energy structure, analyzes potential causes, and compares models to identify the most probable explanation related to flux prediction uncertainties.

Findings

Consistent excess of antineutrinos between 4 and 6 MeV observed

Current models have potential inaccuracies affecting flux predictions

Experimental data needed to refine models and understand the structure

Abstract

The recent observation of an energy structure in the reactor antineutrino spectrum is reviewed. The reactor experiments Daya Bay, Double Chooz and RENO have reported a consistent excess of antineutrinos deviating from the flux predictions, with a local significance of about 4$\sigma$ between 4 and 6 MeV of the positron energy spectrum. The possible causes of the structure are analyzed in this work, along with the different experimental approaches developed to identify its origin. Considering the available data and results from the three experiments, the most likely explanation concerns the reactor flux predictions and the associated uncertainties. Therefore, the different current models are described and compared. The possible sources of incompleteness or inaccuracy of such models are discussed, as well as the experimental data required to improve their precision.