The Reactor Antineutrino Anomaly

TL;DR

This paper identifies a significant discrepancy between observed and predicted reactor antineutrino fluxes, suggesting the possible existence of a new neutrino state, supported by combined experimental data analysis.

Contribution

It provides a revised flux evaluation and demonstrates a statistically significant reactor antineutrino anomaly indicating potential new physics beyond the standard model.

Findings

Observed-to-predicted event ratio is 0.943(0.023).

Anomaly suggests a possible fourth neutrino state with specific oscillation parameters.

Combined data disfavors no-oscillation hypothesis at 99.8% confidence level.

Abstract

Recently new reactor antineutrino spectra have been provided for 235U, 239Pu, 241Pu and 238U, increasing the mean flux by about 3 percent. To good approximation, this reevaluation applies to all reactor neutrino experiments. The synthesis of published experiments at reactor-detector distances <100 m leads to a ratio of observed event rate to predicted rate of 0.976(0.024). With our new flux evaluation, this ratio shifts to 0.943(0.023), leading to a deviation from unity at 98.6% C.L. which we call the reactor antineutrino anomaly. The compatibility of our results with the existence of a fourth non-standard neutrino state driving neutrino oscillations at short distances is discussed. The combined analysis of reactor data, gallium solar neutrino calibration experiments, and MiniBooNE-neutrino data disfavors the no-oscillation hypothesis at 99.8% C.L. The oscillation parameters are such that |Delta m_{new}^2|>1.5 eV^2 (95%) and sin^2(2\theta_{new})=0.14(0.08) (95%). Constraints on the theta13 neutrino mixing angle are revised.