Revival of the Reactor Antineutrino Anomaly

TL;DR

This paper revisits the Reactor Antineutrino Anomaly using a 2023 flux calculation, finding a revival of the anomaly and analyzing sterile neutrino oscillation constraints with a comprehensive uncertainty assessment.

Contribution

It introduces the first summation model with a full uncertainty budget for reactor flux calculations and revisits the anomaly's significance and sterile neutrino constraints.

Findings

Reactor Antineutrino Anomaly revived to 2.2σ significance.

Global analysis with enlarged uncertainties reduces tension to 1.3σ.

Constraints on sterile neutrino parameters are updated considering new flux data.

Abstract

The Reactor Antineutrino Anomaly refers to the deficit observed between the average event rate measured in reactor antineutrino experiments with respect to the theoretical prediction. This anomaly was first identified in 2011 ($2.5\sigma$) as a consequence of the Huber-Muller reactor antineutrino flux calculation. It was thought to be resolved in 2021 as a result of new reactor antineutrino flux calculations, with a reduction to about $1 \sigma$. In this work, we examine the latest reactor antineutrino flux calculation published in 2023 by a French research group. This work represents the first summation model to include a comprehensive uncertainty budget. The result indicates a revival of the Reactor Antineutrino Anomaly at the level of $2.2\,\sigma$. We also consider the usual simplest explanation of the Reactor Antineutrino Anomaly by active-sterile neutrino oscillations. We present the constraints on the oscillation parameters and we derive a tension of $3.8\sigma$ with the results of gallium source experiments (Gallium Anomaly) taking into account also the solar neutrino and KATRIN bounds, that of the combined short-baseline reactor spectral ratio measurements, and that of the Daya Bay search for a sub-eV sterile neutrino. Since the tension may be due to underestimated systematic uncertainties and the main tension is between the gallium data and the other data, we finally present the results of a global analysis with enlarged gallium uncertainties, which reduce the global tension to $1.3\sigma$.