BEST Impact on Sterile Neutrino Hypothesis

TL;DR

The BEST experiment's results strongly support the sterile neutrino hypothesis, and combined analyses with other experiments suggest a possible sterile neutrino with specific mass and mixing parameters, impacting particle physics and cosmology.

Contribution

This paper provides the strongest experimental evidence for sterile neutrinos from the BEST results and combines them with other data to constrain sterile neutrino parameters.

Findings

BEST confirms gallium anomaly at >5σ significance.

Part of the BEST-favored parameter space is consistent with other experiments.

Joint analysis suggests a sterile neutrino with m²≈7.3 eV² and sin²2θ≈0.38.

Abstract

Recently the Baksan Experiment on Sterile Transitions (BEST) has presented results confirming the gallium anomaly -- a lack of electron neutrinos $\nu_e$ at calibrations of SAGE and GALLEX -- at the statistical significance exceeding 5$\,\sigma$. This result is consistent with explanation of the gallium anomaly as electron neutrino oscillations into sterile neutrino, $\nu_s$. Within this explanation the BEST experiment itself provides the strongest evidence for the sterile neutrino among all the previous anomalous results in the neutrino sector. We combine the results of gallium experiments with searches for sterile neutrinos in reactor antineutrino experiments (assuming CPT-conservation in the $3+1$ neutrino sector). While the "gallium" best fit point in the model parameter space (sterile neutrino mass squared $m_{\nu_s}^2\approx 1.25\,$eV$^2$, sterile-electron neutrino mixing $\sin^22\theta\approx 0.34$) is excluded by these searches, a part of the BEST-favored 2$\,\sigma$ region with $m^2_{\nu_s}>5\,$eV$^2$ is consistent with all of them. Remarkably, the regions advertised by anomalous results of the NEUTRINO-4 experiment overlap with those of the BEST experiment: the best fit point of the joint analysis is $\sin^22\theta\approx 0.38$, $m_{\nu_s}^2\approx7.3\,$eV$^2$, the favored region will be explored by the KATRIN experiment. The sterile neutrino explanation of the BEST results would suggest not only the extension of the Standard Model of particle physics, but also either serious modifications of the Standard Cosmological Model and Solar Model, or a specific modification of the sterile sector needed to suppress the sterile neutrino production in the early Universe and in the Sun.