Neutrino-4 anomaly: Oscillations or fluctuations?

We present a deep study of the Neutrino-4 data aimed at finding the statistical significance of the large-mixing short-baseline neutrino oscillation signal claimed by the Neutrino-4 collaboration at more than 3 sigma. We found that the results of the Neutrino-4 collaboration can be reproduced approximately only by neglecting the effects of the energy resolution of the detector. Including these effects, we found that the best fit is obtained for a mixing that is even larger, close to maximal, but the statistical significance of the short-baseline neutrino oscillation signal is only about 2.7 sigma if evaluated with the usual method based on Wilks' theorem. We show that the large Neutrino-4 mixing is in strong tension with the KATRIN, PROSPECT, STEREO, and solar nu(e) bounds. Using a more reliable Monte Carlo simulation of a large set of Neutrino-4-like data, we found that the statistical significance of the Neutrino-4 short-baseline neutrino oscillation signal decreases to about 2.2 sigma. We also show that it is not unlikely to find a best-fit point that has a large mixing, even maximal, in the absence of oscillations. Therefore, we conclude that the claimed Neutrino-4 indication in favor of short-baseline neutrino oscillations with very large mixing is rather doubtful. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

The statistical significance of the large-mixing short-baseline neutrino oscillation signal claimed by the Neutrino-4 collaboration is found to be only about 2.7 sigma, and this result is influenced by the energy resolution of the detector. Through a more reliable simulation, this significance decreases to around 2.2 sigma.