Revised neutrino-gallium cross section and prospects of BEST in resolving the gallium anomaly

Abstract

Oð1ÞeV sterile neutrino can be responsible for a number of anomalous results of neutrino oscillation experiments. This hypothesis may be tested at short base line neutrino oscillation experiments, several of which are either ongoing or under construction. Here, we concentrate on the so-called gallium anomaly, found by SAGE and GALLEX experiments, and its foreseeable future tests with BEST experiment at Baksan Neutrino Observatory. We start with a revision of the neutrino-gallium cross section that is performed by utilizing the recent measurements of the nuclear final state spectra. We accordingly correct the parameters of gallium anomaly and refine the BEST prospects in testing it and searching for sterile neutrinos. We further evolve the previously proposed idea to investigate the anomaly with 65 Zn artificial neutrino source as a next option available at BEST and estimate its sensitivity to the sterile neutrino model parameters following the Bayesian approach. We show that after the two stages of operation BEST will make 5σ discovery of the sterile neutrinos, if they are behind the gallium anomaly.

Status of light sterile neutrino searches

“…In Sec. 4.2.2 we briefly describe the BEST experiment [132,133] in Baksan in Russia: the new 71 Ga radiochemical experiment plans to apply 3 MCi 51 Cr neutrino source fron July 2019. In Sec.…”

“…A new gallium experiment, BEST, has been proposed for the Baksan Neutrino Observatory [132,133]. BEST aims to provide a definite experimental test of the gallium anomaly (Sec.…”

“…Measurements are due to start in July 2019 [139]. Figure 18: BEST sensitivity to electron neutrino disappearance based on a single run with a 51 Cr source [133].…”

“…In the first run, the combined event rate in both gallium vessels is expected to be ∼65 per day. Based on the statistics expected for the total exposure, the ν e neutrino flux crossing both vessels can be determined with an accuracy of 4.2 % [133]. Fig.…”

“…While this sensitivity is relatively low compared to many of the running short-baseline reactor antineutrino experiments, BEST is nevertheless very interesting because it is sensitive to the disappearance of electron neutrinos (instead of antineutrinos). Assuming not one but two source runs, the second potentially with a 65 Zn neutrino source, the authors state that they can exclude the gallium anomaly at a 5σ significance level [133].…”