Abstract
The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the “gallium anomaly,” which could be interpreted as evidence for oscillations between and sterile neutrino () states. A 3.414-MCi source was placed at the center of two nested Ga volumes and measurements were made of the production of through the charged current reaction, , at two average distances. The measured production rates for the inner and the outer targets, respectively, are [] and [] atoms of . The ratio () of the measured rate of production at each distance to the expected rate from the known cross section and experimental efficiencies are and . The ratio of the outer to the inner result is , which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20%–24% lower than expected, thus reaffirming the anomaly. These results are consistent with oscillations with a relatively large () and mixing ().
- Received 23 September 2021
- Revised 18 January 2022
- Accepted 28 February 2022
DOI:https://doi.org/10.1103/PhysRevLett.128.232501
© 2022 American Physical Society