Results from the Baksan Experiment on Sterile Transitions (BEST)
The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos νe 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 νe and sterile neutrino (νs) states. A 3.414-MCi 51Cr νe source was placed at the center of two nested Ga volumes and measurements were made of the production of 71Ge through the charged current reaction, 71Ga (νe,e-)71Ge , at two average distances. The measured production rates for the inner and the outer targets, respectively, are [54.9-2.4+2.5(stat )±1.4 (syst ) ] and [55.6-2.6+2.7(stat )±1.4 (syst ) ] atoms of 71Ge /d . The ratio (R ) of the measured rate of 71Ge production at each distance to the expected rate from the known cross section and experimental efficiencies are Rin=0.79 ±0.05 and Rout=0.77 ±0.05 . The ratio of the outer to the inner result is 0.97 ±0.07 , 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 νe→νs oscillations with a relatively large Δ m2 (>0.5 eV2 ) and mixing sin22 θ (≈0.4 ).
Physical Review Letters
- Pub Date:
- June 2022
- Nuclear Experiment;
- High Energy Physics - Experiment
- Paper updated to final version