A Search for Electron Neutrino Transitions to Sterile States in the BEST Experiment

Abstract

The Baksan Experiment on Sterile Transitions (BEST) probes the gallium anomaly and its possible connections to oscillations between active and sterile neutrinos. Based on the Gallium-Germanium Neutrino Telescope (GGNT) technology of the SAGE experiment, BEST employs two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Oscillations on this short scale could produce deficits in the 71 Ge production rates within the two zones, as well as a possible rate difference between the zones.From July 5th to October 13th 2019, the two-zone target was exposed to a primarily monoenergetic, 3.4-MCi 51 Cr neutrino source 10 times for a total of 20 independent 71 Ge extractions from the two Ga targets. The 71 Ge production rates from the neutrino source were measured from July 2019 to March 2020. At the end of these measurements, the counters were filled with 71 Ge doped gas and calibrated during November 2020. In this paper, results from the BEST sterile neutrino oscillation experiment are presented in details. The ratio of the measured 71 Ge production rates to the predicted rates for the inner and the outer target volumes are calculated from the known neutrino capture cross section. Comparable deficits in the measured ratios relative to predicted values are found for both zones, with the 4σ deviations from unity consistent with the previously reported gallium anomaly. If interpreted in the context of neutrino oscillations, the deficits give best

No CC-NSI explanation of the Gallium anomaly

“…Depending on the cross section model [10,11], the statistical significance of the Gallium anomaly was between 1.9σ and 2.7σ. The results from the GALLEX and SAGE experiments have been recently confirmed by the BEST collaboration [12,13], which performed two measurements using two detector volumes. The whole detector is cylindrical, with a smaller inner spherical part surrounding the source and a larger outer part.…”

“…The combined analysis of all Gallium data requires sin 2 2θ 14 0.2, see Ref. [12,13]. This result is in tension with the bounds on sin 2 2θ 14 obtained from the analysis of data from solar neutrino experiments [17] and reactor rate data [18].…”

“…The ratios of measured to expected events in the measurements of GALLEX (red), SAGE (blue) and BEST (green). The grey band shows the average ratio, R = 0.80 ± 0.047 [13]. 0.047 [13], depicted by the grey band, is mostly due to the measurement of the BEST experiment.…”

“…The grey band shows the average ratio, R = 0.80 ± 0.047 [13]. 0.047 [13], depicted by the grey band, is mostly due to the measurement of the BEST experiment.…”

White Paper on Light Sterile Neutrino Searches and Related Phenomenology

“…A preliminary analysis [290] of reported MicroBooNE results [286][287][288][289] finds a preference for ν e disappearance in the various results (which are not statistically independent) at the ∼2σ level. This disappearance requires large mixing, sin 2 (2θ 14 ) ∼ 0.2 − 0.3 with a mass-squared splitting of ∼1.4 eV 2 , overlapping with the region preferred by the Gallium anomaly [137,260,293,294]. However, a more recent analysis [180] incorporating systematic uncertainties from the collaboration's data release and accounting for neutrino energy reconstruction smearing finds this preference for ν e disappearance to be statistically insignificant.…”