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Particle Physics Seminars at BNL

Results from the Baksan Experiment on Sterile Transitions

by Steve Elliott (LANL)


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+2.5−2.4(stat)±1.4(syst)) and (55.6+2.7−2.6(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=0.791±0.05 and Rout=0.766±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 Δm2 (>1 eV2) and mixing sin22θ (≈0.4).

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Angelo Di Canto