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Title: Why do gallium detectors see about 20 percent fewer neutrino captures?
Plain: Experiments placing strong radioactive neutrino sources inside gallium consistently record fewer captures than predicted. The cause, new physics or a wrong cross section, is unknown.
Precise: The BEST (2022), GALLEX and SAGE source experiments measure $R = \mathrm{observed}/\mathrm{predicted} \sim 0.8$ for Ga-71(nu_e, e-)Ge-71 with Cr-51 and Ar-37 sources, about $4\sigma$ below 1. Determine whether the deficit comes from the capture cross section (Ge-71 excited-state transitions, half-life), the source activity, or oscillation, in tension with reactor and solar limits.
Settled by: An independent source experiment with a different target and an improved measurement of the Ga-71 to Ge-71 matrix elements and Ge-71 half-life.
Kind: well-posed
Answer type: identification
References: (empty)
Literature status: open
Status note: Remeasurements of the Ge-71 half-life (2023 to 2024) did not remove the deficit; sterile oscillation explanations conflict with reactor and solar data.
Posed since: (empty)