HEP In the literature: open

Why do gallium detectors see about 20 percent fewer neutrino captures?

In plain words

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 statement

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.

What would settle it

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.

Status in the literature

Unverified 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.