Researchers with the TEXONO experiment used very low-threshold germanium detectors to search for coherent elastic scattering of reactor electron antineutrinos off whole nuclei. The experiment ran at the Kuo-Sheng Reactor Neutrino Laboratory using electro-cooled p-type point-contact germanium detectors of 523 g and 1,434 g. They report results from a combined exposure of 404 kilogram-days with the reactor on and 813.7 kilogram-days with the reactor off, with a detector threshold of 200 eV electron-equivalent energy.

Coherent elastic neutrino-nucleus scattering (often abbreviated CEνNS) is a Standard Model process in which a low-energy neutrino scatters off an entire nucleus at once. Coherence boosts the interaction rate because the scattering amplitudes from many nucleons add together. The effect is strongest when the neutrino momentum transfer is small, which is the case for reactor antineutrinos. The downside is that the nucleus recoils with only a tiny kinetic energy, typically well below a few kilo-electronvolts, so experiments need detectors that can see sub-keV signals.

To convert the tiny nuclear recoils into the measured ionization signal, the team used the Lindhard model to describe the quenching factor — the suppression of ionization yield from nuclear recoils compared with electron recoils. That model is parameterized by a single parameter k. Using a benchmark value k = 0.162, they set an upper limit of ρ < 2.0 at 90% confidence level, where ρ is the ratio of the observed νA_el (CEνNS) rate to the Standard Model prediction. Using the Standard Model prediction for the CEνNS rate, they also exclude values of k > 0.205 at 90% confidence. From the same data they derive a bound on an anomalous neutrino magnetic moment of μν < 5.9 × 10^−10 Bohr magnetons at 90% confidence level.