Measurement of Coherent Elastic Neutrino-Nucleus Scattering from Reactor Antineutrinos

The 96.4 day exposure of a 3 kg ultralow noise germanium detector to the high flux of antineutrinos from a power nuclear reactor is described. A very strong preference $(p <1.2 ×10^{−3})$ for the presence of a coherent elastic neutrino-nucleus scattering $(CE⁢𝜈⁢NS)$ component in the data is found, when compared to a background-only model. No such effect is visible in 25 days of operation during reactor outages. The best-fit $CE⁢𝜈⁢NS$ signal is in good agreement with expectations based on a recent characterization of germanium response to sub-keV nuclear recoils. Deviations of order 60% from the standard model $CE⁢𝜈⁢NS$ prediction can be excluded using present data. Standing uncertainties in models of germanium quenching factor, neutrino energy spectrum, and background are examined.