Measurement of Coherent Elastic Neutrino-Nucleus Scattering from Reactor Antineutrinos

Abstract

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 ($p<1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$) for the presence of a coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$) 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 $\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$ 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 $\mathrm{CE}\ensuremath{\nu}\mathrm{NS}$ prediction can be excluded using present data. Standing uncertainties in models of germanium quenching factor, neutrino energy spectrum, and background are examined.