Nuclear and electron scattering by neutrinos and dark matter in condensed systems

Low-threshold dark matter detectors, in particular cryogenic detectors based on dielectric materials, are among the best tools for probing sub-GeV dark matter masses. In the coming years, detectors of this type will become sensitive to solar neutrino scattering. Previous work has shown that, for dark matter scattering at very low recoil energies, one must include collective excitations of the electrons in the solid. In this work, we have computed the collective excitations due to neutrino scattering on electrons and nuclei. We find the full electron-scattering response at leading order is captured by five structure factors and identify the leading component with the electron energy-loss function. Then, using silicon and germanium detectors as an example, we perform a dark matter sensitivity study and compute their respective neutrino floors—taking the electronic structure into account for all dark matter and neutrino scattering channels. Lastly, we show that these detectors are sensitive to unexplored scenarios of beyond-Standard Model neutrino physics, within the exposure required to reach the neutrino floor.