Electron Recoils from Light Dark Matter: Ionisation Yields in Silicon and the Exposure Needed Below One GeV

This study computes electron recoil signals from light dark matter scattering in silicon, for candidate masses from 1 MeV to 1 GeV, using a reference electron cross section and a simple ionisation yield model. Below about 100 MeV the number of electron-hole pairs per event falls to one or two, so the signal lives in the lowest charge bins where dark counts and leakage currents dominate real detectors. The rate per kilogram-year is large at the reference cross section, but the useful rate is the rate in bins that a detector can keep quiet, and the paper separates the two throughout. Candidates are also screened against a mass-dependent density bound, which removes none of this mass range because the bound rises steeply only at much larger masses when expressed per particle. All results are computed, not measured.