Daily and annual modulation rate of low mass dark matter in silicon detectors

Abstract

Low-threshold solid-state detectors with single electron excitation sensitivity can probe nuclear recoil energies in the sub-100 eV range, coinciding with the typical threshold displacement energies in the detector material. We investigate the daily and annual modulation of the observable event rate for dark matter mass ranging from 0.2 to 5 GeV/c^2 in a silicon detector, considering the energy threshold and the direction of the nuclear recoil. The data for the energy threshold is obtained from a molecular dynamics simulation. It is shown that the directional dependence of the threshold energy and the motion of the laboratory result in the modulation of the interaction event rate. We demonstrate silicon’s average annual interaction rate is more considerable than germanium for low-mass dark matter. However, their event rates take a similar trend in large dark matter masses. Thus, silicon can be a reliable target to discriminate low-mass dark matter from backgrounds. We also find 8-hour and 12-hour periodicities in the time series of event rates for silicon detectors due to the 45-degree symmetry in the silicon crystal structure.