PNNL

Abstract

Recent experiments searching for sub-GeV/c2 dark matter have observed event excesses close to their respective energy thresholds. Although specic to the individual technologies, the measured excess event rates have been consistently reported at or below event energies of a few-hundred eV, or with charges of a few electron-hole pairs. In the present work, we operated a 1-gram silicon SuperCDMS-HVeV detector at three voltages across the crystal (0 V, 60V and 100 V). The 0V data show an excess of events in the tens of eV region. Despite this event excess, we demonstrate the ability to set a competitive exclusion limit on the spin-independent dark matter{nucleon elastic scattering cross section for dark matter masses of O(100) MeV/c2, enabled by operation of the detector at 0V potential and achievement of a very low O(10) eV threshold for nuclear recoils. Comparing the data acquired at 0 V, 60V and 100V potentials across the crystal, we investigated possible sources of the unexpected events observed at low energy. The data indicate that the dominant contribution to the excess is consistent with a hypothesized luminescence from the printed circuit boards used in the detector holder.