Recent experiments searching for sub-GeV/c2 dark matter have observed event excesses close to their respective energy thresholds. Although specific 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-g silicon SuperCDMS-HVeV detector at three voltages across the crystal (0, 60 and 100 V). The 0 V 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 0 V potential and achievement of a very low O(10) eV threshold for nuclear recoils. Comparing the data acquired at 0, 60 and 100 V 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.
Bibliographical noteFunding Information:
We thank Noemie Bastidon for her work in the preliminary design of our optical fiber setup and wire bonding. We gratefully acknowledge support from the U.S. Department of Energy (DOE) Office of High Energy Physics and from the National Science Foundation (NSF). This work was supported in part under NSF Grants No. 1809730 and No. 1707704, as well as by the Arthur B. McDonald Canadian Astroparticle Physics Research Institute, NSERC Canada, the Canada Excellence Research Chair Fund, Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Project No. 420484612 and under Germany’s Excellence Strategy—EXC 2121 “Quantum Universe”—390833306, and the Department of Atomic Energy Government of India (DAE) under the project “Research in basic sciences” (Dark matter). Fermilab is operated by Fermi Research Alliance, LLC, under Contract No. DE-AC02-37407CH11359 with the U.S. Department of Energy. Pacific Northwest National Laboratory (PNNL) is operated by Battelle Memorial Institute for the DOE under Contract No. DE-AC05-76RL01830. SLAC is operated under Contract No. DEAC02-76SF00515 with the United States Department of Energy.
© 2022 authors. Published by the American Physical Society.