Results from a 3.1 kg day Target Exposure with Skipper CCDs from DAMIC at SNOLAB and other Beyond the Standard Model Searches with Semiconductor Detectors

Abstract

We present here progress on a dark matter (DM) and neutrionless double beta decay (\nldbd) experimental search. We constrained the WIMP-nucleon scattering cross section $<9 \ \rm GeV / c^2$ in a silicon target with an 11 kg days exposure from CCD detectors in the DAMIC at SNOLAB experiment. We also observed an unexplained excess of $17.1\pm6.7$ bulk events with exponential decay length of $67 \pm 37 \ \rm eV_{ee}$ above our background model. To investigate, we deployed skipper CCDs with significantly lower readout noise at SNOLAB and acquired 3.1 kg days\textemdash the largest skipper CCD exposure ever recorded\textemdash of data with an analysis threshold ($10 \%$ reconstruction efficiency) of $6 \ \rm e^-$. We found a population of 11 (15) clusters below 200 (400) $\rm eV_{ee}$, which is above the expected background rate. We characterized this excess over the known bulk backgrounds as a decaying exponential with $12.3 \pm 3.9$ events and decay length of $89 \pm 30 \ \rm eV_{ee}$. A comparison of the energy scale and event rate of the two excesses suggest the data between the traditional and skipper CCD data sets are compatible and could share a common origin. We also operated skipper CCDs at the Modane Underground Laboratory and constrained new parameter space for the DM-$\rm e^-$ scattering cross section in the mass range $1.6\text{-}1000 \ \rm MeV / c^2$ for the ultra-light and $1.5\text{-}15.1 \ \rm MeV / c^2$ for the heavy mediator. Finally, as a proof-of-concept for the Selena Neutrino Experiment, we developed a pixelated amorphous selenium sensor sensitive to single $\gamma/\beta$ interactions.