Investigating the sources of low-energy events in a SuperCDMS-HVeV detector

TL;DR

This study investigates low-energy event excesses in a SuperCDMS-HVeV detector, identifying potential sources such as luminescence from detector components, and demonstrates competitive dark matter detection limits at very low energy thresholds.

Contribution

It is the first to analyze the sources of low-energy excess events in a SuperCDMS-HVeV detector and links these excesses to luminescence from printed circuit boards.

Findings

Excess events observed at tens of eV are likely due to luminescence from detector components.

Operation at 0 V enables setting competitive dark matter exclusion limits.

The excess is consistent across different voltages, indicating a common source.

Abstract

Recent experiments searching for sub-GeV/$c^2$ 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-gram silicon SuperCDMS-HVeV detector at three voltages across the crystal (0 V, 60 V 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 $\mathcal{O}(100)$ MeV/$c^2$, enabled by operation of the detector at 0 V potential and achievement of a very low $\mathcal{O}(10)$ eV threshold for nuclear recoils. Comparing the data acquired at 0 V, 60 V 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.