SENSEI at SNOLAB: Single-Electron Event Rate and Implications for Dark Matter

TL;DR

The SENSEI experiment at SNOLAB achieved a record low single-electron event rate, enabling new constraints on sub-GeV dark matter, with improvements attributed to upgraded sensors and detector design.

Contribution

This work reports the first results from a major upgrade of the SENSEI detector, significantly reducing the single-electron background and setting new limits on dark matter interactions.

Findings

Single-electron event rate of (1.39 ± 0.11) × 10^{-5} e^-/pix/day

Order-of-magnitude improvement over previous detectors

Set constraints on sub-GeV dark matter candidates

Abstract

We present results from data acquired by the SENSEI experiment at SNOLAB after a major upgrade in May 2023, which includes deploying 16 new sensors and replacing the copper trays that house the CCDs with a new light-tight design. We observe a single-electron event rate of $(1.39 \pm 0.11) \times 10^{-5}$ e$^-$/pix/day, corresponding to $(39.8 \pm 3.1)$ e$^-$/gram/day. This is an order-of-magnitude improvement compared to the previous lowest single-electron rate in a silicon detector and the lowest for any photon detector in the near-infrared-ultraviolet range. We use these data to obtain a 90% confidence level upper bound of $1.53 \times 10^{-5}$ e$^-$/pix/day and to set constraints on sub-GeV dark matter candidates that produce single-electron events. We hypothesize that the data taken at SNOLAB in the previous run, with an older tray design for the sensors, contained a larger rate of single-electron events due to light leaks. We test this hypothesis using data from the SENSEI detector located in the MINOS cavern at Fermilab.