# SENSEI: Direct-Detection Constraints on Sub-GeV Dark Matter from a Shallow Underground Run Using a Prototype Skipper-CCD

## TL;DR

This paper reports new constraints on sub-GeV dark matter interactions with electrons using a prototype Skipper-CCD detector, demonstrating improved sensitivity and background reduction techniques in a shallow underground setting.

## Contribution

The study introduces a novel application of Skipper-CCD technology for direct dark matter detection, with innovative readout strategies to reduce background noise and set new experimental limits.

## Key findings

- Achieved world-leading constraints on dark matter-electron scattering for 500 keV to 5 MeV masses.
- Demonstrated significant reduction in one-electron background rate using amplifier-off readout.
- No events with three or more electrons observed in the dataset.

## Abstract

We present new direct-detection constraints on eV-to-GeV dark matter interacting with electrons using a prototype detector of the Sub-Electron-Noise Skipper-CCD Experimental Instrument. The results are based on data taken in the MINOS cavern at the Fermi National Accelerator Laboratory. We focus on data obtained with two distinct readout strategies. For the first strategy, we read out the Skipper-CCD continuously, accumulating an exposure of 0.177 gram-days. While we observe no events containing three or more electrons, we find a large one- and two-electron background event rate, which we attribute to spurious events induced by the amplifier in the Skipper-CCD readout stage. For the second strategy, we take five sets of data in which we switch off all amplifiers while exposing the Skipper-CCD for 120k seconds, and then read out the data through the best prototype amplifier. We find a one-electron event rate of (3.51 +- 0.10) x 10^(-3) events/pixel/day, which is almost two orders of magnitude lower than the one-electron event rate observed in the continuous-readout data, and a two-electron event rate of (3.18 +0.86 -0.55) x 10^(-5) events/pixel/day. We again observe no events containing three or more electrons, for an exposure of 0.069 gram-days. We use these data to derive world-leading constraints on dark matter-electron scattering for masses between 500 keV to 5 MeV, and on dark-photon dark matter being absorbed by electrons for a range of masses below 12.4 eV.