Charge Trap Analysis in a SENSEI Skipper-CCD: Understanding Low-Energy Backgrounds in Rare-Event Searches

TL;DR

This study characterizes charge traps in a Skipper-CCD used in rare-event searches, revealing that a subset of traps does not significantly contribute to low-energy backgrounds, aiding in background mitigation strategies.

Contribution

It provides the first detailed trap characterization in a SENSEI-like Skipper-CCD, linking defect properties to background levels in rare-event detection.

Findings

A subset of traps does not significantly contribute to backgrounds.

Charge-pumping technique effectively identifies trap dipoles.

Further work needed to assess uncharacterized traps.

Abstract

Skipper Charge-Coupled Devices (Skipper-CCDs) are ultra-low-threshold detectors capable of detecting energy deposits in silicon at the eV scale. Increasingly used in rare-event searches, one of the major challenges in these experiments is mitigating low-energy backgrounds. In this work, we present results on trap characterization in a silicon Skipper-CCD produced in the same fabrication run as the SENSEI experiment at SNOLAB. Lattice defects contribute to backgrounds in rare-event searches through single-electron charge trapping. To investigate this, we employ the charge-pumping technique at different temperatures to identify dipoles produced by traps in the CCD channel. We fully characterize a fraction of these traps and use this information to extrapolate their contribution to the single-electron background in SENSEI. We find that this subpopulation of traps does not contribute significantly but more work is needed to assess the impact of the traps that can not be characterized.