Correlated Single- and Few-Electron Backgrounds Milliseconds after Interactions in Dual-Phase Liquid Xenon Time Projection Chambers

TL;DR

This study characterizes long-timescale single- and few-electron backgrounds in liquid xenon detectors, revealing their dependence on detector conditions and ruling out infrared photon stimulation as a mitigation strategy, thereby informing future dark matter searches.

Contribution

It provides a detailed characterization of delayed electron backgrounds in liquid xenon detectors and tests potential mitigation methods, advancing understanding of instrumental backgrounds in rare event detection.

Findings

Background rates follow power-laws with time after interactions.

Rates increase with higher extraction and drift fields.

Infrared light does not reduce electron background rates.

Abstract

We characterize single- and few-electron backgrounds that are observed in dual-phase liquid xenon time projection chambers at timescales greatly exceeding a maximum drift time after an interaction. These instrumental backgrounds limit a detector's sensitivity to dark matter and cosmogenic neutrinos. Using the ~150g liquid xenon detector at Purdue University, we investigate how these backgrounds, produced after 122keV $^{57}$Co Compton interactions, behave under different detector conditions. We find that the rates of single- and few-electron signals follow power-laws with time after the interaction. We observe linearly increasing rates with increased extraction field, and increased rates in the single-electron background with increased drift field. Normalizing the rates to the primary interaction's measured ionization signal, the rates increase linearly with the depth of the interaction. We test the hypothesis that infrared photons (1550nm) would stimulate and accelerate electron emission via photodetachment from impurities, but find that even 1 Watt of infrared light fails to reduce these backgrounds. We thus provide a characterization that can inform background models for low-energy rare event searches.