Improving sensitivity to low-mass dark matter in LUX using a novel electrode background mitigation technique

TL;DR

This paper introduces a machine learning method to reduce electrode background noise in xenon detectors, significantly enhancing the sensitivity of low-mass dark matter searches and setting new limits on particle interactions.

Contribution

A novel ionization pulse shape-based machine learning technique for electrode background rejection in xenon TPCs, improving low-mass dark matter detection sensitivity.

Findings

Improved Poisson limits on low-mass DM by a factor of 2-7.

Applied technique to LUX data, setting strong constraints on DM with masses 0.15-10 GeV.

Technique is promising for future experiments like LZ and XENONnT.

Abstract

This paper presents a novel technique for mitigating electrode backgrounds that limit the sensitivity of searches for low-mass dark matter (DM) using xenon time projection chambers. In the LUX detector, signatures of low-mass DM interactions would be very low energy ($\sim$keV) scatters in the active target that ionize only a few xenon atoms and seldom produce detectable scintillation signals. In this regime, extra precaution is required to reject a complex set of low-energy electron backgrounds that have long been observed in this class of detector. Noticing backgrounds from the wire grid electrodes near the top and bottom of the active target are particularly pernicious, we develop a machine learning technique based on ionization pulse shape to identify and reject these events. We demonstrate the technique can improve Poisson limits on low-mass DM interactions by a factor of $2$-$7$ with improvement depending heavily on the size of ionization signals. We use the technique on events in an effective $5$ tonne$\cdot$day exposure from LUX's 2013 science operation to place strong limits on low-mass DM particles with masses in the range $m_{\chi}\in0.15$-$10$ GeV. This machine learning technique is expected to be useful for near-future experiments, such as LZ and XENONnT, which hope to perform low-mass DM searches with the stringent background control necessary to make a discovery.