A coherent understanding of low-energy nuclear recoils in liquid xenon

TL;DR

This work tackles the challenge of interpreting low-energy nuclear recoils in liquid xenon detectors by linking the NR band to the energy dependence of $\mathcal{L}_{eff}$ and $\mathcal{Q}_y$. By constraining $\mathcal{L}_{eff}$ via the observable ratio $N_e/N_\gamma$ and employing a rigorous Monte Carlo treatment of threshold, efficiency, and detector resolution, the authors derive self-consistent estimates for $\mathcal{Q}_y$ and $\mathcal{L}_{eff}$ under several scenarios, identifying Case 2 as the most reasonable. They demonstrate how detector effects, particularly the 50% NR acceptance box and non-Poisson resolution, strongly influence dark matter exclusion limits, and they apply these methods to XENON10 and XENON100 to challenge recent light-dark-matter interpretations. The study emphasizes the need for simultaneous, in-situ measurements of $\mathcal{Q}_y$ and $\mathcal{L}_{eff}$ to reduce systematics and produce robust constraints on light DM. Overall, the paper provides a comprehensive framework to translate low-energy xenon signals into reliable DM limits while highlighting critical calibration needs.

Abstract

Liquid xenon detectors such as XENON10 and XENON100 obtain a significant fraction of their sensitivity to light (<10 GeV) particle dark matter by looking for nuclear recoils of only a few keV, just above the detector threshold. Yet in this energy regime a correct treatment of the detector threshold and resolution remains unclear. The energy dependence of the scintillation yield of liquid xenon for nuclear recoils also bears heavily on detector sensitivity, yet numerous measurements have not succeeded in obtaining concordant results. In this article we show that the ratio of detected ionization to scintillation can be leveraged to constrain the scintillation yield. We also present a rigorous treatment of liquid xenon detector threshold and energy resolution. Notably, the effective energy resolution differs significantly from a simple Poisson distribution. We conclude with a calculation of dark matter exclusion limits, and show that existing data from liquid xenon detectors strongly constrain recent interpretations of light dark matter.