A Model of Nuclear Recoil Scintillation Efficiency in Noble Liquids

TL;DR

This paper presents a combined theoretical model using Lindhard's theory and Birk's law to explain the reduced scintillation efficiency in noble liquids caused by nuclear recoils, aiding dark matter detection.

Contribution

It introduces a unified approach to model scintillation efficiency reduction by integrating energy loss and quenching mechanisms, with parameters fitted to existing data.

Findings

Nuclear stopping power dominates energy loss in scintillation reduction.

Nonlinear scintillation response significantly contributes to quenching.

Model predictions align with observed scintillation yields in noble liquids.

Abstract

Scintillation efficiency of low-energy nuclear recoils in noble liquids plays a crucial role in interpreting results from some direct searches for Weakly Interacting Massive Particle (WIMP) dark matter. However, the cause of a reduced scintillation efficiency relative to electronic recoils in noble liquids remains unclear at the moment. We attribute such a reduction of scintillation efficiency to two major mechanisms: 1) energy loss and 2) scintillation quenching. The former is commonly described by Lindhard's theory and the latter by Birk's saturation law. We propose to combine these two to explain the observed reduction of scintillation yield for nuclear recoils in noble liquids. Birk's constants $kB$ for argon, neon and xenon determined from existing data are used to predict noble liquid scintillator's response to low-energy nuclear recoils and low-energy electrons. We find that energy loss due to nuclear stopping power that contributes little to ionization and excitation is the dominant reduction mechanism in scintillation efficiency for nuclear recoils, but that significant additional quenching results from the nonlinear response of scintillation to the ionization density.