Nuclear recoil scintillation and ionisation yields in liquid xenon from ZEPLIN-III data

TL;DR

This study measures how liquid xenon scintillates and ionizes when struck by nuclear recoils above 10 keVnr, using ZEPLIN-III data, detailed simulations, and a new analysis method to improve understanding for dark matter detection.

Contribution

It provides new measurements of scintillation and ionisation yields in liquid xenon, including a novel method that accounts for sub-threshold events, enhancing accuracy for dark matter experiments.

Findings

Scintillation yield decreases below ~40 keVnr

Ionisation yield increases as energy decreases

Results agree with recent independent measurements

Abstract

Scintillation and ionisation yields for nuclear recoils in liquid xenon above 10 keVnr (nuclear recoil energy) are deduced from data acquired using broadband Am-Be neutron sources. The nuclear recoil data from several exposures to two sources were compared to detailed simulations. Energy-dependent scintillation and ionisation yields giving acceptable fits to the data were derived. Efficiency and resolution effects are treated using a light collection Monte Carlo, measured photomultiplier response profiles and hardware trigger studies. A gradual fall in scintillation yield below ~40 keVnr is found, together with a rising ionisation yield; both are in good agreement with the latest independent measurements. The analysis method is applied to both the most recent ZEPLIN-III data, acquired with a significantly upgraded detector and a precision-calibrated Am-Be source, as well as to the earlier data from the first run in 2008. A new method for deriving the recoil scintillation yield, which includes sub-threshold S1 events, is also presented which confirms the main analysis.