A Review of NEST Models, and Their Application to Improvement of Particle Identification in Liquid Xenon Experiments

This paper discusses microphysics simulation of interactions in liquid xenon, the medium in many leading rare-event physics searches, and describes experimental observables useful to understanding detector performance. Scintillation and ionization yield distributions for signal and background are presented using the Noble Element Simulation Technique (NEST), a toolkit based on experimental data and simple, empirical formulae. NEST models of light and charge production as a function of particle type, energy, and electric field are reviewed, as well as of energy resolution and final pulse areas. After vetting of NEST against raw data, with several specific examples pulled from XENON, ZEPLIN, LUX / LZ, and PandaX, we interpolate and extrapolate its models to draw new conclusions on the properties of future detectors (e.g., XLZD), in terms of the best possible discrimination of electron(ic) recoil backgrounds from a potential nuclear recoil signal, especially WIMP dark matter. We discover that the oft-quoted value of 99.5% discrimination is overly conservative. NEST shows that another order of magnitude improvement (99.95% discrimination) can be achieved with a high photon detection efficiency (g1 ~ 15-20%) at reasonably achievable drift fields of 200 to 350 V/cm.