Cherenkov Related Backgrounds in the DarkSide-50 Experiment

Abstract

Weakly Interacting Massive Particles (WIMPs) remain the most popular dark matter candidate as of 2018. DarkSide-50 is a dark matter direct detection experiment at Gran Sasso National Laboratory in Italy. The primary mission of DarkSide-50 is to detect the nuclear recoil signals created by WIMPs scattering off Argon nuclei in a background-free operation.

While DarkSide-50 had demonstrated various background suppression techniques toward the background-free operation, Cherenkov radiation in coincidence with LAr scintillation remains the most severe background. In this work, I will first describe the discovery of this troublesome background in a non-blind analysis, followed by detailed background characterizations in a GEANT4-based Monte Carlo simulation. I will take you through various benchmarks of the background study, from tuning the Cherenkov related optics, to building data-driven F90 and S2 models, to exploring the analysis cuts, and finally to validating the background predictions in a recently published blind analysis. The study of Cherenkov background turns out to be crucial to establishing the background-free liquid argon technology in the field.