The SABRE South Experiment: Simulation and analysis of the target NaI(Tl) Crystals

The SABRE (Sodium-iodide with Active Background REjection) experiment aims to search for the dark matter annual modulation signal with ultra-pure NaI(Tl) crystals. Twin detectors in different hemispheres, SABRE South at the Stawell Underground Physics Laboratory (SUPL) in Australia, and SABRE North at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy, will be commissioned to disentangle seasonal or site-related effects from the dark-matter-like modulated signal. The SABRE South detector consists of an array of seven ultra-pure NaI(Tl) crystals surrounded by a 12 kL liquid scintillator veto system placed inside passive shielding to reduce the intrinsic and external background contributions. In order to attain the sensitivity to test the results reported by DAMA/LIBRA, SABRE is working to produce NaI(Tl) crystals with low background in the 1-6 keVee recoil region where DAMA/LIBRA reports a clear modulation. The radiogenic and cosmogenic contaminants dominate the signals produced in the crystals in this region, but noise introduced by the photomultipliers and readout system can also become important. This article presents results on the simulation of the expected background from radiogenic and cosmogenic contamination. Studies to understand and reduce noise associated with the SABRE South crystal PMTs and their electronics are briefly discussed.