Monte Carlo simulation of the SABRE PoP background

Abstract

SABRE (Sodium-iodide with Active Background REjection) is a direct dark matter search experiment based on an array of radio-pure NaI(Tl) crystals surrounded by a liquid scintillator veto. Twin SABRE experiments in the Northern and Southern Hemispheres will differentiate a dark matter signal from seasonal and local effects. The experiment is currently in a Proof-of-Principle (PoP) phase, whose goal is to demonstrate that the background rate is low enough to carry out an independent search for a dark matter signal, with sufficient sensitivity to confirm or refute the DAMA result during the following full-scale experimental phase. The impact of background radiation from the detector materials and the experimental site needs to be carefully investigated, including both intrinsic and cosmogenically activated radioactivity. Based on the best knowledge of the most relevant sources of background, we have performed a detailed Monte Carlo study evaluating the expected background in the dark matter search spectral region. The simulation model described in this paper guides the design of the full-scale experiment and will be fundamental for the interpretation of the measured background and hence for the extraction of a possible dark matter signal.

Annual modulation in direct dark matter searches

“…The Sodium-iodide Active Background Rejection Experiment (SABRE) is the sole dual hemisphere effort capable of unambiguously detecting and determining the phase of a DAMA-like annual modulation signature [98]. Currently the Proof-of-Principle (SABRE-PoP) experiment is already housed [146] in Italy's LNGS while the Southern Hemisphere based-detector will be operated at the Stawell Underground Physics Laboratory in Victoria, Australia. This Southern detector in Australia is on track for commencement at the start of 2021.…”

The SABRE project and the SABRE Proof-of-Principle

“…1. For a study of the background contribution from internal radioactivity of the SABRE crystals we refer to the Monte Carlo simulations performed for the Proof-of-Principle phase [17].…”

“…Experiments such as DAMA and ANAIS [25] can only reject events with coincident energy deposition in neighbouring crystals, achieving a partial suppression of this background. However, the SABRE strategy (adopted also by the COSINE experiment [26]) with 4π active volume around the crystal matrix, has the potential to identify and suppress the 40 K background with higher efficiency (expected rejection of 84% in 2-6 keV ee region [17]). We anticipate using an organic scintillator mixture based on pseudocumene and high quantum efficiency PMTs.…”

“…The control of radioactive contamination levels of the detector components (crystals, PMTs, copper enclosure and its parts, vessel, liquid scintillator, etc...), was either performed directly by the SABRE collaboration through radioactivity measurements of various samples, or based on the results of similar screening measurements performed by other experiments for the same material or item, as described in [17] and references therein.…”

“…As the design of the SABRE experiment is not finalized yet, pending the results of the PoP phase, we estimated the background level, as is it customary in our field, using Geant4-based [30] Monte Carlo simulations. These are performed for the PoP setup only and are described in details in [17]. The predicted background level in the energy interval [2][3][4][5][6] keV ee for the SABRE-PoP setup is 0.36 cpd/kg/keV ee .…”