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1. Status and prospects of SABRE North

   https://doi.org/10.21468/SciPostPhysProc.12.026  

   Mariani, Ambra (January 2023, SciPost Physics Proceedings)

   We present the characterization of a low background NaI(Tl) crystal for the SABRE North experiment. The crystal NaI-33, was studied in two different setups at Laboratori Nazionali del Gran Sasso, Italy. The Proof-of-Principle (PoP) detector was equipped with a liquid scintillator veto and collected data for about one month (90 kg \times × days). The PoP-dry setup consisted of NaI-33 in a purely passive shielding and collected data for almost one year (891 kg \times × days). The average background in the energy region of interest (1-6 keV) for dark matter search was 1.20 \pm ± 0.05 and 1.39 \pm ± 0.02 counts/day/kg/keV within the PoP and the PoP-dry setup, respectively. This result opens to a new shielding design for the physics phase of the SABRE North detector, that does not foresee the use of an organic liquid scintillator external veto, in compliance with the new safety and environmental requirements of Laboratori Nazionali del Gran Sasso. 

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2. Characterization of an ultra-high purity NaI(Tl) crystal scintillator with the SABRE Proof-of-Principle detector

   https://doi.org/10.1088/1742-6596/2156/1/012022  

   Mariani, A. (December 2021, Journal of Physics: Conference Series)

   Abstract The SABRE experiment aims to detect the annual modulation of the dark matter interaction rate by means of ultra-high purity NaI(Tl) crystals. It focuses on the achievement of a very low background to carry out a model-independent and high sensitivity test of the long-standing DAMA result. SABRE has recently completed a Proof-of-Principle (PoP) phase at the Gran Sasso National Laboratory, devoted to assess the radiopurity of the crystals. The results on the radiopurity of a 3.4-kg NaI(Tl) crystal scintillator grown within the SABRE Collaboration and operated underground in the SABRE-PoP setup, will be reported and discussed. The amount of potassium content in the crystal, determined by direct counting of 40 K, is found to be < 4.7 ppb at 90% CL. The average background rate in the 1-6 keV energy region of interest (ROI) is 1.20 ± 0.05 counts/day/kg/keV, which is, for the first time, comparable with DAMA/LIBRA-phasel. Our background model indicates that this rate is dominated by 210 Pb, and that about half of this contamination is located in the PTFE reflector wrapped around the crystal. Ongoing developments aimed at a further reduction of radioactive contaminants in the crystal indicates that a background rate ≤ 0.3 counts/day/kg/keV in the ROI is within reach. This value represents a benchmark for the development of next-generation NaI(Tl) detector arrays for the direct detection of dark matter particles. 

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3. Characterization of SABRE crystal NaI-33 with direct underground counting

   https://doi.org/10.1140/epjc/s10052-021-09098-5  

   Antonello, M.; Arnquist, I. J.; Barberio, E.; Baroncelli, T.; Benziger, J.; Bignell, L. J.; Bolognino, I.; Calaprice, F.; Copello, S.; Dafinei, I.; et al (April 2021, The European Physical Journal C)

   Abstract Ultra-pure NaI(Tl) crystals are the key element for a model-independent verification of the long standing DAMA result and a powerful means to search for the annual modulation signature of dark matter interactions. The SABRE collaboration has been developing cutting-edge techniques for the reduction of intrinsic backgrounds over several years. In this paper we report the first characterization of a 3.4 kg crystal, named NaI-33, performed in an underground passive shielding setup at LNGS. NaI-33 has a record low $$^{39}$$ 39 K contamination of 4.3 ± 0.2 ppb as determined by mass spectrometry. We measured a light yield of 11.1 ± 0.2 photoelectrons/keV and an energy resolution of 13.2% (FWHM/E) at 59.5 keV. We evaluated the activities of $$^{226}$$ 226 Ra and $$^{228}$$ 228 Th inside the crystal to be $$5.9\pm 0.6~\upmu $$ 5.9 ± 0.6 μ Bq/kg and $$1.6\pm 0.3~\upmu $$ 1.6 ± 0.3 μ Bq/kg, respectively, which would indicate a contamination from $$^{238}$$ 238 U and $$^{232}$$ 232 Th at part-per-trillion level. We measured an activity of 0.51 ± 0.02 mBq/kg due to $$^{210}$$ 210 Pb out of equilibrium and a $$\alpha $$ α quenching factor of 0.63 ± 0.01 at 5304 keV. We illustrate the analyses techniques developed to reject electronic noise in the lower part of the energy spectrum. A cut-based strategy and a multivariate approach indicated a rate, attributed to the intrinsic radioactivity of the crystal, of $$\sim $$ ∼ 1 count/day/kg/keV in the [5–20] keV region. 

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4. The SABRE experiment for dark matter search

   https://doi.org/10.22323/1.340.0653  

   D'imperio, Giulia; Antonello, M.; Barberio, E.; Baroncelli, T.; Benziger, J.; Bignell, L.J.; Bolognino, I.; Calaprice, F.; Copello, S.; D’Angelo, D.; et al (August 2019, The SABRE experiment for dark matter search)

   The SABRE (Sodium-iodide with Active Background REjection) experiment is a new detector based on NaI(Tl) scintillating crystals for the dark matter detection through the annual modulation. With ultra-pure crystals and an active veto system, based on liquid scintillator surrounding the crystal array, SABRE will reach unprecedented low background and the highest sensitivity among the present NaI(Tl) experiments. Moreover SABRE will be the first dark matter search with twin detectors located in the North and South hemispheres, in Gran Sasso National Laboratories (LNGS), Italy, and Stawell Underground Laboratories (SUPL), Australia, respectively. The double location will help to quantify possible seasonal effects, and is a unique feature to identify a modulation of dark matter origins. SABRE is presently in the Proof-of-Principle (PoP) phase, with the goal to measure the crystal intrinsic and cosmogenic backgrounds of one 5 kg crystal and the active veto efficiency. We have performed a full geometry Monte Carlo simulation in order to evaluate the background contributions in the two distinct operation modes foreseen for the PoP: the potassium Measurement Mode (KMM) and the Dark Matter Measurement Mode (DMM), where the liquid scintillator detector is used in coincidence or anti-coincidence with the crystal, respectively. This paper presents the results of a detailed background simulation and the expected sensitivity for the SABRE full scale experiment. 

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5. Dark matter search with the SABRE experiment

   https://doi.org/10.1088/1742-6596/1342/1/012060  

   D’Imperio, Giulia (January 2020, Journal of Physics: Conference Series)

   Abstract The SABRE (Sodium Iodide with Active Background REjection) experiment will search for an annually modulating signal from dark matter using an array of ultra-pure NaI(Tl) detectors surrounded by an active scintillator veto to further reduce the background. The first phase of the experiment is the SABRE Proof of Principle (PoP), a single 5 kg crystal detector operated in a liquid scintillator filled vessel at Laboratori Nazionali del Gran Sasso (LNGS). The SABRE-PoP installation is underway with the goal of running in 2018 and performing the first in situ measurement of the crystal background, testing the veto efficiency, and validating the SABRE concept. The second phase of SABRE will be twin arrays of NaI(Tl) detectors operating at LNGS and at the Stawell Underground Physics Laboratory (SUPL) in Australia. By locating detectors in both hemispheres, SABRE will minimize seasonal systematic effects. This paper presents the status report of the SABRE activities as well as the results from the most recent Monte Carlo simulation and the expected sensitivity. 

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