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1. The SABRE project and the SABRE Proof-of-Principle

   https://doi.org/10.1140/epjc/s10052-019-6860-y  

   Antonello, M.; Barberio, E.; Baroncelli, T.; Benziger, J.; Bignell, L. J.; Bolognino, I.; Calaprice, F.; Copello, S.; D’Angelo, D.; D’Imperio, G.; et al (April 2019, The European Physical Journal C)
2. The SABRE experiment

   https://doi.org/10.1142/S0217751X22400164  

   Zani, A.; D’Angelo, D.; Vignoli, C.; Di Carlo, G.; Di Giacinto, A.; Ianni, A.; Orlandi, D.; Mariani, A.; Copello, S.; Tomei, C.; et al (March 2022, International Journal of Modern Physics A)

   The dark matter interpretation of the DAMA/LIBRA annual modulation signal represents a long-standing open question in astroparticle physics. The SABRE experiment aims to test such claim, bringing the same detection technique to an unprecedented sensitivity. Based on ultra-low background NaI(Tl) scintillating crystals like DAMA, SABRE features a liquid scintillator Veto system, surrounding the main target, and it will deploy twin detectors: one in the Northern hemisphere at Laboratori Nazionali del Gran Sasso (LNGS), Italy and the other in the Stawell Underground Physics Laboratory (SUPL), Australia, first laboratory of this kind in the Southern hemisphere. The first very-high-purity crystal produced by the collaboration was shipped to LNGS in 2019 for characterization. It features a potassium contamination, measured by mass spectroscopy, of the order of 4 ppb, about three times lower than DAMA/LIBRA crystals. The first phase of the SABRE experiment is a Proof-of-Principle (PoP) detector featuring one crystal and a liquid scintillator Veto, at LNGS. This contribution will present the results of the stand-alone characterization of the first SABRE high-purity crystal, as well as the status of the PoP detector, commissioned early in the summer of 2020. 

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3. The SABRE Proof of Principle

   https://doi.org/10.1088/1742-6596/1468/1/012029  

   Copello, Simone; Antonello, M.; Barberio, E.; Baroncelli, T.; Benziger, J.; Bignell, L.J.; Bolognino, I.; Calaprice, F.; Copello, S.; D’Angelo, D.; et al (February 2020, Journal of Physics: Conference Series)

   Abstract SABRE is a dark matter direct detection experiment based on NaI(Tl) scintillating crystals. The primary goal of the experiment is to test the dark matter interpretation of the DAMA/LIBRA annual modulation signal. To reach its purpose, SABRE will operate an array of ultra-low background NaI(Tl) crystals within an active veto, based on liquid scintillator. Finally two twin detectors will be used, one in the northern hemisphere at Laboratori Nazionali del Gran Sasso, Italy (LNGS) and the other, first of its kind, in the southern hemisphere, in the Stawell Underground Physic Laboratory (SUPL). The collaboration has successfully developed a NaI(Tl) crystal with the impressive potassium content of about 4 ppb, according to the mass spectroscopy measurements. A value that, if confirmed, would be about 3 times lower than the DAMA/LIBRA crystals one. The first phase of the SABRE experiment, called SABRE Proof of Principle (PoP), aims to prove the achieved radiopurity by direct measurement of crystals at LNGS. This work reports the status of the PoP setup and the recent progresses on the development of low radioactivity NaI(Tl) crystals. 

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4. 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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5. SABRE enhancement with oscillating pulse sequences

   https://doi.org/10.1039/d2cp00899h  

   Li, Xiaoqing; Lindale, Jacob R.; Eriksson, Shannon L.; Warren, Warren S. (May 2022, Physical Chemistry Chemical Physics)

   SABRE (Signal Amplification by Reversible Exchange) methods provide a simple, fast, and cost-effective method to hyperpolarize a wide variety of molecules in solution, and have been demonstrated with protons and, more recently, with heteronuclei (X-SABRE). Here, we present several oscillating pulse sequences that use magnetic fields far away from the resonance condition of continuous excitation and can commonly triple the polarization. An analysis with average Hamiltonian theory indicates that the oscillating pulse, in effect, adjusts the J-couplings between hydrides and target nuclei and that a much weaker coupling produces maximum polarization. This theoretical treatment, combined with simulations and experiment, shows substantial magnetization improvements relative to traditional X-SABRE methods. It also shows that, in contrast to most pulse sequence applications, waveforms with reduced time symmetry in the toggling frame make magnetization generation more robust to experimental imperfections. 

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