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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 bymore »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.« less

Abstract The search for neutrino events in correlation with 42 most intense fast radio bursts (FRBs) has been performed using the Borexino dataset from 05/2007 to 06/2021. We have searched for signals with visible energies above 250 keV within a time window of $$\pm \, 1000$$ ± 1000  s corresponding to detection time of a particular FRB. We also applied an alternative approach based on searching for specific shapes of neutrino-electron scattering spectra in the full exposure data of the Borexino detector. In particular, two incoming neutrino spectra were considered: the monoenergetic line and the spectrum expected from supernovae. The samemore »spectra were considered for electron antineutrinos detected through inverse beta-decay reaction. No statistically significant excess over the background was observed. As a result, the strongest upper limits on FRB-associated neutrino fluences of all flavors have been obtained in the 0.5–50 MeV neutrino energy range.« less

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 energymore »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\pm 0.6\mu$Bq/kg and$$1.6\pm 0.3~\upmu $$$1.6\pm 0.3\mu$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$$\alpha $$$\alpha$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$$\sim $$$\sim$1 count/day/kg/keV in the [5–20] keV region.

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Abstract Cosmogenic radio-nuclei are an important source of background for low-energy neutrino experiments. In Borexino, cosmogenic $$^{11}$$ 11 C decays outnumber solar pep and CNO neutrino events by about ten to one. In order to extract the flux of these two neutrino species, a highly efficient identification of this background is mandatory. We present here the details of the most consolidated strategy, used throughout Borexino solar neutrino measurements. It hinges upon finding the space-time correlations between $$^{11}$$ 11 C decays, the preceding parent muons and the accompanying neutrons. This article describes the working principles and evaluates the performance of thismore »Three-Fold Coincidence (TFC) technique in its two current implementations: a hard-cut and a likelihood-based approach. Both show stable performances throughout Borexino Phases II (2012–2016) and III (2016–2020) data sets, with a $$^{11}$$ 11 C tagging efficiency of $$\sim 90$$ ∼ 90  % and $$\sim $$ ∼  63–66 % of the exposure surviving the tagging. We present also a novel technique that targets specifically $$^{11}$$ 11 C produced in high-multiplicity during major spallation events. Such $$^{11}$$ 11 C appear as a burst of events, whose space-time correlation can be exploited. Burst identification can be combined with the TFC to obtain about the same tagging efficiency of $$\sim 90\%$$ ∼ 90 % but with a higher fraction of the exposure surviving, in the range of $$\sim $$ ∼  66–68 %.« less

Abstract Neutrinos emitted in the carbon, nitrogen, oxygen (CNO) fusion cycle in the Sun are a sub-dominant, yet crucial component of solar neutrinos whose flux has not been measured yet. The Borexino experiment at the Laboratori Nazionali del Gran Sasso (Italy) has a unique opportunity to detect them directly thanks to the detector’s radiopurity and the precise understanding of the detector backgrounds. We discuss the sensitivity of Borexino to CNO neutrinos, which is based on the strategies we adopted to constrain the rates of the two most relevant background sources, $$pep$$ pep neutrinos from the solar pp -chain and $$^{210}$$more »210 Bi beta decays originating in the intrinsic contamination of the liquid scintillator with $$^{210}$$ 210 Pb. Assuming the CNO flux predicted by the high-metallicity Standard Solar Model and an exposure of 1000 days $$\times $$ × 71.3 t, Borexino has a median sensitivity to CNO neutrino higher than 3 $$\sigma $$ σ . With the same hypothesis the expected experimental uncertainty on the CNO neutrino flux is 23%, provided the uncertainty on the independent estimate of the $$^{210}\text {Bi}$$ 210 Bi  interaction rate is 1.5 $$\hbox {cpd}/100~\hbox {ton}$$ cpd / 100 ton  . Finally, we evaluated the expected uncertainty of the C and N abundances and the expected discrimination significance between the high and low metallicity Standard Solar Models (HZ and LZ) with future more precise measurement of the CNO solar neutrino flux.« less