Search

Abstract Neutrinoless double-beta decay is a key process in particle physics. Its experimental investigation is the only viable method that can establish the Majorana nature of neutrinos, providing at the same time a sensitive inclusive test of lepton number violation. CROSS (Cryogenic Rare-event Observatory with Surface Sensitivity) aims at developing and testing a new bolometric technology to be applied to future large-scale experiments searching for neutrinoless double-beta decay of the promising nuclei 100Mo and 130Te. The limiting factor in large-scale bolometric searches for this rare process is the background induced by surface radioactive contamination, as shown by the results of the CUORE experiment. The basic concept of CROSS consists of rejecting this challenging background component by pulse-shape discrimination, assisted by a proper coating of the faces of the crystal containing the isotope of interest and serving as energy absorber of the bolometric detector. In this paper, we demonstrate that ultra-pure superconductive Al films deposited on the crystal surfaces act successfully as pulse-shape modifiers, both with fast and slow phonon sensors. Rejection factors higher than 99.9% of α surface radioactivity have been demonstrated in a series of prototypes based on crystals of Li2MoO4 and TeO2. We have also shown that point-like energy depositions can be identified up to a distance of ∼ 1 mm from the coated surface. The present program envisions an intermediate experiment to be installed underground in the Canfranc laboratory (Spain) in a CROSS-dedicated facility. This experiment, comprising ∼ 3×1025 nuclei of 100Mo, will be a general test of the CROSS technology as well as a worldwide competitive search for neutrinoless double-beta decay, with sensitivity to the effective Majorana mass down to 70 meV in the most favorable conditions.

Abstract We report the measurement of the two-neutrino double-beta ($$2\nu \beta \beta $$ 2νββ ) decay of $$^{100}$$ 100 Mo to the ground state of $$^{100}$$ 100 Ru using lithium molybdate ($$\hbox {Li}_2^{\;\;100}\hbox {MoO}_4$$ Li2100MoO4 ) scintillating bolometers. The detectors were developed for the CUPID-Mo program and operated at the EDELWEISS-III low background facility in the Modane underground laboratory (France). From a total exposure of 42.235 kg$$\times $$ × day, the half-life of $$^{100}$$ 100 Mo is determined to be $$T_{1/2}^{2\nu }=[7.12^{+0.18}_{-0.14}\,\mathrm {(stat.)}\pm 0.10\,\mathrm {(syst.)}]\times 10^{18}$$ T1/22ν=[7.12-0.14+0.18(stat.)±0.10(syst.)]×1018 years. This is the most accurate determination of the $$2\nu \beta \beta $$ 2νββ half-life of $$^{100}$$ 100 Mo to date.

Abstract CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay ($$0\nu \beta \beta $$ 0νββ ) of $$^{100}\hbox {Mo}$$ 100Mo . In this article, we detail the CUPID-Mo detector concept, assembly and installation in the Modane underground laboratory, providing results from the first datasets. The CUPID-Mo detector consists of an array of 20 $$^{100}\hbox {Mo}$$ 100Mo -enriched 0.2 kg $$\hbox {Li}_2\hbox {MoO}_4$$ Li2MoO4 crystals operated as scintillating bolometers at $$\sim 20\hbox { mK}$$ ∼20mK . The $$\hbox {Li}_2\hbox {MoO}_4$$ Li2MoO4 crystals are complemented by 20 thin Ge optical bolometers to reject $$\alpha $$ α events by the simultaneous detection of heat and scintillation light. We observe a good detector uniformity and an excellent energy resolution of 5.3 keV (6.5 keV) FWHM at 2615 keV, in calibration (physics) data. Light collection ensures the rejection of $$\alpha $$ α particles at a level much higher than 99.9% – with equally high acceptance for $$\gamma $$ γ /$$\beta $$ β events – in the region of interest for $$^{100}\hbox {Mo}$$ 100Mo $$0\nu \beta \beta $$ 0νββ . We present limits on the crystals’ radiopurity: $$\le 3~\mu \hbox {Bq/kg}$$ ≤3μBq/kg of $$^{226}\hbox {Ra}$$ 226Ra and $$\le 2~\mu \hbox {Bq/kg}$$ ≤2μBq/kg of $$^{232}\hbox {Th}$$ 232Th . We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the $$^{100}\hbox {Mo}$$ 100Mo $$0\nu \beta \beta $$ 0νββ decay in half-a-year’s livetime. The achieved results show that CUPID-Mo is a successful demonstrator of the technology developed by the LUMINEU project and subsequently selected for the CUPID experiment, a proposed follow-up of CUORE, the currently running first tonne-scale bolometric $$0\nu \beta \beta $$ 0νββ experiment.