Abstract
CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay (0nu beta beta ) of ^{100}hbox {Mo}. 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}-enriched 0.2 kg hbox {Li}_2hbox {MoO}_4 crystals operated as scintillating bolometers at sim 20hbox { mK}. The hbox {Li}_2hbox {MoO}_4 crystals are complemented by 20 thin Ge optical bolometers to reject alpha 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 particles at a level much higher than 99.9% – with equally high acceptance for gamma /beta events – in the region of interest for ^{100}hbox {Mo}0nu beta beta . We present limits on the crystals’ radiopurity: le 3~mu hbox {Bq/kg} of ^{226}hbox {Ra} and le 2~mu hbox {Bq/kg} of ^{232}hbox {Th}. We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the ^{100}hbox {Mo}0nu beta beta 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 0nu beta beta experiment.
Highlights
Two-neutrino double-beta decay (2νββ) is one of the rarest processes in nature
Light collection ensures the rejection of α particles at a level much higher than 99.9% – with high acceptance for γ /β events – in the region of interest for 100Mo 0νββ
The preliminary γ /β selection by Relative Light Yield (RLY) defined before eliminates a significant population of α events with ∼20% of the RLY of γ /β events and a few remaining events at higher light yield than expected. This particular crystal is characterized by the highest contamination level of 210Po with ∼ 0.5 mBq/kg and best exemplifies the alpha discrimination power achieved for a scintillating bolometer with typical performance values of 0.67 keV/MeV RLY and 0.18 keV FWHMNoise of a coupled light detector (LD)
Summary
Two-neutrino double-beta decay (2νββ) is one of the rarest processes in nature. Initially proposed by Maria GoeppertMeyer in [1], it has since been observed for 11 nuclei with typical half-lives ranging from 1018 to 1024 year [2,3]. The CUORE (Cryogenic Underground Observatory for Rare Events) experiment [14,19], currently collecting data at Laboratori Nazionali del Gran Sasso (LNGS, Italy), demonstrates the feasibility of a tonne-scale detector based on this technology. The success of this experiment is the starting point of CUPID (CUORE Upgrade with Particle IDentification), which aims to increase the mass of the 0νββ decay isotope via isotopic enrichment while decreasing the background in the region of interest. A further background suppression can be attained by choosing 0νββ decay emitters with a Qββ well above the 2.6 MeV line of 208Tl, which is typically the end-point of natural γ radioactivity In this paper we present the CUPID-Mo detector concept and construction (Sect. 2), the operation and initial performance of the first Physics run dataset (Sect. 3), and the prospects of the experiment in 0νββ decay search (Sect. 4)
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