The CUPID-Mo experiment for neutrinoless double-beta decay: performance and prospects

CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay ( $$0\nu \beta \beta $$ 0 ν β β ) of $$^{100}\hbox {Mo}$$ 100 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 $$^{100}\hbox {Mo}$$ 100 Mo -enriched 0.2 kg $$\hbox {Li}_2\hbox {MoO}_4$$ Li 2 MoO 4 crystals operated as scintillating bolometers at $$\sim 20\hbox { mK}$$ ∼ 20 mK . The $$\hbox {Li}_2\hbox {MoO}_4$$ Li 2 MoO 4 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 $$^{100}\hbox {Mo}$$ 100 Mo $$0\nu \beta \beta $$ 0 ν β β . We present limits on the crystals’ radiopurity: $$\le 3~\mu \hbox {Bq/kg}$$ ≤ 3 μ Bq/kg of $$^{226}\hbox {Ra}$$ 226 Ra and $$\le 2~\mu \hbox {Bq/kg}$$ ≤ 2 μ Bq/kg of $$^{232}\hbox {Th}$$ 232 Th . We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the $$^{100}\hbox {Mo}$$ 100 Mo $$0\nu \beta \beta $$ 0 ν β β 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 $$0\nu \beta \beta $$ 0 ν β β experiment.