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CUPID-Mo is a bolometric experiment to search for neutrinoless double-beta decay ( 0 ν β β ) of 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 Mo -enriched 0.2 kg Li 2 MoO 4 crystals operated as scintillating bolometers at ∼ 20 mK . The Li 2 MoO 4 crystals are complemented by 20 thin Ge optical bolometers to reject 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 α particles at a level much higher than 99.9% – with equally high acceptance for γ / β events – in the region of interest for 100 Mo 0 ν β β . We present limits on the crystals’ radiopurity: ≤ 3 μ Bq/kg of 226 Ra and ≤ 2 μ Bq/kg of 232 Th . We discuss the science reach of CUPID-Mo, which can set the most stringent half-life limit on the 100 Mo 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 ν β β experiment.

Neutrinoless double-beta ( 0 ν β β ) decay is a hypothetical rare nuclear transition ( T 1 / 2 > 10 25 – 10 26 year). Its observation would provide an important insight into the nature of neutrinos (Dirac or Majorana particle) demonstrating that the lepton number is not conserved. This decay can be investigated with bolometers embedding the double-beta decay isotope ( 76 Ge , 82 Se , 100 Mo , 116 Cd , 130 Te ...), which perform as low-temperature calorimeters (few tens of mK) detecting particle interactions via a small temperature rise read out by a dedicated thermometer. Cryogenic Rare-event Observatory with Surface Sensitivity (CROSS) aims at the development of bolometric detectors (based on Li 2 MoO 4 and TeO 2 crystals) capable of discriminating surface α and β interactions by exploiting superconducting properties of Al film deposited on the detector surface. We report in this paper the results of tests on prototypes performed at CSNSM (Orsay, France) that showed the capability of a-few- μ m -thick superconducting Al film deposited on crystal surface to discriminate surface α from bulk events, thus providing the detector with the required pulse shape discrimination capability. The CROSS technology would further improve the background suppression and simplify the detector construction (no auxiliary light detector is needed to reject alpha surface events) with a view to future competitive double-beta decay searches.

We report the measurement of the two-neutrino double-beta ( 2 ν β β ) decay of 100 Mo to the ground state of 100 Ru using lithium molybdate ( Li 2 100 MoO 4 ) 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 × day, the half-life of 100 Mo is determined to be T 1 / 2 2 ν = [ 7 . 12 - 0.14 + 0.18 ( stat . ) ± 0.10 ( syst . ) ] × 10 18  years. This is the most accurate determination of the 2 ν β β half-life of 100 Mo to date.

Cadmium-116 is one of the favorable candidates for neutrinoless double-beta decay ( 0 ν β β ) searches from both theoretical and experimental points of view, in particular thanks to the high energy of the decay (2813.49 keV), the possibility of the industrial enrichment in 116 Cd and its use in the well-established production of cadmium tungstate crystal scintillators. In this work, we present low-temperature tests of two 0.6 kg 116 CdWO 4 crystals enriched in 116 Cd to 82 % as scintillating bolometers. These detectors were operated underground, with one at the Laboratoire Souterrain de Modane (LSM) in France and the second at the Laboratorio Subterraneo de Canfranc (LSC) in Spain. The two crystals are coupled to bolometric Ge light detectors in order to register the scintillation light. The double readout of heat and scintillation enables reduction in the background in the region of interest by discriminating between different populations of particles. The main goal of these tests is the study of the crystals’ radiopurity and the detectors’ performance. The achieved results are extremely promising, in particular, the detectors demonstrate a high energy resolution (11–16 keV FWHM at 2615 keV) and a high-efficiency discrimination of the alpha background ( ∼ 20 σ ). These results, achieved for the first time with large mass enriched 116 CdWO 4 crystals, demonstrate prospects of the bolometric technology for high-sensitivity searches of 116 Cd 0 ν β β decay.

We report the measurement of the two-neutrino double-beta ($2\\nu\\beta\\beta$) decay of $^{100}$Mo to the ground state of $^{100}$Ru using lithium molybdate (\\crystal) 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. From a total exposure of $42.235$ kg$\\times$d, the half-life of $^{100}$Mo is determined to be $T_{1/2}^{2\\nu}=[7.12^{+0.18}_{-0.14}\\,\\mathrm{(stat.)}\\pm0.10\\,\\mathrm{(syst.)}]\\times10^{18}$ years. This is the most accurate determination of the $2\\nu\\beta\\beta$ half-life of $^{100}$Mo to date. We also confirm, with the statistical significance of $>3\\sigma$, that the single-state dominance model of the $2\\nu\\beta\\beta$ decay of $^{100}$Mo is favored over the high-state dominance model.

The CUPID-Mo experiment to search for 0νββ decay in 100Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator for CUPID, a next generation 0νββ decay experiment. CUPID-Mo was comprised of 20 enriched Li2100MoO4 scintillating calorimeters, each with a mass of ∼0.2 kg, operated at ∼20 mK. We present here the final analysis with the full exposure of CUPID-Mo (100Mo exposure of 1.47 kg×year) used to search for lepton number violation via 0νββ decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the 100Mo 0νββ decay half-life of T1/20ν>1.8×1024 year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of mββ <(0.28-0.49) eV, dependent upon the nuclear matrix element utilized.

Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of 100 Mo with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li 2 MoO 4 crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov–Trofimov–Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: (a) an experimental work performed with a Li 2 MoO 4 scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; (b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; (c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index ∼ 10 - 4 counts/keV/kg/year with 280 g Li 2 MoO 4 ( 100 Mo enriched) bolometers at 3034 keV, the Q β β of the double-beta decay, and target the goal of a next generation experiment like CUPID.

CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation 0 ν β β decay experiment, CUPID. It consisted of an array of 20 enriched Li 2 100 MoO 4 bolometers and 20 Ge light detectors and has demonstrated that the technology of scintillating bolometers with particle identification capabilities is mature. Furthermore, CUPID-Mo can inform and validate the background prediction for CUPID. In this paper, we present a detailed model of the CUPID-Mo backgrounds. This model is able to describe well the features of the experimental data and enables studies of the 2 ν β β decay and other processes with high precision. We also measure the radio-purity of the Li 2 100 MoO 4 crystals which are found to be sufficient for the CUPID goals. Finally, we also obtain a background index in the region of interest of 3.7  - 0.8 + 0.9  (stat) - 0.7 + 1.5  (syst)  × 10 - 3  counts/ Δ E FWHM / mol iso / year , the lowest in a bolometric 0 ν β β decay experiment.

Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of$$^{100}$$100 Mo with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li$$_2$$2 MoO$$_4$$4 crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov–Trofimov–Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: (a) an experimental work performed with a Li$$_2$$2 MoO$$_4$$4 scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; (b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; (c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index$$\\sim $$∼$$10^{-4}$$10 - 4 counts/keV/kg/year with 280 g Li$$_2$$2 MoO$$_4$$4 ($$^{100}$$100 Mo enriched) bolometers at 3034 keV, the Q$$_{\\beta \\beta }$$β β of the double-beta decay, and target the goal of a next generation experiment like CUPID.

Random coincidences of events could be one of the main sources of background in the search for neutrino-less double-beta decay of $^{100}$Mo with macro-bolometers, due to their modest time resolution. Scintillating bolometers as those based on Li$_2$MoO$_4$ crystals and employed in the CROSS and CUPID experiments can eventually exploit the coincident fast signal detected in a light detector to reduce this background. However, the scintillation provides a modest signal-to-noise ratio, making difficult a pile-up pulse-shape recognition and rejection at timescales shorter than a few ms. Neganov-Trofimov-Luke assisted light detectors (NTL-LDs) offer the possibility to effectively increase the signal-to-noise ratio, preserving a fast time-response, and enhance the capability of pile-up rejection via pulse shape analysis. In this article we present: a) an experimental work performed with a Li$_2$MoO$_4$ scintillating bolometer, studied in the framework of the CROSS experiment, and utilizing a NTL-LD; b) a simulation method to reproduce, synthetically, randomly coincident two-neutrino double-beta decay events; c) a new analysis method based on a pulse-shape discrimination algorithm capable of providing high pile-up rejection efficiencies. We finally show how the NTL-LDs offer a balanced solution between performance and complexity to reach background index $\\sim$$10^{-4}$ counts/keV/kg/year with 280~g Li$_2$MoO$_4$ ($^{100}$Mo enriched) bolometers at 3034 keV, the Q-value of the double-beta decay, and target the goal of a next generation experiment like CUPID.