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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.

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.

CUPID, the CUORE Upgrade with Particle Identification, is a next-generation experiment to search for neutrinoless double beta decay ( 0 ν β β ) and other rare events using enriched Li 2 100 MoO 4 scintillating bolometers. It will be hosted by the CUORE cryostat located at the Laboratori Nazionali del Gran Sasso in Italy. The main physics goal of CUPID is to search for 0 ν β β of 100 Mo with a discovery sensitivity covering the full neutrino mass regime in the inverted ordering scenario, as well as the portion of the normal ordering regime with lightest neutrino mass larger than 10 meV. With a conservative background index of 10 - 4  cts / ( keV · kg · yr ) , 240 kg isotope mass, 5 keV FWHM energy resolution at 3 MeV and 10 live-years of data taking, CUPID will have a 90% C.L. half-life exclusion sensitivity of 1.8 · 10 27  yr, corresponding to an effective Majorana neutrino mass ( m β β ) sensitivity of 9–15 meV, and a 3 σ discovery sensitivity of 1 · 10 27  yr, corresponding to an m β β range of 12–21 meV.

The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of \\[^{100}\\]Mo to the ground state of \\[^{100}\\]Ru, \\[T_{1/2} = \\left[ 6.81 \\pm 0.01\\,\\left( \\text{ stat }\\right) ^{+0.38}_{-0.40}\\,\\left( \\text{ syst }\\right) \\right] \\times 10^{18}\\] year. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of \\[5\\times 10^5\\] events and a signal-to-background ratio of \\[\\sim \\] 80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of \\[\\mathrm{n}=2,3,7\\], as well as constraints on Lorentz invariance violation and on the bosonic neutrino contribution to the two-neutrino double beta decay mode are obtained.

The$$2\\nu 2\\beta $$2 ν 2 β decay of$$^{150}\\hbox {Nd}$$150 Nd to the first excited 740.5 keV$$0^{+}_{1}$$0 1 + level of$$^{150}\\hbox {Sm}$$150 Sm was measured over 5.845 years with the help of a four-crystal low-background HPGe$$\\gamma $$γ spectrometry system in the underground low-background laboratory STELLA of LNGS-INFN. A 2.381 kg highly purified Nd-containing sample was employed as the decay source. The expected de-excitation gamma-quanta of the$$0^{+}_{1}$$0 1 + level with energies 334.0 keV and 406.5 keV were observed both in one-dimensional spectrum and in coincidence data resulting in the half-life$$T_{1/2}=[0.83^{+0.18}_{-0.13}\\mathrm {(stat)}^{+0.16}_{-0.19}\\mathrm {(syst)}]\\times 10^{20}$$T 1 / 2 = [ 0 . 83 - 0.13 + 0.18 ( stat ) - 0.19 + 0.16 ( syst ) ] × 10 20 year. Interpreting an excess of the 334.0-keV peak area as an indication of the$$2\\beta $$2 β decay of$$^{150}\\hbox {Nd}$$150 Nd to the 334.0 keV$$2^+_1$$2 1 + excited level of$$^{150}\\hbox {Sm}$$150 Sm with a half-life of$$T_{1/2}=[1.5^{+2.3}_{-0.6}\\mathrm {(stat)}\\pm 0.4\\mathrm {(syst)}]\\times 10^{20}$$T 1 / 2 = [ 1 . 5 - 0.6 + 2.3 ( stat ) ± 0.4 ( syst ) ] × 10 20 year, the$$2\\nu 2\\beta $$2 ν 2 β half-life of$$^{150}\\hbox {Nd}$$150 Nd for the transition to the 0$$^{+}_{1}$$1 + level is$$T_{1/2}=[1.03^{+0.35}_{-0.22}\\mathrm {(stat)}^{+0.16}_{-0.19}\\mathrm {(syst)}]\\times 10^{20}$$T 1 / 2 = [ 1 . 03 - 0.22 + 0.35 ( stat ) - 0.19 + 0.16 ( syst ) ] × 10 20 year, in agreement with the previous experiments. Both half-life values reasonably agree with the theoretical calculations in the framework of proton-neutron QRPA with isospin restoration combined with like nucleon QRPA for description of excited states in the final nuclei. For$$2\\nu 2\\beta $$2 ν 2 β and$$0\\nu 2\\beta $$0 ν 2 β transitions of$$^{150}\\hbox {Nd}$$150 Nd and$$^{148}\\hbox {Nd}$$148 Nd to several excited levels of$$^{150}\\hbox {Sm}$$150 Sm and$$^{148}\\hbox {Sm}$$148 Sm , limits were set at level of$$T_{1/2}>10^{20}-10^{21}$$T 1 / 2 > 10 20 - 10 21 year.

The 2 ν 2 β decay of 150 Nd to the first excited 740.5 keV 0 1 + level of 150 Sm was measured over 5.845 years with the help of a four-crystal low-background HPGe γ spectrometry system in the underground low-background laboratory STELLA of LNGS-INFN. A 2.381 kg highly purified Nd-containing sample was employed as the decay source. The expected de-excitation gamma-quanta of the 0 1 + level with energies 334.0 keV and 406.5 keV were observed both in one-dimensional spectrum and in coincidence data resulting in the half-life T 1 / 2 = [ 0 . 83 - 0.13 + 0.18 ( stat ) - 0.19 + 0.16 ( syst ) ] × 10 20 year. Interpreting an excess of the 334.0-keV peak area as an indication of the 2 β decay of 150 Nd to the 334.0 keV 2 1 + excited level of 150 Sm with a half-life of T 1 / 2 = [ 1 . 5 - 0.6 + 2.3 ( stat ) ± 0.4 ( syst ) ] × 10 20 year, the 2 ν 2 β half-life of 150 Nd for the transition to the 0 1 + level is T 1 / 2 = [ 1 . 03 - 0.22 + 0.35 ( stat ) - 0.19 + 0.16 ( syst ) ] × 10 20 year, in agreement with the previous experiments. Both half-life values reasonably agree with the theoretical calculations in the framework of proton-neutron QRPA with isospin restoration combined with like nucleon QRPA for description of excited states in the final nuclei. For 2 ν 2 β and 0 ν 2 β transitions of 150 Nd and 148 Nd to several excited levels of 150 Sm and 148 Sm , limits were set at level of T 1 / 2 > 10 20 - 10 21 year.

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.

Cryogenic calorimeters are among the leading technologies for searching for rare events. The CUPID experiment is exploiting this technology to deploy a tonne-scale detector to search for neutrinoless double-beta decay of$$^{100}$$100 Mo. The CUPID collaboration proposed an innovative approach to assembling cryogenic calorimeters in a stacked configuration, held in position solely by gravity. This gravity-based assembly method is unprecedented in the field of cryogenic calorimeters and offers several advantages, including relaxed mechanical tolerances and simplified construction. To assess and optimize its performance, we constructed a medium-scale prototype hosting 28  Li$$_2$$2 MoO$$_4$$4 crystals and 30 Ge light detectors, both operated as cryogenic calorimeters at the Laboratori Nazionali del Gran Sasso (Italy). Despite an unexpected excess of noise in the light detectors, the results of this test proved (i) a thermal stability better than ±0.5 mK at 10 mK, (ii) a good energy resolution of Li$$_2$$2 MoO$$_4$$4 cryogenic calorimeters, (6.6 ± 2.2) keV FWHM at 2615 keV, and (iii) a Li$$_2$$2 MoO$$_4$$4 light yield measured by the closest light detector of 0.36 keV/MeV, sufficient to guarantee the particle identification requested by CUPID.

In the originally published version of this article, several errors were identified in the author list and acknowledgements section. These have now been corrected as follows: Corrections to the Author List: Barrera has been corrected to Barresi. Copello (affiliation 18) has been corrected to Copello (affiliation 19). F. De Domizio has been corrected to S. Di Domizio. Figueros-Feliciamo has been corrected to Figueroa-Feliciano. Mancarella (affiliations 8, 17) has been corrected to Mancarella (affiliations 8, 18). Manenti (affiliations 18, 19) has been corrected to Manenti (affiliations 19, 20). Mayer (affiliations 3, 20, 31) has been corrected to Mayer (affiliations 3, 21, 31). Pagot has been corrected to Pageot. Puranam (affiliation 20) has been corrected to Puranam (affiliation 21). O. Penek has been corrected to Ö. Penek. L. Pettinacci has been corrected to V. Pettinacci. P. Pirro has been corrected to S. Pirro. Previtale has been corrected to Previtali. Rappoldi (affiliation 18) has been corrected to Rappoldi (affiliation 19). Raselli (affiliation 18) has been corrected to Raselli (affiliation 19). Rizzoli (affiliations 8, 17) has been corrected to Rizzoli (affiliations 8, 18). Rossella (affiliation 18) has been corrected to Rossella (affiliation 19). Correction to the Acknowledgements Section: The following grant numbers were missing and have now been added: This work was supported by NSF-PHY-2412377 and NSF-PHY-1913374. Additionally, on page 11, Section 5, second line, the chemical formula was incorrectly given as Li2MO4. The correct formula is Li2MoO4. The original article has been updated to reflect these corrections. The publisher apologizes for the inconvenience.

Cryogenic calorimeters are among the leading technologies for searching for rare events. The CUPID experiment is exploiting this technology to deploy a tonne-scale detector to search for neutrinoless double-beta decay of 100Mo. The CUPID collaboration proposed an innovative approach to assembling cryogenic calorimeters in a stacked configuration, held in position solely by gravity. This gravity-based assembly method is unprecedented in the field of cryogenic calorimeters and offers several advantages, including relaxed mechanical tolerances and simplified construction. To assess and optimize its performance, we constructed a medium-scale prototype hosting 28 Li2 MoO4 crystals and 30 Ge light detectors, both operated as cryogenic calorimeters at the Laboratori Nazionali del Gran Sasso (Italy). Despite an unexpected excess of noise in the light detectors, the results of this test proved (i) a thermal stability better than ±0.5 mK at 10 mK, (ii) a good energy resolution of Li2 MoO4 cryogenic calorimeters, (6.6 ± 2.2) keV FWHM at 2615 keV, and (iii) a Li2 MoO4 light yield measured by the closest light detector of 0.36 keV/MeV, sufficient to guarantee the particle identification requested by CUPID.