Cryogenic calorimetric experiments to search for neutrinoless double-beta decay ($0\nu\beta\beta$) are highly competitive, scalable and versatile in isotope. The largest planned detector array, CUPID, is comprised of about 1500 individual Li$_2^{100}$MoO$_{4}$ detector modules with a further scale up envisioned for a follow up experiment (CUPID-1T). In this article, we present a novel detector concept targeting this second stage with a low impedance TES based readout for the Li$_2$MoO$_{4}$ absorber that is easily mass-produced and lends itself to a multiplexed readout. We present the detector design and results from a first prototype detector operated at the NEXUS shallow underground facility at Fermilab. The detector is a 2-cm-side cube with 21$\,$g mass that is strongly thermally coupled to its readout chip to allow rise-times of $\sim$0.5$\,$ms. This design is more than one order of magnitude faster than present NTD based detectors and is hence expected to effectively mitigate backgrounds generated through the pile-up of two independent two neutrino decay events coinciding close in time. Together with a baseline resolution of 1.95$\,$keV (FWHM) these performance parameters extrapolate to a background index from pile-up as low as $5\cdot 10^{-6}\,$counts/keV/kg/yr in CUPID size crystals. The detector was calibrated up to the MeV region showing sufficient dynamic range for $0\nu\beta\beta$ searches. In combination with a SuperCDMS HVeV detector this setup also allowed us to perform a precision measurement of the scintillation time constants of Li$_2$MoO$_{4}$. The crystal showed a significant fast scintillation emission with O(10$\,\mu$s) time-scale, more than an order below the detector response of presently considered light detectors suggesting the possibility of further progress in pile-up rejection through better light detectors in the future.

Abstract Cryogenic calorimetric experiments to search for neutrinoless double-beta decay ( $$0\nu \beta \beta $$ 0 ν β β ) are highly competitive, scalable and versatile in isotope. The largest planned detector array, CUPID, is comprised of about 1500 individual Li $$_{2}$$ 2 $$^{100}$$ 100 MoO $$_4$$ 4 detector modules with a further scale up envisioned for a follow up experiment (CUPID-1T). In this article, we present a novel detector concept targeting this second stage with a low impedance TES based readout for the Li $$_2$$ 2 MoO $$_4$$ 4 absorber that is easily mass-produced and lends itself to a multiplexed readout. We present the detector design and results from a first prototype detector operated at the NEXUS shallow underground facility at Fermilab. The detector is a 2-cm-side cube with 21 g mass that is strongly thermally coupled to its readout chip to allow rise-times of $$\sim $$ ∼ 0.5 ms. This design is more than one order of magnitude faster than present NTD based detectors and is hence expected to effectively mitigate backgrounds generated through the pile-up of two independent two neutrino decay events coinciding close in time. Together with a baseline resolution of 1.95 keV (FWHM) these performance parameters extrapolate to a background index from pile-up as low as $$5\cdot 10^{-6}$$ 5 · 10 - 6 counts/keV/kg/yr in CUPID size crystals. The detector was calibrated up to the MeV region showing sufficient dynamic range for $$0\nu \beta \beta $$ 0 ν β β searches. In combination with a SuperCDMS HVeV detector this setup also allowed us to perform a precision measurement of the scintillation time constants of Li $$_2$$ 2 MoO $$_4$$ 4 , which showed a primary component with a fast O(20 $$\upmu $$ μ s) time scale.

BINGO is a project aiming to set the grounds for large-scale bolometric neutrinoless double-beta-decay experiments capable of investigating the effective Majorana neutrino mass at a few meV level. It focuses on developing innovative technologies (a detector assembly, cryogenic photodetectors and active veto) to achieve a very low background index, of the order of 10 -5 counts/(keV kg yr) in the region of interest. The BINGO demonstrator, called MINI-BINGO, is designed to investigate the promising double-beta-decay isotopes 100 Mo and 130 Te and it will be composed of Li2MoO4 and TeO2 crystals coupled to bolometric light detectors and surrounded by a Bi4Ge3O12-based veto. This will allow us to reject a significant background in bolometers caused by surface contamination from a-active radionuclides by means of light yield selection and to mitigate other sources of background, such as surface contamination from ,3-active radionuclides, external y radioactivity, and pile-up due to random coincidence of background events. This paper describes an R&D program towards the BINGO goals, particularly focusing on the development of an innovative assembly designed to reduce the passive materials within the line of sight of the detectors, which is expected to be a dominant source of background in next-generation bolometric experiments. We present the performance of two prototype modules - housing four cubic (4.5-cm side) Li2MoO4 crystals in total - operated in the Canfranc underground laboratory in Spain within a facility developed for the CROSS double-beta-decay experiment.

The CROSS experiment will search for neutrinoless double-beta decay using a specific mechanical structure to hold thermal detectors. The design of the structure was tuned to minimize the background contribution, keeping an optimal detector performance. A single module of the structure holds two scintillating bolometers (with a crystal size of 45 x 45 x 45 mm and a Ge slab facing the crystal's upper side) in the Cu frame, allowing for a modular construction of a large-scale array. Two designs are released: the initial Thick version contains around 15% of Cu over the crystal mass (lithium molybdate, LMO), while this ratio is reduced to similar to 6% in a finer ( Slim ) design. Both designs were tested extensively at aboveground (IJCLab, France) and underground (LSC, Spain) laboratories. In particular, at LSC we used a pulse-tube-based CROSS facility to operate a 6-crystal array of LMOs enriched/depleted in Mo-100. The tested LMOs show high spectrometric performance in both designs; notably, the measured energy resolution is 5-7 keV FWHM at 2615 keV gamma s, nearby the Q-value of Mo-100 (3034 keV). Due to the absence of a reflective cavity around LMOs, a low scintillation signal is detected by Ge bolometers: similar to 0.3 keV (150 photons) for 1-MeV gamma(beta) LMO-event. Despite that, an acceptable separation between alpha and gamma(beta) events is achieved with most devices. The highest efficiency is reached with light detectors in the Thick design thanks to a lower baseline noise width (0.05-0.09 keV RMS) when compared to that obtained in the Slim version (0.10-0.35 keV RMS). Given the pivotal role of bolometric photodetectors for particle identification and random coincidences rejection, we will use the structure here described with upgraded light detectors, featuring thermal signal amplification via the Neganov-Trofimov-Luke effect, as also demonstrated in the present work.

Highly forbidden β decays provide a sensitive test to nuclear models in a regime in which the decay goes through high spin-multipole states, similar to the neutrinoless double- β decay process. There are only 3 nuclei (50V, 113Cd, 115In) which undergo a 4^th forbidden non-unique β decay. In this work, we compare the experimental 113Cd spectrum to theoretical spectral shapes in the framework of the spectrum-shape method. We measured with high precision, with the lowest energy threshold and the best energy resolution ever, the β spectrum of 113Cd embedded in a 0.43 kg CdWO_4 crystal, operated over 26 days as a bolometer at low temperature in the Canfranc underground laboratory (Spain). We performed a Bayesian fit of the experimental data to three nuclear models (IBFM-2, MQPM and NSM) allowing the reconstruction of the spectral shape as well as the half-life. The fit has two free parameters, one of which is the effective weak axial-vector coupling constant, g_A^eff , which resulted in g_A^eff between 1.0 and 1.2, compatible with a possible quenching. Based on the fit, we measured the half-life of the 113Cd β decay including systematic uncertainties as 7.73^+0.60_-0.57× 10^15 yr, in agreement with the previous experiments. These results represent a significant step towards a better understanding of low-energy nuclear processes.

The current experiments searching for neutrinoless double- β ( 0νββ ) decay also collect large statistics of Standard Model allowed two-neutrino double- β ( 2νββ ) decay events. These can be used to search for Beyond Standard Model (BSM) physics via 2νββ decay spectral distortions. 100Mo has a natural advantage due to its relatively short half-life, allowing higher 2νββ decay statistics at equal exposures compared to the other isotopes. We demonstrate the potential of the dual read-out bolometric technique exploiting a 100Mo exposure of 1.47 kg × years, acquired in the CUPID-Mo experiment at the Modane underground laboratory (France). We set limits on 0νββ decays with the emission of one or more Majorons, on 2νββ decay with Lorentz violation, and 2νββ decay with a sterile neutrino emission. In this analysis, we investigate the systematic uncertainty induced by modeling the 2νββ decay spectral shape parameterized through an improved model, an effect never considered before. This work motivates searches for BSM processes in the upcoming CUPID experiment, which will collect the largest amount of 2νββ decay events among the next-generation experiments.

Abstract The current experiments searching for neutrinoless double- $$\beta $$ β ( $$0\nu \beta \beta $$ 0 ν β β ) decay also collect large statistics of Standard Model allowed two-neutrino double- $$\beta $$ β ( $$2\nu \beta \beta $$ 2 ν β β ) decay events. These can be used to search for Beyond Standard Model (BSM) physics via $$2\nu \beta \beta $$ 2 ν β β decay spectral distortions. 100Mo has a natural advantage due to its relatively short half-life, allowing higher $$2\nu \beta \beta $$ 2 ν β β decay statistics at equal exposures compared to the other isotopes. We demonstrate the potential of the dual read-out bolometric technique exploiting a 100Mo exposure of 1.47 kg $$\times $$ × years, acquired in the CUPID-Mo experiment at the Modane underground laboratory (France). We set limits on $$0\nu \beta \beta $$ 0 ν β β decays with the emission of one or more Majorons, on $$2\nu \beta \beta $$ 2 ν β β decay with Lorentz violation, and $$2\nu \beta \beta $$ 2 ν β β decay with a sterile neutrino emission. In this analysis, we investigate the systematic uncertainty induced by modeling the $$2\nu \beta \beta $$ 2 ν β β decay spectral shape parameterized through an improved model, an effect never considered before. This work motivates searches for BSM processes in the upcoming CUPID experiment, which will collect the largest amount of $$2\nu \beta \beta $$ 2 ν β β decay events among the next-generation experiments.

We report on the development of thermal detectors based on large-size tellurium dioxide crystals (45 x 45 x 45 mm), containing tellurium enriched in 130 Te to about 91%, for the CROSS double-beta decay experiment. A powder used for the crystals growth was additionally purified by the directional solidification method, resulting in the reduction of the concentration of impurities by a factor 10, to a few ppm of the total concentration of residual elements (the main impurity is Fe). The purest part of the ingot (the first 200 mm, about 80% of the total length of the cylindrical part of the ingot) was determined by scanning segregation profiles of impurities and used for the 130 TeO 2 powder production with no evidence of re-contamination. The crystal growth was verified with precursors produced from a powder with natural Te isotopic composition, and two small-size (20 x 20 x 10 mm) samples were tested at a sea-level laboratory showing high bolometric and spectrometric performance together with acceptable 210 Po content (below 10 mBq/kg). This growth method was then applied for the production of six large cubic 130 TeO 2 crystals and 4 of them were taken randomly to be characterized at the Canfranc underground laboratory, in the CROSS-dedicated low-background cryogenic facility. Two 130 TeO 2 samples were coated with a thin, O (100 nm), metal film in form of Al layer (on 4 sides) or AlPd grid (on a single side) to investigate the possibility to tag surface events by pulse-shape discrimination. Similarly to the small natural precursors, large-volume 130 TeO 2 bolometers show high performance and even better internal purity (210Po 210 Po activity 1 mBq/kg, while activities of 228 Th and 226 Ra are below 0.01 mBq/kg), satisfying requirements for the CROSS and, potentially, next-generation experiments.

The first detailed study on the performance of a ZnO-based cryogenic scintillating bolometer as a detector to search for rare processes in zinc isotopes was carried out. A 7.2 g ZnO low-temperature detector, containing more than 80% of zinc in its mass, exhibits good energy resolution of baseline noise 1.0-2.7 keV FWHM at various working temperatures resulting in a low-energy threshold for the experiment, 2.0-6.0 keV. The light yield for /3/y events was measured as 1.5(3) keV/MeV, while it varies for a particles in the range of 0.2-3.0 keV/MeV. The detector demonstrates an effective identification of /3/y events from a events using time-properties of only heat signals. The radiopurity of the ZnO crystal was evaluated using the Inductively Coupled Plasma Mass Spectrometry, an ultra-low-background High Purity Ge y-spectrometer, and bolometric measurements. Only limits were set at the level of O(1-100) mBq/kg on activities of 40K, 137Cs and daughter nuclides from the U/Th natural decay chains. The total internal a-activity was measured as 22(2) mBq/kg, with a major contribution caused by 6(1) mBq/kg of 232Th and 12(2) mBq/kg of 234U. Limits on double beta decay (DBD) processes in 64Zn and 70Zn isotopes were set on the level of O (1017-1018) yr for various decay modes, profiting from 271 h of acquired background data inthe above-ground lab. This study shows a good potential for ZnO-based scintillating bolometers to search for DBD processes of Zn isotopes, especially in 64Zn, with the most prominent spectral features at similar to 10-20 keV, like the two-neutrino double electron capture. A 10 kg-scale experiment can reach the experimental sensitivity at the level of O(1024) yr.

CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation 0νββ 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 2νββ 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 ^+0.9_-0.8 (stat) ^+1.5_-0.7 (syst) × 10 ^-3 counts/ Δ E_FWHM/mol_iso/year, the lowest in a bolometric 0νββ decay experiment.

The CUPID-Mo experiment, located at the Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of 20 Li-2 Mo-100 O-4 (LMO) calorimeters, each equipped with a Ge light detector for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double-beta decays of Mo-100 to the first 0(+) and 2(+) excited states of Ru-100 using the full CUPID-Mo exposure (2.71 kg yr of LMO). We measure the half-life of 2 nu beta beta decay to the 0(1)(+) state as T-1/2(2 nu -> 01+) = (7.5 +/- 1 0.8 (stat.)(-0.3)(+0.4) (syst.)) x 10(20) yr. The bolometric technique enables measurement of the electron energies as well as the gamma rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the 2(1)(+) state of T-1/2(2 nu -> 21+) > 4.4 x 10(21) yr (90% c.i.) and on the neutrinoless modes of T-1/2(0 nu -> 21+) > 2.1 x 10(23) yr (90% c.i.), T-1/2(0 nu -> 01+) > 1.2 x 10(23) yr (90% c.i.). Information on the electrons' spectral shape is obtained, which allows us to 1 make the first comparison of the single and higher state dominance 2 nu beta beta decay models for the 0(1)(+) excited state of Ru-100.

Neutrinoless double beta decay (0νββ) is a yet unobserved nuclear process that would demonstrate Lepton number violation, a clear evidence of beyond standard model physics. The process two neutrino double beta decay (2νββ) is allowed by the standard model and has been measured in numerous experiments. In this Letter, we report a measurement of 2νββ decay half-life of ^{100}Mo to the ground state of ^{100}Ru of [7.07±0.02(stat)±0.11(syst)]×10^{18}  yr by the CUPID-Mo experiment. With a relative precision of ±1.6% this is the most precise measurement to date of a 2νββ decay rate in ^{100}Mo. In addition, we constrain higher-order corrections to the spectral shape, which provides complementary nuclear structure information. We report a novel measurement of the shape factor ξ_{3,1}=0.45±0.03(stat)±0.05(syst) based on a constraint on the ratio of higher-order terms from theory, which can be reliably calculated. This is compared to theoretical predictions for different nuclear models. We also extract the first value for the effective axial vector coupling constant obtained from a spectral shape study of 2νββ decay.

An array of twelve 0.28 kg lithium molybdate (LMO) low-temperature bolometers equipped with 16 bolometric Ge light detectors, aiming at optimization of detector structure for CROSS and CUPID double-beta decay experiments, was constructed and tested in a low-background pulse-tube-based cryostat at the Canfranc underground laboratory in Spain. Performance of the scintillating bolometers was studied depending on the size of phonon NTD-Ge sensors glued to both LMO and Ge absorbers, shape of the Ge light detectors (circular vs. square, from two suppliers), in different light collection conditions (with and without reflector, with aluminum coated LMO crystal surface). The scintillating bolometer array was operated over 8 months in the low-background conditions that allowed to probe a very low, μBq/kg, level of the LMO crystals radioactive contamination by ^228Th and ^226Ra.

We report on the development of scintillating bolometers based on lithium molybdate crystals containing molybdenum depleted in the double-β active isotope ^100Mo (Li_2^100deplMoO_4). We used two Li_2^100deplMoO_4 cubic samples, 45 mm side and 0.28 kg each, produced following purification and crystallization protocols developed for double-β search experiments with ^100Mo-enriched Li_2MoO_4 crystals. Bolometric Ge detectors were utilized to register scintillation photons emitted by the Li_2^100deplMoO_4 crystal scintillators. The measurements were performed in the CROSS cryogenic set-up at the Canfranc underground laboratory (Spain). We observed that the Li_2^100deplMoO_4 scintillating bolometers are characterized by excellent spectrometric performance (∼3–6 keV FWHM at 0.24–2.6 MeV γ's), moderate scintillation signal (∼0.3–0.6 keV/MeV depending on light collection conditions) and high radiopurity (^228Th and ^226Ra activities are below a few μBq/kg), comparable to the best reported results of low-temperature detectors based on Li_2MoO_4 with natural or ^100Mo-enriched molybdenum content. Prospects of Li_2^100deplMoO_4 bolometers for use in rare-event search experiments are briefly discussed.

CUPID is a next-generation bolometric experiment aiming at searching for neutrinoless double-beta decay with ∼250 kg of isotopic mass of 100 Mo. It will operate at ∼10 mK in a cryostat currently hosting a similar-scale bolometric array for the CUORE experiment at the Gran Sasso National Laboratory (Italy). CUPID will be based on large-volume scintillating bolometers consisting of 100 Mo-enriched Li 2 MoO 4 crystals, facing thin Ge-wafer-based bolometric light detectors. In the CUPID design, the detector structure is novel and needs to be validated. In particular, the CUORE cryostat presents a high level of mechanical vibrations due to the use of pulse tubes and the effect of vibrations on the detector performance must be investigated. In this paper we report the first test of the CUPID-design bolometric light detectors with NTD-Ge sensors in a dilution refrigerator equipped with a pulse tube in an above-ground lab. Light detectors are characterized in terms of sensitivity, energy resolution, pulse time constants, and noise power spectrum. Despite the challenging noisy environment due to pulse-tube-induced vibrations, we demonstrate that all the four tested light detectors comply with the CUPID goal in terms of intrinsic energy resolution of 100 eV RMS baseline noise. Indeed, we have measured 70–90 eV RMS for the four devices, which show an excellent reproducibility. We have also obtained high energy resolutions at the 356 keV line from a 133 Ba source, as good as Ge semiconductor γ detectors in this energy range.

Abstract CUPID-Mo, located in the Laboratoire Souterrain de Modane (France), was a demonstrator for the next generation $$0\nu \beta \beta $$ 0 ν β β decay experiment, CUPID. It consisted of an array of 20 enriched Li $$_{2}$$ 2 $$^{100}$$ 100 MoO $$_4$$ 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 $$2\nu \beta \beta $$ 2 ν β β decay and other processes with high precision. We also measure the radio-purity of the Li $$_{2}$$ 2 $$^{100}$$ 100 MoO $$_4$$ 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 $$^{+0.9}_{-0.8}$$ - 0.8 + 0.9 (stat) $$^{+1.5}_{-0.7}$$ - 0.7 + 1.5 (syst) $$\times ~10 ^{-3}$$ × 10 - 3 counts/ $$\Delta E_{\text {FWHM}}/\text {mol}_{\text {iso}}/\text {year},$$ Δ E FWHM / mol iso / year , the lowest in a bolometric $$0\nu \beta \beta $$ 0 ν β β decay experiment.

The CUPID-Mo experiment, located at the Laboratoire Souterrain de Modane (France), was a demonstrator experiment for CUPID. It consisted of an array of 20Li2Mo100O4 (LMO) calorimeters, each equipped with a Ge light detector for particle identification. In this work, we present the result of a search for two-neutrino and neutrinoless double-β decays of Mo100 to the first 0+ and 2+ excited states of Ru100 using the full CUPID-Mo exposure (2.71kgyr of LMO). We measure the half-life of 2νββ decay to the 01+ state as T1/22ν→01+=(7.5±0.8(stat.)−0.3+0.4(syst.))×1020yr. The bolometric technique enables measurement of the electron energies as well as the γ rays from nuclear deexcitation and this allows us to set new limits on the two-neutrino decay to the 21+ state of T1/22ν→21+>4.4×1021yr(90% c.i.) and on the neutrinoless modes of T1/20ν→21+>2.1×1023yr(90% c.i.), T1/20ν→01+>1.2×1023yr(90% c.i.). Information on the electrons' spectral shape is obtained, which allows us to make the first comparison of the single and higher state dominance 2νββ decay models for the 01+ excited state of Ru100.8 MoreReceived 1 August 2022Accepted 2 December 2022DOI:https://doi.org/10.1103/PhysRevC.107.025503©2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasDouble beta decayNeutrinoless double beta decayNuclear structure & decaysPhysical SystemsMajorana neutrinosNeutrinosProperties90 ≤ A ≤ 149Nuclear Physics

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 _ββ of the double-beta decay, and target the goal of a next generation experiment like CUPID.

In preparation for the CROSS experiment to search for double-beta (2/3) decay of 100Mo, we upgraded a low-background facility at the Canfranc underground laboratory (Spain) by installing a magnetic damping-based detector suspension inside a pulse-tube cryostat. We tested the suspension in low-temperature (15 mK) measurements with two scintillating bolometers made of large-volume crystals of 116CdWO4 (reference of the set-up) and Li2MoO4 (R&D of the CLYMENE project in view of the CUPID 2/3 experiment), each coupled to a thin Ge bolometric light detector. Despite the evidence of a residual pulse-tube-induced noise, picked up by cabling, we achieved high performance with all tested devices. In particular, the energy resolution for 2615 keV y-ray measured with both 116CdWO4 and Li2MoO4 bolometers is -6 keV FWHM, among the best-reported results for thermal detectors based on such compounds representing a great interest to searches for 2/3 decay in 116Cd (Q-value is 2813 keV) and 100Mo (3034 keV) respectively. Highly efficient particle identification (a vs. /3/y) is achieved also with the scintillating bolometer made of a low light yield crystal (Li2MoO4), thanks to the low noise (10 eV RMS) exhibited by the light detector exploiting the Neganov-Trofimov-Luke effect for signal amplification. We also found a rather high level of radiopurity in the Li2MoO4 crystal; only traces of 210Po and 226Ra were detected (- 0.1 mBq/kg each), while the 228Th activity is expected to be at least an order of magnitude lower, as well as a 40K activity is below 6 mBq/kg.

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.