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1. A first test of CUPID prototypal light detectors with NTD-Ge sensors in a pulse-tube cryostat

   https://doi.org/10.1088/1748-0221/18/06/P06033  

   Alfonso, K.; Armatol, A.; Augier, C.; Avignone, F.T.; Azzolini, O.; Balata, M.; Barabash, A.S.; Bari, G.; Barresi, A.; Baudin, D.; et al (June 2023, Journal of Instrumentation)

   Abstract 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. 

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2. First demonstration of a TES based cryogenic Li₂¹⁰⁰MoO₄ detector for neutrinoless double beta decay search

   https://doi.org/10.1140/epjc/s10052-025-13844-4  

   Bratrud, G; Chang, C L; Chen, R; Cudmore, E; Figueroa-Feliciano, E; Hong, Z; Kennard, K T; Lewis, S; Lisovenko, M; Mateo, L O; et al (March 2025, The European Physical Journal C)

   Cryogenic calorimetric experiments to search for neutrinoless double-beta decay (0νββ) are highly competitive, scalable, and versatile in isotope choice. The largest planned detector array, CUPID, consists of about 1500 individual Li₂¹⁰⁰MoO₄ detector modules, with further scaling envisioned for a follow-up experiment (CUPID-1T). In this article, we present a novel detector concept targeting this second stage, using a low-impedance TES-based readout for the Li₂MoO₄ absorber. This design is easily mass-produced and supports multiplexed readout. We describe the detector design and results from a first prototype operated at the NEXUS shallow underground facility at Fermilab. The detector is a 2-cm-side cube with a mass of 21 g, strongly thermally coupled to its readout chip, allowing rise-times of approximately 0.5 ms. This is more than an order of magnitude faster than current NTD-based detectors and is expected to effectively mitigate backgrounds caused by pile-up of two independent two-neutrino decay events occurring close in time. With a baseline resolution of 1.95 keV (FWHM), these performance parameters extrapolate to a background index from pile-up as low as 5 × 10⁻⁶ counts/keV/kg/year in CUPID-sized crystals. The detector was calibrated up to the MeV region, demonstrating sufficient dynamic range for 0νββ searches. In combination with a SuperCDMS HVeV detector, this setup also enabled a precision measurement of the scintillation time constants of Li₂MoO₄, revealing a primary component with a fast ~20 μs time scale. 

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3. Sensitivity of the CUPID experiment to $$0\nu \beta \beta $$ decay of 100Mo

   https://doi.org/10.1140/epjc/s10052-026-15296-w  

   Alfonso, K; Armatol, A; Augier, C; Avignone, F T; Azzolini, O; Barabash, A S; Bari, G; Barresi, A; Baudin, D; Bellini, F; et al (June 2026, The European Physical Journal C)

   Abstract CUPID is a next-generation bolometric experiment to search for neutrinoless double-beta decay ($$0\nu \beta \beta $$ $0\nu \beta \beta$ ) of¹⁰⁰Mo using Li$$_2$$ $_2^{}$ MoO$$_4$$ $_4^{}$ scintillating crystals. It will operate 1596 crystals at$$\sim $$ $\sim$ 10 mK in the CUORE cryostat at the Laboratori Nazionali del Gran Sasso in Italy. Each crystal will be facing two Ge-based bolometric light detectors for$$\alpha $$ $\alpha$ rejection. We compute the discovery and the exclusion sensitivity of CUPID to$$0\nu \beta \beta $$ $0\nu \beta \beta$ in a Frequentist and a Bayesian framework. This computation is done numerically based on pseudo-experiments. For the CUPIDbaselinescenario, with a background and an energy resolution of$$1.0 \times 10^{-4}$$ $1.0\times {10}^{-4}$ counts/keV/kg/yr and 5 keV FWHM at the Q-value, respectively, this results in a Bayesian exclusion sensitivity (90% c.i.) of$$\hat{T}_{1/2} > 1.6 \times 10^{27} \ \textrm{yr}$$ ${\hat{T}}_{1/2}>1.6\times {10}^{27}\text{yr}$ , corresponding to the effective Majorana neutrino mass of$$\hat{m}_{\beta \beta } < \ 9.6$$ ${\hat{m}}_{\beta \beta }<9.6$ –$$28 \ \textrm{meV}$$ $28\text{meV}$ . The Frequentist discovery sensitivity (3$$\sigma $$ $\sigma$ ) is$$\hat{T}_{1/2}= 1.0 \times 10^{27} \ \textrm{yr}$$ ${\hat{T}}_{1/2}=1.0\times {10}^{27}\text{yr}$ , corresponding to$$\hat{m}_{\beta \beta }= \ 12$$ ${\hat{m}}_{\beta \beta }=12$ –$$36 \ \textrm{meV}$$ $36\text{meV}$ . 

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4. $$\alpha $$-event characterization and rejection in point-contact HPGe detectors

   https://doi.org/10.1140/epjc/s10052-022-10161-y  

   Arnquist, I. J.; Avignone, F. T.; Barabash, A. S.; Barton, C. J.; Bertrand, F. E.; Blalock, E.; Bos, B.; Busch, M.; Buuck, M.; Caldwell, T. S.; et al (March 2022, The European Physical Journal C)

   Abstract P-type point contact (PPC) HPGe detectors are a leading technology for rare event searches due to their excellent energy resolution, low thresholds, and multi-site event rejection capabilities. We have characterized a PPC detector’s response to $$\alpha $$ α particles incident on the sensitive passivated and p $$^+$$ + surfaces, a previously poorly-understood source of background. The detector studied is identical to those in the Majorana Demonstrator experiment, a search for neutrinoless double-beta decay ( $$0\nu \beta \beta $$ 0 ν β β ) in $$^{76}$$ 76 Ge. $$\alpha $$ α decays on most of the passivated surface exhibit significant energy loss due to charge trapping, with waveforms exhibiting a delayed charge recovery (DCR) signature caused by the slow collection of a fraction of the trapped charge. The DCR is found to be complementary to existing methods of $$\alpha $$ α identification, reliably identifying $$\alpha $$ α background events on the passivated surface of the detector. We demonstrate effective rejection of all surface $$\alpha $$ α events (to within statistical uncertainty) with a loss of only 0.2% of bulk events by combining the DCR discriminator with previously-used methods. The DCR discriminator has been used to reduce the background rate in the $$0\nu \beta \beta $$ 0 ν β β region of interest window by an order of magnitude in the Majorana Demonstrator   and will be used in the upcoming LEGEND-200 experiment. 

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5. Exploring the keV-scale physics potential of CUORE

   https://doi.org/10.1103/fv25-bfgx  

   Adams, D Q; Alduino, C; Alfonso, K; Armatol, A; Avignone, F T; Azzolini, O; Bari, G; Bellini, F; Benato, G; Beretta, M; et al (January 2026, Physical Review D)

   We present the analysis techniques developed to explore the keV-scale energy region of the Cryogenic Underground Observatory for Rare Events (CUORE) experiment, based on more than 2 metric ton yr of data collected over five years. By prioritizing a stricter selection over a larger exposure, we are able to optimize data selection for thresholds at 10 keV and 3 keV with 691 kg yr and 11 kg yr of data, respectively. We study how the performance varies among the 988-detector array with different detector characteristics and data-taking conditions. We achieve an average baseline resolution of $2.54\pm 0.14\mathrm{keV}$ FWHM and $1.18\pm 0.02\mathrm{keV}$ FWHM for the data selection at 10 keV and 3 keV, respectively. The analysis methods employed reduce the overall background by about an order of magnitude, reaching $2.06\pm 0.05\mathrm{counts}/\left(\mathrm{keV}\mathrm{kg}\mathrm{days}\right)$ and $16\pm 2\mathrm{counts}/\left(\mathrm{keV}\mathrm{kg}\mathrm{days}\right)$ at the thresholds of 10 keV and 3 keV. We evaluate for the first time the near-threshold reconstruction efficiencies of the CUORE experiment, and find these to be $50\pm 2\%$ and $26\pm 4\%$ at 10 keV and 3 keV, respectively. This analysis provides crucial insights into rare decay studies, new physics searches, and keV-scale background modeling with CUORE. We demonstrate that ton-scale cryogenic calorimeters can operate across a wide energy range, from keV to MeV, establishing their scalability as versatile detectors for rare event and dark matter physics. These findings also inform the optimization of future large mass cryogenic calorimeters to enhance the sensitivity to low-energy phenomena. 

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