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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. 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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3. Transition Edge Sensor Chip Design of a Modular CEvNs Detector for the Ricochet Experiment

   https://doi.org/10.1007/s10909-022-02927-1  

   Chen, Ran; Pinckney, H. Douglas; Figueroa-Feliciano, Enectali; Hong, Ziqing; Schmidt, Benjamin (December 2022, Journal of Low Temperature Physics)

   Coherent elastic neutrino-nucleus scattering (CEνNS) offers a valuable approach in searching for physics beyond the Standard Model. The Ricochet experiment aims to perform a precision measurement of the CEνNS spectrum at the Institut Laue-Langevin nuclear reactor with cryogenic solid-state detectors. The experiment will employ an array of cryogenic thermal detectors, each with a mass of around 30 g and an energy threshold of 50 eV. One section of this array will contain 9 Transition Edge Sensor (TES)-based calorimeters. The design will not only fulfill requirements for Ricochet, but also act as a demonstrator for future neutrino experiments that will require thousands of macroscopic detectors. In this article, we present an updated TES chip design, as well as performance predictions based on a numerical modeling. 

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4. Developing a Large-Scale Cryogenic System for the Simultaneous Operation of Three Detector Focal Planes in TolTEC, A New Multichroic Imaging Polarimeter

   https://doi.org/10.1007/s10909-019-02319-y  

   DeNigris, N. S.; Wilson, G. W.; Eiben, M. E.; Lunde, E.; Mauskopf, P.; Contente, R. (May 2020, Journal of Low Temperature Physics)

   TolTEC is an upcoming millimeter-wave imaging polarimeter designed to fill the focal plane of the 50-m-diameter Large Millimeter Telescope (LMT). Combined with the LMT, TolTEC will offer high-angular-resolution (5–10 ) simultaneous, polarization-sensitive observations in three wavelength bands: 1.1, 1.4, and 2.0 mm. Additionally, TolTEC will feature mapping speeds greater than 2 deg2∕mJy2∕h , thus enabling wider surveys of large-scale structure, galaxy evolution, and star formation. These improvements are only possible through the integration of approximately 7000 low-noise, high-responsivity superconducting Lumped Element Kinetic Inductance Detectors. Utilizing three focal planes of detector arrays requires the design, fabrication, and characterization of a unique, large-scale cryogenic system. Based on thermal models and expected photon loading, the focal planes must have a base operational temperature below 150 mK. To achieve this base temperature, TolTEC utilizes two cryocoolers, a Cryomech pulse tube cooler and an Oxford Instruments dilution refrigerator, to establish four thermal stages: 45 K, 4 K, 1 K, and 100 mK. During the design phase, we developed an object-oriented Python code to model the heat loading on each stage as well as the thermal gradients throughout the system. This model has allowed us to improve thermal gradients in the system as well as locate areas of poor thermal conductivity prior to ending a cooldown. The results of our model versus measurements from our cooldowns will be presented along with a detailed overview of TolTEC’s cryogenic system. We anticipate TolTEC to be commissioned at the LMT by Spring 2020. 

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5. Optimization of the first CUPID detector module

   https://doi.org/10.1140/epjc/s10052-022-10720-3  

   Alfonso, K.; Armatol, A.; Augier, C.; Avignone, F. T.; Azzolini, O.; Balata, M.; Barabash, A. S.; Bari, G.; Barresi, A.; Baudin, D.; et al (September 2022, The European Physical Journal C)

   Abstract CUPID will be a next generation experiment searching for the neutrinoless double $$\beta $$ β decay, whose discovery would establish the Majorana nature of the neutrino. Based on the experience achieved with the CUORE experiment, presently taking data at LNGS, CUPID aims to reach a background free environment by means of scintillating Li $$_{2}$$ 2 $$^{100}$$ 100 MoO $$_4$$ 4 crystals coupled to light detectors. Indeed, the simultaneous heat and light detection allows us to reject the dominant background of $$\alpha $$ α particles, as proven by the CUPID-0 and CUPID-Mo demonstrators. In this work we present the results of the first test of the CUPID baseline module. In particular, we propose a new optimized detector structure and light sensors design to enhance the engineering and the light collection, respectively. We characterized the heat detectors, achieving an energy resolution of (5.9 ± 0.2) keV FWHM at the Q -value of $$^{100}$$ 100 Mo (about 3034 keV). We studied the light collection of the baseline CUPID design with respect to an alternative configuration which features gravity-assisted light detectors’ mounting. In both cases we obtained an improvement in the light collection with respect to past measures and we validated the particle identification capability of the detector, which ensures an $$\alpha $$ α particle rejection higher than 99.9%, fully satisfying the requirements for CUPID. 

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