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1. Twelve-crystal prototype of Li ₂ MoO ₄ scintillating bolometers for CUPID and CROSS experiments

   https://doi.org/10.1088/1748-0221/18/06/P06018  

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

   Abstract 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 228 Th and 226 Ra. 

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2. First demonstration of a TES based cryogenic Li$$_2$$MoO$$_4$$ 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 (January 2025, The European Physical Journal C)

   Abstract Cryogenic calorimetric experiments to search for neutrinoless double-beta decay ($$0\nu \beta \beta $$ $0\nu \beta \beta$) are highly competitive, scalable and versatile in isotope. The largest planned detector array, CUPID, is comprised of about 1500 individual Li$$_{2}$$ $_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$$\sim $$ $\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$$0\nu \beta \beta $$ $0\nu \beta \beta$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$$_2$$ $_2^{}$MoO$$_4$$ $_4^{}$, which showed a primary component with a fast O(20 $$\upmu $$ $\mu$s) time scale. 

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3. Search for double-beta decay of $$\mathrm {^{130}Te}$$ to the $$0^+$$ states of $$\mathrm {^{130}Xe}$$ with CUORE

   https://doi.org/10.1140/epjc/s10052-021-09317-z  

   Adams, D. Q.; Alduino, C.; Alfonso, K.; Avignone, F. T.; Azzolini, O.; Bari, G.; Bellini, F.; Benato, G.; Biassoni, M.; Branca, A.; et al (July 2021, The European Physical Journal C)

   null (Ed.)

   Abstract The CUORE experiment is a large bolometric array searching for the lepton number violating neutrino-less double beta decay ( $$0\nu \beta \beta $$ 0 ν β β ) in the isotope $$\mathrm {^{130}Te}$$ 130 Te . In this work we present the latest results on two searches for the double beta decay (DBD) of $$\mathrm {^{130}Te}$$ 130 Te to the first $$0^{+}_2$$ 0 2 + excited state of $$\mathrm {^{130}Xe}$$ 130 Xe : the $$0\nu \beta \beta $$ 0 ν β β decay and the Standard Model-allowed two-neutrinos double beta decay ( $$2\nu \beta \beta $$ 2 ν β β ). Both searches are based on a 372.5 kg $$\times $$ × yr TeO $$_2$$ 2 exposure. The de-excitation gamma rays emitted by the excited Xe nucleus in the final state yield a unique signature, which can be searched for with low background by studying coincident events in two or more bolometers. The closely packed arrangement of the CUORE crystals constitutes a significant advantage in this regard. The median limit setting sensitivities at 90% Credible Interval (C.I.) of the given searches were estimated as $$\mathrm {S^{0\nu }_{1/2} = 5.6 \times 10^{24} \, \mathrm {yr}}$$ S 1 / 2 0 ν = 5.6 × 10 24 yr for the $${0\nu \beta \beta }$$ 0 ν β β decay and $$\mathrm {S^{2\nu }_{1/2} = 2.1 \times 10^{24} \, \mathrm {yr}}$$ S 1 / 2 2 ν = 2.1 × 10 24 yr for the $${2\nu \beta \beta }$$ 2 ν β β decay. No significant evidence for either of the decay modes was observed and a Bayesian lower bound at $$90\%$$ 90 % C.I. on the decay half lives is obtained as: $$\mathrm {(T_{1/2})^{0\nu }_{0^+_2} > 5.9 \times 10^{24} \, \mathrm {yr}}$$ ( T 1 / 2 ) 0 2 + 0 ν > 5.9 × 10 24 yr for the $$0\nu \beta \beta $$ 0 ν β β mode and $$\mathrm {(T_{1/2})^{2\nu }_{0^+_2} > 1.3 \times 10^{24} \, \mathrm {yr}}$$ ( T 1 / 2 ) 0 2 + 2 ν > 1.3 × 10 24 yr for the $$2\nu \beta \beta $$ 2 ν β β mode. These represent the most stringent limits on the DBD of $$^{130}$$ 130 Te to excited states and improve by a factor $$\sim 5$$ ∼ 5 the previous results on this process. 

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4. Measurement of the distribution of 207Bi depositions on calibration sources for SuperNEMO

   https://doi.org/doi:10.1088/1748-0221/16/07/T07012  

   SuperNEMO Collaboration, R. Arnold1 (July 2021, Journal of instrumentation)

   The SuperNEMO experiment will search for neutrinoless double-beta decay (0νββ), and study the Standard-Model double-beta decay process (2νββ). The SuperNEMO technology can measure the energy of each of the electrons produced in a double-beta (ββ) decay, and can reconstruct the topology of their individual tracks. The study of the double-beta decay spectrum requires very accurate energy calibration to be carried out periodically. The SuperNEMO Demonstrator Module will be calibrated using 42 calibration sources, each consisting of a droplet of 207Bi within a frame assembly. The quality of these sources, which depends upon the entire ^207Bi droplet being contained within the frame, is key for correctly calibrating SuperNEMO's energy response. In this paper, we present a novel method for precisely measuring the exact geometry of the deposition of 207Bi droplets within the frames, using Timepix pixel detectors. We studied 49 different sources and selected 42 high-quality sources with the most central source positioning. 

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5. Topologies of $$^{76}$$Ge double-beta decay events and calibration procedure biases

   https://doi.org/10.1140/epjc/s10052-023-11396-z  

   Comellato, Tommaso; Agostini, Matteo; Schönert, Stefan (March 2023, The European Physical Journal C)

   Abstract The analysis of the time profile of electrical signals produced by energy depositions in germanium detectors allows discrimination of events with different topologies. This is especially relevant for experiments searching for the neutrinoless double beta decay of $$^{76}$$ 76 Ge to distinguish the sought-after signal from other background sources. The standard calibration procedures used to tune the selection criteria for double-beta decay events use a $$^{228}$$ 228 Th source, because it provides samples of signal-like events. These samples exhibit energy spatial distributions with subtle different topologies compared to neutrinoless double-beta decay events. In this work, we will characterize these topological differences and, with the support of a $$^{56}$$ 56 Co source, evaluate biases and precision of calibration techniques which use such event samples. Our results will be particularly relevant for future experiments in which a solid estimation of the efficiency is required. 

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