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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. 

We present results of a search for spin-independent dark matter-nucleus interactions in a $1{\mathrm{cm}}^2$by 1 mm thick (0.233 g) high-resolution silicon athermal phonon detector operated above ground. For interactions in the substrate, this detector achieves an rms baseline energy resolution of $361.5\left(4\right)\mathrm{m}\mathrm{eV}$(statistical error), the best for any athermal phonon detector to date. With an exposure of $0.233\mathrm{g}\times 12$hours, we place the most stringent constraints on dark matter masses between 44 and $87\mathrm{M}\mathrm{eV}/{\mathrm{c}}^2$, with the lowest unexplored cross section of $4\times {10}^{-32}{\mathrm{c}\mathrm{m}}^2$at $87\mathrm{M}\mathrm{eV}/{\mathrm{c}}^2$. We employ a conservative salting technique to reach the lowest dark matter mass ever probed via direct detection experiment. This constraint is enabled by two-channel rejection of low energy backgrounds that are coupled to individual sensors. 

Abstract CUPID, the CUORE Upgrade with Particle Identification, is a next-generation experiment to search for neutrinoless double beta decay ($$0\mathrm {\nu \beta \beta }$$ $0\nu \beta \beta$) and other rare events using enriched Li$$_{2}$$ $_2^{}$$$^{100}$$ $_{}^{100}$MoO$$_{4}$$ $_4^{}$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$$0\mathrm {\nu \beta \beta }$$ $0\nu \beta \beta$of$$^{100}$$ $_{}^{100}$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$$^{-4}$$ $_{}^{-4}$ cts$$/($$ $/($keV$$\cdot $$ $·$kg$$\cdot $$ $·$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$$1.8\cdot 10^{27}$$ $1.8·{10}^{27}$ yr, corresponding to an effective Majorana neutrino mass ($$m_{\beta \beta }$$ $m_{\beta \beta }$) sensitivity of 9–15 meV, and a$$3\sigma $$ $3\sigma$discovery sensitivity of$$1\cdot 10^{27}$$ $1·{10}^{27}$ yr, corresponding to an$$m_{\beta \beta }$$ $m_{\beta \beta }$range of 12–21 meV.