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We report the first search for nuclear ultra-heavy dark matter (UHDM) in a dual-phase liquid argon time projection chamber using the DarkSide-50 experiment. Unlike conventional weakly interacting massive particles (WIMPs), nuclear UHDM candidates may be composed of many dark nucleons and scatter numerous times while passing through the detector. Accounting for energy loss through the Earth's overburden, we apply selection criteria optimized for multi-scatter event topologies using the 532-day low-radiation campaign of the DarkSide-50 detector. Excluded limits on the UHDM-nucleon scattering cross section for dark nucleon masses of mχ=10,50,100,500GeV/c2 are presented. 

Abstract We report the in-situ 3D reconstruction of through-going muons in the CUORE experiment, a cryogenic calorimeter array searching for neutrinoless double beta ($$0\nu \beta \beta $$ $0\nu \beta \beta$ ) decay, leveraging the segmentation of the detector. Due to the slow time response of the detector, time-of-flight estimation is not feasible. Therefore, the track reconstruction is performed using a multi-objective optimization algorithm that relies on geometrical information from the detector as a whole. We measure the integral flux of cosmic-ray muons underground at theLaboratori Nazionali del Gran Sasso, and find our value to be in good agreement with other experiments that have performed a similar measurement. To our knowledge, this work represents the first demonstration of 3D particle tracking and reconstruction of through-going muons with per-event angular determination in a millikelvin cryogenic detector array. The analysis performed for this work will be critical for validating the muon-related background in CUPID, a next-generation$$0\nu \beta \beta $$ $0\nu \beta \beta$ experiment, and for follow-up studies on detector response and on delayed products induced by cosmic-ray muons. 

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. 

Abstract The Recoil Directionality project (ReD) within the DarkSide-20k Collaboration characterizedthe response of a liquid argon (LAr) dual-phase Time Projection Chamber (TPC) to neutron induced nuclear recoils,to measure the ionization yield at low-energy. The ionization yield is a critical parameter for the experiments searchingfor Dark Matter in the form of low-mass WIMPs and measurements in Ar below 10 keV are scarce in theliterature. ReD was designed to cover the gap down to 2 keV. The ReD data taking took place in 2023 at the INFNSezione di Catania. The TPC was irradiated by neutrons from an intense²⁵²Cf fission source in orderto produce Ar recoils inthe energy range of interest. The energy of the nuclear recoils produced within the TPC by (n,n')scattering was determined by detecting the outgoing neutrons with a dedicated neutron spectrometermade of 18 plastic scintillators. The kinetic energy of neutrons interacting in the TPC was evaluatedevent-by-event by measuring the time of flight. ReD collected and characterized a sample of nuclearrecoils down to 2 keV, thus meeting its design goal.The ReD effort will be further extended by a new project, ReD+, funded by a PRIN grant from theItalian Ministry of Research. ReD+ is designed to push the sensitivity down to 0.5 keV, by using thesame conceptual design of ReD and improved components. A new TPC is being re-designed andoptimized in order to increase the signal rate and the signal-to-background ratio, which limited thesensitivity of ReD. 

Abstract Vibrations from experimental setups and the environment are a persistent source of noise for low-temperature calorimeters searching for rare events, including neutrinoless double beta (0νββ) decay or dark matter interactions. Such noise can significantly limit experimental sensitivity to the physics case under investigation. Here, we report the detection of marine microseismic vibrations using mK-scale calorimeters. This study employs a multi-device analysis correlating data from CUORE, the leading experiment in the search for 0νββdecay with mK-scale calorimeters, and the Copernicus Earth Observation program, revealing the seasonal impact of Mediterranean Sea activity on CUORE’s energy thresholds, resolution, and sensitivity over four years. The detection of marine microseisms underscores the need to address faint environmental noise in ultra-sensitive experiments. Understanding how such noise couples to the detector and developing mitigation strategies is essential for next-generation experiments. We demonstrate one such strategy: a noise decorrelation algorithm implemented in CUORE using auxiliary sensors, which reduces vibrational noise and improves detector performance. Enhancing sensitivity to 0νββdecay and to rare events with low-energy signatures requires identifying unresolved noise sources, advancing noise reduction methods, and improving vibration suppression systems, all of which inform the design of next-generation rare event experiments. 

Dark matter detection experiments using liquid argon rely on a precise characterization of the ionization response to nuclear recoils, especially in the keV energy range relevant for light dark matter interactions. In this work, we present a comprehensive analysis that combines new measurements from the ReD setup, part of the DarkSide experimental program, with calibration data from DarkSide-50, as well as results from the ARIS and SCENE experiments. These combined datasets enable improved constraints on atomic screening effects in the modeling of the ionization response of liquid argon to nuclear recoils. The analysis is performed within the Thomas-Imel recombination framework adopted in previous DarkSide studies, and is here further constrained by the inclusion of ReD data, which allow the screening function to be determined from calibration measurements. By including the updated ionization model into the DarkSide-50 analysis framework, we obtain stronger exclusion limits on low-mass weakly interacting massive particle (WIMP) interactions, setting new world-leading constraints in the $1–3\mathrm{GeV}/{\mathrm{c}}^2$ WIMP mass range. Finally, we recast the sensitivity projections for the upcoming DarkSide-20k detector, demonstrating a significantly enhanced discovery potential for low-mass dark matter candidates. 

Borexino could efficiently distinguish between $\alpha$ and $\beta$ radiation in its liquid scintillator by the characteristic time profile of its scintillation pulse. This $\alpha /\beta$ discrimination, first demonstrated on the ton scale in the counting test facility prototype, was used throughout the lifetime of the experiment between 2007 and 2021. With this method, the $\alpha$ events are identified and subtracted from the solar neutrino events similar to $\beta$ . This is particularly important in liquid scintillators, as the $\alpha$ scintillation is strongly quenched. In Borexino, the prominent ${}^{210}\mathrm{Po}$ decay peak was a background in the energy range of electrons scattered from ${}^7\mathrm{Be}$ solar neutrinos. Optimal $\alpha /\beta$ discrimination was achieved with a , with a higher ability to leverage the timing information of the scintillation photons detected by the photomultiplier tubes. An event-by-event, high efficiency, stable, and uniform pulse shape discrimination was essential in characterizing the spatial distribution of background in the detector. This benefited most Borexino measurements, including solar neutrinos in the $pp$ chain and the first direct observation of the CNO cycle in the Sun. This paper presents key milestones in $\alpha /\beta$ discrimination in Borexino as a term of comparison for current and future large liquid scintillator detectors. Published by the American Physical Society2024 

Abstract Directional sensitivity to nuclear recoils would provide a smoking gun for a possible discovery of dark matter in the form of WIMPs (Weakly Interacting Massive Particles). A hint of directional dependence of the response of a dual-phase argon Time Projection Chamber (TPC) was found in the SCENE experiment. Given the potential importance of such a capability in the framework of dark matter searches, a new dedicated experiment, ReD (Recoil Directionality), was designed by the Global Argon Dark Matter Collaboration, in order to scrutinise this hint. A small dual-phase argon TPC was irradiated with neutrons produced by the p(⁷Li,⁷Be)n reaction using the 15 MV TANDEM accelerator of the INFN - Laboratori Nazionali del Sud, Catania, Italy, so as to produce argon nuclear recoils in the range (20 - 100) keV of interest for dark matter searches. Energy and direction of nuclear recoils are inferred by the detection of the elastically-scattered neutron by a set of scintillation detectors. Events were selected by gating of the associated⁷Be, which is detected by a telescope of Si detectors. 

Abstract In this work we will document the design and the performances of a SiPM-based photo-detector with a surface area of 100 cm 2 conceived to operate as a replacement for PMTs. The signals from 94 SiPMs are summed up to produce an aggregated output that exhibits in liquid nitrogen a dark count rate (DCR) lower than 100 cps over the entire surface, a signal to noise ratio better than 13, and a timing resolution better than 5.5 ns. The module feeds about 360 mW at 5 V with a dynamic range in excess of 500 photo-electrons on a 100 Ω differential line. The unit can also operate at room temperature, at the cost of an increase of DCR to 10 8 cps.