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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 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. 

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. 

The Cosmic Dawn Survey pre-launch catalogues cover an effective 10.13 deg²area with uniform deepSpitzer/IRAC data (m ∼ 25 mag, 5σ), the largest area covered to these depths at IR wavelengths. We used these data to gain new insight into the growth of stellar mass across cosmic history by characterising the evolution of the galaxy stellar mass function through 0.2 < z ≤ 6.5. The total volume (0.62 Gpc³) represents an order of magnitude increase compared to previous works that exploredz > 3 and significantly reduces cosmic variance, thus yielding strong constraints on the abundance of galaxies above the characteristic stellar mass (ℳ^★) across this ten billion year period. The evolution of the galaxy stellar mass function is generally consistent with results from the literature but now provides firm estimates of the number density where only upper limits were previously available. Contrasting the galaxy stellar mass function with the dark matter halo mass function suggests that massive galaxies (ℳ ≳ 10¹¹M_⊙) atz > 3.5 required integrated star-formation efficiencies of ℳ/(ℳ_hf_b)≳ 0.25–0.5, in excess of the commonly held view of a ‘universal peak efficiency’ from studies on the stellar-to-halo mass relation. Such increased efficiencies imply an evolving peak in the stellar-to-halo mass relation atz > 3.5 that can be maintained if feedback mechanisms from active galactic nuclei and stellar processes are ineffective at early times. In addition, a significant fraction of the most massive quiescent galaxies are observed to be in place byz ∼ 2.5–3. The apparent lack of change in their number density byz ∼ 0.2 is consistent with relatively little mass growth from mergers. Utilising the unique volume, we find evidence of an environmental dependence of the galaxy stellar mass function all the way throughz ∼ 3.5 for the first time, though a more careful characterisation of the density field is ultimately required for confirmation. 

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. 

In the direct searches for Weakly Interacting Massive Particles (WIMPs) as Dark Matter candidates, the sensitivity of the detector to the incom- ing particle direction could provide a smoking gun signature for an interesting event. The SCENE collaboration firstly suggested the possible directional de- pendence of a dual-phase argon Time Projection Chamber through the columnar recombination effect. The Recoil Directionality project (ReD) within the Global Argon Dark Matter Collaboration aims to characterize the light and charge re- sponse of a liquid Argon dual-phase TPC to neutron-induced nuclear recoils to probe for the hint by SCENE. In this work, the directional sensitivity of the de- tector in the energy range of interest for WIMPs (20-100 keV) is investigated with a data-driven analysis involving a Machine Learning algorithm.