DarkSide-20k is a novel liquid argon dark matter detector currently under construction at the Laboratori Nazionali del Gran Sasso (LNGS) of the Istituto Nazionale di Fisica Nucleare (INFN) that will push the sensitivity for Weakly Interacting Massive Particle (WIMP) detection into the neutrino fog. The core of the apparatus is a dual-phase Time Projection Chamber (TPC), filled with 50 tonnes of low radioactivity underground argon (UAr) acting as the WIMP target. NUV-HD-cryo Silicon Photomultipliers (SiPM)s designed by Fondazione Bruno Kessler (FBK) (Trento, Italy) were selected as the photon sensors covering two $$10.5~\text {m}^2$$ 10.5 m 2 Optical Planes, one at each end of the TPC, and a total of $$5~\text {m}^2$$ 5 m 2 photosensitive surface for the liquid argon veto detectors. This paper describes the Quality Assurance and Quality Control (QA/QC) plan and procedures accompanying the production of FBK NUV-HD-cryo SiPM wafers manufactured by LFoundry s.r.l. (Avezzano, AQ, Italy). SiPM characteristics are measured at 77 K at the wafer level with a custom-designed probe station. As of March 2025, 1314 of the 1400 production wafers (94% of the total) for DarkSide-20k were tested. The wafer yield is $$93.2\pm 2.5$$ 93.2 ± 2.5 %, which exceeds the 80% specification defined in the original DarkSide-20k production plan.

DarkSide-20k (DS-20k) is a dark matter detection experiment under construction at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. It utilises similar to 100 t of low radioactivity argon from an underground source (UAr) in its inner detector, with half serving as target in a dual-phase time projection chamber (TPC). The UAr cryogenics system must maintain stable thermodynamic conditions throughout the experiment's lifetime of over 10 years. Continuous removal of impurities and radon from the UAr is essential for maximising signal yield and mitigating background. We are developing an efficient and powerful cryogenics system with a gas purification loop with a target circulation rate of 1000 slpm. Central to its design is a condenser operated with liquid nitrogen which is paired with a gas heat exchanger cascade, delivering a combined cooling power of more than 8 kW. Here we present the design choices in view of the DS-20k requirements, in particular the condenser's working principle and the cooling control, and we show test results obtained with a dedicated benchmarking platform at CERN and LNGS. We find that the thermal efficiency of the recirculation loop, defined in terms of nitrogen consumption per argon flow rate, is 95% and the pressure in the test cryostat can be maintained within +/-(0.1-0.2) mbar. We further detail a 5-day cool-down procedure of the test cryostat, maintaining a cooling rate typically within -2K/h, as required for the DS-20k inner detector. Additionally, we assess the circuit's flow resistance, and the heat transfer capabilities of two heat exchanger geometries for argon phase change, used to provide gas for recirculation. We conclude by discussing how our findings influence the finalisation of the system design, including necessary modifications to meet requirements and ongoing testing activities.

The stability of a dark matter detector on the timescale of a few years is a key requirement due to the large exposure needed to achieve a competitive sensitivity. It is especially crucial to enable the detector to potentially detect any annual event rate modulation, an expected dark matter signature. In this work, we present the performance history of the DarkSide-50 dual-phase argon time projection chamber over its almost three-year low-radioactivity argon run. In particular, we focus on the electroluminescence signal that enables sensitivity to sub-keV energy depositions. The stability of the electroluminescence yield is found to be better than 0.5%. Finally, we show the temporal evolution of the observed event rate around the sub-keV region being consistent to the background prediction.

In the following, the first measurement of CNO solar neutrinos obtained by Borexino by exploiting the directional information retained by solar neutrino is summarized [1]. The Correlated Integrated Directionality (CID) method makes use of the sub-dominant Cherenkov light emitted by the Borexino liquid scintillator to correlate between the first few detected photons in each event and the known position of the Sun for each event and, therefore, to discriminate between the signal and the radioactive background on a statistical basis. By applying this technique to the complete 2007-2021 Borexino dataset, the hypothesis of no CNO neutrinos is rejected with > 5 sigma posterior probability, without making use of any information on the background levels in the scintillator.

Liquid Argon (LAr) Time Projection Chambers (TPC) operating in double-phase candetect the nuclear recoils (NR) possibly caused by the elastic scattering of WIMP dark matter particlesvia light signals from both scintillation and ionization processes. In the scenario of a low-mass WIMP(<2GeV/c(2)), the energy range for the NRs would be below 20 keV, thus making it crucial to characterizethe ionization response in LAr TPCs as the lone available detection channel at such low energy. TheRecoil Directionality (ReD) project, within the Global Argon Dark Matter Collaboration, aims tomeasure the ionization yield of a LAr TPC in the recoil energy range of 2-5 keV. The measurementwas performed in winter 2023 at the INFN Sezione of Catania and the analysis is ongoing

The dual-phase liquid argon time projection chamber is presently one of the leading technologies to search for dark matter particles with masses below 10 GeV c(-2). This was demonstrated by the DarkSide-50 experiment with approximately 50 kg of low-radioactivity liquid argon as target material. The next generation experiment DarkSide-20k, currently under construction, will use 1,000 times more argon and is expected to start operation in 2027. Based on the DarkSide-50 experience, here we assess the DarkSide-20k sensitivity to models predicting light dark matter particles, including Weakly Interacting Massive Particles (WIMPs) and sub-GeV c(-2) particles interacting with electrons in argon atoms. With one year of data, a sensitivity improvement to dark matter interaction cross-sections by at least one order of magnitude with respect to DarkSide-50 is expected for all these models. A sensitivity to WIMP-nucleon interaction cross-sections below 1x10(-42) cm(2) is achievable for WIMP masses above 800 MeV c(-2). With 10 years exposure, the neutrino fog can be reached for WIMP masses around 5 GeV c(-2).

Experiments aimed at direct searches for WIMP dark matter require highly effective reduction of backgrounds and control of any residual radioactive contamination. In particular, neutrons interacting with atomic nuclei represent an important class of backgrounds due to the expected similarity of a WIMP-nucleon interaction, so that such experiments often feature a dedicated neutron detector surrounding the active target volume. In the context of the development of DarkSide-20k detector at INFN Gran Sasso National Laboratory (LNGS), several R D projects were conceived and developed for the creation of a new hybrid material rich in both hydrogen and gadolinium nuclei to be employed as an essential element of the neutron detector. Thanks to its very high cross-section for neutron capture, gadolinium is one of the most widely used elements in neutron detectors, while the hydrogen-rich material is instrumental in efficiently moderating the neutrons. In this paper results from one of the R Ds are presented. In this effort the new hybrid material was obtained as a poly(methyl methacrylate) (PMMA) matrix, loaded with gadolinium oxide in the form of nanoparticles. We describe its realization, including all phases of design, purification, construction, characterization, and determination of mechanical properties of the new material.

Borexino, placed at LNGS in Italy, was a 280-ton liquid scintillator detector that took data from May 2007 to October 2021. Thanks to its unprecedented radio-purity, the real time spectroscopic measurement of solar neutrinos from both the pp-chain and Carbon-Nitrogen-Oxygen (CNO) fusion cycle of the Sun has been performed. Borexino also reported the first directional measurement of sub-MeV Be-7 solar neutrinos with the Phase-I period (May 2007-May 2010) using a novel technique called Correlated and Integrated Directionality (CID), exploiting the sub-dominant and directional Cherenkov photons detected at early times. For the first time, we provide the CNO solar neutrinos measurement without using an independent constraint on Bi-210 background rate by exploiting the CID technique on the complete Borexino detector live time dataset. This article presents the complete analysis strategy and the latest results on CNO solar neutrinos obtained by using the CID technique in Borexino. In addition, we also present the most precise CNO measurement obtained by Borexino using a spectral fit on the Phase-III dataset as used in 2022 analysis, where the novel CID result is now applied as an additional constraint.

Borexino could efficiently distinguish between α and β radiation in its liquid scintillator by the characteristic time profile of its scintillation pulse. This α/β 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 α events are identified and subtracted from the solar neutrino events similar to β. This is particularly important in liquid scintillators, as the α scintillation is strongly quenched. In Borexino, the prominent Po210 decay peak was a background in the energy range of electrons scattered from Be7 solar neutrinos. Optimal α/β 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 α/β discrimination in Borexino as a term of comparison for current and future large liquid scintillator detectors. Published by the American Physical Society 2024

Dark matter induced event rate in an Earth-based detector is predicted to show an annual modulation as a result of the Earth's orbital motion around the Sun. We searched for this modulation signature using the ionization signal of the DarkSide-50 liquid argon time projection chamber. No significant signature compatible with dark matter is observed in the electron recoil equivalent energy range above $40~{\rm eV_{ee}}$, the lowest threshold ever achieved in such a search.

The Recoil Directionality project (ReD) within the Global Argon Dark Matter Collaboration aims to characterize the response of a liquid argon (LAr) Time Projection Chamber (TPC) to neutron-induced nuclear recoils and to measure the charge yield for low-energy recoils. The charge yield is a critical parameter for the experiments searching for dark matter in the form of low-mass WIMPs and measurements in argon below 10 keV are scarce in the literature. This project covers the gap down to 2 keV.

The Recoil Directionality project (ReD) within the Global Argon Dark Matter Collaboration aims to characterize the response of an argon dual-phase Time Projection Chamber (TPC) to neutron-induced nuclear recoils, and to measure the charge yield for low-energy recoils. The charge yield is a critical parameter for the experiments searching for dark matter in the form of low-mass WIMPs and measurements in Ar below 10 keV are scarce in the literature. ReD was designed to cover this gap, by irradiating a miniaturized TPC with neutrons produced by an intense Cf-252 fission source, such to generate Ar recoils in the energy range of interest. Data were collected during the Winter of 2023 at the INFN Sezione di Catania. The energy of the nuclear recoils produced within the TPC by (n,n') scattering was determined by detecting the outgoing neutrons by a neutron spectrometer made of 18 plastic scintillators. The neutron kinetic energy was evaluated event-by-event by using a time-of-flight approach. The ionization signal was measured for Ar recoils down to 2 keV.

The recent observation of CNO solar neutrinos by Borexino (BX) has proven the high potential offered by large underground ultrapure liquid scintillators to disclose weak neutrino and antineutrino fluxes. Supernovae explosions, gamma-ray bursts, solar flares and Gravitational Waves (GW) are among the possible extra-terrestrial sources of neutrinos and antineutrinos. The extreme radiopurity of the BX detector has already allowed to get the best upper limits on all flavor fluences in the few MeV energy range from gamma ray bursts, to set limits on the diffuse supernova antineutrino background in the unexplored energy region below 8 MeV and to get the strongest upper limits on fast radio bursts associated neutrino fluences up to 50 MeV. Recently, BX has searched for neutrino events in correlation with GW events from 2015 to 2020 using the BX data-set of the same periods. The strongest upper limits on GW-associated neutrino and antineutrino fluences have been obtained in the (0.5 - 5.0) MeV neutrino energy range. The present contribution is aimed to describe the analysis procedures and the deduced upper limits for all neutrino flavors.

The NUOVA OFFICINA ASSERGI (NOA) is a new facility for the production and integration of large-area silicon photodetectors operating at cryogenic temperatures. Silicon photomultipliers are proving to be a promising technology for next-generation experiments searching for rare events in underground laboratories. New photosensor technology with high performance at cryogenic temperature has been developed by Fondazione Bruno Kessler (FBK) and integrated at Laboratori Nazionali del Gran Sasso (LNGS) into large-area optical units, thus opening the frontiers toward the realization of scalable liquid argon experiments probing dark matter. The massive production of such detectors is now feasible in NOA, a clean room of 421 m2 designed to operate in a radon-free mode. NOA, commissioned and operational at LNGS, hosts the most advanced packaging machines and electronic test facilities for the integration of silicon devices in a dust-controlled environment. The infrastructure layout is split into two experimental areas: one for the production of electronic devices and cryogenic temperature tests and the other for operating with large detector installations. The NOA facility can be operated with a radon abatement system, making it a unique facility for packaging and testing SiPM-based photosensors and for assembling detector components in a radon-free environment. Therefore, NOA supports the deployment of underground experiments at LNGS and the development of new technologies for the search of rare events, such as dark matter and neutrinoless double-beta decay.

The largest amount of antineutrinos detected about the Earth is emitted by the natural radioactive decays of Th-232 and U-238 chains isotopes and of K-40. Other flux components are yielded by cosmic rays interactions in the atmosphere or by possible extra-terrestrial sources such as supernovae explosions, gamma ray bursts, GW events and solar flares. This contribution is aimed to summarise the results obtained by the Borexino experiment about antineutrinos from the Earth and from extraterrestrial sources.

The Borexino has recently reported the first experimental evidence of neutrinos from the CNO cycle. Since this process accounts only for about 1% of the total energy production in the Sun, the associated neutrino flux is extremely low as compared with the one from the pp-chain, the dominant process of hydrogen burning. This experimental evidence of the CNO neutrinos was obtained using the highly radio-pure liquid scintillator of Borexino. Improvements in the thermal stabilization of the detector over the last five years enabled us to exploit a method to constrain the rate of Bi-210 background. Since the CNO cycle is dominant in massive stars, this result gives the first experimental proof of the primary mechanism for stellar conversion of hydrogen into helium in the Universe.

We present a novel approach for the search of dark matter in the DarkSide-50 experiment, relying on Bayesian Networks. This method incorporates the detector response model into the likelihood function, explicitly maintaining the connection with the quantity of interest. No assumptions about the linearity of the problem or the shape of the probability distribution functions are required, and there is no need to morph signal and background spectra as a function of nuisance parameters. By expressing the problem in terms of Bayesian Networks, we have developed an inference algorithm based on a Markov Chain Monte Carlo to calculate the posterior probability. A clever description of the detector response model in terms of parametric matrices allows us to study the impact of systematic variations of any parameter on the final results. Our approach not only provides the desired information on the parameter of interest, but also potential constraints on the response model. Our results are consistent with recent published analyses and further refine the parameters of the detector response model.

Borexino has been a neutrino detector based on ultrapure liquid scintillator, located at the Laboratori Nazionali del Gran Sasso, Italy. Its main scientific goal was the real-time measurement of solar neutrino fluxes, which play an irreplaceable role for the comprehension of the mechanisms powering our star. Over the past two years, the Borexino collaboration has pursued the improvement of the CNO flux measurement, obtaining further indications about the solar metallicity. In a parallel way, Borexino has demonstrated for the first time the possibility of exploiting the directional Cherenkov information, in a liquid scintillator detector, for the detection of sub-MeV solar neutrinos.

The search for neutrino events in correlation with gravitational wave (GW) events for three observing runs (O1, O2 and O3) from 09/2015 to 03/2020 has been performed using the Borexino data-set of the same period. We have searched for signals of neutrino-electron scattering and inverse beta-decay (IBD) within a time window of ± 1000 s centered at the detection moment of a particular GW event. The search was done with three visible energy thresholds of 0.25, 0.8 and 3.0 MeV. Two types of incoming neutrino spectra were considered: the mono-energetic line and the supernova-like spectrum. GW candidates originated by merging binaries of black holes (BHBH), neutron stars (NSNS) and neutron star and black hole (NSBH) were analyzed separately. Additionally, the subset of most intensive BHBH mergers at closer distances and with larger radiative mass than the rest was considered. In total, follow-ups of 74 out of 93 gravitational waves reported in the GWTC-3 catalog were analyzed and no statistically significant excess over the background was observed. As a result, the strongest upper limits on GW-associated neutrino and antineutrino fluences for all flavors ( ν _e, ν _μ , ν _τ ) at the level 10^9-10^15 cm^-2 GW^-1 have been obtained in the 0.5–5 MeV neutrino energy range.

Since the beginning of 2012, the Borexino collaboration has been reporting precision measurements of the solar neutrino fluxes, emitted in the proton-proton chain and in the Carbon-Nitrogen-Oxygen cycle. The experimental sensitivity achieved in Phase-II and Phase-III of the Borexino data taking made it possible to detect the annual modulation of the solar neutrino interaction rate due to the eccentricity of Earth's orbit, with a statistical significance greater than 5$\sigma$. This is the first precise measurement of the Earth's orbital parameters based solely on solar neutrinos and an additional signature of the solar origin of the Borexino signal. The complete periodogram of the time series of the Borexino solar neutrino detection rate is also reported, exploring frequencies between one cycle/year and one cycle/day. No other significant modulation frequencies are found. The present results were uniquely made possible by Borexino's decade-long high-precision solar neutrino detection.