arXiv subjects

Z. Balmforth

Publications and source records attributed to Z. Balmforth.

16 recordsLinked to original sources

arXiv2026

Response of a nitrogen-filled spherical proportional counter to mono-energetic neutrons

Neutron spectroscopy is an invaluable tool for a wide range of scientific and industrial applications, however, current approaches suffer from limitations that restrict their field of applicability. A safe and inexpensive alternative approach to neutron detection and spectroscopy is the use of a nitrogen-filled spherical proportional counter that exploits the $^{14}\rm{N(n,p)}^{14}\rm{C}$ and $^{14}\rm{N(n},\alpha)^{11}\rm{B}$ reactions. The neutron spectroscopy capabilities of the detector are demonstrated using beams of mono-energetic neutrons. A nitrogen-filled spherical proportional counter, operating at a pressure of $1$ bar, is exposed to neutrons with energies from $0.75$ MeV to $2.75$ MeV at the Tandem accelerator of the National Centre for Scientific Research ``Demokritos'' in Athens. A linear energy response is observed, within the statistical precision of the measurements.

hep-ex↗

arXiv2026

Radiation Hardness of Commercially Available NUV-MT Silicon Photomultipliers

Silicon Photomultipliers (SiPMs) based on the near-ultraviolet, metal-filled trench (NUV-MT) technology offer improved photon detection efficiency and reduced correlated noise relative to earlier designs, making them attractive for a broad range of particle- and astroparticle-physics applications. As such devices may be deployed in high-radiation environments, quantifying their performance after irradiation is essential. Commercially available Broadcom AFBR-S4N series NUV-MT SiPMs were irradiated with 1 MeV neutrons to fluences between 2x10^{9} and 1.1x10^{10} n_{eq}/cm^2 at the TANDEM accelerator facility of NCSR "Demokritos" in Athens, and characterised before and after irradiation and over successive thermal-annealing stages. Irradiation increased the dark noise by up to three orders of magnitude and degraded the single-photon resolution by up to a factor of ten, with resolution lost entirely at the highest fluence, while no shift in breakdown voltage was observed. Thermal annealing partially recovered the performance, reducing the dark noise by up to a factor of two and restoring the single-photon resolution.

physics.ins-det↗

arXiv2026

Characterisation of Commercially Available NUV-MT Silicon Photomultipliers

Silicon Photomultipliers (SiPMs) based on NUV-MT technology offer improved photo-detection efficiency and reduced correlated noise compared to earlier designs, making them increasingly attractive for particle and astroparticle physics applications. We present a systematic characterisation of commercially available Broadcom AFBR-S4N series NUV-MT SiPMs over a wide range of temperatures and overvoltages, from -85oC to 23oC and from 10-16V overvoltage (VoV). Key performance parameters are measured, including breakdown voltage, gain, signal-to-noise ratio, dark count rate, afterpulsing probability, and both internal and external optical crosstalk. At 12Vov and 23oC a dark noise of 107.2+/-2.1 kcps/mm^2 is measured, consistent with manufacturer specifications. At 12Vov and -30oC the measurements yielded an average dark noise of 1.69+/-0.12 kcps/mm^2, an average gain of (6.88+/-0.15)x10^6, an average signal to noise ratio of 13.6+/-0.9, an average afterpulsing probability of (0.59+/-0.06)%, an average direct crosstalk probability of (26.49+/-0.28)%, an average delayed crosstalk probability of (0.72+/-0.10)%, and an average external crosstalk probability of (0.10+/-0.04)%.

physics.ins-det↗

arXiv2025

Sensitivity to low-mass WIMPs with an improved liquid argon ionization response model within the DarkSide programme

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 WIMP interactions, setting new world-leading constraints in the 1-3 GeV/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.

hep-ex↗

arXiv2025

Production, Quality Assurance and Quality Control of the SiPM Tiles for the DarkSide-20k Time Projection Chamber

The DarkSide-20k dark matter direct detection experiment will employ a 21 m^2 silicon photomultiplier (SiPM) array, instrumenting a dual-phase 50 tonnes liquid argon Time Projection Chamber (TPC). SiPMs are arranged into modular photosensors called Tiles, each integrating 24 SiPMs onto a printed circuit board (PCB) that provides signal amplification, power distribution, and a single-ended output for simplified readout. 16 Tiles are further grouped into Photo-Detector Units (PDUs). This paper details the production of the Tiles and the quality assurance and quality control (QA-QC) protocol established to ensure their performance and uniformity. The production and QA-QC of the Tiles are carried out at Nuova Officina Assergi (NOA), an ISO-6 clean room facility at LNGS. This process includes wafer-level cryogenic characterisation, precision flip-chip bonding, wire bonding, and extensive electrical and optical validation of each Tile. The overall production yield exceeds 83.5%, matching the requirements of the DarkSide-20k production plan. These results validate the robustness of the Tile design and its suitability for operation in a cryogenic environment.

physics.ins-det↗

arXiv2025

Flow and thermal modelling of the argon volume in the DarkSide-20k TPC

The DarkSide-20k dark matter experiment, currently under construction at LNGS, features a dual-phase time projection chamber (TPC) with a ~50 t argon target from an underground well. At this scale, it is crucial to optimise the argon flow pattern for efficient target purification and for fast distribution of internal gaseous calibration sources with lifetimes of the order of hours. To this end, we have performed computational fluid dynamics simulations and heat transfer calculations. The residence time distribution shows that the detector is well-mixed on time-scales of the turnover time (~40 d). Notably, simulations show that despite a two-order-of-magnitude difference between the turnover time and the half-life of $^{83\text{m}}$Kr of 1.83 h, source atoms have the highest probability to reach the centre of the TPC 13 min after their injection, allowing for a homogeneous distribution before undergoing radioactive decay. We further analyse the thermal aspects of dual-phase operation and define the requirements for the formation of a stable gas pocket on top of the liquid. We find a best-estimate value for the heat transfer rate at the liquid-gas interface of 62 W with an upper limit of 144 W and a minimum gas pocket inlet temperature of 89 K to avoid condensation on the acrylic anode. This study also informs the placement of liquid inlets and outlets in the TPC. The presented techniques are widely applicable to other large-scale, noble-liquid detectors.

physics.ins-det↗

arXiv2024

Quality Assurance and Quality Control of the $26~\text{m}^2$ SiPM production for the DarkSide-20k dark matter experiment

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 \SI{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 $10.5~\text{m}^2$ Optical Planes, one at each end of the TPC, and a total of $5~\text{m}^2$ 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 $93.2\pm2.5$\%, which exceeds the 80\% specification defined in the original DarkSide-20k production plan.

physics.ins-det↗

arXiv2024

Benchmarking the design of the cryogenics system for the underground argon in DarkSide-20k

DarkSide-20k (DS-20k) is a dark matter detection experiment under construction at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy. It utilises ~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 $\pm$(0.1-0.2) mbar. We further detail a 5-day cool-down procedure of the test cryostat, maintaining a cooling rate typically within -2 K/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.

physics.ins-det↗

arXiv2024

DarkSide-20k sensitivity to light dark matter particles

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 $1\times10^{-42}$ 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$^2$.

hep-ex↗

arXiv2024

A new hybrid gadolinium nanoparticles-loaded polymeric material for neutron detection in rare event searches

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.

physics.ins-det↗

arXiv2023

Directionality of nuclear recoils in a liquid argon time projection chamber

The direct search for dark matter in the form of weakly interacting massive particles (WIMP) is performed by detecting nuclear recoils (NR) produced in a target material from the WIMP elastic scattering. A promising experimental strategy for direct dark matter search employs argon dual-phase time projection chambers (TPC). One of the advantages of the TPC is the capability to detect both the scintillation and charge signals produced by NRs. Furthermore, the existence of a drift electric field in the TPC breaks the rotational symmetry: the angle between the drift field and the momentum of the recoiling nucleus can potentially affect the charge recombination probability in liquid argon and then the relative balance between the two signal channels. This fact could make the detector sensitive to the directionality of the WIMP-induced signal, enabling unmistakable annual and daily modulation signatures for future searches aiming for discovery. The Recoil Directionality (ReD) experiment was designed to probe for such directional sensitivity. The TPC of ReD was irradiated with neutrons at the INFN Laboratori Nazionali del Sud, and data were taken with 72 keV NRs of known recoil directions. The direction-dependent liquid argon charge recombination model by Cataudella et al. was adopted and a likelihood statistical analysis was performed, which gave no indications of significant dependence of the detector response to the recoil direction. The aspect ratio R of the initial ionization cloud is estimated to be 1.037 +/- 0.027 and the upper limit is R < 1.072 with 90% confidence level

physics.ins-det↗

arXiv2023

X-Arapuca long term test

The photon detection system of the DUNE experiment is based on the X-ARAPUCA light trap. The basic elements of the X-ARAPUCA are the dichroic filters coated with wavelength shifter (para-Therphenyl), a waveshifting plate and an array of SiPMs which detects the trapped photons. A small scale prototype of the X-ARAPUCA has been installed in liquid argon in a dedicated facility at INFN-Napoli and exposed to alpha particles from a source. In order to test the stability of the overall device response the X-ARAPUCA was kept for 10 days in liquid argon continuously purified. The performed tests allowed for a preliminary estimation of the X-ARAPUCA absolute photon detection efficiency.

physics.ins-det↗

arXiv2022

A large facility for photosensors test at cryogenic temperature

Current generation of detectors using noble gases in liquid phase for direct dark matter search and neutrino physics need large area photosensors. Silicon based photo-detectors are innovative light collecting devices and represent a successful technology in these research fields. The DarkSide collaboration started a dedicated development and customization of SiPM technology for its specific needs resulting in the design, production and assembly of large surface modules of 20x20 cm^2 named Photo Detection Unit for the DarkSide-20k experiment. Production of a large number of such devices, as needed to cover about 20 m^2 of active surface inside the DarkSide-20k detector, requires a robust testing and validation process. In order to match this requirement a dedicated test facility for the photosensor test was designed and commissioned at INFN-Naples laboratory. The first commissioning test was successfully performed in 2021. Since then a number of testing campaigns were performed. Detailed description of the facility is reported as well as results of some tests.

physics.ins-det↗

arXiv2022

Sensitivity projections for a dual-phase argon TPC optimized for light dark matter searches through the ionization channel

Dark matter lighter than 10 GeV/c$^2$ encompasses a promising range of candidates. A conceptual design for a new detector, DarkSide-LowMass, is presented, based on the DarkSide-50 detector and progress toward DarkSide-20k, optimized for a low-threshold electron-counting measurement. Sensitivity to light dark matter is explored for various potential energy thresholds and background rates. These studies show that DarkSide-LowMass can achieve sensitivity to light dark matter down to the solar neutrino floor for GeV-scale masses and significant sensitivity down to 10 MeV/c$^2$ considering the Migdal effect or interactions with electrons. Requirements for optimizing the detector's sensitivity are explored, as are potential sensitivity gains from modeling and mitigating spurious electron backgrounds that may dominate the signal at the lowest energies.

physics.ins-det↗

arXiv2021

Separating $^{39}$Ar from $^{40}$Ar by cryogenic distillation with Aria for dark matter searches

The Aria project consists of a plant, hosting a 350 m cryogenic isotopic distillation column, the tallest ever built, which is currently in the installation phase in a mine shaft at Carbosulcis S.p.A., Nuraxi-Figus (SU), Italy. Aria is one of the pillars of the argon dark-matter search experimental program, lead by the Global Argon Dark Matter Collaboration. Aria was designed to reduce the isotopic abundance of $^{39}$Ar, a $\beta$-emitter of cosmogenic origin, whose activity poses background and pile-up concerns in the detectors, in the argon used for the dark-matter searches, the so-called Underground Argon (UAr). In this paper, we discuss the requirements, design, construction, tests, and projected performance of the plant for the isotopic cryogenic distillation of argon. We also present the successful results of isotopic cryogenic distillation of nitrogen with a prototype plant, operating the column at total reflux.

physics.ins-det↗

arXiv2020

Sensitivity of future liquid argon dark matter search experiments to core-collapse supernova neutrinos

Future liquid-argon DarkSide-20k and ARGO detectors, designed for direct dark matter search, will be sensitive also to core-collapse supernova neutrinos, via coherent elastic neutrino-nucleus scattering. This interaction channel is flavor-insensitive with a high-cross section, enabling for a high-statistics neutrino detection with target masses of $\sim$50~t and $\sim$360~t for DarkSide-20k and ARGO, respectively. Thanks to the low-energy threshold of $\sim$0.5~keV$_{nr}$ achievable by exploiting the ionization channel, DarkSide-20k and ARGO have the potential to discover supernova bursts throughout our galaxy and up to the Small Magellanic Cloud, respectively, assuming a 11-M$_{\odot}$ progenitor star. We report also on the sensitivity to the neutronization burst, whose electron neutrino flux is suppressed by oscillations when detected via charged current and elastic scattering. Finally, the accuracies in the reconstruction of the average and total neutrino energy in the different phases of the supernova burst, as well as its time profile, are also discussed, taking into account the expected background and the detector response.

astro-ph.HE↗