arXiv subjects

B. Suerfu

Publications and source records attributed to B. Suerfu.

17 recordsLinked to original sources

arXiv2026

Measurement of the cosmic muon flux at the Stawell Underground Physics Laboratory

We report the first measurement of the underground cosmic muon flux at the Stawell Underground Physics Laboratory. The measurement uses eight EJ200 plastic scintillator panels, equipped with Hamamatsu R13089 PMT pairs at the ends, which are the primary components of the muon veto system for the upcoming SABRE South experiment. The measured muon flux is f = (6.33 +/- 0.04_stat +/- 0.35_sys) x 10^{-8} [s^{-1} cm^{-2}]. This measurement is in excellent agreement with simulations, with a relative uncertainty an order of magnitude smaller than the modelling uncertainty.

hep-ex↗

arXiv2025

Spontaneous generation of athermal phonon bursts within bulk silicon causing excess noise, low energy background events and quasiparticle poisoning in superconducting sensors

Solid state phonon detectors used in the search for dark matter and coherent neutrino nucleus interactions (CE$\nu$NS) require excellent energy resolution (eV-scale or below) and low backgrounds. An unknown source of phonon bursts, the low energy excess (LEE), dominates other above-threshold backgrounds and generates excess shot noise from sub-threshold bursts. In this paper, we measure these phonon bursts for 12 days after cooldown in two nearly identical 1 cm$^2$ silicon detectors that differ only in the thickness of their substrate (1 mm vs. 4 mm thick). We find that both the channel-correlated shot noise and near-threshold shared LEE relax with time since cooldown. Additionally, both the correlated shot noise and LEE rates scale linearly with substrate thickness. When combined with previous measurements of other silicon phonon detectors with different substrate geometries and mechanical support strategies, these measurements strongly suggest that the dominant source of both above and below threshold LEE is the bulk substrate. By monitoring the relation between bias power and excess phonon shot noise, we estimate that the energy scale for sub-threshold noise events is $0.68 \pm 0.38$ meV. In our final dataset, we report a world-leading energy resolution of 258.5$\pm$0.4 meV in the 1 mm thick detector. Simple calculations suggest that these silicon substrate phonon bursts are likely a significant source of quasiparticle poisoning in superconducting qubits operated in well shielded and vibration free environments.

physics.ins-det↗

arXiv2025

Photomultiplier Requirements and Pre-Calibration for the SABRE South Liquid Scintillator Veto

We present a study of the oil-proof base Hamamatsu R5912 photomultiplier tubes that will be used in the SABRE South linear-alkylbenzene liquid scintillator veto. SABRE South is a dark matter direct detection experiment at the Stawell Underground Physics Laboratory, aiming to test the DAMA/LIBRA dark matter annual modulation signal. We discuss the requirements of the liquid scintillator system and its photomultipliers, outline the methods and analysis used for the characterisation measurements, and results from initial tests. We discuss the impact of these measurements on the performance of the active veto system and explore analysis methods to allow for low threshold operation. Finally, we include results from a small scale liquid scintillator detector prototype used to assess the future performance of pulse shape discrimination in the liquid scintillator veto, and how well accommodated it is by the R5912 PMTs.

physics.ins-det↗

arXiv2025

Characterisation of Hamamatsu R11065-20 PMTs for use in the SABRE South NaI(Tl) Crystal Detectors

The SABRE Experiment is a direct detection dark matter experiment using a target composed of multiple NaI(Tl) crystals. The experiment aims to be an independent check of the DAMA/LIBRA results with a detector in the Northern (Laboratori Nazionali Del Gran Sasso, LNGS) and Southern (Stawell Underground Physics Laboratory, SUPL) hemispheres. The SABRE South photomultiplier tubes (PMTs) will be used near the low energy noise threshold and require a detailed calibration of their performance and contributions to the background in the NaI(Tl) dark matter search, prior to installation. We present the development of the pre-calibration procedures for the R11065-20 Hamamatsu PMTs. These PMTs are directly coupled to the NaI(Tl) crystals within the SABRE South experiment. In this paper we present methodologies to characterise the gain, dark rate, and timing properties of the PMTs. We develop a method for in-situ calibration without a light injection source. Additionally we explore the application of machine learning techniques using a Boosted Decision Tree (BDT) trained on the response of single PMTs to understand the information available for background rejection. Finally, we briefly present the simulation tool used to generate digitised PMT data from optical Monte Carlo simulations.

physics.ins-det↗

arXiv2024

The SABRE South Technical Design Report Executive Summary

In this technical design report (TDR) executive summary we describe the SABRE South detector to be built at the Stawell Underground Physics Laboratory (SUPL). The SABRE South detector is designed to test the long-standing DAMA/LIBRA signal of an annually modulating rate consistent with dark matter by using the same target material. Located in the Southern Hemisphere, the detector is uniquely positioned to disentangle modulating seasonal effects. SABRE South uses seven ultra-high purity NaI(Tl) crystals (with a total target mass of either 35 kg or 50 kg), hermetically sealed in copper enclosures that are suspended within a liquid scintillator active veto. High quantum efficiency and low background Hamamatsu R11065 photomultiplier tubes are directly coupled to both ends of the crystal, and enclosed with the crystal in an oxygen free copper enclosure. The active veto system consists of 11.6 kL of linear alkylbenzene (LAB) doped with a mixture of fluorophores and contained in a steel vessel, which is instrumented with at least 18 Hamamatsu R5912 photomultipliers. The active veto tags key radiogenic backgrounds intrinsic to the crystals, such as ${^{40}}$K, and is expected to suppress the total background by 27% in the 1-6 keV region of interest. In addition to the liquid scintillator veto, a muon veto is positioned above the detector shielding. This muon veto consists of eight EJ-200 scintillator modules, with Hamamatsu R13089 photomultipliers coupled to both ends. With an expected total background of 0.72 cpd/kg/keV, SABRE South can test the DAMA/LIBRA signal with 5$\sigma$ discovery or 3$\sigma$ exclusion after two years of data taking.

physics.ins-det↗

arXiv2024

The DAMA/LIBRA signal: an induced modulation effect?

The persistence of the DAMA/LIBRA (DAMA) modulation over the past two decades has been a source of great contention within the dark matter community. The DAMA collaboration reports a persistent, modulating event rate within their setup of NaI(Tl) scintillating crystals at the INFN Laboratori Nazionali del Gran Sasso (LNGS) underground laboratory. A recent work alluded that this signal could have arisen due to an analysis artefact, caused by DAMA not accounting for time variation of decaying background radioisotopes in their analysis procedure. In this work, we examine in detail this 'induced modulation' effect, arguing that a number of aspects of the DAMA signal are incompatible with an induced modulation arising from decays of background isotopes over the lifetime of the experiment. Using a toy model of the DAMA/LIBRA experiment, we explore the induced modulation effect under different variations of the activities of the relevant isotopes - namely, $^3$H and $^{210}$Pb - highlighting the various inconsistencies between the resultant toy datasets and the DAMA signal. We stress the importance of the SABRE experiment, whose goal is to unambiguously test for the presence of such a modulating signal in an experiment using the same target material and comparable levels of background.

hep-ex↗

arXiv2023

First Demonstration of the HeRALD Superfluid Helium Detector Concept

The SPICE/HeRALD collaboration is performing R&D to enable studies of sub-GeV dark matter models using a variety of target materials. Here we report our recent progress on instrumenting a superfluid $^4$He target mass with a transition-edge sensor based calorimeter to detect both atomic signals (scintillation) and $^4$He quasiparticle (phonon and roton) excitations. The sensitivity of HeRALD to the critical "quantum evaporation" signal from $^4$He quasiparticles requires us to block the superfluid film flow to the calorimeter. We have developed a heat-free film-blocking method employing an unoxidized Cs film, which we implemented in a prototype "HeRALD v0.1" detector of ~10 g target mass. This article reports initial studies of the atomic and quasiparticle signal channels. A key result of this work is the measurement of the quantum evaporation channel's gain of 0.15 $\pm$ 0.01, which will enable $^4$He-based dark matter experiments in the near term. With this gain the HeRALD detector reported here has an energy threshold of 145 eV at 5 sigma, which would be sensitive to dark matter masses down to 220 MeV/c$^2$.

physics.ins-det↗

arXiv2023

A portable and high intensity 24 keV neutron source based on $^{124}$Sb-$^{9}$Be photoneutrons and an iron filter

A portable monoenergetic 24 keV neutron source based on the $^{124}$Sb-$^9$Be photoneutron reaction and an iron filter has been constructed and characterized. The coincidence of the neutron energy from SbBe and the low interaction cross-section with iron (mean free path up to 29 cm) makes pure iron specially suited to shield against gamma rays from $^{124}$Sb decays while letting through the neutrons. To increase the $^{124}$Sb activity and thus the neutron flux, a $>$1 GBq $^{124}$Sb source was produced by irradiating a natural Sb metal pellet with a high flux of thermal neutrons in a nuclear reactor. The design of the source shielding structure makes for easy transportation and deployment. A hydrogen gas proportional counter is used to characterize the neutrons emitted by the source and a NaI detector is used for gamma background characterization. At the exit opening of the neutron beam, the characterization determined the neutron flux in the energy range 20-25 keV to be 5.36$\pm$0.20 neutrons per cm$^2$ per second and the total gamma flux to be 213$\pm$6 gammas per cm$^2$ per second (numbers scaled to 1 GBq activity of the $^{124}$Sb source). A liquid scintillator detector is demonstrated to be sensitive to neutrons with incident kinetic energies from 8 to 17 keV, so it can be paired with the source as a backing detector for neutron scattering calibration experiments. This photoneutron source provides a good tool for in-situ low energy nuclear recoil calibration for dark matter experiments and coherent elastic neutrino-nucleus scattering experiments.

physics.ins-det↗

arXiv2022

Status and prospects of SABRE North

We present the characterization of a low background NaI(Tl) crystal for the SABRE North experiment. The crystal NaI-33, was studied in two different setups at Laboratori Nazionali del Gran Sasso, Italy. The Proof-of-Principle (PoP) detector was equipped with a liquid scintillator veto and collected data for about one month (90 kg$\times$days). The PoP-dry setup consisted of NaI-33 in a purely passive shielding and collected data for almost one year (891 kg$\times$days). The average background in the energy region of interest (1-6 keV) for dark matter search was 1.20 $\pm$ 0.05 and 1.39 $\pm$ 0.02 counts/day/kg/keV within the PoP and the PoP-dry setup, respectively. This result opens to a new shielding design for the physics phase of the SABRE North detector, that does not foresee the use of an organic liquid scintillator external veto.

physics.ins-det↗

arXiv2022

Performance of the SABRE detector module in a purely passive shielding

We present here a characterization of the low background NaI(Tl) crystal NaI-33 based on a period of almost one year of data taking (891 kgxdays exposure) in a detector configuration with no use of organic scintillator veto. This remarkably radio-pure crystal already showed a low background in the SABRE Proof-of-Principle (PoP) detector, in the low energy region of interest (1-6 keV) for the search of dark matter interaction via the annual modulation signature. As the vetoable background components, such as $^{40}$K, are here sub-dominant, we reassembled the PoP setup with a fully passive shielding. We upgraded the selection of events based on a Boosted Decision Tree algorithm that rejects most of the PMT-induced noise while retaining scintillation signals with > 90% efficiency in 1-6 keV. We find an average background of 1.39 $\pm$ 0.02 counts/day/kg/keV in the region of interest and a spectrum consistent with data previously acquired in the PoP setup, where the external veto background suppression was in place. Our background model indicates that the dominant background component is due to decays of $^{210}$Pb, only partly residing in the crystal itself. The other location of $^{210}$Pb is the reflector foil that wraps the crystal. We now proceed to design the experimental setup for the physics phase of the SABRE North detector, based on an array of similar crystals, using a low radioactivity PTFE reflector and further improving the passive shielding strategy, in compliance with the new safety and environmental requirements of Laboratori Nazionali del Gran Sasso.

physics.ins-det↗

arXiv2022

Scintillation yield from electronic and nuclear recoils in superfluid $^4$He

Superfluid $^4$He is a promising target material for direct detection of light ($<$ 1 GeV) dark matter. Possible signal channels available for readout in this medium include prompt photons, triplet excimers, and roton and phonon quasiparticles. The relative yield of these signals has implications for the sensitivity and discrimination power of a superfluid $^4$He dark matter detector. Using a 16~cm$^3$ volume of 1.75~K superfluid $^4$He read out by six immersed photomultiplier tubes, we measured the scintillation from electronic recoils ranging between 36.3 and 185 keV$_\mathrm{ee}$, yielding a mean signal size of $1.25^{+0.03}_{-0.03}$~phe/keV$_\mathrm{ee}$, and nuclear recoils from 53.2 to 1090 keV$_\mathrm{nr}$. We compare the results of our relative scintillation yield measurements to an existing semiempirical model based on helium-helium and electron-helium interaction cross sections. We also study the behavior of delayed scintillation components as a function of recoil type and energy, a further avenue for signal discrimination in superfluid $^4$He.

physics.ins-det↗

arXiv2022

A backing detector for order-keV neutrons

We have designed and tested a large-area (0.15~m$^2$) neutron detector based on neutron capture on \ce{^{6}Li}. The neutron detector design has been optimized for the purpose of tagging the scattering angle of keV-scale neutrons. These neutron detectors would be employed to calibrate the low-energy ($<$100 eV) nuclear recoil in detectors for dark matter and coherent elastic neutrino nucleus scattering (CE$ν$NS). We describe the design, construction, and characterization of a prototype. The prototype is designed to have a tagging efficiency of $\sim$25\% at the relevant $\mathcal{O}$(keV) neutron energies, and with a mean capture time of $\sim$17$~μ$s. The prototype was characterized using a \ce{^{252}Cf} neutron source and agreement with the simulation was observed within a few percent level.

physics.ins-det↗

arXiv2021

High sensitivity characterization of an ultra-high purity NaI(Tl) crystal scintillator with the SABRE proof-of-principle detector

We present new results on the radiopurity of a 3.4-kg NaI(Tl) crystal scintillator operated in the SABRE proof-of-principle detector setup. The amount of potassium contamination, determined by the direct counting of radioactive $^{40}$K, is found to be $2.2\pm1.5$ ppb, lowest ever achieved for NaI(Tl) crystals. With the active veto, the average background rate in the crystal in the 1-6 keV energy region-of-interest (ROI) is $1.20\pm0.05$ counts/day/kg/keV, which is a breakthrough since the DAMA/LIBRA experiment. Our background model indicates that the rate is dominated by $^{210}$Pb and that about half of this contamination is located in the PTFE reflector. We discuss ongoing developments of the crystal manufacture aimed at the further reduction of the background, including data from purification by zone refining. A projected background rate lower than $\sim$0.2 counts/day/kg/keV in the ROI is within reach. These results represent a benchmark for the development of next-generation NaI(Tl) detector arrays for the direct detection of dark matter particles.

physics.ins-det↗

arXiv2021

Characterization of SABRE crystal NaI-33 with direct underground counting

Ultra-pure NaI(Tl) crystals are the key element for a model-independent verification of the long standing DAMA result and a powerful means to search for the annual modulation signature of dark matter interactions. The SABRE collaboration has been developing cutting-edge techniques for the reduction of intrinsic backgrounds over several years. In this paper we report the first characterization of a 3.4 kg crystal, named NaI-33, performed in an underground passive shielding setup at LNGS. NaI-33 has a record low $^{39}$K contamination of 4.3$\pm$0.2 ppb as determined by mass spectrometry. We measured a light yield of 11.1$\pm$0.2 photoelectrons/keV and an energy resolution of 13.2% (FWHM/E) at 59.5 keV. We evaluated the activities of $^{226}$Ra and $^{228}$Th inside the crystal to be $5.9\pm0.6 μ$Bq/kg and $1.6\pm0.3 μ$Bq/kg, respectively, which would indicate a contamination from $^{238}$U and $^{232}$Th at part-per-trillion level. We measured an activity of 0.51$\pm$0.02 mBq/kg due to $^{210}$Pb out of equilibrium and a $α$ quenching factor of 0.63$\pm$0.01 at 5304 keV. We illustrate the analyses techniques developed to reject electronic noise in the lower part of the energy spectrum. A cut-based strategy and a multivariate approach indicated a rate, attributed to the intrinsic radioactivity of the crystal, of $\sim$1 count/day/kg/keV in the [5-20] keV region.

physics.ins-det↗

arXiv2018

The SABRE project and the SABRE PoP

SABRE aims to directly measure the annual modulation of the dark matter interaction rate with NaI(Tl) crystals. A modulation compatible with the standard hypothesis in which our Galaxy is embedded in a dark matter halo has been measured by the DAMA experiment in the same target material. Other direct detection experiments, using different target materials, seem to exclude the interpretation of such modulation in the simplest scenario of WIMP-nucleon elastic scattering. The SABRE experiment aims to carry out an independent search with sufficient sensitivity to confirm or refute the DAMA claim. The SABRE concept and goal is to obtain a background rate of the order of 0.1 cpd/kg/keVee in the energy region of interest. This challenging goal is achievable by operating high-purity crystals inside a liquid scintillator veto for active background rejection. In addition, twin detectors will be located in the northern and southern hemispheres to identify possible contributions to the modulation from seasonal or site-related effects. The SABRE project includes an initial Proof-of-Principle phase at LNGS (Italy), to assess the radio-purity of the crystals and the efficiency of the liquid scintillator veto. This paper describes the general concept of SABRE and the expected sensitivity to WIMP annual modulation.

physics.ins-det↗

arXiv2018

Monte Carlo simulation of the SABRE PoP background

SABRE (Sodium-iodide with Active Background REjection) is a direct dark matter search experiment based on an array of radio-pure NaI(Tl) crystals surrounded by a liquid scintillator veto. Twin SABRE experiments in the Northern and Southern Hemispheres will differentiate a dark matter signal from seasonal and local effects. The experiment is currently in a Proof-of-Principle (PoP) phase, whose goal is to demonstrate that the background rate is low enough to carry out an independent search for a dark matter signal, with sufficient sensitivity to confirm or refute the DAMA result during the following full-scale experimental phase. The impact of background radiation from the detector materials and the experimental site needs to be carefully investigated, including both intrinsic and cosmogenically activated radioactivity. Based on the best knowledge of the most relevant sources of background, we have performed a detailed Monte Carlo study evaluating the expected background in the dark matter search spectral region. The simulation model described in this paper guides the design of the full-scale experiment and will be fundamental for the interpretation of the measured background and hence for the extraction of a possible dark matter signal.

physics.ins-det↗

arXiv2016

Response of a proportional counter to $^{37}$Ar and $^{71}$Ge: measured spectra versus Geant4 simulation

The energy deposition spectra of $^{37}$Ar and $^{71}$Ge in a miniature proportional counter are measured and compared in detail to the model response simulated with Geant4. A certain modification of the Geant4 code, making it possible to trace the deexcitation of atomic shells properly, is suggested. Modified Geant4 is able to reproduce a response of particle detectors in detail in the keV energy range. This feature is very important for the laboratory experiments that search for massive sterile neutrinos as well as for dark matter searches that employ direct detection of recoil nuclei. This work demonstrates the reliability of Geant4 simulation at low energies.

physics.ins-det↗