A device filled with pure xenon first demonstrated the ability to operate simultaneously as a bubble chamber and scintillation detector in 2017. Initial results from data taken at thermodynamic thresholds down to 4keV showed sensitivity to 20 keV nuclear recoils with no observable bubble nucleation by gamma-ray interactions. This paper presents results from further operation of the same device at thermodynamic thresholds as low as 0.50 keV, hardware limited. The bubble chamber has now been shown to have sensitivity to 1 keV nuclear recoils while remaining insensitive to bubble nucleation by gamma-rays. A data- driven calibration of the chamber's nuclear recoil nucleation response, as a function of nuclear recoil energy and thermodynamic state, is presented. Stringent upper limits are established for the probability of bubble nucleation by gamma-ray-induced Auger cascades, with a limit of < 1.1 x 10(-6) set at 0.50 keV, the lowest thermodynamic threshold explored.

The Scintillating Bubble Chamber (SBC) collaboration purchased 32 Hamamatsu VUV4 silicon photomultipliers (SiPMs) for use in SBC-LAr10, a bubble chamber containing 10 kg of liquid argon. A dark-count characterization technique, which avoids the use of a single-photon source, was used at two temperatures to measure the VUV4 SiPMs breakdown voltage (V-BD), the SiPM gain (g(SiPM)), the rate of change of g(SiPM) with respect to voltage (m), the dark count rate (DCR), and the probability of a correlated avalanche (P-CA) as well as the temperature coefficients of these parameters. A Peltier-based chilled vacuum chamber was developed at Queen's University to cool down the Quads to 233.15 +/- 0.2 K and 255.15 +/- 0.2 K with average stability of +/- 20 mK. An analysis framework was developed to estimate V-BD to tens of mV precision and DCR close to Poissonian error. The temperature dependence of V-BD was found to be 56 +/- 2 mV K-1, and m on average across all Quads was found to be (459 +/- 3(stat.)+/- 23(sys.))x 10(3) e(-) PE-1 V-1. The average DCR temperature coefficient was estimated to be 0.099 +/- 0.008 K(-1)corresponding to a reduction factor of 7 for every 20 K drop in temperature. The average temperature dependence of P(CA)was estimated to be 4000 +/- 1000 ppm K-1. P-CA estimated from the average across all SiPMs is a better estimator than the P-CA calculated from individual SiPMs, for all of the other parameters, the opposite is true. All the estimated parameters were measured to the precision required for SBC-LAr10, and the Quads will be used in conditions to optimize the signal-to-noise ratio.

The first detailed study on the performance of a ZnO-based cryogenic scintillating bolometer as a detector to search for rare processes in zinc isotopes was carried out. A 7.2 g ZnO low-temperature detector, containing more than 80% of zinc in its mass, exhibits good energy resolution of baseline noise 1.0-2.7 keV FWHM at various working temperatures resulting in a low-energy threshold for the experiment, 2.0-6.0 keV. The light yield for /3/y events was measured as 1.5(3) keV/MeV, while it varies for a particles in the range of 0.2-3.0 keV/MeV. The detector demonstrates an effective identification of /3/y events from a events using time-properties of only heat signals. The radiopurity of the ZnO crystal was evaluated using the Inductively Coupled Plasma Mass Spectrometry, an ultra-low-background High Purity Ge y-spectrometer, and bolometric measurements. Only limits were set at the level of O(1-100) mBq/kg on activities of 40K, 137Cs and daughter nuclides from the U/Th natural decay chains. The total internal a-activity was measured as 22(2) mBq/kg, with a major contribution caused by 6(1) mBq/kg of 232Th and 12(2) mBq/kg of 234U. Limits on double beta decay (DBD) processes in 64Zn and 70Zn isotopes were set on the level of O (1017-1018) yr for various decay modes, profiting from 271 h of acquired background data inthe above-ground lab. This study shows a good potential for ZnO-based scintillating bolometers to search for DBD processes of Zn isotopes, especially in 64Zn, with the most prominent spectral features at similar to 10-20 keV, like the two-neutrino double electron capture. A 10 kg-scale experiment can reach the experimental sensitivity at the level of O(1024) yr.

The Scintillating Bubble Chamber (SBC) collaboration is developing liquid-noble bubble chambers for the detection of sub-keV nuclear recoils. These detectors benefit from the electron recoil rejection inherent in moderately-superheated bubble chambers with the addition of energy reconstruction provided from the scintillation signal. The ability to measure low-energy nuclear recoils allows the search for GeV-scale dark matter and the measurement of coherent elastic neutrino-nucleus scattering on argon from MeV-scale reactor antineutrinos. The first physics-scale detector, SBC-LAr10, is in the commissioning phase at Fermilab, where extensive engineering and calibration studies will be performed. In parallel, a functionally identical low-background version, SBC-SNOLAB, is being built for a dark matter search underground at SNOLAB. SBC-SNOLAB, with a 10 kg-yr exposure, will have sensitivity to a dark matter–nucleon cross section of 2×10−42 cm2 at 1 GeV/c2 dark matter mass, and future detectors could reach the boundary of the argon neutrino fog with a tonne-yr exposure. In addition, the deployment of an SBC detector at a nuclear reactor could enable neutrino physics investigations including measurements of the weak mixing angle and searches for sterile neutrinos, the neutrino magnetic moment, and the light Z’ gauge boson.

PICO bubble chambers have exceptional sensitivity to inelastic dark matter-nucleus interactions due to a combination of their extended nuclear-recoil energy detection window from a few keV to $O(100\text{ }\text{ }\mathrm{keV})$ or more and the use of iodine as a heavy target. Inelastic dark matter-nucleus scattering is interesting for studying the properties of dark matter, where many theoretical scenarios have been developed. This study reports the results of a search for dark matter inelastic scattering with the PICO-60 bubble chambers. The analysis reported here comprises physics runs from PICO-60 bubble chambers using ${\mathrm{CF}}_{3}\mathrm{I}$ and ${\mathrm{C}}_{3}{\mathrm{F}}_{8}$. The ${\mathrm{CF}}_{3}\mathrm{I}$ run consisted of 36.8 kg of ${\mathrm{CF}}_{3}\mathrm{I}$ reaching an exposure of $3415\text{ }\text{ }\mathrm{kg}\text{\ensuremath{-}}\mathrm{day}$ operating at thermodynamic thresholds between 7 and 20 keV. The ${\mathrm{C}}_{3}{\mathrm{F}}_{8}$ runs consisted of 52 kg of ${\mathrm{C}}_{3}{\mathrm{F}}_{8}$ reaching exposures of 1404 and $1167\text{ }\text{ }\mathrm{kg}\text{\ensuremath{-}}\mathrm{day}$ running at thermodynamic thresholds of 2.45 and 3.29 keV, respectively. The analysis disfavors various scenarios, in a wide region of parameter space, that provide a feasible explanation of the signal observed by the DAMA experiment, assuming an inelastic interaction, considering that the PICO ${\mathrm{CF}}_{3}\mathrm{I}$ bubble chamber used iodine as the target material.

Abstract A 510 day long-term measurement of a 45.3 g platinum foil acting as the sample and high voltage contact in an ultra-low-background high purity germanium detector was performed at Laboratori Nazionali del Gran Sasso (Italy). The data was used for a detailed study of double beta decay modes in natural platinum isotopes. Limits are set in the range $${\mathcal {O}}(10^{14}{-} 10^{19})$$ O ( 10 14 - 10 19 ) years (90% C.L.) for several double beta decay transitions to excited states confirming, and partially extending existing limits. The highest sensitivity of the measurement, greater than $$10^{19}$$ 10 19 years, was achieved for the two neutrino and neutrinoless double beta decay modes of the isotope $$^{198}$$ 198 Pt. Additionally, novel limits for inelastic dark matter scattering on $$^{195}$$ 195 Pt are placed up to mass splittings of approximately 500 keV. We analyze several techniques to extend the sensitivity and propose a few approaches for future medium-scale experiments with platinum-group elements.

The specific activity of the β decay of ^39 Ar in atmospheric argon is measured using the DEAP-3600 detector. DEAP-3600, located 2 km underground at SNOLAB, uses a total of (3269 ± 24) kg of liquid argon distilled from the atmosphere to search for dark matter. This detector is well-suited to measure the decay of ^39 Ar owing to its very low background levels. This is achieved in two ways: it uses low background construction materials; and it uses pulse-shape discrimination to differentiate between nuclear recoils and electron recoils. With 167 live-days of data, the measured specific activity at the time of atmospheric extraction is (0.964 ± 0.001 _stat ± 0.024 _sys ) Bq/kg _atmAr , which is consistent with results from other experiments. A cross-check analysis using different event selection criteria and a different statistical method confirms the result.

The Scintillating Bubble Chamber (SBC) collaboration is combining the well-established liquid argon and bubble chamber technologies to search for low-mass, GeV-scale dark matter. Liquid-noble bubble chambers benefit from the excellent electron-recoil insensitivity inherent in bubble chambers with the addition of energy reconstruction provided from the scintillation signal for background rejection. The projected sensitivity with a quasi-background-free 10-kg-year exposure at a 100 eV nuclear recoil threshold is approximately 10 ^{-43} cm −43cm ^2$ for a 1 GeV/c ^2 2 dark matter mass.

As experiments searching for neutrinoless double beta decay push into the inverted hierarchy, enriched isotope target masses of hundreds of kilograms are required. Due to unavoidable losses throughout the entire production chain, the recovery of expensive enriched material used in crystal-based experiments should be given special attention. The CUPID-0 experiment using Zn 82 Se scintillating bolomoters provides a unique opportunity at the 10-kg-scale to test a recovery process for enriched 82 Se. We present a multi-stage, high-yield method consisting of wet chemistry and vacuum distillation. The chemical purity, isotopic abundance, and radiopurity is demonstrated to be preserved after the 82 Se extraction with recovery efficiency no less than 86.4% (that potentially can be higher than 94.7%) and chemical purity of 99.999%.

In this article we report on a detailed study of the internal radioactive and chemical contamination of the Li6Eu(BO3)(3) scintillating crystal operated as a cryogenic scintillating bolometer over 359 h. The excellent discrimination power of the detector allows to distinguish effectively beta/gamma events from alpha events. Whilst a weak activity of daughter nuclides from U/Th chains at the level few mBq/kg was observed, this crystal was found to be significantly contaminated by Sm-147, an alpha-active nuclide, at the level of about 0.5 Bq/kg. The light yield for beta/gamma events was determined to be 7.4(6) keV/MeV. The light yield and quenching factor for alpha particles vary in the range of (0.5-1.2) keV/MeV and (0.07-0.17), respectively, due to energy dependence of the emitted scintillating light in the energy interval (2.0-7.0) MeV. The integral luminescence intensity of the Li6Eu(BO3)(3) crystal increases by more than four times only at low temperatures, below 80 K. Therefore, the Li6Eu(BO3)(3)-based cryogenic scintillating bolometers can be attractive detectors for direct neutron flux monitoring, to search for rare alpha decays or solar axions.

PICO bubble chambers have exceptional sensitivity to inelastic dark matter-nucleus interactions due to a combination of their extended nuclear-recoil energy detection window from a few keV to Oo100 keV thorn or more and the use of iodine as a heavy target. Inelastic dark matter-nucleus scattering is interesting for studying the properties of dark matter, where many theoretical scenarios have been developed. This study reports the results of a search for dark matter inelastic scattering with the PICO-60 bubble chambers. The analysis reported here comprises physics runs from PICO-60 bubble chambers using CF3I and C3F8. The CF3I run consisted of 36.8 kg of CF3I reaching an exposure of 3415 kg-day operating at thermodynamic thresholds between 7 and 20 keV. The C3F8 runs consisted of 52 kg of C3F8 reaching exposures of 1404 and 1167 kg-day running at thermodynamic thresholds of 2.45 and 3.29 keV, respectively. The analysis disfavors various scenarios, in a wide region of parameter space, that provide a feasible explanation of the signal observed by the DAMA experiment, assuming an inelastic interaction, considering that the PICO CF3I bubble chamber used iodine as the target material.

Many compelling models predict dark matter coupling to the electromagnetic current through higher multipole interactions, while remaining electrically neutral. Different multipole couplings have been studied, among them anapole moment, electric and magnetic dipole moments, and millicharge. This study sets limits on the couplings for these photon-mediated interactions using non-relativistic contact operators in an effective field theory framework. Using data from the PICO-60 bubble chamber leading limits for dark matter masses between 2.7 GeV/c$^2$ and 24 GeV/c$^2$ are reported for the coupling of these photon-mediated dark matter-nucleus interactions. The detector was filled with 52 kg of C$_3$F$_8$ operating at thermodynamic thresholds of 2.45 keV and 3.29 keV, reaching exposures of 1404 kg-day and 1167 kg-day, respectively.

The bubble nucleation efficiency of low-energy nuclear recoils in superheated liquids plays a crucial role in interpreting results from direct searches for weakly interacting massive particle (WIMP) dark matter. The PICO collaboration presents the results of the efficiencies for bubble nucleation from carbon and fluorine recoils in superheated C-3 F-8 from calibration data taken with five distinct neutron spectra at various thermodynamic thresholds ranging from 2.1 to 3.9 keV. Instead of assuming any particular functional forms for the nuclear recoil efficiency, a generalized piecewise linear model is proposed with systematic errors included as nuisance parameters to minimize model-introduced uncertainties. A Markov chain Monte Carlo routine is applied to sample the nuclear recoil efficiency for fluorine and carbon at 2.45 and 3.29 keV thermodynamic thresholds simultaneously. The nucleation efficiency for fluorine was found to be >= 50% for nuclear recoils of 3.3 keV (3.7 keV) at a thermodynamic Seitz threshold of 2.45 keV (3.29 keV), and for carbon the efficiency was found to be >= 50% for recoils of 10.6 keV (11.1 keV) at a threshold of 2.45 keV (3.29 keV). Simulated datasets are used to calculate a p value for the fit, confirming that the model used is compatible with the data. The fit paradigm is also assessed for potential systematic biases, which although small, are corrected for. Additional steps are performed to calculate the expected interaction rates of WIMPs in the PICO-60 detector, a requirement for calculating WIMP exclusion limits.

At the Montreal Tandem accelerator, an experiment is being set up to measure internal pair creation from the decay of nuclear excited states using a multiwire proportional chamber and scintillator bars surrounding it from the DAPHNE experiment. The acceptance covers a solid angle of nearly 4π. Preamplifiers and the data acquisition hardware have been designed and tested. The water-cooled ^7LiF target, mounted on an Al foil is in a thin carbon fiber section of the beamline. The experiment will focus at first on a measurement of the internal pair creation from the 18.15 MeV state of ^8Be. Assuming the ATOMKI evaluation of the electron-pair production rate from X17, a Geant4 simulation predicts observation of a clear signal after about two weeks of data taking with a 2 μA proton beam. The IPC measurement could eventually be extended to the giant dipole resonance of ^8Be, as well as to other nuclei, in particular to ^10B.

The Scintillating Bubble Chamber (SBC) Collaboration is developing liquid-noble bubble chambers for the quasi-background-free detection of low-mass (GeV-scale) dark matter and coherent scattering of low-energy (MeV-scale) neutrinos (CE$\nu$NS). The first physics-scale demonstrator of this technique, a 10-kg liquid argon bubble chamber dubbed SBC-LAr10, is now being commissioned at Fermilab. This device will calibrate the background discrimination power and sensitivity of superheated argon to nuclear recoils at energies down to 100 eV. A second functionally-identical detector with a focus on radiopure construction is being built for SBC's first dark matter search at SNOLAB. The projected spin-independent sensitivity of this search is approximately $10^{-43}$ cm$^2$ at 1 GeV$/c^2$ dark matter particle mass. The scalability and background discrimination power of the liquid-noble bubble chamber make this technique a compelling candidate for future dark matter searches to the solar neutrino fog at 1 GeV$/c^2$ particle mass (requiring a $\sim$ton-year exposure with non-neutrino backgrounds sub-dominant to the solar CE$\nu$NS signal) and for high-statistics CE$\nu$NS studies at nuclear reactors.

The DEAP-3600 detector searches for the scintillation signal from dark matter particles scattering on a 3.3 tonne liquid argon target. The largest background comes from 39 Ar beta decays and is suppressed using pulse-shape discrimination (PSD). We use two types of PSD estimator: the prompt-fraction, which considers the fraction of the scintillation signal in a narrow and a wide time window around the event peak, and the log-likelihood-ratio, which compares the observed photon arrival times to a signal and a background model. We furthermore use two algorithms to determine the number of photons detected at a given time: (1) simply dividing the charge of each PMT pulse by the mean single-photoelectron charge, and (2) a likelihood analysis that considers the probability to detect a certain number of photons at a given time, based on a model for the scintillation pulse shape and for afterpulsing in the light detectors. The prompt-fraction performs approximately as well as the log-likelihood-ratio PSD algorithm if the photon detection times are not biased by detector effects. We explain this result using a model for the information carried by scintillation photons as a function of the time when they are detected.

The bubble chambers of the PICO collaboration use the acoustic signal generated from nucleations to classify nuclear recoil events from alpha decays in the bulk fluid. The success of these detectors in probing the potential WIMP-proton cross section comes in part from the low energy threshold that can be achieved. This nucleation threshold, based on the Seitz model, is dependent on fluid type, pressure, and temperature. At higher thresholds bubble nucleation does occur but with a significant loss in the measurable acoustic signal. To investigate this, the acoustic response of bulk nuclear recoil events was measured as a function of pressure and temperature and found to depend exponentially on both parameters.

A measurement of hafnium foil using a modified ultra-low-background high purity detector with optimized sample-to-detector geometry was performed at Laboratori Nazionale del Gran Sasso. Radiopurity of the stock Hf foil was studied in detail, in addition to an analysis of data collected over 310 days to search for rare processes that can occur in natural Hf isotopes. Firstly, limits on alpha decays of all natural Hf isotopes to the first excited state of the daughter nuclides were established in the range of 10(16)-10(18)a (90% C.L.). Secondly, a search for modes of double electron capture and electron capture with positron emission in Hf-174 was performed, yielding half-life limits 10(16)-10(18)a (90% C.L.). Lastly, novel dark matter-induced nuclear excitations in hafnium isotopes were investigated. For dark matter with 1 TeV/c(2) mass, leading limits on the inelastic dark matter-nucleon cross section are set for mass splittings in the range 428 keV < delta(M) < 473 keV in the adopted model framework. (C) 2021 Elsevier B.V. All rights reserved.

AbstractDEAP-3600 is a liquid-argon scintillation detector looking for dark matter. Scintillation events in the liquid argon (LAr) are registered by 255 photomultiplier tubes (PMTs), and pulseshape discrimination (PSD) is used to suppress electromagnetic background events. The excellent PSD performance of LAr makes it a viable target for dark matter searches, and the LAr scintillation pulseshape discussed here is the basis of PSD. The observed pulseshape is a combination of LAr scintillation physics with detector effects. We present a model for the pulseshape of electromagnetic background events in the energy region of interest for dark matter searches. The model is composed of (a) LAr scintillation physics, including the so-called intermediate component, (b) the time response of the TPB wavelength shifter, including delayed TPB emission at $${\mathcal {O}}$$O(ms) time-scales, and c) PMT response. TPB is the wavelength shifter of choice in most LAr detectors. We find that approximately 10% of the intensity of the wavelength-shifted light is in a long-lived state of TPB. This causes light from an event to spill into subsequent events to an extent not usually accounted for in the design and data analysis of LAr-based detectors.