Russell G Neilson

The Scintillating Bubble Chamber (SBC) Collaboration isdesigning a new generation of low background, noble liquid bubblechamber experiments with sub-keV nuclear recoil threshold. Theseexperiments combine the electronic recoil blindness of a bubblechamber with the energy resolution of noble liquid scintillation,and maintain electron recoil discrimination at higher degrees ofsuperheat (lower nuclear recoil thresholds) than Freon-based bubblechambers. A 10-kg liquid argon bubble chamber has the potential toset world leading limits on the dark matter nucleon cross-sectionfor 𝒪(GeV/c$^{2}$) masses, and to perform a highstatistics coherent elastic neutrino nuclear scattering measurementwith reactor neutrinos. This work presents a detailed calibrationplan to measure the detector response of these experiments,combining photoneutron scattering with two new techniques to inducesub-keV nuclear recoils: nuclear Thomson scattering and thermalneutron capture.

The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, was a segmented antineutrino detector that successfully operated at the High Flux Isotope Reactor in Oak Ridge, TN, during its 2018 run. Despite challenges with photomultiplier tube base failures affecting some segments, innovative machine learning approaches were employed to perform position and energy reconstruction, and particle classification. This work highlights the effectiveness of convolutional neural networks and graph convolutional networks in enhancing data analysis. By leveraging these techniques, a 3.3% increase in effective statistics was achieved compared to traditional methods, showcasing their potential to improve analysis performance. Furthermore, these machine learning methodologies offer promising applications for other segmented particle detectors, underscoring their versatility and impact.

Fermionic dark matter absorption on nuclear targets via neutral current interactions is explored using a nonrelativistic effective field theory framework. An analysis of data from the PICO-60 C3F8 bubble chamber sets leading constraints on spin-independent absorption for dark matter masses below 23 MeV/c2 and establishes the first limits on spin-dependent absorptive interactions. These results demonstrate the sensitivity of bubble chambers to low-mass dark matter and underscore the importance of absorption searches in expanding the parameter space of direct detection experiments.

The PROSPECT experiment is designed to perform precise searches for antineutrino disappearance at short distances (7–9 m) from compact nuclear reactor cores. This Letter reports results from a new neutrino oscillation analysis performed using the complete data sample from the PROSPECT-I detector operated at the High Flux Isotope Reactor in 2018. The analysis uses a multiperiod selection of inverse beta decay neutrino interactions with reduced backgrounds and enhanced statistical power to set limits on electron neutrino disappearance caused by mixing with sterile neutrinos with 0.2 – 20 eV 2 mass splittings. Inverse beta decay positron energy spectra from six different reactor-detector distance ranges are found to be statistically consistent with one another, as would be expected in the absence of sterile neutrino oscillations. The data excludes at 95% confidence level the existence of sterile neutrinos in regions above 3 eV 2 previously unexplored by terrestrial experiments, including all space below 10 eV 2 suggested by the recently strengthened Gallium Anomaly. The best-fit point of the Neutrino-4 reactor experiment’s claimed observation of short-baseline oscillation is ruled out at more than 5 standard deviations.

The PROSPECT-I detector has several features that enable measurement of the direction of a compact neutrino source. In this paper, a detailed report on the directional measurements made on electron antineutrinos emitted from the High Flux Isotope Reactor is presented. With an estimated true neutrino (reactor to detector) direction of % = 40.8 degrees + 0.7 degrees and theta = 98.6 degrees + 0.4 degrees, the PROSPECT-I detector is able to reconstruct an average neutrino direction of % = 39.4 degrees + 2.9 degrees and theta = 97.6 degrees + 1.6 degrees. This measurement is made with approximately 48 000 inverse beta decay signal events and is the most precise directional reconstruction of reactor antineutrinos to date.

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.

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.

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 x 10(-42) cm(2) at 1 GeV/ c(2) 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.