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The possibility of the BEST experiment on electron neutrino disappearance with intense artificial sources of electron neutrino 51Cr is considered. BEST has the great potential to search for transitions of active neutrinos to sterile states with Δm 2 ∼1 eV2 and to set the limits on short baseline electron neutrino disappearance oscillation parameters. The possibility of the further constraints the oscillation parameters region with using 65Zn source is discussed.

The status of the feasibility studies for a proposed Ga source experiment to search for possible electron neutrino transitions into sterile states is presented. The advantages of the proposed technique are considered. The experiment has the potential to detect neutrino oscillation transitions with mass-squared difference Δm2 > 0.5 eV2 with a sensitivity to disappearance of electron neutrinos of a few percent

DEAP-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 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.

The specific activity of the$$\\beta $$β decay of$$^{39}$$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$$^{39}$$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$$_\\textrm{stat}$$stat ± 0.024$$_\\textrm{sys}$$sys ) Bq/kg$$_\\textrm{atmAr}$$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 half-life of$$^{39}$$39 Ar is measured using the DEAP-3600 detector located 2 km underground at SNOLAB. Between 2016 and 2020, DEAP-3600 used a target mass of (3269 ± 24) kg of liquid argon distilled from the atmosphere in a direct-detection dark matter search. Such an argon mass also enables direct measurements of argon isotope properties. The decay of$$^{39}$$39 Ar in DEAP-3600 is the dominant source of triggers by two orders of magnitude, ensuring high statistics and making DEAP-3600 well-suited for measuring this isotope’s half-life. Use of the pulse-shape discrimination technique in DEAP-3600 allows powerful discrimination between nuclear recoils and electron recoils, resulting in the selection of a clean sample of$$^{39}$$39 Ar decays. Observing over a period of 3.4 years, the$$^{39}$$39 Ar half-life is measured to be$$(302 \\pm 8_\\textrm{stat} \\pm 6_\\textrm{sys})$$( 302 ± 8 stat ± 6 sys ) years. This new direct measurement suggests that the half-life of$$^{39}$$39 Ar is significantly longer than the accepted value, with potential implications for measurements using this isotope’s half-life as input.

The knowledge of scintillation quenching of α -particles plays a paramount role in understanding α -induced backgrounds and improving the sensitivity of liquid argon-based direct detection of dark matter experiments. We performed a relative measurement of scintillation quenching in the MeV energy region using radioactive isotopes ( 222 Rn, 218 Po and 214 Po isotopes) present in trace amounts in the DEAP-3600 detector and quantified the uncertainty of extrapolating the quenching factor to the low-energy region.

The Baksan Experiment on Sterile Transitions (BEST) probes the gallium anomaly and its possible connections to oscillations between active and sterile neutrinos. Based on the Gallium-Germanium Neutrino Telescope (GGNT) technology of the SAGE experiment, BEST employs two zones of liquid Ga target to explore neutrino oscillations on the meter scale. Oscillations on this short scale could produce deficits in the \\(^{71}\\)Ge production rates within the two zones, as well as a possible rate difference between the zones. From July 5th to October 13th 2019, the two-zone target was exposed to a primarily monoenergetic, 3.4-MCi \\(^{51}\\)Cr neutrino source 10 times for a total of 20 independent \\(^{71}\\)Ge extractions from the two Ga targets. The \\(^{71}\\)Ge production rates from the neutrino source were measured from July 2019 to March 2020. At the end of these measurements, the counters were filled with \\(^{71}\\)Ge doped gas and calibrated during November 2020. In this paper, results from the BEST sterile neutrino oscillation experiment are presented in details. The ratio of the measured \\(^{71}\\)Ge production rates to the predicted rates for the inner and the outer target volumes are calculated from the known neutrino capture cross section. Comparable deficits in the measured ratios relative to predicted values are found for both zones, with the \\(4 \\sigma\\) deviations from unity consistent with the previously reported gallium anomaly. If interpreted in the context of neutrino oscillations, the deficits give best fit oscillation parameters of \\(\\Delta m^2=3.3^{+\\infty}_{-2.3}\\) eV\\(^2\\) and sin\\(^2 2\\theta=0.42^{+0.15}_{-0.17}\\), consistent with \\(\\nu_e \\rightarrow \\nu_s\\) oscillations governed by a surprisingly large mixing angle.

The Baksan Experiment on Sterile Transitions (BEST) was designed to investigate the deficit of electron neutrinos, \\(_e\\), observed in previous gallium-based radiochemical measurements with high-intensity neutrino sources, commonly referred to as the gallium anomaly, which could be interpreted as evidence for oscillations between \\(_e\\) and sterile neutrino (\\(_s\\)) states. A 3.414-MCi 51Cr \\(_e\\) source was placed at the center of two nested Ga volumes and measurements were made of the production of 71Ge through the charged current reaction, 71Ga(\\(_e\\),e\\(^-\\))71Ge, at two average distances. The measured production rates for the inner and the outer targets respectively are (\\(54.9^+2.5_-2.4(stat)1.4 (syst)\\)) and (\\(55.6^+2.7_-2.6(stat)1.4 (syst)\\)) atoms of 71Ge/d. The ratio (\\(R\\)) of the measured rate of 71Ge production at each distance to the expected rate from the known cross section and experimental efficiencies are \\(R_in=0.790.05\\) and \\(R_out= 0.770.05\\). The ratio of the outer to the inner result is 0.97\\(\\)0.07, which is consistent with unity within uncertainty. The rates at each distance were found to be similar, but 20-24\\% lower than expected, thus reaffirming the anomaly. These results are consistent with \\(_e _s\\) oscillations with a relatively large \\( m^2\\) (\\(>\\)0.5 eV\\(^2\\)) and mixing sin\\(^2 2\\) (\\(\\)0.4).

Dark matter particles with Planck-scale mass (\\(\\simeq10^{19}\\text{GeV}/c^2\\)) arise in well-motivated theories and could be produced by several cosmological mechanisms. Using a blind analysis of data collected over a 813 d live time with DEAP-3600, a 3.3 t single-phase liquid argon-based dark matter experiment at SNOLAB, a search for supermassive dark matter was performed, looking for multiple-scatter signals. No candidate signal events were observed, leading to the first direct detection constraints on Planck-scale mass dark matter. Leading limits constrain dark matter masses between \\(8.3\\times10^{6}\\) and \\(1.2\\times10^{19} \\text{GeV}/c^2\\), and cross sections for scattering on \\(^{40}\\)Ar between \\(1.0\\times10^{-23}\\) and \\(2.4\\times10^{-18} \\text{cm}^2\\). These are used to constrain two composite dark matter models.

DEAP-3600 is a single-phase liquid argon detector aiming to directly detect Weakly Interacting Massive Particles (WIMPs), located at SNOLAB (Sudbury, Canada). After analyzing data taken during the first year of operation, a null result was used to place an upper bound on the WIMP-nucleon spin-independent, isoscalar cross section. This study reinterprets this result within a Non-Relativistic Effective Field Theory framework, and further examines how various possible substructures in the local dark matter halo may affect these constraints. Such substructures are hinted at by kinematic structures in the local stellar distribution observed by the Gaia satellite and other recent astronomical surveys. These include the Gaia Sausage (or Enceladus), as well as a number of distinct streams identified in recent studies. Limits are presented for the coupling strength of the effective contact interaction operators \\(\\mathcal{O}_1\\), \\(\\mathcal{O}_3\\), \\(\\mathcal{O}_5\\), \\(\\mathcal{O}_8\\), and \\(\\mathcal{O}_{11}\\), considering isoscalar, isovector, and xenonphobic scenarios, as well as the specific operators corresponding to millicharge, magnetic dipole, electric dipole, and anapole interactions. The effects of halo substructures on each of these operators are explored as well, showing that the \\(\\mathcal{O}_5\\) and \\(\\mathcal{O}_8\\) operators are particularly sensitive to the velocity distribution, even at dark matter masses above 100 GeV/\\(c^2\\).