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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.

Abstract 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.

Abstract The specific activity of theβ β decay of³⁹39 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 of³⁹39 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.

Fermionic dark matter absorption on nuclear targets via neutral current interactions is explored using a non-relativistic effective field theory framework. An analysis of data from the PICO-60 C\\(_3\\)F\\(_8\\) bubble chamber sets leading constraints on spin-independent absorption for dark matter masses below 23 MeV/\\(c^2\\) 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.

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\\).

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.

We present here a search for WIMP dark matter using 790.8 live-days of data collected with 3269 kg of liquid argon (1266 kg fiducial) by the DEAP-3600 detector at SNOLAB, using the Profile Likelihood Ratio method. The likelihood model is based on three parameters: estimated energy, pulse-shape discrimination parameter, and reconstructed position within the detector. Using this method, the expected signal sensitivity of DEAP-3600 benefits from an increased fiducial volume and improved event selection acceptance. Alpha-decays from a small number of dust particulates circulating within the liquid argon target are the dominant source of background events and limit the sensitivity of this search. This result provides improved exclusion upper limits on the WIMP-nucleon spin-independent cross section on liquid argon for WIMP masses between 20 GeV/\\(c^{2}\\) and 100 GeV/\\(c^{2}\\). At 100 GeV/\\(c^{2}\\) the observed limit is 3.4 \\(\\times\\) 10\\(^{-45}\\) cm\\(^2\\) at 90% confidence level.

The knowledge of scintillation quenching of \\(\\)-particles plays a paramount role in understanding \\(\\)-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.