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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 39Ar 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.

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.

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.

The purpose of this study was to explore the effectiveness of undergraduate academic and clinical training programs for music therapy in addressing the subject of personal growth, as it relates to the development of critical self-awareness and self-care strategies. The study further attempted to identify which self-care strategies are being used by practicing music therapy clinicians and how a practice of self-care impacts their work with distressed and/or traumatized individuals. An electronic survey sent to all board-certified music therapists (MT-BCs) (N = 6369) generated a demographic profile of music therapy practitioners who identified their clientele as distressed and/or traumatized. The survey doubled as a means to identify a sample population for participation in face-to-face interviews. These interviews disclosed the clinicians’ perception of the effectiveness of their educational programs in preparing them to work with trauma-informed populations. An arts-based response further provided qualitative information corroborating the interviews. An open-ended survey questionnaire sent to academic directors of AMTA approved program directors (N = 79), investigated whether curricula related to self-care was included. The results revealed that 63.83% of MT-BCs (bachelor, masters, and doctorate levels) identified their clientele as distressed and/or traumatized. Specifically, 45.03% were bachelor-level clinicians. Results of the survey questionnaire to academic program directors (n = 16; 20.25% responding) indicated that 50% did not include a dedicated unit on self-care in their curricula. Interviews with clinicians exposed that 37.5% graduated from either graduate or undergraduate programs where the topic of self-care was not addressed. A thematic analysis of interview data and mandala arts-based responses, generated five primary and secondary themes; the analysis further identified indicators of vicarious traumatization related to the work experience. A plethora of self-care strategies and practices were communicated throughout the interview and creative response. The results of the survey suggest that more emphasis related to self-care in music therapy academic and clinical training programs would serve to provide graduates with increased knowledge and resources regarding self-care, thereby enabling clinicians to mitigate or circumvent the potential professional risks associated with treating a distressed and/or traumatized clientele. Key Words: music therapy, education, self-care, trauma, creative arts, self-care strategies, clinical preparation

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 \\(\\mathcal 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.

DEAP-3600 is a single-phase liquid argon (LAr) direct-detection dark matter experiment, operating 2 km underground at SNOLAB (Sudbury, Canada). The detector consists of 3279 kg of LAr contained in a spherical acrylic vessel. This paper reports on the analysis of a 758 tonne\\cdot day exposure taken over a period of 231 live-days during the first year of operation. No candidate signal events are observed in the WIMP-search region of interest, which results in the leading limit on the WIMP-nucleon spin-independent cross section on a LAr target of \\(3.9\\times10^{-45}\\) cm\\(^{2}\\) (\\(1.5\\times10^{-44}\\) cm\\(^{2}\\)) for a 100 GeV/c\\(^{2}\\) (1 TeV/c\\(^{2}\\)) WIMP mass at 90\\% C. L. In addition to a detailed background model, this analysis demonstrates the best pulse-shape discrimination in LAr at threshold, employs a Bayesian photoelectron-counting technique to improve the energy resolution and discrimination efficiency, and utilizes two position reconstruction algorithms based on PMT charge and photon arrival times.

The specific activity of the beta 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 \\(\\pm\\) 24) kg of liquid argon distilled from the atmosphere to search for dark matter. This detector with very low background uses pulseshape discrimination to differentiate between nuclear recoils and electron recoils and is well-suited to measure the decay of \\(^{39}\\)Ar. With 167 live-days of data, the measured specific activity at the time of atmospheric extraction is [0.964 \\(\\pm\\) 0.001 (stat) \\(\\pm\\) 0.024 (sys)] Bq/kg\\(_{\\rm atmAr}\\) which is consistent with results from other experiments. A cross-check analysis using different event selection criteria provides a consistent result.

The DEAP-3600 experiment is searching for WIMP dark matter with a 3.3 tonne single phase liquid argon (LAr) target, located 2.1 km underground at SNOLAB. The experimental signature of dark matter interactions is keV-scale \\(^{40}\\)Ar nuclear recoils (NR) producing 128 nm LAr scintillation photons observed by PMTs. The largest backgrounds in DEAP-3600 are electronic recoils (ER) induced by \\(\\beta\\) and \\(\\gamma\\)-rays originating from internal and external radioactivity in the detector material. A background model of the ER interactions in DEAP-3600 was developed and is described in this work. The model is based on several components which are expected from radioisotopes in the LAr, from ex-situ material assay measurements, and from dedicated independent in-situ analyses. This prior information is used in a Bayesian fit of the ER components to a 247.2 d dataset to model the radioactivity in the surrounding detector materials. While excellent discrimination between ERs and NRs is reached with pulse shape discrimination, utilizing the large difference between fast and slow components of LAr scintillation light, detailed knowledge of the ER background and activity of detector components, sets valuable constraints on other key types of backgrounds in the detector: neutrons and alphas. In addition, the activity of \\(^{42}\\)Ar in LAr in DEAP-3600 is determined by measuring the daughter decay of \\(^{42}\\)K. This cosmogenically activated trace isotope is a relevant background at higher energies for other rare event searches using atmospheric argon e.g. DarkSide-20k, GERDA or LEGEND. The specific activity of \\(^{42}\\)Ar in the atmosphere is found to be \\(40.4 \\pm 5.9\\) \\(\\mu\\)Bq/kg of argon.

The Hamamatsu R5912-HQE photomultiplier-tube (PMT) is a novel high-quantum efficiency PMT. It is currently used in the DEAP-3600 dark matter detector and is of significant interest for future dark matter and neutrino experiments where high signal yields are needed. We report on the methods developed for in-situ characterization and monitoring of DEAP's 255 R5912-HQE PMTs. This includes a detailed discussion of typical measured single-photoelectron charge distributions, correlated noise (afterpulsing), dark noise, double, and late pulsing characteristics. The characterization is performed during the detector commissioning phase using laser light injected through a light diffusing sphere and during normal detector operation using LED light injected through optical fibres.