Dark matter with Planck-scale mass (≃10^{19} GeV/c^{2}) arises in well-motivated theories and could be produced by several cosmological mechanisms. A search for multiscatter signals from ...supermassive dark matter was performed with a blind analysis of data collected over a 813 d live time with DEAP-3600, a 3.3 t single-phase liquid argon-based detector at SNOLAB. No candidate signals were observed, leading to the first direct detection constraints on Planck-scale mass dark matter. Leading limits constrain dark matter masses between 8.3×10^{6} and 1.2×10^{19} GeV/c^{2}, and ^{40}Ar-scattering cross sections between 1.0×10^{-23} and 2.4×10^{-18} cm^{2}. These results are interpreted as constraints on composite dark matter models with two different nucleon-to-nuclear cross section scalings.
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
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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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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 nonrelativistic 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 O1, O3, O5, O8, and O11, 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 O5 and O8 operators are particularly sensitive to the velocity distribution, even at dark matter masses above 100 GeV / c2.
Acrylic (poly(methyl methacrylate) or PMMA) is commonly used as a material for vessels to hold scintillating liquids in rare-event searches. Certain types of PMMA can fluoresce with a low efficiency ...at room temperature. We have investigated the fluorescence spectra under 280 nm ultraviolet (UV) excitation of the PMMA used in the DEAP-3600 dark matter search at various low temperatures. Fluorescence of this PMMA is observed, with an increasing intensity as the sample is cooled from a temperature of 300 K down to 4 K . The common wavelength-shifter tetraphenyl butadiene (TPB) is also measured for use as a reference.
Background
Freeze dried bone allograft (FDBA) and solvent dehydrated bone allograft (SDBA) are both commonly used in alveolar ridge preservation. Previous studies have suggested SDBA may have ...advantages over FDBA due to a unique processing method. The primary objective of this study was to histologically compare the healing outcome between FDBA and SDBA when used for ridge preservation. Changes in morphometric ridge parameters were evaluated as a secondary outcome.
Methods
Forty‐four patients requiring extraction and ridge preservation were randomized into two groups: FDBA (control group) or SDBA (test group). Patients returned 12 weeks post‐extraction and ridge preservation for implant placement. A bone core was taken in the planned implant osteotomy site and evaluated histomorphometrically to determine the percentage of vital bone, residual graft material, and connective/other tissue. Changes in clinical ridge dimensions were also evaluated for patients in both treatment groups.
Results
The FDBA group showed a mean of 24.08% vital bone, 22.96% residual graft material, and 52.95% CT/other. The SDBA group showed a mean of 27.19% vital bone, 23.38% residual graft material, and 49.41% CT/other. No statistical differences were found between groups in the mean outcomes for histologic parameters or in dimensional change of the alveolar ridge.
Conclusion
This study provides the first histologic comparison between the wound healing of FDBA and SDBA over a 12‐week healing period in a ridge preservation application. The findings suggest no significant benefit or drawback with the use of either FDBA or SDBA when comparing histomorphometric parameters or clinical dimensional changes.
The SNO+ Collaboration reports the first evidence of reactor antineutrinos in a Cherenkov detector. The nearest nuclear reactors are located 240 km away in Ontario, Canada. This analysis uses events ...with energies lower than in any previous analysis with a large water Cherenkov detector. Two analytical methods are used to distinguish reactor antineutrinos from background events in 190 days of data and yield consistent evidence for antineutrinos with a combined significance of 3.5σ.
Several particle-physics experiments use poly(methyl methacrylate) (a.k.a. PMMA or acrylic) vessels to contain liquid scintillators. Superluminal charged particles emitted from radioactive impurities ...in or near the acrylic can emit Cherenkov radiation in the ultraviolet (UV) spectra range. If acrylic fluoresces in the visible range due to this UV light, it could be a source of background in experiments where the main signal is visible scintillation light, or UV scintillation light that is absorbed and re-emitted at visible wavelengths by a wavelength shifter. Some of these experiments operate at low temperature. The fluorescence of these materials could change with temperature so we have studied the fluorescence of the acrylic used in the DEAP-3600 experiment down to a temperature of 4 K, and compared it to the common wavelength shifter 1,1,4,4-tetraphenyl-1,3-butadiene (TPB). The light yield and wavelength spectra of these materials were characterized by exciting the sample with 285 nm UV light, which acted as a proxy for Cherenkov light in the detector. Spectral measurements indicate at least part of the fluorescence of the acrylic is due to additives. Time-resolved measurements show the light yields of our acrylic sample, TPB sample, and the relative light between both samples, all increase when cooling down. At room temperature, the light yield of our acrylic sample relative to the TPB sample is 0.27%, while it reaches 0.48% at 4 K. The main fluorescence time constant of the acrylic is less than a few nanoseconds.
The direction of individual
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solar neutrinos has been reconstructed using the
SNO
+
liquid scintillator detector. Prompt, directional Cherenkov light was separated from the slower, isotropic ...scintillation light using time information, and a maximum likelihood method was used to reconstruct the direction of individual scattered electrons. A clear directional signal was observed, correlated with the solar angle. The observation was aided by a period of low primary fluor concentration that resulted in a slower scintillator decay time. This is the first time that event-by-event direction reconstruction in high light-yield liquid scintillator has been demonstrated in a large-scale detector.
Published by the American Physical Society
2024
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