Abstract
Dual phase xenon detectors are widely used in experimental
searches for galactic dark matter particles. The origin of single
electron backgrounds following prompt scintillation and ...proportional
scintillation signals in these detectors is not fully understood,
although there has been progress in recent years. In this paper, we
describe single electron backgrounds in
83m
Kr
calibration events and their correlation with drift and extraction
fields, using the Particle Identification in Xenon at Yale (PIXeY)
dual-phase xenon time projection chamber. The single electron
background induced by the Fowler-Nordheim (FN) effect is measured,
and its electric field dependence is quantified. The photoionization
of grids and impurities by prompt scintillation and proportional
scintillation also contributes to the single electron background.
Recent N-body simulations are in favor of the presence of a co-rotating Dark Disk that might contribute significantly (10%–50%) to the local Dark Matter density. Such substructure could have dramatic ...effect on directional detection. Indeed, in the case of a null lag velocity, one expects an isotropic WIMP velocity distribution arising from the Dark Disk contribution, which might weaken the strong angular signature expected in directional detection. For a wide range of Dark Disk parameters, we evaluate in this Letter the effect of such dark component on the discovery potential of upcoming directional detectors. As a conclusion of our study, using only the angular distribution of nuclear recoils, we show that Dark Disk models as suggested by recent N-body simulations will not affect significantly the Dark Matter reach of directional detection, even in extreme configurations.
As noble liquid time projection chambers grow in size their high voltage requirements increase, and detailed, reproducible studies of dielectric breakdown and the onset of electroluminescence are ...needed to inform their design. The Xenon Breakdown Apparatus (XeBrA) is a 5-liter cryogenic chamber built to characterize the DC high voltage breakdown behavior of liquid xenon and liquid argon. Electrodes with areas up to 33 cm2 were tested while varying the cathode-anode separation from 1 to 6 mm with a voltage difference up to 75 kV. A power-law relationship between breakdown field and electrode area was observed. The breakdown behavior of liquid argon and liquid xenon within the same experimental apparatus was comparable.
The comparison of the results of direct detection of dark matter, obtained with various target nuclei, requires model-dependent, or even arbitrary, assumptions. Indeed, to draw conclusions either the ...spin-dependent (SD) or the spin-independent (SI) interaction has to be neglected. In the light of the null results from supersymmetry searches at the LHC, the squark sector is pushed to high masses. We show that for a squark sector at the TeV scale, the framework used to extract constraints from direct detection searches can be redefined as the number of free parameters is reduced. Moreover, the correlation observed between SI and SD proton cross sections constitutes a key issue for the development of the next generation of dark matter detectors.
Prompt scintillation signals from 83mKr calibration sources are a useful metric to calibrate the spatial variation of light collection efficiency and electric field magnitude of a two phase ...liquid-gas xenon time projection chamber. Because 83mKr decays in two steps, there are two prompt scintillation pulses for each calibration event, denoted S1a and S1b. We study the ratio of S1b to S1a signal sizes in the Particle Identification in Xenon at Yale (PIXeY) experiment and its dependence on the time separation between the two signals (Δt), notably its increase at low Δt. In PIXeY data, the Δt dependence of S1b/S1a is observed to exhibit two exponential components: one with a time constant of 0.05±0.02 μs, which can be attributed to processing effects and pulse overlap and one with a time constant of 10.2±2.2 μs that increases in amplitude with electric drift field, the origin of which is not yet understood.
Low-pressure gaseous TPCs are well suited detectors to correlate the directions of nuclear recoils to the galactic Dark Matter (DM) halo. Indeed, in addition to providing a measure of the energy ...deposition due to the elastic scattering of a DM particle on a nucleus in the target gas, they allow for the reconstruction of the track of the recoiling nucleus. In order to exclude the background events originating from radioactive decays on the surfaces of the detector materials within the drift volume, efforts are ongoing to precisely localize the track nuclear recoil in the drift volume along the axis perpendicular to the cathode plane. We report here the implementation of the measure of the signal induced on the cathode by the motion of the primary electrons toward the anode in a MIMAC chamber. As a validation, we performed an independent measurement of the drift velocity of the electrons in the considered gas mixture, correlating in time the cathode signal with the measure of the arrival times of the electrons on the anode.
The aim is to characterize the energy distribution of neutron fluence in the energy range 8 keV-5 MeV based on a primary standard: the LNE-IRSN/MIMAC microTPC. The microTPC is a time projection ...chamber. Time projection chambers are gaseous detectors able to measure charged particles energy and to reconstruct their track. The gas is used as a (n, p) converter in order to detect neutrons down to few keV. The neutron energy is reconstructed event by event thanks to proton scattering angle and proton ionization energy measurements. The scattering angle is deduced from the 3-D track. The proton energy is obtained by charge collection measurements, knowing the ionization quenching factor. The fluence is reconstructed thanks to the detected events number and the simulation of the detector response. The microTPC is a new reliable detector able to measure energy distribution of the neutron fluence without unfolding procedure or prior neutron calibration contrary to usual gaseous counters. The microTPC is characterized at the AMANDE facility, with neutron energies going from 8 keV to 565 keV. This work shows the first direct reconstruction of neutron energy and fluence, simultaneously, at 27.2 keV in a continuous irradiation mode.
Abstract
The scintillation time response of liquid argon has a key
role in the discrimination of electronic backgrounds in dark matter
search experiments. However, its extraordinary rejection power ...can
be affected by various detector effects such as the delayed light
emission of TetraPhenyl Butadiene, the most commonly used wavelength
shifter, and the electric drift field applied in Time Projection
Chambers. In this work, we characterized the TetraPhenyl Butadiene
delayed response and the dependence of the pulse shape
discrimination on the electric field, exploiting the data acquired
with the ARIS, a small-scale single-phase liquid argon detector
exposed to monochromatic neutron and gamma sources at the ALTO
facility of IJC Lab in Orsay.
We examine the sensitivity of a large scale two-phase liquid argon detector to the directionality of the dark matter signal. This study was performed under the assumption that, above 50 keV of recoil ...energy, one can determine (with some resolution) the direction of the recoil nucleus without head-tail discrimination, as suggested by past studies that proposed to exploit the dependence of columnar recombination on the angle between the recoil nucleus direction and the electric field. In this paper we study the differential interaction recoil rate as a function of the recoil direction angle with respect to the zenith for a detector located at the Laboratori Nazionali del Gran Sasso and we determine its diurnal and seasonal modulation. Using a likelihood-ratio based approach we show that, with the angular information alone, 100 (250) events are enough to reject the isotropic hypothesis at three standard deviation level, for a perfect (400 mrad) angular resolution. For an exposure of 100 tonne years this would correspond to a spin independent WIMP-nucleon cross section of about 10−46cm2 at 200 GeV WIMP mass. The results presented in this paper provide strong motivation for the experimental determination of directional recoil effects in two-phase liquid argon detectors.
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