563 research outputs found
Modelling the behaviour of microbulk Micromegas in Xenon/trimethylamine gas
We model the response of a state of the art micro-hole single-stage charge
amplication device (`microbulk' Micromegas) in a gaseous atmosphere consisting
of Xenon/trimethylamine at various concentrations and pressures. The amplifying
structure, made with photo-lithographic techniques similar to those followed in
the fabrication of gas electron multipliers (GEMs), consisted of a 100 um-side
equilateral-triangle pattern with 50 um-diameter holes placed at its vertexes.
Once the primary electrons are guided into the holes by virtue of an optimized
field configuration, avalanches develop along the 50 um-height channels etched
out of the original doubly copper-clad polyimide foil. In order to properly
account for the strong field gradients at the holes' entrance as well as for
the fluctuations of the avalanche process (that ultimately determine the
achievable energy resolution), we abandoned the hydrodynamic framework,
resorting to a purely microscopic description of the electron trajectories as
obtained from elementary cross-sections. We show that achieving a satisfactory
description needs additional assumptions about atom-molecule (Penning) transfer
reactions and charge recombination to be made
Gaseous time projection chambers for rare event detection: Results from the T-REX project. II. Dark matter
As part of the T-REX project, a number of R&D and prototyping activities have
been carried out during the last years to explore the applicability of
Micromegas-read gaseous TPCs in rare event searches like double beta decay
(DBD), axion research and low-mass WIMP searches. While in the companion paper
we focus on DBD, in this paper we focus on the results regarding the search for
dark matter candidates, both axions and WIMPs. Small ultra-low background
Micromegas detectors are used to image the x-ray signal expected in axion
helioscopes like CAST at CERN. Background levels as low as
c keVcms have already been achieved in CAST while values
down to c keVcms have been obtained in a
test bench placed underground in the Laboratorio Subterr\'aneo de Canfranc.
Prospects to consolidate and further reduce these values down to
c keVcmswill be described. Such detectors, placed at the
focal point of x-ray telescopes in the future IAXO experiment, would allow for
10 better signal-to-noise ratio than CAST, and search for solar axions with
down to few 10 GeV, well into unexplored axion
parameter space. In addition, a scaled-up version of these TPCs, properly
shielded and placed underground, can be competitive in the search for low-mass
WIMPs. The TREX-DM prototype, with 0.300 kg of Ar at 10 bar, or
alternatively 0.160 kg of Ne at 10 bar, and energy threshold well below 1
keV, has been built to test this concept. We will describe the main technical
solutions developed, as well as the results from the commissioning phase on
surface. The anticipated sensitivity of this technique might reach
cm for low mass ( GeV) WIMPs, well beyond current
experimental limits in this mass range.Comment: Published in JCAP. New version with erratum incorporated (new figure
14
Microbulk Micromegas in non-flammable mixtures of argon and neon at high pressure
We report on a systematic characterization of microbulk Micromegas readouts
in high-pressure Ar+1%iC4H10 and Ne+2%iC4H10 mixtures. Experimental data on
gain, electron transmission and energy resolution are presented for a wide
range of drift and amplification voltages and pressures from 1 bar to 10 bar
for argon and from 5 bar to 10 bar in neon, in steps of 1 bar. Maximum gains
higher than 1.7e3 (1.7e4) in argon (neon) are measured for all pressures,
remarkably without the significant decrease with pressure typically observed in
other amplification structures. A competitive energy resolution at 22.1 keV,
but with a slight degradation with pressure, is observed:from 10.8% at 1 bar to
15.6% FWHM at 10 bar in argon and from 8.3% at 5 bar to 15.0% FWHM at1 10 bar
in neon. The experimental setup, procedure and the results will be presented
and discussed in detail. The work is motivated by the TREX-DM experiment, that
is operating in the Laboratorio Subterr\'aneo de Canfranc with the mentioned
mixtures, although the results may be of interest for other applications of
time projection chambers at high pressures.Comment: 11 pages, 8 figures, prepared for JINST, minor changes in th text,
added a referenc
The potential of discrimination methods in a high pressure xenon TPC for the search of the neutrinoless double-beta decay of Xe-136
In the search for the neutrinoless double beta decay of 136Xe, a high pressure xenon time projection chamber (HPXe-TPC) has two advantages over liquid xenon TPCs: a better energy resolution and the access to topological features, which may provide extra discrimination from background events. The PandaX-III experiment has recently proposed a 200 kg HPXe-TPC based on Micromegas readout planes, to be located at the Jinping Underground Laboratory in China. Its detection concept is based on two results obtained within the T-REX project: Micromegas readouts can be built with extremely low levels of radioactivity; and the operation in xenon-trimethylamine at 10 bar in realistic experimental conditions has proven an energy resolution of 3% FWHM at the region of interest. In this work, two discrimination methods are applied to simulated signal and background data in a generic 200 kg HPXe-TPC, based on two well-known algorithms of graph theory: the identification of connections and the search for the longest path. Rejection factors greater than 100 are obtained for small pixel sizes and a signal efficiency of 40%. Moreover, a new observable (the blob charge density) rejects better surface contaminations, which makes the use of a trigger signal (T0) not imperative in this experiment
Lessons from the operation of the "Penning-Fluorescent" TPC and prospects
We have recently reported the development of a new type of high-pressure
Xenon time projection chamber operated with an ultra-low diffusion mixture and
that simultaneously displays Penning effect and fluorescence in the
near-visible region (300 nm). The concept, dubbed `Penning-Fluorescent' TPC,
allows the simultaneous reconstruction of primary charge and scintillation with
high topological and calorimetric fidelity
Background assessment for the TREX Dark Matter experiment
TREX-DM is conceived to look for low-mass Weakly Interacting Massive
Particles (WIMPs) using a gas Time Projection Chamber equipped with micromegas
readout planes at the Canfranc Underground Laboratory. The detector can hold in
the active volume 20 l of pressurized gas up to 10 bar, corresponding to 0.30
kg of Ar or 0.16 kg of Ne. The micromegas are read with a self-triggered
acquisition, allowing for thresholds below 0.4 keV (electron equivalent). A low
background level in the lowest energy region is another essential requirement.
To assess the expected background, all the relevant sources have been
considered, including the measured fluxes of gamma radiation, muons and
neutrons at the Canfranc Laboratory, together with the activity of most of the
components used in the detector and ancillary systems, obtained in a complete
assay program. The background contributions have been simulated by means of a
dedicated application based on Geant4 and a custom-made code for the detector
response. The background model developed for the detector presently installed
in Canfranc points to levels from 1 to 10 counts keV-1 kg-1 d-1 in the region
of interest, making TREX-DM competitive in the search for low-mass WIMPs. A
roadmap to further decrease it down to 0.1 counts keV-1 kg-1 d-1 is underway.Comment: Final version, as accepted in Eur. Phys. J.
Status of low mass WIMP detector TREX-DM
TREX-DM (TPC Rare Event eXperiment for Dark Matter) is a high-pressure Micromegas-based TPC designed to host a few hundreds of grams of light nuclei (argon or neon) with energy thresholds potentially at the level of 0.4 keVee or below. Preliminary background studies suggest that the levels expected are of the order of 1-10 counts keV-1 kg-1 d-1, making TREX-DM competitive in the search for low mass WIMPs (<10 GeV). The experiment has been approved by the LSC (Laboratorio Subterrneo de Canfranc) and the last months have been devoted to its installation underground. Here we will report on the first commissioning phase
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