Abstract
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 sim 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, being thresholds below 0.4 keV (electron equivalent) at reach. 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 hbox {keV}^{-1} hbox {kg}^{-1} hbox {day}^{-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 hbox {keV}^{-1} hbox {kg}^{-1} hbox {day}^{-1} is underway.
Highlights
Different detector technologies have been developed in the last decades with the aim to directly detect dark matter particles which could be pervading the galactic halo [1]
A sample of the copper provided by Sanmetal and used at the vessel of TREX-DM, having the same origin and history of exposure to cosmic rays on surface as the vessel itself, has been screened using one of the germanium detectors of the LSC Radiopurity Service with the aim to evaluate the cosmogenic activation induced in the vessel and to assess its suitability for a low background measurement at LSC
The background levels quoted in the following are referred to a Region of Interest (RoI) of 0.2 − 7 keVee; the upper value is fixed to avoid the interference from the copper fluorescence peak at 8.0 keV while the low energy threshold assumed is equivalent to 1 keV for Ar and Ne nuclear recoils
Summary
Different detector technologies have been developed in the last decades with the aim to directly detect dark matter particles which could be pervading the galactic halo [1]. Different technologies have been built: bulk Micromegas have the readout plane and the mesh all in one and microbulk Micromegas are in addition more homogeneous and radiopure [16]. They offer important advantages for rare event detection [15,17]: the possibility of scaling-up, topological information to discriminate backgrounds from the expected signal (just a few microns track for dark matter particles, giving a point-like event) and low intrinsic radioactivity as they are made out of kapton and copper, potentially very clean. The corresponding sensitivity for WIMP direct detection and conclusions are discussed in Sects. 6 and 7
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