TREX-DM: a low-background Micromegas-based TPC for low-mass WIMP detection

Abstract

If Dark Matter is made of Weakly Interacting Massive Particles (WIMPs) with masses below GeV, the corresponding nuclear recoils in mainstream WIMP experiments are of energies too close, or below, the experimental threshold. Gas Time Projection Chambers (TPCs) can be operated with a variety of target elements, offer good tracking capabilities and, on account of the amplification in gas, very low thresholds are achievable. Recent advances in electronics and in novel radiopure TPC readouts, especially micro-mesh gas structure (Micromegas), are improving the scalability and low-background prospects of gaseous TPCs. Here we present TREX-DM, a prototype to test the concept of a Micromegas-based TPC to search for low-mass WIMPs. The detector is designed to host an active mass of kg of Ar at 10 bar, or alternatively kg of Ne at 10 bar, with an energy threshold below 0.4 keVee, and is fully built with radiopure materials. We will describe the detector in detail, the results from the commissioning phase on surface, as well as a preliminary background model. The anticipated sensitivity of this technique may go beyond current experimental limits for WIMPs of masses of 2–8 GeV.

Background assessment for the TREX dark matter experiment

“…Gas Time Projection Chambers (TPCs) equipped with Micromegas planes have excellent features to fulfill these requirements. TREX-DM (TPC for Rare Event eXperiments-Dark Matter) [11,12] is a Micromegas-read High Pressure TPC for low mass WIMP searches using Ar or Ne mixtures, not focused on directionality. The detector was built and operated at surface in the University of Zaragoza as proof of concept.…”

“…In this kind of experiments, the construction of reliable background models, based on an accurate assay of background sources and on a careful computation of their contribution to the experiment, is essential; they provide guidance and constraints for design and allow robust estimations of the experiment sensitivity (some recent examples can be found at [15,16,17,18,19,20,21,22,23]). The preliminary background model of TREX-DM for operation at LSC presented in [11,24] has now been completed and updated, including as inputs the activities from a dedicated material screening program together with the measured fluxes of different backgrounds at LSC (gamma-rays, neutrons and muons).…”

Exploring the hidden interior of the Earth with directional neutrino measurements

“…A scale-up of a similar size has been proposed by the LUX-ZEPLIN (LZ) experiment30, relative to its predecessor34, with a projected improvement in the electronic recoil background rate of a factor of ∼1,000. Additional background reduction can be achieved by using lower-background material for the detector vessel, such as the high-purity copper used to construct the pressure vessel for the TREX-DM experiment35, a high-pressure TPC searching for low-mass dark matter. The radioactive contamination of the TREX-DM copper pressure vessel due to 238 U, 232 Th, and 40 K is a factor of 8, 3 and 9 lower, respectively, than that of the LZ titanium cryostat vessel30.…”

Small scale direct dark matter search experiments

“…The single electron response (gain, drift or diffusion times) has been characterized with a laser system [51] and quenching factor measurements at Grenoble for H and at TUNL (Duke University) for Ne-CH 4 are underway. TREX-DM (Tpcs for Rare Event eXperiments-Dark Matter) is based on a gas TPC holding a pressurized gas at 10 bar inside a copper vessel, equipped with the largest Micromegas readouts ever built [52,53,54]. It operates at the Canfranc Underground Laboratory, being presently at the commissioning phase.…”