Abstract
The most compelling candidates for Dark Matter to day are WIMPs and axions. The applicability of gasesous Time Projection Chambers (TPCs) with Micromesh Gas Structures (Micromegas) to the search of these particles is explored within this work. Both particles would produce an extremely low rate at very low energies in particle detectors. Micromegas detectors can provide both low background rates and low energy threshold, due to the high granularity, radiopurity and uniformity of the readout. Small (few cm wide) Micromegas detectors are used to image the axion-induced x-ray signal expected in the CERN Axion Solar Telescope (CAST) experiment. We show the background levels obtained in CAST and the prospects to further reduce them to the values required by the Internation Axion Observatory (IAXO). We also present TREX-DM, a scaled-up version of the Micromegas used in axion research, but this time dedicated to the low-mass WIMP detection. TREX-DM 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 100 eV. The detector is described in detail, as well as the results of the commissioning and characterization phase on surface. Besides, the background model of TREX-DM is presented, along with the anticipated sensitivity of this search, which could go beyond current experimental limits.
Highlights
The development of Micromegas-based gaseous Time Projection Chambers (TPCs) for the search of rare events has been the goal of the ERC-funded T-REX project [1]
In this document we present the application of this concept to the search of two of the most compelling dark matter candidates: axions and WIMPs, which arise in independent extensions of the Standard Model
Ultra-low background x-ray detectors are a technological pillar of axion helioscopes
Summary
The development of Micromegas-based gaseous Time Projection Chambers (TPCs) for the search of rare events has been the goal of the ERC-funded T-REX project [1]. The detection of axions and WIMPs is conceptually very different, both searches share the extreme low rates and low energy of the expected signal events. The experimental challenge is to achieve background rates and energy thresholds as low as possible. If axions exist, they would be copiously produced in the Sun’s core with ∼keV energies and they could be converted back to detectable x-rays in a laboratory magnetic field aligned with the Sun. The expected signal is an excess of x-rays at the exit of the magnet over the background measured at non-alignment periods. We present the small Micromegas TPCs used in the CERN Axion Solar Telescope (CAST) since 2003, where they pioneered the application of these readouts to rare event searches. The background reduction techniques and the rates achieved are reviewed in section 2, as well as the prospects for using this detection system for the future International Axion Observatory (IAXO) [2], the generation axion helioscope, under proposal
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