Low background x-ray detection with Micromegas for axion research

TL;DR

This paper reviews recent advancements in Micromegas x-ray detectors for axion searches, highlighting significant background reduction techniques that enhance the sensitivity of helioscope experiments like CAST and future IAXO.

Contribution

It presents new low-background Micromegas detector developments, including shielding, discrimination, and radiopure components, with detailed R&D and simulation insights.

Findings

Achieved background levels of 1.5×10⁻⁶ cts/cm²/s in CAST detectors.

Demonstrated potential for background levels as low as 10⁻⁷ cts/cm²/s in underground tests.

Showcased the effectiveness of shielding and radiopure materials in reducing detector backgrounds.

Abstract

Axion helioscopes aim at the detection of solar axions through their conversion into x-rays in laboratory magnetic fields. The use of low background x-ray detectors is an essential component contributing to the sensitivity of these searches. Here we review the recent advances on Micromegas detectors used in the CERN Axion Solar Telescope (CAST) and proposed for the future International Axion Observatory (IAXO). The most recent Micromegas setups in CAST have achieved background levels of 1.5$\times10^{-6}$\ckcs, a factor of more than 100 lower than the ones obtained by the first generation of CAST detectors. This improvement is due to the development of active and passive shielding techniques, offline discrimination techniques allowed by highly granular readout patterns, as well as the use of radiopure detector components. The status of the intensive R&D to reduce the background levels will be described, including the operation of replica detectors in test benches and the detailed Geant4 simulation of the detector setup and the detector response, which has allowed the progressive understanding of background origins. The best levels currently achieved in a test setup operating in the Canfranc Underground Laboratory (LSC) are as low as $\sim10^{-7}$\ckcs, showing the good prospects of this technology for application in the future IAXO.