Micromegas with GEM preamplification for enhanced energy threshold in low-background gaseous time projection chambers

TL;DR

This paper introduces a combined Micromegas and GEM preamplification system to significantly improve energy detection thresholds in gaseous TPCs, enhancing dark matter search sensitivity.

Contribution

It demonstrates the successful implementation of a GEM preamplification stage with Micromegas for low-background TPCs, achieving higher gain and lower energy thresholds.

Findings

GEM provides effective gain factors up to 90 in 1 bar of argon-based gas.

The system can potentially lower detection thresholds to 50 eV, improving sensitivity.

The approach is tested in realistic conditions for dark matter experiments.

Abstract

Background: we develop the concept of a Micromegas (MICRO-MEsh GAseous Structure) readout plane with an additional GEM (Gas Electron Multiplier) preamplification stage placed a few mm above it, to increase the maximum effective gain of the combined readout. We implement it and test it in realistic conditions for its application to low-background dark matter searches like the TREX-DM experiment. Methods: for this, we use a Micromegas of microbulk type, built with radiopure materials. A small test chamber allowing for systematic scanning of voltages and pressures is used. In addition, a TREX-DM full-scale set-up has also been built and tested, featuring a replica of the fully-patterned TREX-DM microbulk readout. Results: we report on GEM effective extra gain factors of about 90, 50 and 20 in 1, 4 and 10 bar of Ar-1%iC$_{4}$H$_{10}$. Conclusions: the results here obtained show promise to lower the threshold of the experiment down to 50 eV$_{ee}$, corresponding to substantially enhanced sensitivity to low-mass WIMPs (Weakly Interacting Massive Particles).