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

Abstract

<h4>Background</h4>We develop the concept of a Micromegas readout plane with an additional GEM preamplification stage placed a few millimetres above it to increase the maximum effective gain of the combined readout.<h4>Methods</h4>We implement it and test it in realistic conditions for its application to low-background dark matter searches like the TREX-DM experiment. For this, we use a Micromegas of Microbulk type, built with radiopure materials.<h4>Results</h4>We report on GEM effective extra gain factors of about 90, 50 and 20 in 1, 4 and 10 bar of Ar-1%iC ₄H ₁₀. These results are obtained in a small test chamber allowing for systematic scanning of voltages and pressures. 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.<h4>Conclusions</h4>The results here obtained show promise to lower the threshold of the experiment down to 50 eV _<i>ee</i> , corresponding to substantially enhanced sensitivity to low-mass WIMPs.