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%iC4H10. Conclusions: the results here obtained show promise to lower the threshold of the experiment down to 50 eVee, corresponding to substantially enhanced sensitivity to low-mass WIMPs (Weakly Interacting Massive Particles).
@article{arxiv.2412.19864,
title = {Micromegas with GEM preamplification for enhanced energy threshold in low-background gaseous time projection chambers},
author = {J. Castel and S. Cebrián and T. Dafni and D. Díez-Ibáñez and J. Galán and J. A. García and A. Ezquerro and I. G Irastorza and G. Luzón and C. Margalejo and H. Mirallas and L. Obis and A. Ortiz de Solórzano and O. Pérez and J. Porrón and M. J. Puyuelo},
journal= {arXiv preprint arXiv:2412.19864},
year = {2025}
}