ME0 project for the Triple-GEM upgrade of the CMS muon spectrometer: Design, preliminary performance and R&D; perspective

In the framework of the HL-LHC project, the upgrade of the CMS Muon System envisages the installation of three new muon stations based on the GEM technology, named as GE1/1, GE2/1 and ME0. The CMS GEM Group has developed a novel construction design of GE1/1 triple-GEM detectors; in particular, a new self-stretching technique has been introduced to mechanically stretch the GEM foils without using spacer grids or glue inside the gas volume. As has been observed, the PCB boards get deformed under the internal gas overpressure, introducing irregularities in the planarity of the detector, which could potentially affect the uniformity of the detector performance. New solutions and design upgrades have been implemented to prevent such effects in future GE2/1 and ME0 upgrade projects. The contribution will focus on the novel design solutions based on the PCB pillars and their impact on the performance of the detector. Furthermore, early results of the R&D; campaign will be presented regarding the optimization of the detector for the very high hit rate environment and the reduction of the discharge probability.