Advances in triple-GEM detector operation for high-rate particle triggering

We report the results of a systematic study of the time performance of triple-GEM detectors operated with several gas mixtures which are new for this kind of detectors. This study was performed in the framework of an R&D activity on detectors for the level 0 LHCb muon trigger. We show that a considerable improvement, with respect to the traditional gas mixture Ar/CO/sub 2/(70/30), is obtained with the fast and high yield based CF/sub 4/ and iso-C/sub 4/H/sub 10/ gas mixtures; time resolutions better than 5 ns. Discharges studies have been performed with high intensity pion/proton beams at the /spl pi/M1 beam facility of the Paul Sherrer Institute (PSI). The results show that the operation of the detector is very stable, if a small fraction of iSO-C/sub 4/H/sub 10/ or a large amount of CF/sub 4/, is used. The role of the electron diffusion in the formation of discharges, has been studied testing two different detector gap geometries.