Triple-GEM detector operation for high rate particle triggering

We report the results of a study of triple-GEM detectors for high rate charged particle triggering. This study was performed in the framework of an R&D activity on detectors for the level-0 LHCb muon trigger and, in particular, for the inner regions (R1 and R2) of the first station (M1), where particle rates up to 460 kHz/cm/sup 2/ are expected. A crucial requirement in this application is an efficiency higher than 99% per station (two detectors logically OR-ed) in a 25 ns time window. Results of the time performance are compared with the discharge probability per incident particle as results from a study performed with a high intensity hadron beam. We show here the considerable improvement obtained with the addition of CF/sub 4/ and /or iso-C/sub 4/H/sub 10/ to the widely used Ar/CO/sup 2/ mixture, which allows to satisfy the experiment requirements.