Advances in fast multi-GEM-based detector operation for high-rate charged-particle triggering

In this paper, we summarize the results obtained in an R&D work performed in the period 2000-2003 within the LHCb Collaboration to develop a triple gas electron multiplier (GEM) for the inner region of the first muon station. Since the information coming from this detector will be used at the L0 trigger level, many studies were performed in order to optimize its time resolution. By using CF/sub 4/-based gas mixtures, a time resolution of 4.5 ns rms was obtained, which translates to efficiencies higher than 96% in a 20-ns time window for a large operating region. Moreover, measurements of discharge probability per incident charged particle with a high-intensity pion/proton beam for these gas mixture are also reported. All these results show that triple-GEM detectors can be used for triggering in the LHCb muon detector. Preliminary results on a global aging test performed with a 25-kCi /sup 60/Co source are also reported and compared to other aging tests performed with X-rays and hadron beams.