A triple GEM detector with pad readout for high rate charged particle triggering

In this paper, results of a time performance study of triple gas electron multiplier (GEM) detectors are discussed. This study was driven by an R&D activity on detectors for the Level 0 LHCb muon trigger. However, the results presented in this paper are of more general interest, i.e. for experiments with high rate charged particle triggering. Little interest was given so far to time performance of GEM detectors. Only one group measured double GEM detector time resolution with the Ar/CO//2 (70/30) gas mixture. Our study aimed at triple GEM detector optimisation for good time performance through a detailed investigation of the role played by detector geometry, electric fields and gas mixture. The results reported here, in particular when using the gas mixture Ar/CO//2/CF //4 (60/20/20), considerably improve the time performance discussed in the above-mentioned paper and make the triple GEM detector a promising option for high rate charged particle triggering.