A fast multi-GEM based detector for high-rate charged-particle triggering

In this paper results of a time performance study of triple-GEM detectors are discussed. This study was driven by an R&D activity on detectors for the Level 0 LHCb muon trigger. Results presented in this paper are of more general interest, i.e. for experiments in which high-rate charged-particle triggering is needed. Little interest was given so far to time performance of GEM detectors. Only one paper (Bressan et aL, NIMA 425 (1999) 262.), presented measurements of double-GEM detector time resolution with an Ar/CO₂ (70/30) gas mixture. The authors of the paper quoted a resolution for the double-GEM detector such that high efficiency muon triggering at LHCb would be impossible. The results reported, obtained with the addition of CF₄ and/or isobutane to the Ar/CO₂ standard mixture, 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.