Studies on the upgrade of the muon system in the forward region of the CMS experiment at LHC with GEMs

The LHC data-taking will resume in 2015 with energy of 13-14 TeV and luminosity of 2 divided by 5 x 10(34) cm(-2) s(-1). At those energies, a considerable fraction of the particles produced propagate in the high pseudo-rapidity regions. The proposal for the upgrade of the CMS muon forward system involves Gas Electron Multiplier (GEM) chambers to be installed during the second LHC Long Shutdown (LS2) covering the pseudorapidity range 1 : 5 < vertical bar h vertical bar < 2.2. This detector is able to handle the extreme particle rates expected in this region when the LHC will be running at higher luminosity. The GEM is an excellent choice, as its high spatial resolution (order of 100 m m) allows to combine tracking and triggering capabilities, which will improve the CMS muon High Level Trigger, the muon identification and the track reconstruction. Intense R&D has been going on since 2009 and it has lead to the development of several GEM prototypes and associated detector electronics. These GEM prototypes have been subjected to extensive tests in the laboratory and in test beams at the CERN Super Proton Synchrotron (SPS). This contribution will review the status of the CMS upgrade project with GEMs, discussing also the trigger performance.