GEM Detectors for a CMS Muon Endcap Upgrade and Other Uses
Gas Electron Multiplier (GEM) detectors are now being formally considered by the CMS collaboration for an upgrade of the CMS muon system. A GEM "demonstrator" system with limited scope is under study for installation in the high-eta muon region during the second long LHC shutdown around 2018 with potential full implementation during the third long LHC shutdown. GEMs are Micro-Pattern Gaseous Detectors that feature 50-100 microns spatial resolution, 4-5 ns time resolution, high detection efficiency, and proven high-rate capability and resilience against aging effects. Advances in GEM foil production and assembly techniques in the last years now allow the construction of large-area GEM detectors suitable for muon systems.
Expected benefits for muon tracking and triggering, and muon physics with CMS at the high-luminosity LHC are presented. Current uses of GEMs at the LHC are briefly reviewed. I discuss GEM detection principles, beam test result for CMS prototypes of large-area GEM detectors, and Fl. Tech R&D on a GEM readout structures with zigzag strips that promises potentially significant reduction of readout channels (and consequently cost) while maintaining performance. Design plans for GEM stations at 1.6<|eta|<2.4 in the upgraded CMS forward muon system are described including on-detector and off-detector electronics. Finally, an interesting spin-off of GEM technology outside of HEP is also briefly presented, i.e. muon tomography with GEMs for the detection of nuclear contraband in cargo for homeland security purposes.