Muon Chamber Endcap Upgrade of the CMS Experiment with Gas Electron Multiplier (GEM) Detectors and Their Performance

As the CERN LHC is heading towards a high luminosityHigh luminosity phase a very high flux is expected in the endcaps of the CMS Detector. The presence of muons in collision events can be due to rare or new physics so it is important to maintain the high trigger efficiency of the CMS muon system. The CMS Collaboration has proposed to instrument the high- $$\eta $$ region (1.6 $$< \mid \eta \mid<$$ 2.2) of the muon endcaps with Gas Electron Multiplier (GEM)Gas Electron Multiplier (GEM) detectors, referred to as GE1/1 chambers, during the LS2. This technology will help in maintaining optimum trigger performance with maximum selection efficiency of muons even in a high flux environment. We describe plans for a “Slice Test” to install a few GE1/1 chambers covering 50 $$^\circ $$ in azimuthal angle within the CMS detector in 2017, with subsequent operation during the current Run 2 of the LHC. We show the performance of the GE1/1 chambers to be installed during the slice test, specifically: GEM foil leakage currentsLeakage Current, chamber gas volume integrity, high voltageHigh voltage (HV) circuit performance, and effective gain.