Commissioning of the first chambers of the CMS GE1/1 muon station

The upgrades of the LHC planned in the next years will increase the instantaneous luminosity up to $5 \times 10^{34}$ cm$^{-2}$s$^{-1}$ after Long Shutdown 3, a value about five times higher than the nominal one for which the CMS experiment was designed. The resulting larger rate of interactions will produce a higher pileup environment that will challenge the trigger system of the CMS experiment in its original configuration, in particular in the endcap region. As part of the upgrade program of the CMS muon endcaps, additional muon detectors based on Gas Electron Multiplier (GEM) technology will be installed, in order to be able to sustain a physics program during high-luminosity operation without performance losses. The installation of the GE1/1 station is scheduled for Long Shutdown 2 in 2019-2020; already a demonstrator composed of five superchambers has been installed during the Extended Year-End Technical Stop at the beginning of 2017. Its goal is to test the systems operational conditions and also to demonstrate the integration of the GE1/1 chambers into the CMS online system. The status of the installation and commissioning of the GE1/1 demonstrator is presented.