The GEM (GE1/1) Phase II Upgrade for the CMS muon system: results from in-situ tests, production detector qualification, and commissioning plans

In the next years the Large Hadron Collider (LHC) will be upgraded to significantly expand its physics program, increasing the luminosity up to 5 $\times$ 10$^{34}$cm$^{-2}$s$^{-1}$, well beyond the design value. An upgrade of the CMS detector is needed accordingly to cope with the expected growth in background rates, with the goal of keeping a high trigger efficiency. In this context, a first new station called GE1/1 will be installed in 2019-2020 in the CMS muon system. It will be composed by 144 Triple Gas Electron Multiplier (GEM) detectors to be integrated in the CMS muon endcaps in the region closest to the beam line. A fundamental operational experience has been already achieved in 2017-2018, when a demonstrator composed of ten GE1/1 Triple-GEM detectors was installed to prove the integration of the GE1/1 system into CMS itself. In parallel, a dedicated production chain has been setup in seven production sites spread around the world, for the construction and qualification of all the detectors for the complete station. This contribution will give a complete overview of the GE1/1 project the detectors design and performance will be discussed, together with the lessons learned from the GE1/1 demonstrator installation, integration and operation. The construction and qualification processes will be presented, with great emphasis to the results obtained with the 144 GE1/1 detectors. Finally, the plans for the installation and commissioning of the full station will be outlined.