Assembly and Quality Control of GEM detectors for the CMS GE2/1 muon upgrade

In this report, the assembly and some of the quality control tests of the new upgrade to be installed in the Muon tracker system of CMS, based on GEM technologies, is discussed. GEM technology was proven to be the best choice to keep up with high radiation rate thanks to simulation studies. The aim from this new upgrade, to be installed in 2023 in the GE2/1 station, is to prepare CMS for the luminosity upgrade of the HL-LHC intended for Run 3 and Run 4, which is expected to reach $5 \times 10^{34} cm^{−2} s^{−1}$.