Production and quality control of the GEM GE2/1 detector for the upgrade of the CMS endcap muon system

The Compact Muon Solenoid (CMS) experiment is a general-purpose detector installed in the Large Hadron Collider (LHC). The future High Luminosity-LHC (HL-LHC) will provide a factor of 7 increase in luminosity compared with the design value of the LHC. To accommodate this increase and to enhance the performance of the CMS experiment, the forward region of the muon system will be equipped with 3 new sets of stations employing triple-foil Gas Electron Multi- plier (GEM) detectors. These three stations, GE1/1, GE2/1, and ME0 will enhance acceptance, longevity, redundancy, and triggering efficiency while operating in the harsh radiation environ- ment of the HL-LHC. The GE1/1 station was installed during the technical stop of 2019/2020. The GE2/1 station will be installed during the year end technical stop (YETS) of 2023/2024. The GE2/1 detector construction started in 2021 utilizing advanced quality controls (QC) and perfor- mance checks. We describe the GE2/1 chamber geometry, the multi-institutional production of chambers, the QC procedures, and the results from these QC measurements.