Assembly and Quality Control of GEM Detectors for the Future Upgrade of the CMS Muon System

The European Organization for Nuclear Research (CERN) is the world's largest research centre for particle physics, hosting the 27-Km long Large Hadron Collider (LHC), considred to be one of the biggest machine ever built. The latter has four main detector experiments: ATLAS, CMS, ALICE, and LHCb, the second largest being CMS, the Compact Muon Solenoid. GEM is a CMS subdetector that contains a densely pierced polymer foil coated with electrodes on both sides to achieve high amplification gains and performance at a lower cost, even under harsh conditions. The GE1/1 station consists of 36 10° Super Chambers (SC), two layers of triple GEM detectors, and a total of 144 chambers. The GE1/1 SC is mounted in the CMS Nose at the head of the CSC ME1/1 chambers. Here, the SC assembly method used is the mechanical stretching technique without glue in the gas volume. ME0 is a beneficial upgrade for the CMS muon system since it will help lower combinatory in matching muon segments to track muons and improve {\small P}{\tiny T} resolution for muons. ME0 has a good position measurement, essential to reduce the impact of neutron backgrounds and combinatorial matches. The ME0 has six GEM layers, including high precision hit reconstruction of the detector, which makes measurements of both position and direction possible. GE2/1 detector consists of 72 Chambers, and the layout is the same as the GE1/1 layout. The difference is that GE2/1 covers a larger surface. The same technical solution was successfully adopted for the GE1/1 (3/1/2/1 mm gaps). Two independent GE2/1 chambers will form on the YE1/1 disk a Super Chamber. To achieve maximum coverage, modules in the front and back chambers will be staggered. As a consequence, eight different types of modules will be designed and produced. Quality control for GE2/1 consists of ten QCs, named QC1…QC10. After passing the QC2 step, testing the foils, and knowing they have passed QC2, the processes of the chamber assembly can start. The GEM technology is selected for the upgrade of the CMS muon End-Cap.