The GEM detectors within the CMS Experiment

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After the second and the third Long Shutdown (LS2 + LS3), Large Hadron Collider (LHC) luminosity will approach values of 2*10^34cm−2s−1 and 5*10^34cm−2 s−1 respectively. The CMS experiment performances would be severely affected without dedicated detector upgrades, especially in the very forward region where the magnetic field is low; High pile-up conditions and harsh background environment makes muon tracking and triggering very challenging in this region. Introduced in 1996 by F. Sauli, the Gas Electron Multiplier (GEM) technology is going to be used, and planned, for the Muon Spectrometer of CMS Experiment, exploiting its high rate and resolution performances.

The CMS Collaboration finalized the installation and early commissioning of the GE1/1 chambers in 2021, is a new CMS muon detector, 72 Super-Chambers (SC) in total, each containing two gas electron multiplier (GEM) detectors. The SCs have been inserted into the CMS detector in order to detect muons that scatter at an angle of around 10° in relation to the beam axis.

A second GEM detector, the GE2/1 station, still focusing on the region 1.6<|η|<2.4, is planned to be installed during the YETS's between LS2 and LS3, to increase redundancy and enhance trigger and reconstruction capabilities; It is currently in production phase, taking advantage of the multiple lessons learned during the GE1/1 production; the present status of both GE1/1 and GE2/1 detectors will be reviewed.

To profit of the pixel tracking coverage extension, an additional GEM detector, the ME0 station, is in pipeline behind the new forward calorimeter to be installed in LS3, covering up to |η| = 2.8. The ME0 stations will be formed by six-layer stacks of triple-GEM chambers, expected to be operated with background particle fluxes ranging between 3 and 150 kHz/cm2 on the chamber surface. Both the maximum background rate and the large range in particle rate set new challenges for particle detector technologies. Rate capability of GEM…