Commissioning Results and Operational Experience of the First Triple-GEM Station of the CMS Muon System

As part of CMS upgrade strategy of the muon system towards HL-LHC, a new station of triple-GEM detectors (GE1/1) has been installed in both endcaps of the CMS detector. This additional muon station will allow dealing with the high luminosity conditions imposed by HL-LHC, improving the trigger capabilities in the forward region. The station was installed in 2020 and consists of 72 ten-degree super-chambers, each made up of two layers of triple-GEM detectors. GE1/1 provides the CMS muon system with two additional muon hit measurements which will improve muon tracking and triggering performance while allow to keep the muon trigger rate under control without the need to increase the threshold on the muon transverse momentum. This report will describe the status of the commissioning phase of the detector. It will additionally present preliminary results from the first runs with the LHC beams. Attention will be given to issues encountered during CMS magnet commissioning which induced trips and short-circuits in the GEM detectors. Therefore, the results of a dedicated test with magnetic field are shown in light of the observed behavior in CMS.