The GEM (GE1/1) Station of the CMS Muon Detector: Status, Commissioning and Early Performance Studies

During Run 3 the LHC will deliver instantaneous luminosities in the range 5×10
³⁴
cm
⁻²
s
⁻¹
to 7×10
³⁴
cm
⁻²
s
⁻¹
. To cope with the high background rates and to improve the trigger capabilities in the forward region, the muon system of the CMS experiment has been upgraded with two new stations of detectors (GE1/1), one in each endcap, based on triple-GEM technology. The system was installed in 2020 and consists of 72 ten-degree chambers, each made up of two layers of triple-GEM detectors. GE1/1 provides two additional muon hit measurements which will improve muon tracking and triggering performance. We report on the status of the ongoing commissioning phase of the detector and present preliminary results obtained from cosmic-ray events. We discuss detector and readout electronics operation, stability and performance, and preparation for Run 3 of the LHC.