First Measurements of Angular Resolution in the CMS GE1/1 Muon Chambers

The achieving acceptable first level trigger rates for muons with reasonably low transverse momentum (p$_T$) thresholds is viable for the Compact Muon Solenoid (CMS) detector. In order to retain the current standalone muon trigger capability even with high occupancy in the endcap region during the high luminosity LHC (HL-LHC), the Gas Electron Multiplier (GEM) subdetector system was designed. It was installed in the first muon station of the endcap region during the second long shutdown (2019- 2021). Performance improvements in the standalone muon trigger are expected from the p$_T$-dependent bending angles measured between the GEM and Cathode Strip Chambers (CSC) detectors at Endcap Station 1. Thus, position corrections for the GEM position relative to the CSC are crucial. The GEM alignment algorithm was developed and tested using cosmic ray muons (DP-2022-027, DP-2022-028) and the 2021 pilot-beam proton-proton (pp) collision data (DP-2022-035). We also validated muon-track bending angles (DP-2022-069) with alignments. The angular resolution of less than 300 microradians is another requirement specified in CMS Technical Design Report for the Muon Endcap GEM Upgrade (CERN-LHCC-2015- 012). We here report the first measurements of angular resolutions on GE1/1 chambers for muons in 13.6 TeV pp collisions in 2023.