Monitoring and Optimizing GEM Detector Performance for MUSE

The MUon Scattering Experiment (MUSE) at the Paul Scherrer Institute (PSI) aims to address the long-standing discrepancy in the measured proton charge radius. The experiment employs a mixed beams of electrons and muons, either positively and negatively charged, enabling the extraction of the proton charge radius from electron–proton and muon–proton scattering under identical experimental conditions. Accurate tracking of incoming particles is essential for this measurement. To achieve this, a Gas Electron Multiplier (GEM) telescope is installed along the incoming beamline, and its performance directly affects the overall efficiency of the experiment. Therefore, a detailed GEM efficiency analysis was performed to monitor the detector performance. The study includes calculations of overall efficiency, axis-dependent efficiency, and species-dependent efficiency. An overview of the MUSE GEM telescope is presented along with the latest results from the efficiency analysis. Methods used to select optimal tracks for efficiency determination are discussed, as well as applications of this analysis such as high-voltage scans, software optimization, and benchmarking of new software implementations.