Beam Characterization for MUSE at PSI

The Muon Scattering Experiment (MUSE) at Paul Scherrer Institute (PSI) is being prepared to resolve the proton radius puzzle – the six-standard deviation discrepancy between proton charge radius measurements with electronic and muonic probes, respectively. MUSE is designed to measure the proton charge radius with elastic electrons and muons scattering simultaneously and with both charge polarities. For an accurate determination of the lepton scattering angle, event-by-event beam particle tracking is required to reconstruct the incoming particle track. A telescope of Gas Electron Multipliers (GEM), exposed to a high flux of beam particles is used to reconstruct the incoming tracks with high spatial resolution while representing minimal material for the beam to pass through. Additional GEM elements are placed at the intermediate focus between the two dipoles of the PiM1 beamline to study the beam properties. The status of the GEM performance will be reported.