The Physics Program of MUSE*

The MUon Scattering Experiment (MUSE) at the Paul Scherrer Institute (PSI) seeks to address

the proton radius puzzle by performing simultaneous high-precision measurements of elastic

electron-proton and muon-proton scattering. Measurements of the proton charge radius will be

obtained from a beam of both positively and negatively charged particles from a mixture of

electrons, muons, and pions. The experiment runs at beam momenta of 115, 160, and 210

MeV/c. The unique setup of MUSE allows for a direct muon/electron scattering cross section

comparison with coverage of a low-Q2 region of Q2 = 0.002 to 0.082 GeV2 for sensitivity to the

proton charge radius and for the study of possible two-photon exchange mechanisms by

comparing lepton charges. In addition, the experiment is collecting pion-proton elastic scattering

data. The MUSE experiment has recently begun to collect production-quality data. An overview

of the MUSE experiment and current status will be given.