Status of the MUSE experiment

The 5.6 sigma difference in proton radii measured with pp atoms and with ep atoms and scattering remains an unexplained puzzle. MUSE will measure the pp and ep elastic scatterings in the same experiment at the same time. The experiment determines cross-sections, two-photon effects, form-factors, and radii and allows mu p and ep to be compared with reduced systematic uncertainties. These data should provide the best test of the lepton universality in a scattering experiment to date, about an order of magnitude improvement over previous tests, a 7 sigma radius determination, and improved two-photon measurements.