Updates from the MUSE Experiment

The proton-radius puzzle has motivated a series of recent experiments, yet the extraction of the proton charge radius from lepton-scattering and hydrogen-spectroscopy data remains challenging, with results still in tension. The MUon Scattering Experiment (MUSE), located at the πM1 beam line of the Paul Scherrer Institute, is designed to address this issue. Using mixed electron and muon beams with momenta from 115 MeV/c up to 210 MeV/c, MUSE covers a four-momentum transfer range of Q² ≈ 0.002–0.08 GeV². The experiment measures high-precision elastic scattering cross sections and directly compares form factors and charge radii from both particle species. Radiative corrections, a key source of systematic uncertainty, will be investigated, aided by a downstream photon calorimeter that suppresses initial-state radiation contributions. Furthermore, the simultaneous use of positively and negatively charged leptons enables dedicated studies of two-photon exchange effects. MUSE is expected to complete production data taking in December 2025, and this talk will review the current status of the experiment.