Speaker
Description
The proton charge radius $r_{p}$ is a fundamental quantity that characterizes the spatial distribution of the proton’s charge and serves as a crucial input for bound-state Quantum Electrodynamics calculations of hydrogen atomic energy levels. In 2010, a groundbreaking measurement using muonic hydrogen spectroscopy yielded an unprecedentedly precise result. However, this result sparked the “proton charge radius puzzle,” as it was 7$\sigma$ smaller than values obtained from previous electron-proton elastic scattering and ordinary hydrogen spectroscopy experiments. Despite significant experimental and theoretical advancements since then, key questions remain, particularly in lepton scattering. Notably, the proton electric form factor measured by the Jefferson Lab PRad experiment exhibits a large discrepancy from the 2010 Mainz results. In this talk, I will review recent progress in lepton scattering experiments, with an emphasis on the PRad measurement. I will also introduce the next-generation PRad-II experiment, which aims to reduce the total uncertainty of $r_{p}$ by at least a factor of 3 compared to PRad. This new experiment will push the precision frontier of electromagnetic interactions and address discrepancies in proton form factor and radius measurements across different scattering experiments.
