Proton Electric Charge Radius from Lepton Scattering

A proton is a bound state of strong interaction, governed by Quantum Chromodynamics (QCD). The electric charge radius proton, denoted rEp, characterizes the spatial distribution its carried quarks. It an important input for bound-state Electrodynamic (QED) calculations hydrogen atomic energy levels. However, physicists have been puzzled large discrepancy between rEp measurements from muonic spectroscopy and those ep elastic scattering ordinary over decade. Tremendous efforts, both theoretical experimental, dedicated to providing various insights into this puzzle, but certain issues still remain unresolved, particularly in field lepton scatterings. This review will focus on lepton-scattering recent experimental developments field, as well future experiments using technique.