Department of Physics

Abstract: Studies of the internal structure of the proton and neutron, as well as their simplest bound state – deuteron – help improve our understanding of Quantum Chromodynamics in the non-perturbative region. The proton and deuteron charge radii characterize the spatial distributions of their electric charge carried by the quarks. Charge radius is an important input, e.g., for bound-state quantum electrodynamical calculations of the hydrogen atomic energy levels. However, physicists have been puzzled by the large discrepancy between proton radius measurements from muonic hydrogen Lamb shift spectroscopy and those from electron-proton elastic scattering plus those from ordinary atomic hydrogen spectroscopy. A similar puzzling situation happens in the case of the deuteron radius as well. In this talk, I will focus on electron scattering experiments that are used to extract the charge radius, discussing recent theoretical and experimental developments in this field, as well as future experiments using this technique. Afterwards, I will continue with the radius puzzle discussing also the latest developments concerning the proton and deuteron charge radii in light of all available experimental results from both atomic/muonic hydrogen spectroscopy measurements and electron scattering experiments.