Coulomb corrections in the extraction of the proton radius

Abstract

Multi-photon exchange contributions are important in extracting the proton charge radius from elastic electron–proton scattering. So far, only diagrams associated with the exchange of a second photon have been evaluated. At the low Q2 values relevant to the radius extraction, and especially the very low Q2 region to be probed by proposed measurements, higher order contributions may become important. We evaluate these corrections in the Effective Momentum Approximation, which includes the Coulomb interaction to all orders, and find small corrections with a strong Q2 dependence at low Q2 and large scattering angles. This suggests that the higher order terms may be important in the evaluation of the proton magnetic radius.