Effects beyond the Born Approximation for the Elastic Scattering of Leptons by a Nucleon

Abstract

Elastic lepton scattering off of a nucleon has proven to be an efficient tool to study the structure of the hadron. In particular, the spatial distributions of the nucleon's charge and magnetization can be accessed through measurements of its electric (G_E) and magnetic (G _M) form factors. These form factors can be extracted from unpolarized cross sections measurements by using the Rosenbluth separation technique. At the current level of accuracy, a determination of G_E and G_M from an analysis of elastic lepton-nucleon scattering data requires effects beyond the leading-order (Born) approximation to be taken into account.

In this work, I study higher-order QED corrections to elastic lepton-nucleon scattering. First of all, I perform a model-independent calculation of conventional charge-dependent contributions in unpolarized lepton-proton scattering without making use of ultra-relativistic approximations. Second, in a connection to the future MUSE experiment in Switzerland, I estimate helicity-flip meson exchanges that make a difference in a comparison of ultra-relativistic vs non-ultra-relativistic lepton-proton scattering. Finally, I present a model calculation of the target-normal single-spin asymmetry in elastic electron-nucleon scattering. Such an asymmetry gives us a direct tool to studies of the imaginary part of the two-photon exchange amplitude.