Evaluation of Two-Photon Exchange for Semi-Inclusive Deep-Inelastic Electron-Nucleon Scattering*

In this presentation, we analyze the contribution of two-photon exchange (TPE) to electron-nucleon scattering, focusing on the partonic-level. This process provides access to transverse momentum dependent distributions (TMD) of partons within a nucleon. Our investigation combines the contributions of hard and soft-photon exchange processes. Utilizing a quark-diquark model of nucleon structure, we demonstrate that soft-photon exchange process is model-independent, adhering to a low-energy theorem. Conversely, hard-photon approach is analyzed at the quark level to estimate its impact at large momentum transfer scales. Our partonic calculations reveal that TPE contributions result in cross-section modifications of the order of a few percent, which manifest as observable electron-positron asymmetries and modified azimuthal asymmetries. These findings highlight the significance of TPE in precision measurements of electron-nucleon scattering.