Electromagnetic form factors of the nucleon and two-photon exchange effects

This project focused on determining the electromagnetic form factors of the proton and neutron from the worldwide set of elastic electron–nucleon scattering data, and on studying the statistical impact of the two-photon-exchange contribution in elastic electron–proton scattering. The broader goal was to obtain a reliable description of nucleon electromagnetic structure while accounting for corrections that become relevant in precision measurements. :contentReference[oaicite:0]{index=0}

In the first stage of the project, we performed a global fit of proton and neutron electromagnetic form factors and analyzed the associated uncertainties. This provided a consistent parametrization of the nucleon form factors across a broad kinematic range and offered a quantitative basis for comparing different experimental extractions of nucleon structure observables.

In the second stage, we used this framework to investigate the two-photon-exchange effect in elastic electron–proton scattering. By incorporating a phenomenological dispersive correction into the global fit, we predicted the ratio of positron–proton to electron–proton elastic scattering cross sections and showed that it should deviate measurably from unity in the kinematic regions explored by dedicated experiments. This made the project directly relevant to testing radiative corrections beyond the Born approximation.

Together, these studies connected precision nucleon-structure physics with the statistical analysis of higher-order electromagnetic effects. The project provided both an updated determination of proton and neutron form factors and a data-driven assessment of how two-photon exchange modifies experimentally accessible observables. :contentReference[oaicite:3]{index=3}

Funding:WWS project, L'Università di Torino

References:
Phys. Rev. C 79, 065204 (2009)
J. Phys. G 36, 115009 (2009)

Collaborators: Wanda Alberico, Carlo Giunti and Somil Bilenky

Figure: [place for illustration]