Effect of the two photon exchange corrections and Rosenbluth analysis of elastic electron-proton scattering at large momentum transfer
Dr. Nikolai Kivel (Universität Bochum)

Elastic electron-nucleon scattering in the one-photon exchange approximation is a time-honored tool for accessing information on the structure of the nucleon. Precision measurements of the proton electric to magnetic form factor ratio at larger \(Q^2\) using polarization experiments have revealed significant discrepancies in recent years with unpolarized experiments using the Rosenbluth technique.
As no experimental flaw in either technique has been found, two-photon exchange processes are the most likely culprit to explain this difference.
We estimate the two-photon exchange contribution at large momentum transfer \(Q^2\) using QCD factorization approach.
It is shown that the leading two-photon exchange amplitude behaves as \(1/Q^4\), and can be expressed in a model independent way in terms of the leading twist nucleon distribution amplitudes. Using several models for the nucleon distribution amplitudes, we provide estimates for existing data and for ongoing experiments.