Two-photon exchange in elastic electron-proton scatteringP.G. Blunden1, W. Melnitchouk2 and J.A. Tjon2, 3
1 Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB, Canada R3T 2N2,
2 Jefferson Lab, 12000 Jefferson Ave., Newport News, VA 23606, USA
3 Department of Physics, University of Maryland, College Park, MD 20742-4111, USA
(Received 27 September 2004 / Published online 08 February 2005)
Two-photon exchange contributions to unpolarized and polarized elastic electron-proton scattering cross sections are evaluated taking into account nucleon finite size effects using realistic form factors. Contributions from nucleon elastic intermediate states are found to have a strong angular dependence, which partially resolves the discrepancy between Rosenbluth and polarization transfer measurements of the proton electric to magnetic form factor ratio. Two-photon contributions to the longitudinal and transverse polarizations are generally found to be small. A comparison is made of two-photon exchange effects with existing data on the ratio of e+ p to e- p cross sections, which is predicted to be enhanced at backward angles.
PACS: 25.30.Bf Elastic electron scattering - 13.40.Gp Electromagnetic form factors
© Società Italiana di Fisica, Springer-Verlag 2005