Nuclear Physics Seminars

The ratio of the electric to magnetic proton form factors has traditionally been determined using the Rosenbluth separation method, in which the ratio is extracted from the angular dependence of the cross section at fixed momentum transfer Q ² . Measurements at JLab using the alternative, polarization transfer technique found a dramatically different behavior of the ratio compared with the Rosenbluth results. I discuss the resolution of this discrepancy by considering the effects of two-photon exchange in elastic e-p scattering, taking particular account of the nucleon's finite size. Contributions from excited nucleon intermediate states are also considered, and estimates given of two-photon exchange corrections to the form factors of the neutron and He-3.