Two-photon exchange contribution in elastic electron-proton scattering, experiment at the VEPP-3 storage ring

摘要

We describe a precise measurement of the ratio of the (e~+p) to (e~-p) elastic scattering cross sections. This comparison is sensitive to the effect of two-photon exchange contributions which may be the cause for inconsistent extractions of the proton form factors obtained using different methods. The experiment was performed at storage ring VEPP-3, Novosibirsk at energies of positron/electron beams of 1.0 and 1.6 GeV with electron/positron scattering angles θ = 65÷105° for the first case and 15÷25° and. 55÷75° for the second case. Details of the experiment and the preliminary results are presented.