出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We report the experiment on a precise comparison of (e+p) and (ep) elastic scattering cross sections, which gives a direct experimental evidence for the two-photon exchange contribution to this reaction. Such data are in demand now, because they, most likely, may explain the dramatic disagreement of proton electromagnetic form factors measurements in the polarization transfer experiments at TJNAF with previous unpolarized measurements using a Rosenbluth separation technique. Experiment was performed recently at VEPP–3 storage ring at the energy of positron/electron beams of 1.6 GeV and at e+=e scattering angles around 20 and 65. The preliminary results for the cross sections ratio R = s(e+p)=s(ep) are presented.
