Speaker
Alexander Gramolin
(Budker Institute of Nuclear Physics)
Description
The ratio of the elastic $e^+ p$ to $e^- p$ scattering cross sections has been measured precisely at the VEPP-3 storage ring (Novosibirsk, Russia). This allows us to determine the hard two-photon exchange contribution to elastic electron-proton scattering, which is believed to be the cause of the apparent discrepancy between the Rosenbluth and polarization transfer methods of measuring the proton electromagnetic form factors. Our data obtained at $Q^2$ values from $0.3$ to $1.5~\text{GeV}^2$ show evidence of the hard two-photon exchange effect, thus supporting the proposed explanation. The VEPP-3 results are compared with several predictions and with the data from similar measurements reported recently by the CLAS and OLYMPUS collaborations.
Primary author
Alexander Gramolin
(Budker Institute of Nuclear Physics)
