Measurement of the two-photon exchange contribution in elastic $ep$ scattering at VEPP-3

Abstract

We report on the status of the Novosibirsk experiment on a precision measurement of the ratio $R$ of the elastic $e^{+}p$ and $e^{-}p$ scattering cross sections. Such measurements determine the two-photon exchange effect in elastic electron-proton scattering. The experiment is conducted at the VEPP-3 storage ring using a hydrogen internal gas target. The ratio $R$ is measured with a beam energy of 1.6 GeV (electron/positron scattering angles are $\theta =55÷75^{\circ }$ and $\theta =15÷25^{\circ }$) and 1 GeV ($\theta =65÷105^{\circ }$). We briefly describe the experimental method, paying special attention to the radiative corrections. Some preliminary results are presented.

5 pages, 6 figures and 1 table; contribution to the Proceedings of the PHIPSI11 Workshop (Novosibirsk, Russia, 19-22 September 2011)