Measurement of the two-photon exchange contribution in elastic $ep$   scattering at VEPP-3
  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 $\theta = 55 \div 75^{\circ}$ and $\theta = 15 \div 25^{\circ}$) and 1 GeV ($\theta = 65 \div 105^{\circ}$). We briefly describe the experimental method, paying special attention to the radiative corrections. Some preliminary results are presented. 
A. V. Gramolin, J. Arrington, L. M. Barkov, V. F. Dmitriev, V. V.   Gauzshtein, R. A. Golovin, R. J. Holt, V. V. Kaminsky, B...
nucl-ex hep-ex hep-ph