Two-photon exchange in elastic $ep$ scattering and the status of the OLYMPUS experiment

Two-photon exchange in elastic $ep$ scattering is believed to explain the observed discrepancy in the proton electric to magnetic form factor ratio, $\mu_{p}G_{E}^{p}/G_{M}^{p}$, measured by Rosenbluth separation and by polarization transfer methods. To quantitatively determine the contribution of two-photon exchange to elastic scattering the OLYMPUS experiment was proposed and operated at the DESY laboratory in Hamburg, Germany to measure the ratio in the elastic scattering cross sections, $\sigma_{e^{+}p}/\sigma_{e^{-}p}$. The OLYMPUS experiment used the positron and electron beams of the DORIS storage ring at a beam energy of 2.01~GeV incident on a windowless, internal, hydrogen gas target. A left/right symmetric detector measured the rates for elastic scattering over a broad kinematic range together with a redundant set of luminosity monitors. Approximately 4.45~fb$^{-1}$ of integrated luminosity was collected. The current status of the OLYMPUS analysis will be presented.