Overview and Status of the OLYMPUS Experiment

Analysis via Rosenbluth separation of elastic electron-proton scattering has long yielded the ratio of the electric and magnetic form factors ($G_E/G_M$) to be constant as a function of $Q^2$. More recent studies using polarized beams, extracting $G_E/G_M$ through the polarization transfer technique, show it to decrease linearly with $Q^2$. It is suspected that two-photon exchange processes explain the observed discrepancy, though theoretical calculations vary dramatically. OLYMPUS measures the two-photon contribution by studying the ratio of the cross section for electron-proton scattering to positron-proton scattering using DORIS at DESY. With multi-GEV beam energies and $>100$~mA current on an internal hydrogen gas target, OLYMPUS will be able to precisely measure two-proton exchange for $0.5\leq Q^2\leq 2.5$~GeV$^2$. An update of the status of the experiment, and its 2012 data run, will be presented.