New Prediction of the Positron-Proton to Electron-Proton Elastic Scattering Ratio \(R_{e^+e^-}\) from ep Elastic Scattering Data

I present a new extraction of the positron-proton to electron-proton elastic scattering cross sections ratio \(R_{e^+e^-}(\varepsilon ,Q^2)\) . Contrary to several previous phenomenological studies and extractions, which predicted the ratio \(R_{e^+e^-}\) using model-independent parametrization of \(F(\varepsilon ,Q^2)\) , the hard two-photon exchange (TPE) correction to the electron-proton (ep) elastic scattering cross section \(\sigma _R\) , I do not assume prior knowledge of the functional form of \(F(\varepsilon ,Q^2)\) , but rather I use combined unpolarized, and polarized ep elastic scattering experimental data to extract the TPE contributions to \(\sigma _R\) , and provide a simple parametrization of \(F(\varepsilon ,Q^2)\) along with the uncertainties associated with the model dependence of the extractions. I use the new parametrization of \(F(\varepsilon ,Q^2)\) to predict the ratio \(R_{e^+e^-}\) , and then compare my extractions of \(R_{e^+e^-}\) to several previous phenomenological extractions, TPE-hadronic calculations, and world data emphasizing mainly the kinematics range of the recent precise direct measurements from the OLYMPUS, VEPP-3, and CLAS experiments.