A search of an $\epsilon$ dependence of the proton form factor ratio using recoil polarization technique

Intensive theoretical and experimental efforts have been made over the past decade aiming at explaining the discrepancy between the data for the proton form factor ratio, $G_{Ep}/G_{Mp}$, obtained at Jefferson Lab using polarization transfer technique, and the world data obtained by the Rosenbluth method based on cross section measurements. One possible explanation for this difference is a two-photon exchange contribution, where both photons share the momentum transfer about equally. In the Born approximation for a fixed Q$^{2}$, the form factors do not depend upon the energy of the incident electron. We will report the results of the Jlab Hall-C $G_{Ep}-2\gamma$ experiment which was designed to measure a possible kinematical variation of the ratio $G_{Ep}/G_{Mp}$ with statistical uncertainties of $\pm$0.01 at $Q^{2}=2.5 GeV^{2}$, using the recoil polarization technique. Three kinematics were chosen, corresponding to values of the kinematic factor $\epsilon$=0.15, 0.63 and 0.77. We will describe the new detectors built for both $G_{Ep}-2\gamma$ and $G_{Ep}-III$ experiments, the electromagnetic calorimeter BigCal which detected the scattered electron, and the focal plane polarimeter (FPP) which measured the polarization of the recoil proton.