The proton electromagnetic form factors are essential pieces of our knowledge 
of nucleon structure. However, Rosenbluth separation measurements of the proton
 electric form factor, $G_E(Q^2)$, differ from polarization transfer 
measurements by a factor of three at $Q^2  = 5.6$ (GeV/$c$)$^2$. This 
discrepancy must be resolved. One possible resolution is to include the 
difficult-to-calculate contribution of hard two-photon exchange (TPE) 
contributions. This contribution is directly proportional to the difference 
between positron-proton and electron-proton elastic scattering cross sections.

We directly determined the TPE effect by measuring the ratio of the 
positron-proton to electron-proton elastic scattering cross sections, 
$R=\sigma(e^+p)/\sigma(e^-p)$ over a wide range of momentum transfer, $Q^2$, 
and virtual photon polarization, epsilon, using a mixed beam of electrons 
and positrons in Hall B. This talk will describe the experimental techniques 
used to produce this beam, the analysis techniques to identify elastic 
scattering events, and some preliminary results.