Measurement of two-photon exchange effects in CLAS*

There is a significant discrepancy between the Rosenbluth and the polarization transfer measurements of the proton's electric to magnetic form factor ratio $\frac{G^{p}_{E}}{G^{p}_{E}}$. One possible explanation of this discrepancy is the contribution from two-photon exchange (TPE) effects, which are not typically accounted for in standard radiative corrections. The ratio of positron-proton to electron-proton elastic scattering cross sections, $R = \frac{\sigma (e^{+}p)}{\sigma(e^{-}p)}$, provides a model independent measurement of the TPE contribution to elastic electron-proton scattering. We measured this ratio at Jefferson Lab using a mixed electron-positron beam. Both electrons and positrons were elastically scattered from a liquid hydrogen target. The resulting scattered particles were detected in CLAS. The experimental details and results will be discussed.