Two-photon exchange contribution to proton form factors in the time-like region

Abstract

We estimate the two-photon exchange contribution to the process ${e}^{+}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}p+\overline{p} $. The two-photon exchange corrections to double spin polarization observables and form factors in the time-like region are calculated. The corrections are found to be small in magnitude but with a strong angular dependence at fixed momentum transfer. These two features are the same as those in the space-like region. In future experiments, the double spin polarization observable ${P}_{z}$ deserves to be considered.