Two-photon exchange to proton electromagnetic properties in time-like region

摘要

The contributions of two-photon exchange in the process e~+ + e~-→p +(p) including N and △ intermediate states are estimated in a simple hadronic model. The corrections to the unpolarized cross section as well as to the polarized observables P_x and P_z are evaluated. The results show the corrections to unpolarized cross section are small and the angle dependence becomes weak at small s after considering the N and △(1232) contributions simultaneously, while the correction to P_z is enhanced.