Resonances contribution to two-photon exchange effects and possible large forward-backward asymmetry in $e^+ e^- \rightarrow p \bar{p}$

The resonances ($η_c,χ_{c0,c2}$) contribution to two-photon exchange (TPE) effects in $e^+ e^- \leftrightarrow p \bar{p}$ is calculated in a simple hadronic model. The calculation shows the TPE contributions by resonance $χ_{c2}$, which are dependent on the unknown phases $ϕ_{E,M}$ of proton's time-like form factors $G_{E,M}$, are much larger than the TPE contributions by non-resonance and are comparable with measurement precision of coming PANDA detector at $\sqrt{s} \sim M_{χ_{c2}}$ for most $ϕ_{E,M}$.

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