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

TL;DR

This paper calculates the impact of specific resonances on two-photon exchange effects in proton-antiproton production, revealing significant resonance contributions that could influence experimental measurements at future colliders.

Contribution

The study introduces a simple hadronic model to quantify resonance contributions to TPE effects, highlighting the prominent role of the $ ext{chi}_{c2}$ resonance and its dependence on proton form factor phases.

Findings

Resonance $ ext{chi}_{c2}$ significantly enhances TPE effects.

Resonance contributions are comparable to experimental measurement precision.

TPE effects depend on unknown phases of proton form factors.

Abstract

The resonances ($\eta_c,\chi_{c0,c2}$) 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 $\chi_{c2}$, which are dependent on the unknown phases $\phi_{E,M}$ 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 $\sqrt{s} \sim M_{\chi_{c2}}$ for most $\phi_{E,M}$.