Two-Photon Exchange Contribution to Proton Form Factors in Time-Like region

TL;DR

This paper estimates the two-photon exchange effects on proton form factors in the time-like region, revealing small but angular-dependent corrections that are similar to those in the space-like region, with implications for experimental measurements.

Contribution

The study provides the first detailed calculation of two-photon exchange corrections to proton form factors in the time-like region, highlighting their angular dependence and experimental relevance.

Findings

Corrections are small in magnitude.

Corrections exhibit strong angular dependence.

Features are similar to those in the space-like region.

Abstract

We estimate two-photon exchange contribution to the process $e^+ +e^- \to p + \bar{p}$. 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 the view of experiment, the double spin polarization observable $P_z$ deserves to be considered.