The electromagnetic form factors of the proton in the timelike region

TL;DR

This paper analyzes proton-antiproton interactions near threshold using a chiral effective field theory potential, explaining the energy dependence of the electromagnetic form factors and providing predictions for related observables.

Contribution

It introduces a novel application of a chiral EFT potential to model ppbar interactions and explains the energy dependence of form factors near threshold.

Findings

The energy dependence of the e+e- <-> ppbar cross section is mainly due to ppbar interaction.

The steep rise of the effective form factor near threshold is explained by the interaction.

Predictions for G_E, G_M, and spin observables match experimental data.

Abstract

The reactions ppbar -> e+e- and e+e- -> ppbar are analyzed in the near-threshold region. Specific emphasis is put on the role played by the interaction in the initial- or final antinucleon-nucleon state which is taken into account rigorously. For that purpose a recently published NNbar potential derived within chiral effective field theory and fitted to results of a new partial-wave analysis of ppbar scattering data is employed. Our results provide strong support for the conjecture that the pronounced energy dependence of the e+e- <-> ppbar cross section, seen in pertinent experiments, is primarily due to the ppbar interaction. Predictions for the proton electromagnetic form factors G_E and G_M in the timelike region, close to the NNbar threshold, and for spin-dependent observables are presented. The steep rise of the effective form factor for energies close to the ppbar threshold is explained solely in terms of the ppbar interaction. The corresponding experimental information is quantitatively described by our calculation.