Study of the electromagnetic form factors of the nucleons in the timelike region

Abstract

The electromagnetic form factors $G_{\mathrm{E}}$ and $G_{\mathrm{M}}$ of the proton and neutron in the timelike region are extracted in a study of the processes $e^{+}{e}^{-}\to \bar{p}p$ and $e^{+}{e}^{-}\to \bar{n}n$. The reaction amplitude is evaluated within the distorted wave Born approximation, with the interaction of the antinucleon-nucleon ($\bar{N}N$) pair taken into account. The latter is constructed within $SU(3)$ chiral effective field theory up to the next-to-leading order. An excellent description of the $e^{+}{e}^{-}\to \bar{N}N$ data in the energy region from the $\bar{N}N$ threshold up to center-of-mass energies $E_{\mathrm{cm}}=2.2$~GeV is achieved. Results for the electromagnetic form factors $G_{\mathrm{E}},G_{\mathrm{M}}$, $G_{\mathrm{E}}/G_{\mathrm{M}}$, and the subtracted effective form factors, $G_{\mathrm{osc}}$, are provided. These can be helpful for further studies of the properties of the nucleons.

Comments: 37 pages, 10 figures