Understanding oscillating features of the timelike nucleon electromagnetic form factors within the extending vector meson dominance model

TL;DR

This paper models the nonmonotonic features of time-like nucleon electromagnetic form factors using an extended vector meson dominance approach, successfully fitting experimental cross sections and revealing structures linked to excited vector states.

Contribution

It introduces an extended vector meson dominance model including excited states to explain nonmonotonic features in nucleon form factors, challenging the periodic behavior hypothesis.

Findings

Successfully reproduces $e^+ e^- o p ar{p}$ and $e^+ e^- o n ar{n}$ cross sections.

Finds nonmonotonic structures in nucleon form factors due to excited vector states.

Disproves the periodic behavior of nucleon effective form factors.

Abstract

We investigate the nonmonotonic behavior observed in the time-like nucleon electromagnetic form factors. Using a phenomenological extending vector meson dominance model, where the ground states $\rho$ and $\omega$ and their excited states $\rho(2D)$, $\omega(3D)$, and $\omega(5S)$ are taken into account, we have successfully reproduced the cross sections of $e^+ e^- \to p \bar{p}$ and $e^+ e^- \to n \bar{n}$ reactions. Furthermore, we have derived the nucleon electromagnetic form factors in the time-like region, and it is found that the so-called periodic behaviour of the nucleon effective form factors is not confirmed. However, there are indeed nonmonotonic structures in the line shape of nucleon effective form factors, which can be naturally reproduced by considering the contributions from the low-lying excited vector states.