# The electromagnetic form factors of $\Lambda$ hyperon in the vector meson dominance model

## TL;DR

This paper analyzes the electromagnetic form factors of the Lambda hyperon in the time-like region using a modified vector meson dominance model, incorporating resonance states and fitting to experimental data to explain observables and predict polarization effects.

## Contribution

It introduces a comprehensive VMD model including resonance states to accurately describe Lambda hyperon form factors and polarization observables.

## Key findings

- Model successfully fits experimental data on form factors and phase angles.
- Inclusion of resonance states is essential for explaining the ratio |G_E/G_M|.
- Predictions for polarization observables in future experiments.

## Abstract

We perform an analysis on the electromagnetic form factors of the $\Lambda$ hyperon in the time-like reaction $e^+e^-\rightarrow \Lambda\bar\Lambda$ by using a modified vector meson dominance model. We consider both the intrinsic structure components and the meson clouds components. For the latter one, we not only include the contributions from the $\phi$ and $\omega$ mesons, but also take into account the contributions from the resonance states $\omega(1420)$, $\omega(1650)$, $\phi(1680)$ and $\phi(2170)$. We extract the model parameters by combined fit to the time-like effective form factor $|G_{\rm{eff}}|$, the electromagnetic form factor ratio $|G_E/G_M|$ and the relative phase $\Delta\Phi$ of the $\Lambda$ hyperon from the BaBar and BESIII Collaborations. We find that the vector meson dominance model can simultaneously describe these observables. Particularly, the inclusion of the resonance states in the model is necessary for explaining the ratio $|G_E/G_M|$ in a wide range of $\sqrt{s}$ as well as the large phase angle. With the fitted parameters, we predict the single and double polarization observables, which could be measured in polarized annihilation reactions. Moreover, we analytically continue the expression of the form factors to space-like region and estimate the space-like form factors of $\Lambda$ hyperon.