Electromagnetic form factors of Λ hyperon in the vector meson dominance model

We perform an analysis on the electromagnetic form factors of $\mathrm{\Lambda }$ hyperon in the timelike reaction $e^{+}{e}^{-}\to \mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ 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 $\varphi$ and $\omega$ mesons, but also take into account the contributions from the resonance states $\omega (1420)$, $\omega (1650)$, $\varphi (1680)$, and $\varphi (2170)$. We extract the model parameters by combined fit to the timelike effective form factor $|G_{\mathrm{eff}}|$, the electromagnetic form factor ratio $|G_E/G_M|$ of $\mathrm{\Lambda }$ hyperon from 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 form factor ratio. With the fitted parameter, we predict the relative phase $\mathrm{\Delta }\mathrm{\Phi }$, which is consistent with the recent measurement from BES III Collaboration. Moreover, we predict the single and double polarization observables, which could be measured in polarized annihilation reactions. We also analytically continue the expression of the form factors to spacelike region and estimate the spacelike form factors of $\mathrm{\Lambda }$ hyperon.