Speaker
Description
There has been considerable progress in the study of the electromagnetic form factors of baryons in the timelike region, through electron-positron scattering ($e^+ e^- \to B \bar B$ reactions), in the last two decades. Timelike experiments reveal information about the distribution of charge and magnetism inside the hyperons that cannot be obtained in spacelike experiments (electron scattering on baryons). Motivated by the novel data, we extend a covariant quark model that takes into account the meson cloud excitations of the baryon cores, developed for the spacelike region, to the timelike region, without any further parameter fitting. We use the formalism to calculate the electric ($G_E$) and magnetic ($G_M$) form factors of spin 1/2 baryons in the large square transfer momentum $q^2$ region. Our calculations are compared with the available data from CLEO and BESIII above $q^2=10$ GeV$^2$. We conclude that our predictions for the effective form factors(combination between $G_E$ and $G_M$) are in good agreement with the $q^2 > 15$ GeV$^2$ data for $\Lambda$, $\Sigma^+$ and $\Xi^-$. Our predictions can be further tested when large $q^2$ data for $\Sigma^0$, $\Sigma^-$ and $\Xi^-$ become available. We also compare our model calculations with the scarce available data for ratio $|G_E/G_M|$. We conclude that the present $q^2$ data range is not large enough to test our calculations, but that a more definitive test can be performed by upcoming data above $q^2=20$ GeV$^2$.
[1] G.~Ramalho, M.~T.~Pe\~na and K.~Tsushima,
"Hyperon electromagnetic timelike elastic form factors at large $q^2$,"
Phys. Rev. D \textbf{101}, 014014 (2020) [arXiv:1908.04864 [hep-ph]].
[2] G.~Ramalho, M.~T.~Pe\~na, K.~Tsushima and M.~K.~Cheoun,
"Electromagnetic $|G_E/G_M|$ ratios of hyperons at large timelike $q^2$,"
Phys. Lett. B \textbf{858}, 139060 (2024) [arXiv:2407.21397 [hep-ph]].