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Using $e^+e^-$ annihilation data taken at the CESR collider with the CLEO-c detector, measurements of hyperon pair production cross sections and elastic and transition electromagnetic form factors have been made at the charmonium resonances: $psi(2S)$, $sqrt{s}=3.69$ GeV, $|Q^2|=13.6$ GeV$^2$, $mathcal{L}=48$~pb$^{-1}$; $psi(3770)$, $sqrt{s}=3.77$ GeV, $|Q^2|=14.2$ GeV$^2$, $mathcal{L}=805$~pb$^{-1}$; and $psi(4170)$, $sqrt{s}=4.17$ GeV, $|Q^2|=17.4$ GeV$^2$, $mathcal{L}=586$~pb$^{-1}$. %High efficiency particle identification has resulted in good statistical precision in the results. Results with good statistical precision are obtained with high efficiency particle identification. Systematics of pair production cross sections, and form factors with respect to the number of strange quarks in the hyperons are studied, and evidence is presented for effects of diquark correlations in comparative results for $Lambda^0$ and $Sigma^0$, both of which have the same $uds$ quark content.
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A review of recent precision measurements of the electromagnetic form factors of the mesons, pion and kaon, and the hyperons, $Lambda^0$, $Sigma^0$, $Sigma^+$, $Xi^-$, $Xi^0$, $Omega^-$, at large timelike momentum transfers is presented. Evidence is found for diquark correlations in $Lambda^0$, $Sigma^0$ hyperons.
Electromagnetic form factors of hyperons ($Lambda$, $Sigma$, $Xi$) in the timelike region, accessible in the reaction $e^+e^- to bar YY$, are studied. The focus is on energies close to the reaction thresholds, where the properties of these form factors are significantly influenced by the interaction in the final $bar YY$ system. This interaction is taken into account in the calculation, utilizing $bar YY$ potential models that have been constructed by the Julich group for the analysis of data from the reaction $bar pp to bar YY$ in the past. The enhancement of the effective form factor for energies close to the threshold, seen in experiments of $e^+e^- to bar Lambda Lambda$ and $e^+e^- to bar Sigma^0Lambda$, is reproduced. With regard to the reactions $e^+e^- to bar Sigma^- Sigma^+, barSigma^0Sigma^0, barSigma^+Sigma^-$ a delicate interplay between the three channels is observed in the results at low energies, caused by the $barSigmaSigma$ interaction. Predictions for the electromagnetic form factors $G_M$ and $G_E$ in the timelike region are presented for the $Lambda$, $Sigma$, and $Xi$ hyperons.
Using 805 pb^-1 of e+e- annihilation data taken with the CLEO-c detector at psi(3770), sqrt{s}=3770 MeV, we report the first measurements of the electromagnetic form factors of the Lambda0, Sigma0, Sigma+, Xi0, Xi-, and Omega- hyperons for the large timelike momentum transfer of |Q^2|=14.2 GeV^2. The form factors for the different hyperons are found to vary by nearly a factor two. It is found that |G_M(Lambda0)|=1.66(24) x |G_M(Sigma0)|. The Lambda0 and Sigma0 hyperons have the same uds quark content, but differ in their isospin, and therefore the spin of the $ud$ quark pair. It is suggested that the spatial correlation implied by the singlet spin--isospin configuration in the Lambda0 is an example of strong diquark correlations in the Lambda0, as anticipated by Jaffe and Wilczek. Improved measurements of the branching fractions of psi(2S) -> p pbar and hyperon--antihyperon pairs are also reported.
We present a calculation of the SU(3)-breaking corrections to the hyperon transition vector form factors to $mathcal{O}(p^4)$ in heavy baryon chiral perturbation theory with finite-range regularisation. Both octet and decuplet degrees of freedom are included. We formulate a chiral expansion at the kinematic point $Q^2=-(M_{B_1}-M_{B_2})^2$, which can be conveniently accessed in lattice QCD. The two unknown low-energy constants at this point are constrained by lattice QCD simulation results for the $Sigma^-rightarrow n$ and $Xi^0rightarrow Sigma^+$ transition form factors. Hence we determine lattice-informed values of $f_1$ at the physical point. This work constitutes progress towards the precise determination of $|V_{us}|$ from hyperon semileptonic decays.
By the analysis of the world data base of elastic electron scattering on the proton and the neutron (for the latter, in fact, on $^2H$ and $^3He$) important experimental insights have recently been gained into the flavor compositions of nucleon electromagnetic form factors. We report on testing the Graz Goldstone-boson-exchange relativistic constituent-quark model in comparison to the flavor contents in low-energy nucleons, as revealed from electron-scattering phenomenology. It is found that a satisfactory agreement is achieved between theory and experiment for momentum transfers up to $Q^2sim$ 4 GeV$^2$, relying on three-quark configurations only. Analogous studies have been extended to the $Delta$ and the hyperon electromagnetic form factors. For them we here show only some sample results in comparison to data from lattice quantum chromodynamics.
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