Measurements of Sigma+ and Sigma- Time-like Electromagnetic Form Factors for center-of-mass energies from 2.3864 to 3.0200 GeV

The Born cross sections of the $e^{+}e^{-}toSigma^{+}bar{Sigma}^{-}$ and $e^{+}e^{-}toSigma^{-}bar{Sigma}^{+}$ processes are determined with high precision for center-of-mass energy from 2.3864 to 3.0200 GeV with the BESIII detector. Nonzero cross sections near threshold are observed. The resulting ratio of effective form factors for the $Sigma^{+}$ and $Sigma^{-}$ is consistent with 3, agreeing with the ratio of the incoherent sum of the squared charges of the $Sigma^{+}$ and $Sigma^{-}$ valence quarks, but disagreeing with various theoretical predictions. In addition, ratios of the $Sigma^{+}$ electric and magnetic form factors, $|G_{E}/G_{M}|$, are obtained at three center-of-mass energies through an analysis of the angular distributions. These measurements, which are studied for the first time in the off-resonance region, provide precision experimental input for understanding baryonic structure. The observed novel features of the $Sigma^{pm}$ form factors require a new theoretical description for the hyperons.