First observation of $\Sigma^-$-${\rm e}^-$ elastic scattering in the hyperon beam experiment WA89 at CERN

Abstract.

We have investigated the elastic scattering of high energy $\Sigma^-$ off electrons from carbon and copper targets using the CERN hyperon beam. Scattering events are identified using a maximum likelihood technique exploring the kinematical relations of the scattered particles. The observed Q$^2$–distribution of these events suggests a mean square charge radius of the $\Sigma^-$ of $< r^2_{ch}>(\Sigma^-) = 0.91 \pm 0.32 (stat.) \pm 0.4$ (syst.) fm$^2$. This constitutes the first measurement of $< r^2_{ch}>(\Sigma^-)$ and demonstrates the possibility to also measure the charge radii of other hyperons.