Latest Results on Weak Semi-Leptonic Hyperon Decays in KTeV

This suggestion of the author was shown to be accessible in KTeV because even though there was no charged particle vertex, the π decay into two gammas and the high precision electronmagnetic calorimeter permits the vertex to be precisely measured by constraining to the π mass [8]. This along with the high flux of Ξ hyperons in the experiment permitted these analysis. Hyperon semi-leptonic decays with a muon replacing the electron are only energetically permitted for a few decay modes. In all there were only three types of such decays ever observed and all of these with a very small number of events. It was the author who introduced and performed the analysis in KTeV of the Ξ muonic decay [9]. These are important because they can be a first glimpse at the g3 form factor which is multiplied by (Mlepton/Mhyperon); in beta decays this ratio squelches any effect of the g3 form factor, but in muonic decays this term, although small, is no longer negligible [10].