Quark Structure of $\Lambda$ from $\Lambda$-Polarization in Z Decays

Abstract

The flavor and spin structure for the quark distributions of the $\Lambda$-baryon is studied in a perturbative QCD (pQCD) analysis and in the SU(6) quark-diquark model, and then applied to calculate the $\Lambda$-polarization of semi-inclusive $\Lambda$ production in $e^{+}{e}^{-}$-annihilation near the $Z$-pole. It is found that the quark-diquark model gives very good description of the available experimental data. The pQCD model can also give good description of the data by taking into account the suppression of quark helicities compared to the naive SU(6) quark model spin distributions. Further information is required for a clean distinction between different predictions concerning the flavor and spin structure of the $\Lambda$.

Comments: 25 latex pages, eight eps figures, small changes in references and discussions, final version to be published in PRD 61(2000)