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 a very good description of the available experimental data. The PQCD model can also give a 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 $\Lambda .$

• Received 1 June 1999

DOI:https://doi.org/10.1103/PhysRevD.61.034017