Flavor and spin structure of Λ-baryon at large x

It is shown that a perturbative QCD (pQCD) based analysis and the SU(6) quark-diquark model give significant different predictions concerning the flavor and spin structure for the quark distributions of the Lambda-baryon near x=1. Detailed predictions for the ratios u(x)/s(x) of unpolarized quark distributions, Delta s(x)/s(x) of valence strange quark, and Delta u(x)/u(x) of valence up and down quarks of the ii are given from the quark-diquark model and from a pQCD based model. It is found that the up and down quarks are positively polarized at larger, even though their net spin contributions to the Lambda might be zero or negative. The significant difference for u(x)/s(x) between the two different approaches are predicted. The prediction of positively polarized up and down quarks inside the Lambda at large x has been supported by the available data of Lambda-polarization in Z decays and also by the most recent HERMES result of spin transfer to the Lambda in deep elastic scattering of polarized lepton on the nucleon target. (C) 2000 Published by Elsevier Science B.V. All rights reserved.