Flavor and spin structure of Λ-baryon at large x O

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 Λ-baryon near x=1. Detailed predictions for the ratios u(x)/s(x) of unpolarized quark distributions, Δs(x)/s(x) of valence strange quark, and Δu(x)/u(x) of valence up and down quarks of the Λ 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 large x, even though their net spin contributions to the Λ 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 Λ at large x has been supported by the available data of Λ-polarization in Z decays and also by the most recent HERMES result of spin transfer to the Λ in deep elastic scattering of polarized lepton on the nucleon target.