Flavor and Spin Structure of $Λ$-Baryon at Large x

Abstract

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.