Flavor and Spin Structure of $\Lambda$-Baryon at Large x

TL;DR

This paper compares perturbative QCD and quark-diquark models to predict the flavor and spin structure of the Lambda baryon at high momentum fractions, highlighting significant differences and supporting recent experimental data.

Contribution

It provides detailed predictions for quark distribution ratios in the Lambda baryon from two different models, emphasizing their contrasting predictions at large x.

Findings

Up and down quarks are positively polarized at large x.

Significant differences in u(x)/s(x) predictions between models.

Experimental data supports positive polarization of up and down quarks.

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 $\Lambda$-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 $\Lambda$ 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 $\Lambda$ 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.