$Λ$, $\barΛ$ Polarization and Spin Transfer in Lepton Deep-Inelastic Scattering

Abstract

The flavor and helicity distributions of the $Λ$ and $\barΛ$ hyperons for both valence and sea quarks are calculated in a perturbative QCD (pQCD) based model. We relate these quark distributions to the fragmentation functions of the $Λ$ and $\barΛ$, and calculate the $z$-dependence of the longitudinal spin transfer to the $Λ$ and $\barΛ$ in lepton deep-inelastic scattering (DIS). It is shown that the spin transfer to the $Λ$ is compatible with the first HERMES results at DESY and further tests are suggested. We also make predictions for the $z$-dependence of the $Λ$ and $\barΛ$ longitudinal polarizations in neutrino (antineutrino) DIS processes. We investigate the sea contribution to the fragmentation functions, and we test a possible scenario where sea quarks in $Λ$ (or sea antiquarks in $\barΛ$) are negatively polarized, whereas sea antiquarks in the $Λ$ (or sea quarks in $\barΛ$) are positively polarized. The asymmetry of the polarized fragmentation functions of sea quarks and antiquarks to $Λ$ and $\barΛ$ provides a way to understand the different behaviour between the $Λ$ and $\barΛ$ spin transfers observed in the recent E665 experiment at FNAL.