Quark Fragmentation Functions in a Diquark Model for $Λ$ Production

Abstract

Using a simple quark-diquark model, we extract a set of unpolarized and polarized fragmentation functions for the $Λ$ based on the available unpolarized $Λ$ production data in $e^+ e ^- $ annihilation. It is found that there is a strong SU(3) flavor symmetry breaking in the unpolarized $Λ$ fragmentation functions and that the polarized $u$ and $d$ quark contributions to the polarized $Λ$ fragmentation are positive in medium and large $z$ region. The predictions of $Λ$-polarization with the obtained quark fragmentation functions are compatible with the available data on the longitudinally polarized $Λ$ produced in $e^+e^-$-annihilation, polarized charged lepton deep inelastic scattering (DIS), and neutrino DIS. The spin asymmetry for the $Λ$ production in $p\vec{p}$ collisions is also predicted for a future test in experiments at RHIC-BNL.