Quark Fragmentation Functions in a Diquark Model for $\Lambda$ Production

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