Polarization of Lambda^0 hyperons as a signature for the Quark-Gluon Plasma

Abstract

The momentum distribution of Lambda^0 hyperons produced from the quark-gluon plasma (QGP) in ultra-relativistic heavy-ion collisions is calculated in dependence on their polarization. The momentum distribution of Lambda^0 hyperons is defined by matrix elements of relativistic quark Wigner operators, which are calculated within the Effective quark model with chiral U(3)xU(3) symmetry and the Quark-Gluon transport theory. We show that the polarization of the Lambda^0 hyperon depends of the spin of the strange quark that agrees well with the DeGrand-Miettinen model. We show that Lambda^0 hyperons, produced from the QGP, are fully unpolarized. This means that a detection of unpolarized Lambda^0 hyperons, produced in ultra-relativistic heavy-ion collisions, should serve as one of the signatures for the existence of the QGP in intermediate states of ultra-relativistic heavy-ion collisions.