Longitudinal ${\bar{\Lambda }}_0$ polarization in heavy ion collisions as a probe for QGP formation

Abstract

We present an analysis of the longitudinal ${\bar{\Lambda }}_0$ polarization in ultra-relativistic heavy-ion collisions. The polarization of ${\bar{\Lambda }}_0$'s coming from the decay chain $\bar{\Xi }\to {\bar{\Lambda }}_0+\pi$ exhibits a very well differentiated behavior depending on the production region of the primordial $\bar{\Xi }$'s. This effect reflects the different values of the $N_{\bar{\Xi }}/N_{{\bar{\Lambda }}_0}$ ratio in the QGP region, where nucleon-nucleon interactions take place in a hot and dense environment, and the peripherical region, in which ordinary nucleon-nucleon interactions occur. An increase in the longitudinal ${\bar{\Lambda }}_0$ polarization signals a strangeness enhancement which is thought as a property of the QGP phase.

Comments: Latex file, 12 pages, 5 figures. To appear in Eur. Phys. J. C