Longitudinal bar Λ₀ polarization in heavy ion collisions as a probe for QGP formation

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.