Speaker
Description
The Quark Gluon Plasma formed in relativistic heavy ion collisions at finite impact parameter has a finite angular momentum perpendicular to the reaction plane and some fraction thereof may be converted into global polarization of final state hadrons along the angular momentum direction. The polarization can be calculated assuming that the spin degrees of freedom are at local thermodynamical equilibrium at the hadronization stage. The hydrodynamical quantity steering the polarization is the thermal vorticity, that is minus the antisymmetric part of the gradient of four-temperature field $\beta^\mu=u^\mu/T$ [1].
Based on this mechanism, we present a calculation of the global polarization of $\Lambda$ hyperons produced in relativistic Au-Au collisions at RHIC Beam Energy Scan range $\sqrt{s_{\rm NN}}=7.7 - 200$ GeV with a 3+1 dimensional cascade + viscous hydro + cascade model, vHLLE+UrQMD [2]. Within this model, the mean polarization of $\Lambda$ in the out-of-plane direction is predicted to decrease rapidly with collision energy from a top value of about 2% at the lowest energy examined. We explore the connection between the polarization signal and thermal vorticity and estimate the feed-down contribution to $\Lambda$ polarization due to the decay of higher mass hyperons.
[1] F. Becattini et al., Annals Phys. 338, 32-49 (2013);
[2] Iu. Karpenko et al., Phys.Rev. C 91, 064901 (2015).
| Preferred Track | Collective Dynamics |
|---|---|
| Collaboration | Not applicable |
