Hyperon polarization and its correlation with directed flow in high-energy nuclear collisions

Abstract

We investigate the hyperon polarization and its correlation with the directed flow of the quark-gluon plasma (QGP) in non-central Au+Au collisions at $\sqrt{s_{\textrm{NN}}} = 27$ GeV. A modified 3-dimensional (3D) Glauber model is developed and coupled to a (3+1)-D viscous hydrodynamic evolution of the QGP. Within this framework, we obtain a satisfactory simultaneous description of the directed flow of identified particles and $\Lambda$ polarization, and show sensitivity of polarization to both the tilted geometry and the longitudinal flow profile of the QGP. A non-monotonic transverse momentum dependence of the $\Lambda$ polarization is found in our calculation, which is absent from hydrodynamic simulation using other initialization methods and can be tested by future experimental data with higher precision. A strong correlation (or anti-correlation) is found between the global polarization and directed flow of $\Lambda$ when the longitudinal flow field (or medium deformation) varies, indicating the common origin of these two quantities. Therefore, a combination of these observables may provide a more stringent constraint on the initial condition of the QGP.Comment: 15 pages, 12 figures, any comments are welcom