Probing Rotational Dynamics of Quark Gluon Plasma via Global Vorticity

Abstract

The findings on the spin polarization of $Λ$, $Ξ$, and $Ω$ hyperons and spin alignment of $K^{*0}$, $φ$, and $D^{*+}$ mesons in relativistic heavy-ion collision experiments at the RHIC and LHC facilities propose the emergence of a strong vorticity field produced in these collisions. Contemplating the potential impact of vorticity on the space-time evolution of deconfined QCD matter and its freeze-out properties, we aim to investigate its characteristics within the medium. We introduce a complementary and data-driven approach to quantify the global vorticity field by extracting it directly from the transverse momentum spectra of produced hadrons. Employing the experimental data for $Λ$, $Ξ$, $Ω$, $K^{*0}$, $K^{*\pm}$, $φ$, $ρ$, and $D^{*+}$ at mid-rapidity in Au+Au and Pb+Pb collisions over a wide range of beam energies, $\sqrt{s_{\rm NN}}=7.7$ GeV-5.02 TeV, and centrality classes, we systematically examine spin-vorticity coupling in the medium. Our finding on the magnitude of the extracted vorticity is consistent with values deduced from $Λ$ and $\barΛ$ polarization measurements using statistical thermal models under the non-relativistic limit. Notably, we observe a prominent particle-species dependence of the vorticity, as well as a non-trivial variation with collision centrality and beam energy. These results indicate that vorticity-driven spin phenomena are sensitive to hadron structure and freeze-out dynamics, providing new constraints on the rotational properties of the QCD matter.

Figures (6)

• Figure 1: A pictorial representation of the magnitude of the vorticity across different physical systems, ranging from the cosmos to the relativistic heavy-ion collisions laboratory.
• Figure 2: The global vorticity $\Omega$ as a function of collision centrality for $\Lambda$, $\bar{\Lambda}$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, and $\bar{\Omega}^{+}$ obtained from Au+Au collisions at mid-rapidity for various center of mass energies ranging from $\sqrt{s_{\rm NN}}$ = 7.7–64 GeV.
• Figure 3: The global vorticity $\Omega$ as a function of collision centrality for $\Lambda$, $\Xi^{-}$, $\bar{\Xi}^{+}$, $\Omega^{-}$, and $\bar{\Omega}^{+}$ obtained in Pb+Pb collisions at mid-rapidity ($|y| <$ 0.5) for $\sqrt{s_{\rm NN}} =$ 2.76 TeV.
• Figure 4: The global vorticity $\Omega$ as a function of collision center of mass energies $\sqrt{s_{\rm NN}}$ for $\Lambda$, and $\bar{\Lambda}$ obtained in Au+Au and Pb+Pb collisions at mid-rapidity ($|y| <$ 0.5) for 30-40% and 20-40% centrality classes, respectively.
• Figure 5: The global vorticity $\Omega$ for $K^{*0}$, and $\phi$ mesons as a function of collision centrality obtained from Au+Au collisions at mid-rapidity for various center of mass energies ranging from $\sqrt{s_{\rm NN}}$ = 7.7–39 GeV.