Probing Rotational Dynamics of Quark Gluon Plasma via Global Vorticity

TL;DR

This study introduces a data-driven method to measure the global vorticity in quark-gluon plasma from hadron spectra, revealing particle-dependent vorticity features and their dependence on collision parameters, thus advancing understanding of QCD matter rotation.

Contribution

It presents a novel approach to quantify vorticity directly from experimental hadron spectra, linking spin polarization phenomena to the medium's rotational properties in heavy-ion collisions.

Findings

Vorticity magnitude aligns with polarization measurements using thermal models.

Particle species show different vorticity responses.

Vorticity varies with collision centrality and energy.

Abstract

The findings on the spin polarization of $\Lambda$, $\Xi$, and $\Omega$ hyperons and spin alignment of $K^{*0}$, $\phi$, 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 $\Lambda$, $\Xi$, $\Omega$, $K^{*0}$, $K^{*\pm}$, $\phi$, $\rho$, 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 $\Lambda$ and $\bar{\Lambda}$ 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.