Vortical fluid and $\Lambda$ spin correlations in high-energy heavy-ion collisions

TL;DR

This paper investigates how the vortical structure of dense matter in high-energy heavy-ion collisions influences $ ext{Lambda}$ hyperon spin correlations, revealing detailed vortex patterns through hydrodynamic modeling and spin measurements.

Contribution

It introduces a comprehensive hydrodynamic framework to connect fluid vorticity with $ ext{Lambda}$ spin correlations, providing new insights into the vortical structure of quark-gluon plasma.

Findings

Azimuthal transverse spin correlation exhibits a cosine pattern with an offset.

Longitudinal spin correlation indicates vortex pairing in the transverse plane.

Spin correlations depend on collision energy, rapidity, centrality, and shear viscosity.

Abstract

Fermions become polarized in a vortical fluid due to spin-vorticity coupling. The spin polarization density is proportional to the local fluid vorticity at the next-to-leading order of a gradient expansion in a quantum kinetic theory. Spin correlations of two $\Lambda$-hyperons can therefore reveal the vortical structure of the dense matter in high-energy heavy-ion collisions. We employ a (3+1)D viscous hydrodynamic model with event-by-event fluctuating initial conditions from A MultiPhase Transport (AMPT) model to calculate the vorticity distributions and $\Lambda$ spin correlations. The azimuthal correlation of the transverse spin is shown to have a cosine form plus an offset due to a circular structure of the transverse vorticity around the beam direction and global spin polarization. The longitudinal spin correlation shows a structure of vortex-pairing in the transverse plane due to the convective flow of hot spots in the radial direction. The dependence on colliding energy, rapidity, centrality and sensitivity to the shear viscosity are also investigated.