Modified Trento initial condition and its impact on collective flows and global polarization in Cu+Au collisions

TL;DR

This study uses a modified initial condition model coupled with viscous hydrodynamics to analyze collective flow and polarization in asymmetric Cu+Au collisions, revealing how initial geometry and flow affect observable phenomena.

Contribution

The paper extends the TRENTo model to 3D and demonstrates its effectiveness in describing flow and polarization in asymmetric heavy-ion collisions.

Findings

Initial tilted geometry affects directed and elliptic flow.

Longitudinal flow velocity gradient enhances flow and polarization.

Model successfully describes rapidity and transverse momentum dependence.

Abstract

Collective flow coefficients and spin polarization are valuable probes of the geometry and flow velocity field of the quark-gluon plasma (QGP) produced in relativistic heavy-ion collisions. Using a modified TRENTo initial condition coupled to a (3+1)-dimensional (D) viscous hydrodynamic model CLVisc, we study the directed flow and elliptic flow coefficients of hadrons, together with the global polarization of $\Lambda$ and $\bar{\Lambda}$ hyperons in asymmetric Cu+Au collisions. We extend the 2D TRENTo model to the 3D space, and find that the initial tilted geometry of the QGP fireball with respect to the longitudinal direction leads to a decrease of directed flow from positive to negative values with increasing pseudorapidity, an enhancement of elliptic flow at forward and backward pseudorapidities, and a non-monotonic dependence of global polarization on the transverse momentum of hyperons. The initial longitudinal flow velocity gradient further enhances the values of directed flow and global polarization. Our model calculation provides a satisfactory description of the rapidity, transverse momentum, and centrality dependences of the directed flow of charged hadrons in Cu+Au collisions for the first time, and proposes that such asymmetric heavy-ion collisions create a better environment for studying the initial tilted geometry and longitudinal flow field of the QGP than symmetric Au+Au collisions do.