A study of vorticity formation in high energy nuclear collisions

TL;DR

This paper uses advanced relativistic hydrodynamics simulations to study vorticity formation and polarization effects in high-energy nuclear collisions, revealing how initial conditions and viscosity influence these phenomena.

Contribution

It provides a detailed numerical analysis of vorticity and polarization in heavy ion collisions using the Israel-Stewart framework, with new insights into their dependence on initial angular momentum and viscosity.

Findings

Vorticity of order 10^{-2} c/fm can develop at freezeout.

Lambda baryon polarization does not exceed 1.4%.

Directed flow is sensitive to initial angular momentum and viscosity.

Abstract

We present a quantitative study of vorticity formation in peripheral ultrarelativistic heavy ion collisions at sqrt(s)NN = 200 GeV by using the ECHO-QGP numerical code, implementing relativistic dissipative hydrodynamics in the causal Israel-Stewart framework in 3+1 dimensions with an initial Bjorken flow profile. We consider and discuss different definitions of vorticity which are relevant in relativistic hydrodynamics. After demonstrating the excellent capabilities of our code, which proves to be able to reproduce Gubser flow up to 8 fm/c, we show that, with the initial conditions needed to reproduce the measured directed flow in peripheral collisions corresponding to an average impact parameter b=11.6 fm and with the Bjorken flow profile for a viscous Quark Gluon Plasma with \eta/s=0.1 fixed, a vorticity of the order of some 10^{-2} c/fm can develop at freezeout. The ensuing polarization of Lambda baryons does not exceed 1.4% at midrapidity. We show that the amount of developed directed flow is sensitive to both the initial angular momentum of the plasma and its viscosity.