A study of vorticity formation in high energy nuclear collisions

We present a quantitative study of vorticity for- mation in peripheral ultrarelativistic heavy-ion collisions at √sNN = 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 different defini- tions of vorticity which are relevant in relativistic hydrody- namics. 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 η/s = 0.1 fixed, a vorticity of the order of some 10−2 c/fm can develop at freeze-out. The ensuing polariza- tion of 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.