Eur. Phys. J. C (2015) 75: 429
https://doi.org/10.1140/epjc/s10052-015-3646-8

Regular Article - Theoretical Physics

Collective flow without hydrodynamics: simulation results for relativistic ion collisions

University of Colorado at Boulder, Boulder, USA

^* e-mail: paul.romatschke@colorado.edu

Received: 27 April 2015
Accepted: 28 August 2015
Published online: 16 September 2015

Abstract

Flow signatures in experimental data from relativistic ion collisions are usually interpreted as a fingerprint of the presence of a hydrodynamic phase during the evolution of these systems. In this work, flow signatures arising from event-by-event viscous hydrodynamics are compared to those arising from event-by-event non-interacting particle dynamics (free streaming), both followed by a late-stage hadronic cascade, in , at  GeV and collisions at  TeV, respectively. For comparison, also collisions at  TeV are simulated. It is found that non-hydrodynamic evolution can give rise to radial flow equal to or larger than hydrodynamics with in all simulated collision systems. In light-on-heavy-ion collisions, free streaming gives rise to triangular and quadrupolar flow comparable to or larger than that from hydrodynamics, but it generally leads to considerably smaller elliptic flow. As expected, free streaming leads to considerably less elliptic, triangular and quadrupolar flow than hydrodynamics in nucleus–nucleus collisions, such as event-by-event collisions at  TeV.