Quantifying the degree of hydrodynamic behaviour in heavy-ion collisions

¹ Fakultät für Physik, Universität Bielefeld, D-33615 Bielefeld, Germany
² Incubator of Scientific Excellence-Centre for Simulations of Superdense Fluids, University of Wrocław, pl. Maxa Borna 9, 50-204 Wrocław, Poland
³ Department of Physics and Astronomy, Ghent University, 9000 Ghent, Belgium

^* Speaker, e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Published online: 5 November 2025

Abstract

Exploiting the first measurements of the same ion species in O+O collisons at RHIC and LHC, we propose an experimentally accessible observable to distinguish whether collective behaviour builds up through a hydrodynamic expansion of a strongly interacting QGP or through few rescatterings in a non-equilibrated dilute medium. Our procedure allows to disentangle the effects of the initial state geometry and the dynamical response mechanism on the total resulting anisotropic flow. We validate the ability of our proposed observable to discriminate between systems with different interaction rates using results from event-by-event simulations in kinetic theory in the Relaxation Time Approximation (RTA). As a proof of concept, we extract the degree of hydro-dynamization for Pb+Pb collisions at LHC from experimental data.