Emergent hydrodynamics in microscopic modeling of early stage of relativistic heavy-ion collisions

Abstract

Time evolution of hot and dense nuclear matter produced in central gold-gold collisions at energies between $$E_{lab} = 10$$ E lab = 10 and 160 AGeV is studied within two transport string models, UrQMD and QGSM. In contrast to the previous studies, here we investigate the macroscopic characteristics of the system before the state of chemical and thermal equilibrium is attained. For all energies in question two interesting observations are made for times starting already from $$t \ge 1$$ t ≥ 1 fm/c. (1) The matter in the cell expands almost isentropically with nearly constant entropy per baryon. (2) Pressure in the cell appears to be very close to the pressure calculated for equilibrated hadron gas with the same values of energy density, baryon density and strangeness density. The pressure linearly depends on the energy density, $$P = a(\sqrt{s}) \varepsilon $$ P = a ( s ) ε . Therefore, both observations endorses the formal application of relativistic hydrodynamics from the very early stages of heavy-ion collisions, despite of the fact that the matter in the fireball is out of equilibrium.

The applicability of hydrodynamics in heavy ion collisions at $\sqrt{s_{\rm NN}}$= 2.4-7.7 GeV

“…For this purpose the SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) approach is employed to assess the properties of the local energy momentum tensor. In contrast to former work examining the degree of equilibration in a rather large central cell lengths 4-5 fm [46][47][48], we deal with the whole volume of the system at the nodes of a three-dimensional lattice with resolution 1 fm by using a coarse graining method based on smearing kernels. We focus mostly on Au+Au collisions at E lab = 1.23 AGeV in the 0-5% centrality class, but we also explore the energy dependence up to √ s NN = 7.7 GeV, we look at variations as a function of centrality and we analyze light and medium ion collisions like C+C, Ar+KCl and Ag+Ag, again in the 0-5% centrality class and with beam energy between 1.58 and 2 AGeV.…”