Relativistic Heavy-Ion Collisions within 3-Fluid Hydrodynamics: Hadronic Scenario

Abstract

A 3-fluid hydrodynamic model for simulating relativistic heavy-ion collisions is introduced. Alongside with two baryon-rich fluids, the new model considers time-delayed evolution of a third, baryon-free (i.e. with zero net baryonic charge) fluid of newly produced particles. Its evolution is delayed due to a formation time, during which the baryon-free fluid neither thermalizes nor interacts with the baryon-rich fluids. After the formation it starts to interact with the baryon-rich fluids and quickly gets thermalized. Within this model with pure hadronic equation of state, a systematic analysis of various observables at incident energies between few and about 160A GeV has been done as well as comparison with results of transport models. We have succeeded to reasonably reproduce a great body of experimental data in the incident energy range of E_{lab} = (1-160)A GeV. The list includes proton and pion rapidity distributions, proton transverse-mass spectra, rapidity distributions of Lambda and antiLambda hyperons, elliptic flow of protons and pions (with the exception of proton v2 at 40A GeV), multiplicities of pions, positive kaons, phi-mesons, hyperons and antihyperons, including multi-strange particles. This agreement is achieved on the expense of substantial enhancement of the interflow friction as compared to that estimated proceeding from hadronic free cross sections. However, we have also found out certain problems. The calculated yield of K^- is approximately by a factor of 1.5 higher than that in the experiment. We have also failed to describe directed transverse flow of protons and pion at E_{lab} > 40A GeV. This failure apparently indicates that the used EoS is too hard and thereby leaves room for a phase transition.