scholarly journals Relaxation to equilibrium and EOS in ultra-relativistic heavy-ion collisions

2018 ◽  
Vol 191 ◽  
pp. 05005
Author(s):  
E. Zabrodin ◽  
L. Bravina
Keyword(s):  
Linear Dependence ◽  
Heavy Ion Collisions ◽  
Thermal Contact ◽  
Central Zone ◽  
Heavy Ion ◽  
Relativistic Heavy Ion Collisions ◽  
Hydrodynamic Description ◽  
Ion Collisions ◽  
Relaxation To Equilibrium ◽  
Hadron Gas

We study relaxation to equilibrium of hot and dense hadron-string matter produced in the central zone of central heavy-ion collisions at energies 11:6AGeV ≤ Elab ≤ 160AGeV. Two microscopic transport models, UrQMD and QGSM, are employed. The analysis is performed for the central cubic cell with volume V = 125 fm3. To check how close the system is to the equilibrium, its hadron yields and hadron energy spectra are compared with those of the statistical model of ideal hadron gas. For all collision energies it was found that the matter in the cell was approaching the equilibrium state, which lasted about 10 - 20 fm/c. After that the matter became very dilute and the thermal contact between the hadrons was lost. Equation of state is well fitted to linear dependence P/ε = a = c2s, where the square of the sonic velocity c2s increases from 0.12 at Elab = 11:6AGeV to 0.145 at Elab = 160AGeV. These results are valid also for very early times of the system evolution when the matter is still out of equilibrium. Together with the isentropic expansion, the linear dependence of P on ε supports the application of hydrodynamic description to early stages of heavy-ion collisions.

scholarly journals Relaxation to equilibrium in relativistic heavy ion collisions

2018 ◽  
Vol 182 ◽  
pp. 02019
Author(s):  
L. Bravina ◽  
E. Zabrodin
Keyword(s):  
Heavy Ion Collisions ◽  
Thermal Contact ◽  
Central Area ◽  
Dense Matter ◽  
Heavy Ion ◽  
Relativistic Heavy Ion Collisions ◽  
Transport Models ◽  
Ion Collisions ◽  
Relaxation To Equilibrium ◽  
Hadron Gas

Relaxation to equilibrium of hot and dense matter produced in central area of relativistic heavy ion collisions at energies ranging from several AGeV to hundreds AGeV is studied within two Monte Carlo transport models. The analysis was performed for three different areas: (i) fixed cubic cell with volume V = 125 fm3, (ii) fixed asymmetric cell with volume V = 4 x 4 x 1 = 16 fm3, and (iii) expanding cell. In the last case the cell volume follows the growth of the area with uniformly distributed energy. To check whether or not the system is equilibrated, its hadron yields and their energy spectra are compared with those of the statistical model of ideal hadron gas. For all cells and for all collision energies it was found that the matter in the cell was approaching the equilibrium state. The higher the collision energy, the shorter the time of equilibration. The equilibration phase lasts about 10 - 20 fm/c, after that the matter becomes very dilute and the thermal contact between hadrons is lost. Equation of state is well fitted to linear dependence P/ɛ = a = c2s , where the square of the sonic velocity c2s increases from 0.12 at Elab = 11.6AGeV to 0.145 at Elab = 160AGeV. The characteristic kinks observed in the T - μB phase diagrams are linked to inelastic freeze-out in the expanding fireball.

INFLUENCE OF THE EQUATION OF STATE ON THE MOMENTUM ANISOTROPY IN HADRODYNAMIC EVOLUTION OF RELATIVISTIC HEAVY ION COLLISIONS

2007 ◽  
Vol 16 (09) ◽  
pp. 2974-2978
Author(s):  
DETLEF ZSCHIESCHE ◽  
EDUARDO FRAGA ◽  
TAKESHI KODAMA ◽  
TOMOI KOIDE ◽  
BERNARDO TAVARES ◽  
...  
Keyword(s):  
Heavy Ion Collisions ◽  
Equations Of State ◽  
Three Dimensional ◽  
Heavy Ion ◽  
Relativistic Heavy Ion Collisions ◽  
Simulation Code ◽  
Ion Collisions ◽  
First Order Phase Transition ◽  
Hydrodynamical Simulation ◽  
Hadron Gas

We investigate the collective momentum anisotropy in relativistic heavy ion collisions in the BNL-RHIC energy regime with a three-dimensional hydrodynamical simulation code (SPHERIO) for different equations of state. We compare the widely used hadron gas-QGP bag model yielding a strong first order phase transition to other equations of state, which yield a smooth crossover as suggested by lattice QCD calculations.

EQUILIBRATION OF MATTER IN RELATIVISTIC HEAVY-ION COLLISIONS

2007 ◽  
Vol 16 (03) ◽  
pp. 777-786 ◽  
Author(s):  
L. BRAVINA ◽  
I. ARSENE ◽  
M. S. NILSSON ◽  
K. TYWONIUK ◽  
E. ZABRODIN ◽  
...  
Keyword(s):  
Heavy Ion Collisions ◽  
Transport Model ◽  
Central Zone ◽  
Heavy Ion ◽  
Central Cell ◽  
Hadronic Matter ◽  
Relativistic Heavy Ion Collisions ◽  
Thermal Equilibration ◽  
Ion Collisions ◽  
Chemical Equilibration

The chemical and thermal equilibration in the central zone of heavy-ion collisions at energies from AGS to SPS is studied within the microscopic transport model. Yields and energy spectra obtained for the central cell in the reaction are compared to the predictions of the thermal statistical model. It is found that kinetic, thermal, and chemical equilibration of the expanding hadronic matter are nearly approached for the period of 10-18 fm/c. Within this time the matter in the cell expands almost isentropically. For the bombarding energies around 40 AGeV the system crosses the critical point in the T - μB plane predicted by lattice QCD calculations. The net strangeness in the central cell is negative (though small). The characteristic kink in the T - μB diagrams corresponding to beginning of the equilibrated phase is observed for all energies. The origin of this phenomenon deserves further investigation.

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