Fully integrated transport approach to heavy ion reactions with an intermediate hydrodynamic stage

Abstract

We present a coupled Boltzmann and hydrodynamics approach to relativistic heavy ion reactions. This hybrid approach is based on the Ultra-relativistic Quantum Molecular Dynamics (UrQMD) transport approach with an intermediate hydrodynamical evolution for the hot and dense stage of the collision. Event-by-event fluctuations are directly taken into account via the non-equilibrium initial conditions generated by the initial collisions and string fragmentations in the microscopic UrQMD model. After a (3+1)-dimensional ideal hydrodynamic evolution, the hydrodynamical fields are mapped to hadrons via the Cooper-Frye equation and the subsequent hadronic cascade calculation within UrQMD proceeds to incorporate the important final state effects for a realistic freeze-out. This implementation allows to compare pure microscopic transport calculations with hydrodynamic calculations using exactly the same initial conditions and freeze-out procedure. The effects of the change in the underlying dynamics -ideal fluid dynamics vs. non-equilibrium transport theory -will be explored. The freeze-out and initial state parameter dependences are investigated for different observables. Furthermore, the time evolution of the baryon density and particle yields are discussed. We find that the final pion and proton multiplicities are lower in the hybrid model calculation due to the isentropic hydrodynamic expansion while the yields for strange particles are enhanced due to the local equilibrium in the hydrodynamic evolution. The results of the different calculations for the mean transverse mass excitation function, rapidity and transverse mass spectra for different particle species at three different beam energies are discussed in the context of the available data.

Strangeness in Quark Matter: Opening Talk

“…On the other hand it has been shown that thermal models consistently describe the production yields of hadrons (and nuclei [49]) very well. We can therefore assume thermal production of clusters from a fluid dynamical description to heavy ion collisions [50,51]. Figures 1 and 2 show the results for di-baryon and hypernuclei yields in the mid-rapidity region of central, b < 3.4 fm, heavy ion collisions at different beam energies.…”

Resonance studies with the UrQMD model

“…For previous studies of resonances within this model see [14][15][16][17][18][19][20][21][22][23] the UrQMD model the reader is referred to [26,27]. Recent development concerning the inclusion of a hydrodynamic phase are described in [28]. Experimentally, the reconstruction of resonances is challenging.…”

MUSIC with the UrQMD Afterburner

“…Recently, H. Petersen et al has updated the UrQMD code to include hydrodynamics [26] and made it publicly available. The hydrodynamics included in the original version (UrQMD v. 3.3p1) is a 3+1D ideal hydrodynamic simulation in the Cartesian coordinate system with the simple freeze-out surface determined at a constant t. MUSIC on the other hand uses the hyperbolic coordinate system and generates a fairly complicated iso-thermal freeze-out surface.…”