UrQMD+hydrodynamic model
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An integrated Boltzmann+hydrodynamics transport approach is applied to simulate the dynamics of the heavy ion collision. To mimic experimental conditions as realistic as possible the initial conditions and the final hadronic freeze-out are calculated using the UrQMD approach. Especially for an observable like HBT radii it is important to take care of the complexity of the different effects [@Pratt:2008sz; @Lisa:2008gf]. The non-equilibrium dynamics, e.g. fluctuations of the local baryon and energy density [@Bleicher:1998wd], in the very early stage of the collision and the final state hadronic interactions are properly taken into account on an event-by-event-basis.

UrQMD is a microscopic transport approach based on the covariant propagation of constituent (anti-)quarks and diquarks accompanied by mesons and baryons, as well as the corresponding anti-particles, i.e., full baryon-antibaryon symmetry is included. It simulates multiple interactions of ingoing and newly produced particles, the excitation and fragmentation of color strings [@NilssonAlmqvist:1986rx; @Andersson:1986gw; @Sjostrand:1993yb] and the formation and decay of hadronic resonances [@Bass:1998ca; @Bleicher:1999xi]. In principle it is also possible to incorporate mean field interactions in the transport calculation, In the present calculation they are neglected in order to test the hydro-phase and in the following we will refer to the pure cascade 