is stopped immediately after the Cooper-Frye freeze-out from the hydrodynamic phase (GF and $5\cdot\varepsilon_0$ are adopted as default hydro-freeze-out criteria), with instantaneous resonance decays. The observed size of the pion source is small at this hydrodynamic freeze-out. In previous investigations [@Petersen:2008dd] it has been found that binary baryon-meson and meson-meson collisions still frequently happen after the hydrodynamic freeze-out. In baryon-meson reactions, the most abundant interactions are the excitation and the decay of the $\Delta$ resonance (i.e. $\Delta \rightleftharpoons \pi
N$), while in meson-meson collisions, the $\rho \rightleftharpoons
\pi\pi$ process is dominant. A large number of these final hadron interactions in which pions are involved contribute significantly to the final HBT radii of pions in this model.

Let us therefore explore if the finally observed HBT radii do depend on the transition criterion from hydrodynamics to the transport model. The full hybrid model calculations (dashed lines with open symbols) are shown with two different cuts of the energy density ($5\cdot \varepsilon_0$ as default and $4\cdot \varepsilon_0$) for the GF and with the energy density cut $5\cdot \varepsilon_0$ for the IF. It is found that the final state hadronic interactions are sufficient that the effects of different treatments of the hydrodynamic freeze-out 