Highly relativistic nucleus-nucleus collisions: The central rapidity region

The space-time evolution of the hadronic matter produced in the central rapidity region in extreme relativistic nucleus-nucleus collisions is described. We find, in agreement with previous studies, that quark-gluon plasma is produced at a temperature \ensuremath{\gtrsim}200-300 MeV, and that it should survive over a time scale \ensuremath{\gtrsim}5 fm/c. Our description relies on the existence of a flat central plateau and on the applicability of hydrodynamics.