The Maximum Lifetime of the Quark-Gluon Plasma

The width $\Delta T$ of the deconfinement transition region is shown to influence strongly the flow structure in the (Landau-) hydrodynamical expansion of a quark-gluon plasma. For a sharp first order transition ($\Delta T=0$) the mixed phase is rather long-lived, with a lifetime that has a maximum when the initial energy density is at the phase boundary between mixed and pure quark-gluon matter. For increasing $\Delta T$, however, the lifetime decreases rapidly. Hadronic matter, however, remains long-lived as a consequence of the rapid change in the degrees of freedom in the transition region and the corresponding ``softening'' of the equation of state.