that energy density, and if there is a first order phase transition, then the onset of the mixed phase would occur at an even lower density. One possibility is that no phase transition occurs even at these high densities, but it is difficult to understand how composite objects like hadrons can overlap so strongly in position space without the matter undergoing some qualitative change in character. A second possibility is that the distribution of observed hadrons in the final state is insensitive to the dynamics of the matter when it is most hot and dense. (Unfortunately there are no measurements of direct photons or dileptons at the AGS which might probe this stage of the collision.) There is some evidence for this which comes from artificially modifying hadronic cross sections at high density [@pang]. It may be understood by recognizing that once a system reaches local thermal equilibrium it is basically irrelevant how it got there.

Recently we proposed a third possibility [@us]: [*Most collisions at AGS energies produce superheated hadronic matter and are describable with hadronic cascade simulators, but in rare events a droplet of quark–gluon plasma is nucleated which converts most of the matter to plasma.*]{} We estimated 