PHASES OF THE COLLISION

	(1) The two ions approach each other, Lorenz-contracted in the direction of travel.
	(2) Particles (thousands in the case of a RHIC lead-lead central collision) emanate from the space between the receding ion remnants.

One can can divide the collision into 4 phases:
Initial hard processes	Particle production Rescattering Thermalization Formation of QGP? Formation of DCC	Expansion and cooling Phase transition back to hadrons	Free streaming hadrons

If we restrict ourselves to only observing the (free-streaming) hadrons (after all, this is a hadron workshop), then we can only hope to learn about the conditions at the time of the last transition, the hadron freezout time.

If we look into the top of a glass of freshly poured beer, we can only see the foam, that is, the transition from foam to air. The underlying transition, from beer to foam, and the beer itself, are invisible to us.

HvH, Phenix hadron workshop, March '97, Costa mesa back to the index