Equation of state of resonance - rich matter in the central cell in heavy - ion collisions at √ s = 200 A GeV

The equilibration of hot and dense nuclear matter produced in the central cell of central Au+Au collisions at RHIC (√ s = 200A GeV) energies is studied within a microscopic transport model. The pressure in the cell becomes isotropic at t ≈ 5 fm/c after beginning of the collision. Within the next 15 fm/c the expansion of matter in the cell proceeds almost isentropically with the entropy per baryon ratio S/A ∼ = 150, and the equation of state in the (P, ε) plane has a very simple form, P = 0.15ε. Comparison with the statistical model of an ideal hadron gas indicates that the time t ≈ 20 fm/c may be too short to reach the fully equilibrated state. Particularly, the creation of long-lived resonance-rich matter in the cell decelerates the relaxation to chemical equilibrium. This resonance-abundant state can be detected experimentally after the thermal freeze-out of particles.