Equation of state of resonance-rich matter in the central cell in heavy-ion collisions at $\sqrt{s}=200A\mathrm{GeV}$

The equilibration of hot and dense nuclear matter produced in the central cell of central Au+Au collisions at $\sqrt{s}=200A\mathrm{GeV}$ is studied within a microscopic transport model. The pressure in the cell becomes isotropic at $t\approx 5\mathrm{fm}/c$ after beginning of the collision. Within the next $15\mathrm{fm}/c$ the expansion of matter in the cell proceeds almost isentropically with the entropy per baryon ratio $S/A\cong 150,$ and the equation of state in the $(P,\varepsilon )$ plane has a very simple form, $P=0.15\mathrm{}\varepsilon .$ Comparison with the statistical model of an ideal hadron gas indicates that the time $t\approx 20\mathrm{fm}/c$ 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.