Abstract:
The equilibration of hot and dense nuclear
matter produced
in the central cell of central Au+Au
collisions at RHIC
($\sqrt{s}=200$ AGeV) energies is studied
within a
microscopic transport model. The pressure in
the cell
becomes isotropic at $t\approx 5$ 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 $S/A \approx 150$,
and the equation
of state in the $(P,\epsilon)$ plane has a
very simple form,
$P=0.15\epsilon$. Comparison with the
statistical model of
an ideal hadron gas indicates that the time
$t \approx 20$
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.