Abstract:
The hypothesis of local equilibrium (LE) in
relativistic
heavy ion collisions at energies from AGS to
RHIC is checked
in the microscopic transport model. We find
that kinetic,
thermal, and chemical equilibration of the
expanding
hadronic matter is nearly reached in central
collisions at
AGS energy for $t \geq 10$ fm/$c$ in a
central cell. At
these times the equation of state may be
approximated by a
simple dependence $P \cong (0.12-0.15)
\epsilon$. Increasing
deviations of the yields and the energy
spectra of hadrons
from statistical model values are observed
for increasing
bombarding energies. The origin of these
deviations is
traced to the irreversible multiparticle
decays of strings
and many-body $(N \geq 3)$ decays of
resonances. The
violations of LE indicate that the matter in
the cell
reaches a steady state instead of idealized
equilibrium. The
entropy density in the cell is only about 6%
smaller than
that of the equilibrium state.