Abstract:
The assumption of local equilibrium in
relativistic heavy
ion collisions at energies from 10.7 AGeV
(AGS) up to 160
AGeV (SPS) is checked in the microscopic
transport model.
Dynamical calculations performed for a
central cell in the
reaction are compared to the predictions of
the thermal
statistical model. We find that kinetic,
thermal and
chemical equilibration of the expanding
hadronic matter are
nearly approached late 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
energy, 40 AGeV and
160 AGeV. These violations of local
equilibrium indicate
that a fully equilibrated state is not
reached, not even in
the central cell of heavy ion collisions at
energies above
10 AGeV. The origin of these findings is
traced to the
multiparticle decays of strings and many-body
decays of
resonances.