270 research outputs found
Temperature and thermodynamic instabilities in heavy ion collisions
We investigate thermodynamic properties and instability conditions in
intermediate energy heavy ion reactions. We define locally thermodynamic
variables, i.e. density, pressure and temperature, directly from the phase
space distribution of a relativistic transport calculation. In particular,
temperatures are determined by a fit to two covariant hot Fermi distributions
thus taking into account possible anisotropic momentum configurations. We
define instability independent from the nuclear matter spinodal by the
criterion that the effective compressibility becomes negative. The method is
applied to a semi-central Au on Au reaction at 600 MeV/nucleon. We investigate
in particular the center of the participant and the spectator matter. In the
latter we find a clear indication of instability with conditions of density and
temperature that are consistent with experimental determinations.Comment: 20 pages latex, 5 PS-figures, revised version (minor changes)
accepted for publication in Nucl. Phys.
Evidence for Different Freeze-Out Radii of High- and Low-Energy Pions Emitted in Au+Au Collisions at 1 GeV/nucleon
Double differential production cross sections of negative and positive pions
and the number of participating protons have been measured in central Au+Au
collisions at 1 GeV per nucleon incident energy. At low pion energies the pi^-
yield is strongly enhanced over the pi^+ yield. The energy dependence of the
pi^-/pi^+ ratio is assigned to the Coulomb interaction of the charged pions
with the protons in the reaction zone. The deduced Coulomb potential increases
with increasing pion c.m. energy. This behavior indicates different freeze-out
radii for different pion energies in the c.m.~frame.Comment: IKDA is the Institute for Nuclear Physics in Darmstadt/German
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