46 research outputs found
The origin of transverse flow at the SPS
We study the transverse expansion in central Pb+Pb collisions at the CERN SPS. Strong collective motion of hadrons can be created. This flow is mainly due to meson baryon rescattering. It allows to study the angular distribution of intermediate mass meson baryon interactions
Can momentum correlations proof kinetic equilibration in heavy ion collisions at 160/A-GeV?
We perform an event-by-event analysis of the transverse momentum distribution of final state particles in central Pb(160AGeV)+Pb collisions within a microscopic non-equilibrium transport model (UrQMD). Strong influence of rescattering is found. The extracted momentum distributions show less fluctuations in A+A collisions than in p+p reactions. This is in contrast to simplified p+p extrapolations and random walk models
Can Momentum Correlations Proof Kinetic Equilibration in Heavy Ion Collisions at 160 AGeV?
We perform an event-by-event analysis of the transverse momentum distribution
of final state particles in central Pb(160AGeV)+Pb collisions within a
microscopic non-equilibrium transport model (UrQMD). Strong influence of
rescattering is found. The extracted momentum distributions show less
fluctuations in A+A collisions than in p+p reactions. This is in contrast to
simplified p+p extrapolations and random walk models.Comment: 9 pages, 3 eps figures, submitted to Phys. Lett.
Collective flow in heavy ion reactions and the properties of excited nuclear matter
Quantum Molecular Dynamics (QMD) calculations of central collisions between heavy nuclei are used to study fragment production and the creation of collective flow. It is shown that the final phase space distributions are compatible with the expectations from a thermally equilibrated source, which in addition exhibits a collective transverse expansion. However, the microscopic analyses of the transient states in the intermediate reaction stages show that the event shapes are more complex and that equilibrium is reached only in very special cases but not in event samples which cover a wide range of impact parameters as it is the case in experiments. The basic features of a new molecular dynamics model (UQMD) for heavy ion collisions from the Fermi energy regime up to the highest presently available energies are outlined
Microscopic Analysis of Thermodynamic Parameters from 160 MeV/n - 160 GeV/n
Microscopic calculations of central collisions between heavy nuclei are used
to study fragment production and the creation of collective flow. It is shown
that the final phase space distributions are compatible with the expectations
from a thermally equilibrated source, which in addition exhibits a collective
transverse expansion. However, the microscopic analyses of the transient states
in the reaction stages of highest density and during the expansion show that
the system does not reach global equilibrium. Even if a considerable amount of
equilibration is assumed, the connection of the measurable final state to the
macroscopic parameters, e.g. the temperature, of the transient ''equilibrium''
state remains ambiguous.Comment: 13 pages, Latex, 8 postscript figures, Proceedings of the Winter
Meeting in Nuclear Physics (1997), Bormio (Italy
Nucleus-nucleus collisions at highest energies
The microscopic phasespace approach URQMD is used to investigate the stopping power and particle production in heavy systems at SPS and RHIC energies. We find no gap in the baryon rapidity distribution even at RHIC. For CERN energies URQMD shows a pile up of baryons and a supression of multi-nucleon clusters at midrapidity
The Origin of Transverse Flow at the SPS
We study the transverse expansion in central Pb+Pb collisions at the CERN
SPS. Strong collective motion of hadrons can be created. This flow is mainly
due to meson baryon rescattering. It allows to study the angular distribution
of intermediate mass meson baryon interactions.Comment: submitted to Phys. Lett.
Extracting the equation of state from a microscopic non-equilibrium model
We study the thermodynamic properties of infinite nuclear matter with the
Ultrarelativistic Quantum Molecular Dynamics (URQMD), a semiclassical transport
model, running in a box with periodic boundary conditions. It appears that the
energy density rises faster than at high temperatures of ~MeV. This indicates an increase in the number of degrees of freedom.
Moreover, We have calculated direct photon production in Pb+Pb collisions at
160~GeV/u within this model. The direct photon slope from the microscopic
calculation equals that from a hydrodynamical calculation without a phase
transition in the equation of state of the photon source.Comment: Proceedings of the XIV International Conference on Particles and
Nuclei (PANIC'96), 22-28 May 1996, Williamsburg, Virginia, USA, to be
published by World Scientific Publ. Co. (3 pages