172 research outputs found
Microscopic calculations of stopping and flow from 160AMeV to 160AGeV
The behavior of hadronic matter at high baryon densities is studied within
Ultrarelativistic Quantum Molecular Dynamics (URQMD). Baryonic stopping is
observed for Au+Au collisions from SIS up to SPS energies. The excitation
function of flow shows strong sensitivities to the underlying equation of state
(EOS), allowing for systematic studies of the EOS. Effects of a density
dependent pole of the -meson propagator on dilepton spectra are studied
for different systems and centralities at CERN energies.Comment: Proceedings of the Quark Matter '96 Conference, Heidelberg, German
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
Signatures of dense hadronic matter in ultrarelativistic heavy ion reactions
The behavior of hadronic matter at high baryon densities is studied within
Ultrarelativistic Quantum Molecular Dynamics (URQMD). Baryonic stopping is
observed for Au+Au collisions from SIS up to SPS energies. The excitation
function of flow shows strong sensitivities to the underlying equation of state
(EOS), allowing for systematic studies of the EOS. Dilepton spectra are
calculated with and without shifting the pole. Except for S+Au
collisions our calculations reproduce the CERES data.Comment: Invited talk at RHIC-theory workshop at BNL july 8-1
Intermediate mass excess of dilepton production in heavy ion collisions at BEVALAC energies
Dielectron mass spectra are examined for various nuclear reactions recently
measured by the DLS collaboration. A detailed description is given of all
dilepton channels included in the transport model UrQMD 1.0, i.e. Dalitz decays
of mesons and of the resonance, direct
decays of vector mesons and bremsstrahlung. The microscopic calculations
reproduce data for light systems fairly well, but tend to underestimate the
data in at high energies and in at low energies. These conventional
sources, however, cannot explain the recently reported enhancement for
nucleus-nucleus collisions in the mass region 0.15 GeV<<0.6 GeV. Chiral
scaling and meson broadening in the medium are investigated as a
source of this mass excess. They also cannot explain the recent DLS data.Comment: 26 pages, 9 figures, references update
Exploring Pompeii: discovering hospitality through research synergy
Hospitality research continues to broaden through an ever-increasing dialogue and alignment with a greater number of academic disciplines. This paper demonstrates how an enhanced understanding of hospitality can be achieved through synergy between archaeology, the classics and sociology. It focuses on classical Roman life, in particular Pompeii, to illustrate the potential for research synergy and collaboration, to advance the debate on hospitality research and to encourage divergence in research approaches. It demonstrates evidence of commercial hospitality activities through the excavation hotels, bars and taverns, restaurants and fast food sites. The paper also provides an example of the benefits to be gained from multidisciplinary analysis of hospitality and tourism
Microscopic Models for Ultrarelativistic Heavy Ion Collisions
In this paper, the concepts of microscopic transport theory are introduced
and the features and shortcomings of the most commonly used ansatzes are
discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics
(UrQMD) transport model is described in great detail. Based on the same
principles as QMD and RQMD, it incorporates a vastly extended collision term
with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin
is explicitly treated for all hadrons. The range of applicability stretches
from GeV/nucleon, allowing for
a consistent calculation of excitation functions from the intermediate energy
domain up to ultrarelativistic energies. The main physics topics under
discussion are stopping, particle production and collective flow.Comment: 129 pages, pagestyle changed using US letter (8.5x11 in) format. The
whole paper (13 Mb ps file) could also be obtained from
ftp://ftp.th.physik.uni-frankfurt.de/pub/urqmd/ppnp2.ps.g
Dilepton Production in Nucleon-Nucleon Reactions With and Without Hadronic Inelasticities
We calculate elementary proton-proton and neutron-proton bremsstrahlung and
their contribution to the invariant mass distribution. At 4.9 GeV, the
proton-proton contribution is larger than neutron-proton, but it is small
compared to recent data. We then make a first calculation of bremsstrahlung in
nucleon-nucleon reactions with multi-hadron final states. Again at 4.9 GeV, the
many-body bremsstrahlung is larger than simple nucleon-nucleon bremsstrahlung
by more than an order of magnitude in the low-mass region. When the
bremsstrahlung contributions are summed with Dalitz decay of the ,
radiative decay of the and from two-pion annihilation, the result
matches recent high statistics proton-proton data from the Dilepton
Spectrometer collaboration.Comment: 1+17 pages plus 11 PostScript figures uuencoded and appended,
McGill/93-9, TPI-MINN-93/18-
Dilepton production by bremsstrahlung of meson fields in nuclear collisions
We study the bremsstrahlung of virtual omega mesons due to the collective
deceleration of nuclei at the initial stage of an ultrarelativistic heavy-ion
collision. It is shown that electromagnetic decays of these mesons may give an
important contribution to the observed yields of dileptons. Mass spectra of
positron-electron and muon pairs produced in central Au+Au collisions are
calculated under some simplifying assumptions on the space-time variation of
the baryonic current in a nuclear collision process. Comparison with the CERES
data for 160 AGev Pb+Au collisions shows that the proposed mechanism gives a
noticeable fraction of the observed lepton pairs in the intermediate region of
invariant masses. Sensitivity of the dilepton yield to the in-medium
modification of masses and widths of vector mesons is demonstrated.Comment: 14 page
- âŠ