296 research outputs found
Analysis of flow effects in relativistic heavy-ion collisions within the CBUU approach
We study flow phenomena in relativistic heavy-ion collisions, both in
transverse and radial direction, in comparison to experimental data. The
collective dynamics of the nucleus-nucleus collision is described within a
transport model of the coupled channel BUU type (CBUU). This recently developed
version includes all nucleonic resonances up to 1.95 GeV in mass and mean-field
potentials both of the Skyrme and momentum dependent MDYI type. We find that
heavy resonances play an important role in the description of transverse flow
above 1 AGeV incident energy. For radial flow we analyse reaction times and
equilibration and extract the parameters and for temperature and
collective flow velocity within different prescriptions. Furthermore, we apply
a coalescence model for fragment production and check the mass dependence of
the flow signals.Comment: 25 pages, 17 figures, submitted to Europ. Phys. J.
Photoabsorption on nuclei
We calculate the total photoabsorption cross section on nuclei in the energy
range from 300 MeV to 1 GeV within the framework of a semi-classical phase
space model. Besides medium modifications like Fermi motion and Pauli blocking
we focus on the collision broadening of the involved resonances. The resonance
contributions to the elementary cross section are fixed by fits to partial wave
amplitudes of pion photoproduction. The cross sections for ,
needed for the calculation of collision broadening, are obtained by detailed
balance from a fit to cross sections. We show that a
reasonable collision broadening is not able to explain the experimentally
observed disappearance of the -resonance in the photoabsorption
cross section on nuclei.Comment: 26 pages Latex including 9 postscript figure
Probing nuclear expansion dynamics with -spectra
We study the dynamics of charged pions in the nuclear medium via the ratio of
differential - and -spectra in a coupled-channel BUU (CBUU)
approach. The relative energy shift of the charged pions is found to correlate
with the pion freeze-out time in nucleus-nucleus collisions as well as with the
impact parameter of the heavy-ion reaction. Furthermore, the long-range Coulomb
force provides a 'clock' for the expansion of the hot nuclear system. Detailed
comparisons with experimental data for at 1 GeV/A and at
2.0 GeV/A are presented.Comment: 21 pages, latex, figures include
Kaon versus Antikaon Production at SIS Energies
We analyse the production and propagation of kaons and antikaons in Ni + Ni
reactions from 0.8--1.85 GeV/u within a coupled channel transport approach
including the channels as well as and for
the antikaon absorption. Whereas the experimental spectra can be
reproduced without introducing any selfenergies for the mesons in Ni + Ni
collisions from 0.8 to 1.8 GeV/u, the yield is underestimated by a factor
of 5--7 at 1.66 and 1.85 GeV/u. However, introducing density dependent antikaon
masses as proposed by Kaplan and Nelson, the antikaon spectra can be reasonably
well described.Comment: 16 pages, LaTeX, plus 12 postscript figures, submitted to Nucl. Phys.
Photoproduction of pions and etas in nuclei
We calculate the cross sections for inclusive one-pion, two-pion and eta
photoproduction in nuclei in the photon energy range from 300 MeV to 900 MeV
within the framework of a semi-classical BUU transport model. Our results are
compared with existing experimental data and discussed with respect to a
calculation of the total photoabsorption cross section.Comment: 30 pages LaTeX including 13 postscript figure
Water use efficiency as a measure to assess forest carbon uptake for different management strategies
Water use efficiency as a means to assess forest carbon uptake for different management strategies
Reanalysis of antiproton production in proton-nucleus and nucleus-nucleus reactions at subthreshold energies
We reanalyse the production of pairs in proton-nucleus and
nucleus-nucleus collisions employing novel elementary cross sections for
baryon-baryon and pion-baryon production channels based on a boson-exchange
model. In contrast to previous transport studies performed in the literature
the secondary pion induced channel is found to be most important in both p+A
and A+A collisions at subthreshold energies. A detailed comparison with the
experimental data available indicates that sizeable attractive
potentials in the order of - 100 to - 150 MeV at normal nuclear matter density
are needed to reproduce the size and shape of the experimental spectra.Comment: 25 pages, latex, including 15 ps-figures, UGI-97-21, submitted to
Nucl. Phys.
Role of isospin dependent mean field in pion production in heavy ion reactions
The importance of a isospin dependent nuclear mean field (IDMF) in regard to
the pion production mechanism is studied for the reaction at 1
GeV/nucleon using the Quantum Molecular Dynamics (QMD) model. In particular,
the effect of the IDMF on pion spectra and the charged pion ratio are analyzed.
It is found that the inclusion of a IDMF considerably suppresses the low
pions, thus, leading to a better agreement with the data on pion spectra.
Moreover, the rapidity distribution of the charged pion ratio appears to be
sensitive to the isospin dependence of the nuclear mean field.Comment: 16 pages, using RevTex, 6 PS-Figure
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