475 research outputs found
Production of multi-strangeness hypernuclei and the YN-interaction
We investigate for the first time the influence of hyperon-nucleon (YN)
interaction models on the strangeness dynamics of antiproton- and -nucleus
interactions. Of particular interest is the formation of bound
multi-strangeness hypermatter in reactions relevant for \panda. The main
features of two well-established microscopic approaches for YN-scattering are
first discussed and their results are then analysed such that they can be
applied in transport-theoretical simulations. The transport calculations for
reactions induced by antiproton beams on a primary target including also the
secondary cascade beams on a secondary target show a strong sensitivity on the
underlying YN-interaction. In particular, we predict the formation of
-hypernuclei with an observable sensitivity on the underlying
N-interaction. We conclude the importance of our studies for the
forthcoming research plans at FAIR.Comment: 13 pages, 5 figures. Accepted for publication in Physics Letters
Stopping and Isospin Equilibration in Heavy Ion Collisions
We investigate the density behaviour of the symmetry energy with respect to
isospin equilibration in the combined systems at relativistic
energies of 0.4 and . The study is performed within a relativistic
framework and the contribution of the iso-vector, scalar field to the
symmetry energy and the isospin dynamics is particularly explored. We find that
the isospin mixing depends on the symmetry energy and a stiff behaviour leads
to more transparency. The results are also nicely sensitive to the "fine
structure" of the symmetry energy, i.e. to the covariant properties of the
isovector meson fields. The isospin tracing appears much less dependent on the
in-medium neutron-proton cross-sections () and this makes such
observable very peculiar for the study of the isovector part of the nuclear
equation of state. Within such a framework, comparisons with experiments
support the introduction of the meson in the description of the
iso-vector equation of state.Comment: 11 pages, 5 figures. Accepted for publication in Phys.Lett.
Fragment Formation in Central Heavy Ion Collisions at Relativistic Energies
We perform a systematic study of the fragmentation path of excited nuclear
matter in central heavy ion collisions at the intermediate energy of . The theoretical calculations are based on a Relativistic
Boltzmann-Uehling-Uhlenbeck () transport equation including stochastic
effects. A Relativistic Mean Field () approach is used, based on a
non-linear Lagrangian, with coupling constants tuned to reproduce the high
density results of calculations with correlations.
At variance with the case at Fermi energies, a new fast clusterization
mechanism is revealed in the early compression stage of the reaction dynamics.
Fragments appear directly produced from phase-space fluctuations due to
two-body correlations. In-medium effects of the elastic nucleon-nucleon cross
sections on the fragmentation dynamics are particularly discussed. The
subsequent evolution of the primordial clusters is treated using a simple
phenomenological phase space coalescence algorithm.
The reliability of the approach, formation and recognition, is investigated
in detail by comparing fragment momentum space distributions {\it and
simultaneously} their yields with recent experimental data of the
collaboration by varying the system size of the colliding system, i.e. its
compressional energy (pressure, radial flow). We find an excellent agreement
between theory and experiment in almost all the cases and, on the other hand,
some limitations of the simple coalescence model. Furthermore, the temporal
evolution of the fragment structure is explored with a clear evidence of an
earlier formation of the heavier clusters, that will appear as interesting
of the high density phase of the nuclear Equation of State ().Comment: 21 pages, 8 figures, Latex Elsart Style, minor corrections in p.7,
two refs. added, Nucl.Phys.A, accepte
Neutron stars with isovector scalar correlations
Neutron stars with the isovector scalar -field are studied in the
framework of the relativistic mean field () approach in a pure nucleon
plus lepton scheme. The -field leads to a larger repulsion in dense
neutron-rich matter and to a definite splitting of proton and neutron effective
masses. Both features are influencing the stability conditions of the neutron
stars. Two parametrizations for the effective nonlinear Lagrangian density are
used to calculate the nuclear equation of state () and the neutron star
properties, and compared to correlated Dirac-Brueckner results. We conclude
that in order to reproduce reasonable nuclear structure and neutron star
properties within a approach a density dependence of the coupling
constants is required.Comment: 11 pages, 5 figures, revtex4 styl
Thermodynamical description of heavy ion collisions
We analyze the thermodynamical state of nuclear matter in transport
descriptions of heavy ion reactions. We determine thermodynamical variables
from an analysis of local momentum space distributions and compare to blast
model parameters from an analysis of fragment energy spectra. These
descriptions are applied to spectator and fireball matter in semi-central and
central Au+Au collisions at SIS-energies, respectively.Comment: 4 pages, 2 postscript-figures, to be published in the proceedings of
Bologna2000: Structure of the Nucleus at the Dawn of the Century, Bologna,
Italy, 29 May - 3 Jun 200
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