7 research outputs found
Role of the Coulomb interaction in the flow and the azimuthal distribution of kaons from heavy ion reactions
Coulomb final-state interaction of positive charged kaons in heavy ion
reactions and its impact on the kaon transverse flow and the kaon azimuthal
distribution are investigated within the framework of QMD (Quantum Molecular
Dynamics) model. The Coulomb interaction is found to tend to draw the flow of
kaons away from that of nucleons and lead to a more isotropic azimuthal
distribution of kaons in the target rapidity region. The recent FOPI data have
been analyzed by taking into accout both the Coulomb interaction and a kaon
in-medium potential of the strong interaction. It is found that both the
calculated kaon flows with only the Coulomb interaction and with both the
Coulomb interaction and the strong potential agree within the error bars with
the data. The kaon azimuthal distribution exhibits asymmetries of similar
magnitude in both theoretical approaches. This means, the inclusion of the
Coulomb potential makes it more difficult to extract information of the kaon
mean field potential in nuclear matter from the kaon flow and azimuthal
distribution data.Comment: 14 pages Latex, 4 PS-file
Spin polarised nuclear matter and its application to neutron stars
An equation of state(EOS) of nuclear matter with explicit inclusion of a
spin-isospin dependent force is constructed from a finite range, momentum and
density dependent effective interaction. This EOS is found to be in good
agreement with those obtained from more sophisticated models for unpolarised
nuclear matter. Introducing spin degrees of freedom, it is found that at
density about 2.5 times the density of normal nuclear matter the neutron matter
undergoes a ferromagnetic transition. The maximum mass and the radius of the
neutron star agree favourably with the observations. Since finding quark matter
rather than spin polarised nuclear matter at the core of neutron stars is more
probable, the proposed EOS is also applied to the study of hybrid stars. It is
found using the bag model picture that one can in principle describe both the
mass and size as well as the surface magnetic field of hybrid stars
satisfactorily.Comment: 26 pages, 11 figures available on reques
Dilepton production in heavy ion collisions at intermediate energies
We present a unified description of the vector meson and dilepton production
in elementary and in heavy ion reactions. The production of vector mesons
() is described via the excitation of nuclear resonances ().
The theoretical framework is an extended vector meson dominance model (eVMD).
The treatment of the resonance decays with arbitrary spin is
covariant and kinematically complete. The eVMD includes thereby excited vector
meson states in the transition form factors. This ensures correct asymptotics
and provides a unified description of photonic and mesonic decays. The
resonance model is successfully applied to the production in
reactions. The same model is applied to the dilepton production in elementary
reactions (). Corresponding data are well reproduced. However, when
the model is applied to heavy ion reactions in the BEVALAC/SIS energy range the
experimental dilepton spectra measured by the DLS Collaboration are
significantly underestimated at small invariant masses. As a possible solution
of this problem the destruction of quantum interference in a dense medium is
discussed. A decoherent emission through vector mesons decays enhances the
corresponding dilepton yield in heavy ion reactions. In the vicinity of the
-peak the reproduction of the data requires further a substantial
collisional broadening of the and in particular of the meson.Comment: 32 pages revtex, 19 figures, to appear in PR