975 research outputs found
D' Production in Heavy Ion Collisions
The production of d' dibaryons in heavy ion collisions due to the elementary
process NN -> d' + pion is considered. The cross section NN -> d' + pion is
estimated using the vacuum d' width = 0.5 MeV extracted from data on the double
charge exchange reactions on nuclei. The d' production rate per single
collision of heavy ions is estimated at an incident beam energy of 1 A GeV
within the framework of the Quantum Molecular Dynamics transport model. We
suggest to analyse the invariant mass spectrum of the NN + pion system in order
to search for an abundance of events with the invariant mass of the d'
dibaryon. The d' peak is found to exceed the statistical fluctuations of the
background at a level of 6 standard deviations for 2 10^5 A central collisions
of heavy ions with the atomic number A.Comment: 29 pages including 7 figures, REVTe
Pseudorapidity shape of elliptic flow as signature for fast equilibration in relativistic heavy-ion collisions at energies up to sqrt(s) = 200 GeV
The implications of parton recombination processes on the dynamics of
ultrarelativistic heavy-ion reactions are investigated. To do so, the
quark-gluon string transport model has been extended for partonic recombination
and fusion processes. Parton recombination leads to short equilibration times
and improves significantly on the theoretical description of measured directed
and elliptic flow, i.e., v_1 and v_2, distributions in Au+Au collisions at
sqrt(s) = 200 GeV, in particular what concerns their pseudorapidity dependence.
The shape of v_2(eta) is found to be closely related to fast thermalization.Comment: 7 pages (revtex4) with 4 figures, v3: substantially extended
description and discussion of the model and its results, accepted for
publication in Phys. Rev.
Testing Dirac-Brueckner models in collective flow of heavy-ion collisions
We investigate differential in-plane and out-of-plane flow observables in
heavy ion reactions at intermediate energies from AGeV within the
framework of relativistic BUU transport calculations. The mean field is based
on microscopic Dirac-Brueckner-Hartree-Fock (DBHF) calculations. We apply two
different sets of DBHF predictions, those of ter Haar and Malfliet and more
recent ones from the T\"ubingen group, which are similar in general but differ
in details. The latter DBHF calculations exclude spurious contributions from
the negative energy sector to the mean field which results in a slightly softer
equation of state and a less repulsive momentum dependence of the
nucleon-nucleus potential at high densities and high momenta. For the
application to heavy ion collisions in both cases non-equilibrium features of
the phase space are taken into account on the level of the effective
interaction. The systematic comparison to experimental data favours the less
repulsive and softer model. Relative to non-relativistic approaches one obtains
larger values of the effective nucleon mass. This produces a sufficient amount
of repulsion to describe the differential flow data reasonably well.Comment: 14 pages Revtex, 19 figures, discussion extended and two figures
added, accepted for publication in EPJ
Kaon squeeze-out in heavy ion reactions
The squeeze-out phenomenon of and mesons, i.e. the azimuthal
asymmetry of and mesons emitted at midrapidity in heavy ion
reactions, is investigated for beam energies of 1-2 A.GeV. It is found that the
squeeze-out signal is strongly affected by in-medium potentials of these
mesons. The repulsive -nucleus potential gives rise to a pronounced
out-of-plane emission of 's at midrapidity. With the potential we
reproduce well the experimental data of the azimuthal distribution. It is
found that the attractive -nucleus potential cancels to a large extent the
influence of rescattering and reabsorption of the mesons on the
projectile and target residuals (i.e. shadowing). This results in an
azimuthally isotropic emission of the midrapidity mesons with transverse
momentum up to 0.8 GeV/c. Since it is well accepted that the shadowing alone
would lead to a significant out-of-plane preference of particle emission, in
particular at high transverse momenta, the disappearance of the out-of-plane
preference for the mesons can serve as an unambiguous signal of the
attractive potential. We also apply a covariant formalism of the kaon
dynamics to the squeeze-out phenomenon. Discrepancies between the theory and
the experiments and possible solutions are discussed.Comment: 24 pages Latex using Elsevier style, 7 PS figures, accepted for
publication in Euro. Phys. Jour.
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