363 research outputs found
Towards a model-independent constraint of the high-density dependence of the symmetry energy
Neutron-proton elliptic flow difference and ratio have been shown to be
promising observables in the attempt to constrain the density dependence of the
symmetry energy above the saturation point from heavy-ion collision data. Their
dependence on model parameters like microscopic nucleon-nucleon cross-sections,
compressibility of nuclear matter, optical potential, and symmetry energy
parametrization is thoroughly studied. By using a parametrization of the
symmetry energy derived from the momentum dependent Gogny force in conjunction
with the T\"{u}bingen QMD model and comparing with the experimental FOPI/LAND
data for 197Au+197Au collisions at 400 MeV/nucleon, a moderately stiff, x=-1.35
+/- 1.25, symmetry energy is extracted, a result that agrees with that of a
similar study that employed the UrQMD transport model and a momentum
independent power-law parametrization of the symmetry energy. This contrasts
with diverging results extracted from the FOPI ratio
available in the literature.Comment: 18 pages, 3 figures, accepted for publication in Phys. Rev.
Probing the nuclear symmetry energy at high densities with nuclear reactions
The nuclear equation of state is a topic of highest current interest in nuclear structure and reactions as well as in astrophysics. The symmetry energy is the part of the equation of state which is connected to the asymmetry in the neutron/proton content. During recent years a multitude of experimental and theoretical eïŹorts on diïŹerent ïŹelds have been undertaken to constraint its density dependence at low densities but also above saturation density (Ï0 =0 .16fmâ3). Conventionally the symmetry energy is described by its magnitude Sv and the slope parameter L, both at saturation density. Values of L = 44â66MeV and Sv = 31â 33MeV have been deduced in recent compilations of nuclear structure, heavy-ion reaction and astrophysics data. Apart from astrophysical data on mass and radii of neutron stars, heavy-ion reactions at incident energies of several 100MeV are the only means do access the high density behaviour of the symmetry energy. In particular, meson production and collective ïŹows upto about 1 AGeV are predicted to be sensitive to the slope of the symmetry energy as a function of density. From the measurement of elliptic ïŹow of neutrons with respect to charged particles at GSI, a more stringent constraint for the slope of the symmetry energy at supra-saturation densities has been deduced. Future options to reach even higher densities will be discussed
Flow probe of symmetry energy in relativistic heavy-ion reactions
Flow observables in heavy-ion reactions at incident energies up to about 1
GeV per nucleon have been shown to be very useful for investigating the
reaction dynamics and for determining the parameters of reaction models based
on transport theory. In particular, the elliptic flow in collisions of
neutron-rich heavy-ion systems emerges as an observable sensitive to the
strength of the symmetry energy at supra-saturation densities. The comparison
of ratios or differences of neutron and proton flows or neutron and hydrogen
flows with predictions of transport models favors an approximately linear
density dependence, consistent with ab-initio nuclear-matter theories.
Extensive parameter searches have shown that the model dependence is comparable
to the uncertainties of existing experimental data. Comprehensive new flow data
of high accuracy, partly also through providing stronger constraints on model
parameters, can thus be expected to improve our knowledge of the equation of
state of asymmetric nuclear matter.Comment: 20 pages, 24 figures, review to appear in EPJA special volume on
nuclear symmetry energ
Clusters and Hypernuclei Production within PHQM+FRIGA Model
We present a new results on the dynamical modelling of cluster formation with the new combined PHQMD+FRIGA model at Nuclotron and NICA energies. The FRIGA clusterisation algorithm, which can be applied to the n-body transport approaches, is based on the simulated annealing technique to obtain the most bound configuration of fragments and nucleons. The PHQMD+FRIGA model is able to predict isotope yields as well as hyper-nucleus production
FRIGA, A New Approach To Identify Isotopes and Hypernuclei In N-Body Transport Models
We present a new algorithm to identify fragments in computer simulations of
relativistic heavy ion collisions. It is based on the simulated annealing
technique and can be applied to n-body transport models like the Quantum
Molecular Dynamics. This new approach is able to predict isotope yields as well
as hyper-nucleus production. In order to illustrate its predicting power, we
confront this new method to experimental data, and show the sensitivity on the
parameters which govern the cluster formation
Probing resonance matter with virtual photons
In the energy domain of 1-2 GeV per nucleon, HADES has measured rare
penetrating probes (e+e-) in C+C, Ar+KCl, d+p, p+p and p+Nb collisions. For the
first time the electron pairs were reconstructed from quasi-free n+p
sub-reactions by detecting the proton spectator from the deuteron breakup. An
experimentally constrained NN reference spectrum was established. Our results
demonstrate that the gross features of di-electron spectra in C+C collisions
can be explained as a superposition of independent NN collisions. On the other
hand, a direct comparison of the NN reference spectrum with the e+e- invariant
mass distribution measured in the heavier system Ar+KCl at 1.76 GeV/u shows an
excess yield above the reference, which we attribute to radiation from
resonance matter. Moreover, the combined measurement of di-electrons and
strangeness in Ar+KCl collisions has provided further intriguing results which
are also discussed.Comment: 10 pages, 3 figures, proceedings of the International Nuclear Physics
Conference - INPC 2010, Vancouver, Canada, July 4 - 9 201
- âŠ