Using the large acceptance apparatus FOPI, we study pion emission in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 96Ru+96Ru (0.4, 1.0, 1.5), ...96Zr+96Zr (0.4, 1.0, 1.5), 197Au+197Au (0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include longitudinal and transverse rapidity distributions and stopping, polar anisotropies, pion multiplicities, transverse momentum spectra, ratios (π+/π−) of average transverse momenta and of yields, directed flow, elliptic flow. The data are compared to earlier data where possible and to transport model simulations.
Phys. Rev. C 93, 054609 (2016) With the semiclassical Landau-Vlasov transport model we studied the stopping
observable $R_E$, the energy-based isotropy ratio, for the
$^{129}$Xe\,+\,$^{120}$Sn ...reaction at beam energies spanning 12$A$ to 100$A$
MeV. We investigated the impacts of the nonlocality of the nuclear mean field,
of the in-medium modified nucleon-nucleon ($NN$) cross section and of the
reaction centrality. A fixed set of model parameters yields $R_E$ values that
favorably compare with the experimental ones, but only for energies below the
Fermi energy $E_F$. Above $E_F$ agreement is readily possible, but by a smooth
evolution with energy of the parameter that controls the in-medium modification
of $NN$ cross section. By comparing the simulation correction factor ${\cal F}$
applied to the free $NN$ cross section with the one deduced from experimental
data Phys.\ Rev.\ C\,{\bf 90}, 064602 (2014), we infer that the zero-range
mean field almost entirely reproduces it. Also, in accordance with what has
been deduced from experimental data, around $E_F$ a strong reduction of the
free $NN$ cross section is found. In order to test the impact of sampling
central collisions by multiplicity an event generator (HIPSE) was used. We
obtain that high multiplicity events are spread over a broad impact parameter
range, but it turns out that this has a small effect on the observable $R_E$
and, thus, on ${\cal F}$ as well.
ASY-EOS experiment at GSI Russotto, P.; Acosta, L.; Adamczyk, M. ...
EPJ Web of conferences,
01/2012, Volume:
31
Journal Article
Peer reviewed
Open access
The elliptic-flow ratio of neutrons with respect to protons in reactions of neutron rich Heavy-Ion at intermediate energies has been recently proposed as an observable sensitive to the strength of ...the symmetry term in the nuclear equation of state (EOS) at supra-saturation densities. The recent results obtained from the existing FOPI/LAND data for 197Au+197Au collisions at 400 MeV/nucleon in comparison with the UrQMD model allowed a first estimate of the symmetry term of the EOS but suffer from a considerable statistical uncertainty. In order to obtain an improved data set for Au+Au collisions and to extend the study to other systems, a new experiment was carried out at the GSI laboratory by the ASY-EOS collaboration in May 2011.
We present the centrality dependence of the proton rapidity distribution in isospin symmetric nuclear collisions with
A = 96. We also present the methods to test the degree of nuclear stopping power ...by using isospin asymmetric nuclear collisions. The results consistently demonstrate incomplete mixing and partial transparency of the projectile and target nuclei at SIS energies.
We present transverse momentum and rapidity spectra of charged pions in central Ru+Ru collisions at 400A and 1528A MeV. The data exhibit enhanced production at low transverse momenta compared to ...expectations from a thermal model that includes the decay of {delta}(1232) resonances and thermal pions. Modifications of the {delta} spectral function and the Coulomb interaction are necessary to describe the detailed shape of the transverse momentum spectra. Within the framework of the thermal model, the freeze-out radii of pions are similar at both beam energies. The isospin quantum molecular dynamics model reproduces the shapes of the transverse momentum and rapidity spectra of pions, but the predicted absolute yields are larger than in the measurements, especially at lower beam energy.
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