81 research outputs found
Multifragmentation - what the data tell us about the different models
We discuss what the presently collected data tell us about the mechanism of
multifragmentation by comparing the results of two different models, which
assume or show an opposite reaction scenario, with the recent high statistics
experiments performed by the INDRA collaboration. We find that the
statistical multifragmentation model and the dynamical Quantum Molecular
Dynamics approach produce almost the same results and agree both quite well
with experiment. We discuss which observables may serve to overcome this
deadlock on the quest for the reaction mechanism. Finally we proof that even if
the system is in equilibrium, the fluctuation of the temperature due to the
smallness of the system renders the caloric curve useless for the proof of a
first order phase transition.Comment: Proceedings CRIS 200
Role of the experimental filter in obtaining the Arrhenius plot in multifragmentation reactions
Recently it has been argued that the linear relation between the transverse
energy and the apparent probability to emit a fragment proves that the total
system is in thermal equilibrium. It is shown, for a specific reaction Xe+Sn at
50 A.MeV, that the same behavior is obtained in the context of Quantum
Molecular Dynamical without invoking the idea of equilibrium. The linear
dependance is shown to be a detector effect.Comment: 11 pages, 4 Postscript figures. Submitted Phys. Rev. Let
Microscopic approach to the spectator matter fragmentation from 400 to 1000 AMeV
A study of multifragmentation of gold nuclei is reported at incident energies
of 400, 600 and 1000 MeV/nucleon using microscopic theory. The present
calculations are done within the framework of quantum molecular dynamics (QMD)
model. The clusterization is performed with advanced sophisticated algorithm
namely \emph{simulated annealing clusterization algorithm} (SACA) along with
conventional spatial correlation method. A quantitative comparison of mean
multiplicity of intermediate mass fragments with experimental findings of
ALADiN group gives excellent agreement showing the ability of SACA method to
reproduce the fragment yields. It also emphasizes the importance of clustering
criterion in describing the fragmentation process within semi-classical model
Virial corrections to simulations of heavy ion reactions
Within QMD simulations we demonstrate the effect of virial corrections on heavy ion reactions. Unlike in standard codes, the binary collisions are treated as non-local so that the contribution of the collision flux to the reaction dynamics is covered. A comparison with standard QMD simulations shows that the virial corrections lead to a broader proton distribution bringing theoretical spectra closer towards experimental values. Complementary BUU simulations reveal that the non-locality enhances the collision rate in the early stage of the reaction. It suggests that the broader distribution appears due to an enhanced pre-equilibrium emission of particles
Kaon production at subthreshold and threshold energies
We summarize what we have learnt about the kaon production in nucleus-nucleus
collisions in the last decade. We will address three questions: a) Is the
production sensitive to the nuclear equation of state? b) How can it happen
that at the same excess energy the same number of and are produced
in heavy ion collisions although the elementary cross section in pp collisions
differs by orders of magnitudes? and c) Why kaons don't flow?Comment: 5 pages, 4 figures, contribution to Strange Quark Matter 200
Thermodynamics of the 3-flavor NJL model : chiral symmetry breaking and color superconductivity
Employing an extended three flavor version of the NJL model we discuss in
detail the phase diagram of quark matter. The presence of quark as well as of
diquark condensates gives raise to a rich structure of the phase diagram. We
study in detail the chiral phase transition and the color superconductivity as
well as color flavor locking as a function of the temperature and chemical
potentials of the system.Comment: 27 pages, 7 figure
A Quasi-Classical Model of Intermediate Velocity Particle Production in Asymmetric Heavy Ion Reactions
The particle emission at intermediate velocities in mass asymmetric reactions
is studied within the framework of classical molecular dynamics. Two reactions
in the Fermi energy domain were modelized, Ni+C and Ni+Au at 34.5
MeV/nucleon. The availability of microscopic correlations at all times allowed
a detailed study of the fragment formation process. Special attention was paid
to the physical origin of fragments and emission timescales, which allowed us
to disentangle the different processes involved in the mid-rapidity particle
production. Consequently, a clear distinction between a prompt pre- equilibrium
emission and a delayed aligned asymmetric breakup of the heavier partner of the
reaction was achieved.Comment: 8 pages, 7 figures. Final version: figures were redesigned, and a new
section discussing the role of Coulomb in IMF production was include
Color-Neutral Superconducting Quark Matter
We investigate the consequences of enforcing local color neutrality on the
color superconducting phases of quark matter by utilizing the
Nambu-Jona-Lasinio model supplemented by diquark and the t'Hooft six-fermion
interactions. In neutrino free matter at zero temperature, color neutrality
guarantees that the number densities of u, d, and s quarks in the
Color-Flavor-Locked (CFL) phase will be equal even with physical current quark
masses. Electric charge neutrality follows as a consequence and without the
presence of electrons. In contrast, electric charge neutrality in the less
symmetric 2-flavor superconducting (2SC) phase with ud pairing requires more
electrons than the normal quark phase. The free energy density cost of
enforcing color and electric charge neutrality in the CFL phase is lower than
that in the 2SC phase, which favors the formation of the CFL phase. With
increasing temperature and neutrino content, an unlocking transition occurs
from the CFL phase to the 2SC phase with the order of the transition depending
on the temperature, the quark and lepton number chemical potentials. The
astrophysical implications of this rich structure in the phase diagram,
including estimates of the effects from Goldstone bosons in the CFL phase, are
discussed.Comment: 20 pages, 4 figures; version to appear in Phys. Rev.
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