71 research outputs found
Clusters of matter and antimatter
In this talk I first give a short overview of antinuclei production in recent
experiments at RHIC. Then I discuss the possibility of producing new types of
nuclear systems by implanting an antibaryon into ordinary nuclei. The structure
of nuclei containing one antiproton or antilambda is investigated within the
framework of a relativistic mean-field model. Self-consistent calculations
predict an enhanced binding and considerable compression in such systems as
compared with normal nuclei. I present arguments that the life time of such
nuclei with respect to the antibaryon annihilation might be long enough for
their observation. Few experimental signatures are suggested. Possible
formation of multi-quark-antiquark clusters is also discussed.Comment: 9 pages, 6 eps figures, invited talk at the VIII International
Conference on Nucleus-Nucleus Collisions (Moscow, 17-21 June 2003
Entropy puzzle in small exploding systems
We use a simple hard-core gas model to study the dynamics of small exploding
systems. The system is initially prepared in a thermalized state in a spherical
container and then allowed to expand freely into the vacuum. We follow the
expansion dynamics by recording the coordinates and velocities of all particles
until their last collision points (freeze-out). We have found that the entropy
per particle calculated for the ensemble of freeze-out points is very close to
the initial value. This is in apparent contradiction with the Joule experiment
in which the entropy grows when the gas expands irreversibly into a larger
volume.Comment: 10 pages, 4 figures, accepted June 17 2003 for publication in Physics
Letters
Enhanced binding and cold compression of nuclei due to admixture of antibaryons
We discuss the possibility of producing a new kind of nuclear system by
putting a few antibaryons inside ordinary nuclei. The structure of such systems
is calculated within the relativistic mean--field model assuming that the
nucleon and antinucleon potentials are related by the G-parity transformation.
The presence of antinucleons leads to decreasing vector potential and
increasing scalar potential for the nucleons. As a result, a strongly bound
system of high density is formed. Due to the significant reduction of the
available phase space the annihilation probability might be strongly suppressed
in such systems.Comment: 10 pages, 3 figures, to be submitted to Phys. Lett.
Constraints on possible phase transitions above the nuclear saturation density
We compare different models for hadronic and quark phases of cold baryon-rich
matter in an attempt to find a deconfinement phase transition between them. For
the hadronic phase we consider Walecka-type mean-field models which describe
well the nuclear saturation properties. We also use the variational chain model
which takes into account correlation effects. For the quark phase we consider
the MIT bag model, the Nambu-Jona-Lasinio and the massive quasiparticle models.
By comparing pressure as a function of baryon chemical potential we find that
crossings of hadronic and quark branches are possible only in some exceptional
cases while for most realistic parameter sets these branches do not cross at
all. Moreover, the chiral phase transition, often discussed within the
framework of QCD motivated models, lies in the region where the quark phases
are unstable with respect to the hadronic phase. We discuss possible physical
consequences of these findings.Comment: 28 pages, 18 PostScript figures, submitted to Phys. Rev.
Nuclear liquid-gas phase transition within the lattice gas model
We study the nuclear liquid-gas phase transition on the basis of a
two-component lattice gas model. A Metropolis type of sampling method is used
to generate microscopic states in the canonical ensemble. The effective
equation of state and fragment mass distributions are evaluated in a wide range
of temperatures and densities. A definition of the phase coexistence region
appropriate for mesoscopic systems is proposed. The caloric curve resulting
from different types of freeze-out conditions are presented.Comment: 13 pages including 4 figure
Unusual bound states of quark matter within the NJL model
Properties of dense quark matter in and out of chemical equilibrium are
studied within the SU(3) Nambu-Jona-Lasinio model. In addition to the 4-fermion
scalar and vector terms the model includes also the 6-fermion flavour mixing
interaction. First we study a novel form of deconfined matter, meso-matter,
which is composed of equal number of quarks and antiquarks. It can be thought
of as a strongly compressed meson gas where mesons are melted into their
elementary constituents, quarks and antiquarks. Strongly bound states in this
quark-antiquark matter are predicted for all flavour combinations of
quark-antiquark pairs. The maximum binding energy reaches up to 180 MeV per
pair for mixtures with about 70% of strange quark-antiquark pairs. Equilibrated
baryon-rich quark matter with various flavour compositions is also studied. In
this case only shallow bound states appear in systems with a significant
admixture (about 40%) of strange quarks (strangelets). Their binding energies
are quite sensitive to the relative strengths of scalar and vector
interactions. The common property of all these bound states is that they appear
at high particle densities when the chiral symmetry is nearly restored. Thermal
properties of meso-matter as well as chemically equilibrated strange quark
matter are also investigated. Possible decay modes of these bound states are
discussed.Comment: 26 pages, 16 PostScript figures, RevTe
Antiflow of Nucleons at the Softest Point of the EoS
We investigate flow in semi-peripheral nuclear collisions at AGS and SPS
energies within macroscopic as well as microscopic transport models. The hot
and dense zone assumes the shape of an ellipsoid which is tilted by an angle
Theta with respect to the beam axis. If matter is close to the softest point of
the equation of state, this ellipsoid expands predominantly orthogonal to the
direction given by Theta. This antiflow component is responsible for the
previously predicted reduction of the directed transverse momentum around the
softest point of the equation of state.Comment: 13 pages LaTeX, 8 PS figures. Higher-quality PS versions of figures 3
and 4 available at
http://www.th.physik.uni-frankfurt.de/~brachman/afl3f/afl3f.htm
Statistical Multifragmentation in Thermodynamic Limit
An exact analytical solution of the statistical multifragmentation model is
found in thermodynamic limit. The model exhibits a 1-st order phase transition
of the liquid-gas type. The mixed phase region of the phase diagram, where the
gas of nuclear fragments coexists with the infinite liquid condensate, is
unambiguously identified. The peculiar thermodynamic properties of the model
near the boundary between the mixed phase and the pure gaseous phase are
studied. The results for the caloric curve and specific heat are presented and
a physical picture of the nuclear liquid-gas phase transition is clarified.Comment: 4 figure
Formation of hot heavy nuclei in supernova explosions
We point out that during the supernova II type explosion the thermodynamical
condition of stellar matter between the protoneutron star and the shock front
corresponds to the nuclear liquid-gas phase coexistence region, which can be
investigated in nuclear multifragmentation reactions. We have demonstrated,
that neutron-rich hot heavy nuclei can be produced in this region. The
production of these nuclei may influence dynamics of the explosion and
contribute to the synthesis of heavy elements.Comment: 6 pages with 4 figure
Dynamical generation of the constituent mass in expanding plasma
We investigate dynamics of the chiral transition in expanding quark-antiquark
plasma produced in an ultra-relativistic heavy ion collision. The chiral
symmetry break-down and dynamical generation of the constituent quark mass are
studied within the linear sigma model and Nambu-Jona-Lasinio model. Time
dependence of the quark and antiquark densities is obtained from the scaling
solution of the relativistic Vlasov equation. Fast initial growth and strong
oscillations of the constituent quark mass are found in the linear sigma model
as well as in the NJL model, when derivative terms are taken into account.Comment: 7 pages, Latex. To appear in Physics Letters
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