Hydrodynamic modeling of deconfinement phase transition in heavy-ion collisions at NICA-FAIR energies

We use (3+1) dimensional ideal hydrodynamics to describe the space-time evolution of strongly interacting matter created in Au+Au and Pb+Pb collisions. The model is applied for the domain of bombarding energies 1-160 AGeV which includes future NICA and FAIR experiments. Two equations of state are used: the first one corresponding to resonance hadron gas and the second one including the deconfinement phase transition. The initial state is represented by two Lorentz-boosted nuclei. Dynamical trajectories of matter in the central box of the system are analyzed. They can be well represented by a fast shock-wave compression followed by a relatively slow isentropic expansion. The parameters of collective flows and hadronic spectra are calculated under assumption of the isochronous freeze-out. It is shown that the deconfinement phase transition leads to broadening of proton rapidity distributions, increase of elliptic flows and formation of the directed antiflow in the central rapidity region. These effects are most pronounced at bombarding energies around 10 AGeV, when the system spends the longest time in the mixed phase. From the comparison with three-fluid calculations we conclude that the transparency effects are not so important in central collisions at NICA-FAIR energies (below 30 AGeV).Comment: 38 pages, 28 figure

Simultaneous Heavy Ion Dissociation at Ultrarelativistic Energies

We study the simultaneous dissociation of heavy ultrarelativistic nuclei followed by the forward-backward neutron emission in peripheral collisions at colliders. The main contribution to this particular heavy-ion dissociation process, which can be used as a beam luminosity monitor, is expected to be due to the electromagnetic interaction. The Weizsacker-Williams method is extended to the case of simultaneous excitation of collision partners which is simulated by the RELDIS code. A contribution to the dissociation cross section due to grazing nuclear interactions is estimated within the abrasion model and found to be relatively small.Comment: Talk given at Bologna 2000 Conference - Structure of the Nucleus at the Dawn of the Century, May 29 - June 3, 2000, 4 pages, 2 figure

Nuclear multifragmentation induced by electromagnetic fields of ultrarelativistic heavy ions

We study the disintegration of nuclei by strong electromagnetic fields induced by ultrarelativistic heavy ions. The proposed multi-step model includes 1) the absorption of a virtual photon by a nucleus, 2) intranuclear cascades of produced hadrons and 3) statistical decay of the excited residual nucleus. The combined model describes well existing data on projectile fragmentation at energy 200 GeV per nucleon. Electromagnetic multifragmentation of nuclei is predicted to be an important reaction mechanism at RHIC and LHC energies.Comment: 18 LaTeX pages including 4 figures, uses epsf.sty. Submitted to Phys.Rev.

Chiral Fluid Dynamics and Collapse of Vacuum Bubbles

We study the expansion dynamics of a quark-antiquark plasma droplet from an initial state with restored chiral symmetry. The calculations are made within the linear $\sigma$ model scaled with an additional scalar field representing the gluon condensate. We solve numerically the classical equations of motion for the meson fields coupled to the fluid-dynamical equations for the plasma. Strong space-time oscillations of the meson fields are observed in the course of the chiral transition. A new phenomenon, the formation and collapse of vacuum bubbles, is also predicted. The particle production due to the bremsstrahlung of the meson fields is estimated.Comment: 12 pages Revtex,5 figures, Figures modified, minor changes in text. To be published in Phys. Rev. Let

Chiral Phase Transition within Effective Models with Constituent Quarks

We investigate the chiral phase transition at nonzero temperature $T$ and baryon-chemical potential $\mu_B$ within the framework of the linear sigma model and the Nambu-Jona-Lasinio model. For small bare quark masses we find in both models a smooth crossover transition for nonzero $T$ and $\mu_B=0$ and a first order transition for T=0 and nonzero $\mu_B$. We calculate explicitly the first order phase transition line and spinodal lines in the $(T,\mu_B)$ plane. As expected they all end in a critical point. We find that, in the linear sigma model, the sigma mass goes to zero at the critical point. This is in contrast to the NJL model, where the sigma mass, as defined in the random phase approximation, does not vanish. We also compute the adiabatic lines in the $(T,\mu_B)$ plane. Within the models studied here, the critical point does not serve as a ``focusing'' point in the adiabatic expansion.Comment: 22 pages, 18 figure

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.

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

(3+1)-Dimensional Hydrodynamic Expansion with a Critical Point from Realistic Initial Conditions

We investigate a (3+1)-dimensional hydrodynamic expansion of the hot and dense system created in head-on collisions of Pb+Pb/Au+Au at beam energies from $5-200A$ GeV. An equation of state that incorporates a critical end point (CEP) in line with the lattice data is used. The necessary initial conditions for the hydrodynamic evolution are taken from a microscopic transport approach (UrQMD). We compare the properties of the initial state and the full hydrodynamical calculation with an isentropic expansion employing an initial state from a simple overlap model. We find that the specific entropy ($S/A$) from both initial conditions is very similar and only depends on the underlying equation of state. Using the chiral (hadronic) equation of state we investigate the expansion paths for both initial conditions. Defining a critical area around the critical point, we show at what beam energies one can expect to have a sizable fraction of the system close to the critical point. Finally, we emphasise the importance of the equation of state of strongly interacting matter, in the (experimental) search for the CEP.Comment: 8 pages, 8 figure

Strange quark matter within the Nambu-Jona-Lasinio model

Equation of state of baryon rich quark matter is studied within the SU(3) Nambu-Jona-Lasinio model with flavour mixing interaction. Possible bound states (strangelets) and chiral phase transitions in this matter are investigated at various values of strangeness fraction S/3B. The model predictions are very sensitive to the ratio of vector (Gv) and scalar (Gs) coupling constants. At Gv/Gs=0.5 and zero temperature the maximum binding energy (about 15 MeV per baryon) takes place when strangeness fraction is about 0.4. Such strangelets are negatively charged and have typical life times of the order of 100 ns. Calculations are carried out also at finite temperatures. They show that bound states exist up to temperatures of about 15 MeV. The model predicts a first order chiral phase transition at finite baryon densities. The parameters of this phase transition are calculated as function of strangeness fraction.Comment: 29 pages, 10 figures, to be published in Physics of Atomic Nuclei, the memorial volume devoted to the 90th birthday of A.B. Migda

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