Fluid dynamical description of relativistic nuclear collisions

On the basis of both a conventional relativistic nuclear fluid dynamic model and a two fluid generalization that takes into account the interpenetration of the target and projectile upon contact, collisions between heavy nuclei moving at relativistic speeds are calculated. This is done by solving the relevant equations of motion numerically in three spatial dimensions by use of particle in cell finite difference computing techniques. The effect of incorporating a density isomer, or quasistable state, in the nuclear equation of state at three times normal nuclear density, and the effect of doubling the nuclear compressibility coefficient are studied. For the reaction 20Ne + 238U at a laboratory bombarding energy per nucleon of 393 MeV, the calculated distributions in energy and angle of outgoing charged particles are compared with recent experimental data both integrated over all impact parameters and for nearly central collisions

Possible production of exotic baryonia in relativistic heavy-ion collisions

Properties of a hypothetical baryonium with the quark content (uds\ov{u}\ov{d}\ov{s}) are discussed. The MIT bag model predicts its mass to be unexpectedly low, approximately 1210 MeV. Possible hadronic decay modes of this state are analyzed. Ultrarelativistic heavy-ion collisions provide favorable conditions for the formation of such particles from the baryon-free quark-gluon plasma. We estimate multiplicities of such exotic baryonia on the basis of a simple thermal model.Comment: 8 pages, 1 figur

The Linear Correlation Coefficient vs. the Cross Term in Bose-Einstein Correlations

We investigate the nature of the new cross term for Gaussian parameterizations of Bose-Einstein correlations of identical particles emitted from purely chaotic hadron sources formed by relativistic heavy ion collisions. We find that this additional parameter in the so-called Bertsch parameterization can be expressed in terms of a linear ``out-longitudinal'' correlation coefficient for emission of bosons and two already known ``radius'' parameters, $R_l$ and $R_o$. The linear correlation coefficient is of kinematical nature and can be used to determine the widths of longitudinal momentum distributions.Comment: 4 pages, without inclusion of the 3 figures. For PostScript file of the manuscript including the three figures goto http://t2.lanl.gov/schlei/eprint.htm

Chiral dynamics in the gamma p --> pi^0 eta p and gamma p --> pi^0 K^0 Sigma^+ reactions

Using a chiral unitary approach for meson-baryon scattering in the strangeness zero sector, where the $N^*(1535)$ resonance is dynamically generated, we study the reactions $\gamma p \to \pi^0 \eta p$ and $\gamma p \to \pi^0 K^0 \Sigma^+$ at photon energies at which the final states are produced close to threshold. Among several reaction mechanisms, we find the most important is the excitation of the $\Delta^*(1700)$ state which subsequently decays into a pseudoscalar meson and a baryon belonging to the $\Delta(1232)$ decuplet. Hence, the reaction provides useful information with which to test current theories of the dynamical generation of the low-lying $3/2^-$ states. The first reaction is shown to lead to sizable cross sections and the $N^*(1535)$ resonance shape is seen clearly in the $\eta p$ invariant mass distribution. The same dynamical model is shown to lead to much smaller cross sections at low energies in the second reaction. Predictions are made for cross sections and invariant mass distributions which can be compared with forthcoming experiments at ELSA.Comment: 22 pages, 22 figure

The source of elliptic flow and initial conditions for hydrodynamical calculations

A model for energy, pressure and flow velocity distributions at the beginning of relativistic heavy ion collisions is presented, which can be used as initial condition for hydrodynamical calculations. The results show that QGP forms a tilted disk, such that the direction of the largest pressure gradient stays in the reaction plane, but deviates from both the beam and the usual transverse flow directions. Such initial condition may lead to the creation of "antiflow" or "third flow component".Comment: Talk given at the New Trends in High-Energy Physics, Yalta (Crimea), Ukraine, May 27 - June 4, 2000. 8 pages, 2 figures. The misprint t_0 instead of x_0 has been corrected in several place

Multi Module Model for Ultra-Relativistic Heavy Ion Collisions

The Multi Module Model for Ultra-Relativistic Heavy Ion Collisions at RHIC and LHC energies is presented. It uses the Effective String Rope Model for the calculation of the initial stages of the reaction; the output of this model is used as the initial state for the subsequent one-fluid calculations. It is shown that such an initial state leads to the creation of the third flow component. The hydrodynamical evolution of the energy density distribution is also presented.Comment: Talk given at the New Trend in High-Energy Physics, Yalta, Crimea, Ukraine, September 22-29, 2001. To be published in the Proceedings. 8 pages, 2 figures The Fig. 2 has been update