Inertia effects in the mass transport of heavy ion reactions

The general trend of the multi differential cross section plots for the products obtained from the dissipation collisions of the three systems, forming almost the same composite systems but with different degrees of mass asymmetry in the entrance channel,⁵²Cr (261 MeV)+⁵⁶Fe,⁴⁰Ca (182 MeV)+⁶⁴Ni and¹⁶O (187 MeV)+⁹²Mo, were analysed in the frame of the Diffusion Model, assuming that the intermediate system decays with a statistical life time. A fairly good agreement has been obtained between the calculated multi differential plots and the experimental ones. The half life time of the composite systems seem to depend on the mass asymmetry of the entrance channel.     

Mass transport and energy equilibration in heavy ion collisions

The lack of mass drift observed in Kr-induced collisions is explained assuming energy and particle transfer from the light to the heavy fragment during the equilibration stage in asymmetric heavy-ion reactions. Transferred energy and particle number can be estimated from the interfragment thermal equilibrium distribution provided the initial partition is known which we calculate within a semiclassical theory based on TDHF. The experimental findings are consistent with the theoretical predictions. In particular, the experimental mass drift as function of total kinetic energy loss is quantitatively described within a modified diffusion model which takes into account the mass exchange prior to the transport stage.     

Low mass dilepton production in relativistic heavy ion collisions

Mechanisms of formation for low mass dilepton excess observed in the relativistic heavy ion collisions are considered. The experimental data are reviewed. In addition to discussing the standard mechanisms of dilepton production specific to the collisions of relativistic nuclei (the pion annihilation in the hadron-gas stage and the quark-antiquark annihilation in the quark-gluon phase), the mechanism of dilepton production in the mixed phase of nuclear matter is proposed, and its contribution to the low mass dilepton spectrum is estimated. In addition, the first-order corrections in the strong-interaction coupling constant to the dilepton production in the parton medium and the nonperturbative approaches are considered.     

Partonic effects in heavy ion collisions at RHIC

Effects of partonic interactions in heavy ion collisions at RHIC are studied in a multiphase transport model (AMPT) that includes both initial partonic and final hadronic interactions. It is found that a large parton scattering cross section is needed to understand the measured elliptic flow of pions and two-pion correlation function.     

Multicomponent transport theoretical approach to ultrarelativistic heavy ion collisions

A new theoretical model is introduced which is able to describe the initial compression and thermalization stage of an ultrarelativistic heavy-ion collision in a hydrodynamical three-flow picture. The first and second fluid is attributed to the nucleons of target and projectile, while a third component is introduced in order to take into account the gradual thermalization of the incoming flow. Based on relativistic transport theory, hydrodynamic equations of motion are derived for each component including transitions of target and projectile nucleons to the thermalized matter component as well as mutual deceleration accompanied with gradual heat transfer between the components. Hence, the multicomponent formalism contains the former two fluid approach as a limiting case.     

Energy equilibration and anomalous mass drift in heavy ion collisions

The lack of mass drift towards symmetry observed in many Kr-induced reactions, and the excessive mass drift towards larger asymmetry in Ne, Ar-induced reactions, is explained in terms of a dynamical driving force towards larger mass asymmetries due to the attempt of the smaller fragment to contain its temperature gradient with respect to the heavy fragment.     

Equilibrium in heavy ion collisions

We discuss the question of equilibration in heavy ion collisions and how it can be addressed in experiment     

Femtoscopy in heavy ion collisions

Non-trivial space-time geometrical effects are at the core of bulk-sector heavy ion physics, and two-particle correlations at low relative velocity are the most direct probe of this geometry at the femtometer scale. I present a brief overview of the wealth of femtoscopic measurements from the past two decades of heavy ion experiments. Essentially every conceivable “knob” at our disposal has been turned; the response of two-particle correlations to these variations has revealed much about the space-momentum substructure of the hot source created in the collisions. I discuss the present status of the femtoscopic program and questions which remain, and point to new efforts which aim to resolve them. PACS 25.75.Ld; 25.75.Gz; 24.10.Nz     

Nucleon tunnelling model of mass diffusion in deep inelastic heavy ion collisions

We derive a simple expression for the mass diffusion coefficient in deep inelastic collisions, based on a proximity formulation of nucleon tunnelling. The predicted value of the coefficient is consistent with empirical data. The mass diffusion coefficient has a negligible dependence on excitation energy in the physically interesting domain.     

Kaon flow in heavy ion collisions

Using transport models that include explicitly the kaon degree of freedom, we have studied kaon flow, i.e., the average kaon transverse momentum as a function of rapidity, and the associated flow parameter in heavy ion collisions at both SIS and AGS energies. It is found that the pattern of kaon flow in heavy ion collisions is sensitive to the kaon potential used in the model and thus provides a useful means for studying the kaon properties in nuclear medium.     

Event-by-event fluctuations in heavy ion collisions

We discuss the physics underlying event-by-event fluctuations in relativistic heavy ion collision. We will emphasize how the fluctuations of particle ratios can be utilzed to explore the properties of the matter created in these collisions. In particular we will argue that the fluctutions of the ratio of positively over negatively charged particles may serve as a unique signature for the Quark-Gluon Plasma.     

Nuclear flow in heavy ion collisions

Short overview of the flow phenomenon from the low upto relativistic heavy ion energies is given. Strict difference between spectator and participant flow is emphased. The latter is described by the modification of the nuclear blast model. Thermal source expanding in a plane perpendicular to the line connecting the centers of projectile and target is assumed. Observed dependences of squeeze-out, side-splash and of mean transverse-energy in relativistic heavy-ion collisions on the particle's mass are reproduced. Partioning of initial projectile energy into thermal and compressional parts in²⁰⁹Bi(1 GeV/u)+²⁰⁸Pb and¹⁹⁷Au(150–800 MeV/u)+¹⁹⁷Au collisions is discussed.Invited lecture given at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.Experimental data obtained at Bi+Pb collisions [6] are the result of the group effort. The contribution of V. Wagner, M. Pachr, Yu. G. Sobolev, R. Simon, S. Hlava, M. umbera as well as of my student R. Pleska, who carried out most of the fits, is gratefully acknowledged. This work was supported by the Granting Agency of the Czech Republic under contract No. 202/93/1144. A.K. gratefully acknowledges support from EC during his stay at KVI Groningen, where part of this work was done.     

Hadron chemistry in heavy ion collisions

The relaxation times necessary to establish chemical equilibrium among different hadrons in hot, dense hadronic matter are investigated in a statistical model. Consequences for heavy ion collisions are exploited in the framework of a simple reaction model. The possibility of Bose-Einstein pion condensation around the break-up time of the nuclear fireball is pointed out.     

Collective phenomena in heavy ion collisions

Collective flow from ultra-relativistic heavy ion collisions is an important hadronic observable sensitive to the early stages of system evolution. We have calculated flow components from a tilted, ellipsoidally expanding source. We also reviewed the recent experimental techniques used for calculation of the v _nFourier coefficients and pointed out a few possible problems connected to these techniques, which may lead to serious inaccuracy in the flow analysis.     

Pion condensation in heavy ion collisions

We calculate the pion spectrum in dense nuclear matter for finite temperatures. The critical temperatureT _c(ρ) that marks the beginning of a second order phase transition due to pion condensation is given in a phase diagram. We show that in heavy ion collisions, pion condensation should occur, leading to an enhancement in the formation of nuclear shock waves.     

Testing the chiral magnetic and chiral vortical effects in heavy ion collisions

We devise a test of the chiral magnetic and chiral vortical effects (CME and CVE) in relativistic heavy ion collisions that relies only on the general properties of triangle anomalies. We show that the ratio R(EB) = J(E)/J(B) of charge J(E) and baryon J(B) currents for CME is R(EB)(CME) → ∞ for three light flavors of quarks (N(f) = 3), and R(EB)(CME) = 5 for N(f) = 2, whereas for CVE it is R(EB)(CVE) = 0 for N(f) = 3 and R(EB)(CME) = 1/2 for N(f) = 2. The physical world with light u,d quarks and a heavier s quark is in between the N(f) = 2 and N(f) = 3 cases; therefore, the ratios R(EB) for CME and CVE should differ by over an order of magnitude providing a possibility to separate clearly the CME and CVE contributions. In both cases, there has to be a positive correlation between the charge and baryon number asymmetries that can be tested on the event-by-event basis.     

Charmed exotics in heavy ion collisions

Based on the color–spin interaction in diquarks, we argue that charmed multiquark hadrons are likely to exist. Because of the appreciable number of charm quarks produced in central nucleus–nucleus collisions at ultrarelativistic energies, the production of charmed multiquark hadrons is expected to be enhanced in these collisions. Using both the quark coalescence model and the statistical hadronization model, we estimate the yield of charmed tetraquark mesons, T_cc, and pentaquark baryons, Θ_cs, in heavy ion collisions at RHIC and LHC. We further discuss the decay modes of these charmed exotic hadrons in order to facilitate their detections in experiments. PACS 25.75.Dw; 14.20.Lq; 14.40.Lb     

Jet reconstruction in heavy ion collisions

We examine the problem of jet reconstruction at heavy-ion colliders using jet-area-based background subtraction tools as provided by FastJet. We use Monte Carlo simulations with and without quenching to study the performance of several jet algorithms, including the option of filtering, under conditions corresponding to RHIC and LHC collisions. We find that most standard algorithms perform well, though the anti-k _t and filtered Cambridge/Aachen algorithms have clear advantages in terms of the reconstructed p _t offset and dispersion.     

Strangeness in relativistic heavy ion collisions

Abundances of strange antibaryons formed in nuclear collisions at above 10 GeV/A are considered as a most accessible diagnostic tool for the study of the possible formation and physical properties of the quark-gluon plasma phase of hadronic matter. In this report we describe the current status and develop a dynamical approach in order to describe strange particle formation in nuclear collisions at high energy.