V. Greco

Coalescence Models for Hadron Formation from Quark-Gluon Plasma

We review hadron formation from a deconfined quark-gluon plasma (QGP) via coalescence or recombination of quarks and gluons. We discuss the abundant experimental evidence for coalescence from the Relativistic Heavy Ion Collider (RHIC) and compare the various coalescence models advocated in the literature. We comment on the underlying assumptions and remaining challenges as well as the merits of the models. We conclude with a discussion of some recent developments in the field.

Shear Viscosity of a strongly interacting system: Green-Kubo vs. Chapman-Enskog and Relaxation Time Approximation

The shear viscosity has been calculated by using the Green-Kubo relation in the framework of a partonic transport approach solved at cascade level. We compare the numerical results for obtained from the Green-Kubo correlator with the analytical formulas in both the Relaxation Time Approximation (RTA) and the Chapman-Enskog approximation (CE). We investigate and emphasize the dierences between the isotropic and anisotropic cross sections and between the massless and massive particles. We show that in the range of temperature explored in a Heavy Ion collision and for pQCD-like cross section the RTA signicantly underestimates the viscosity by about a factor of 2-3, while a good agreement is found between the CE approximation and GreeKubo relation already at rst order of approximation. The agreement with the CE approximation supplies an analytical formula that allows to develop kinetic transport theory at xed shear viscosity to entropy density ratio, =s . This open the possibility to explore dissipative non-equilibrium evolution of the distribution functions vs T-dependent =s and particle momenta in the dynamics of the Quark-Gluon Plasma created in ultra-relativistic heavy-ion collisions.

Scalings of Elliptic Flow for a Fluid at Finite Shear Viscosity

Abstract Within a parton cascade approach we investigate the scaling of the differential elliptic flow v 2 ( p T ) with eccentricity ϵ x and system size and its sensitivity to finite shear viscosity. We present calculations for shear viscosity to entropy density ratio η / s in the range from 1 / 4 π up to 1 / π , finding that the v 2 saturation value varies by about a factor 2. Scaling of v 2 ( p T ) / ϵ x is seen also for finite η / s which indicates that it does not prove a perfect hydrodynamical behavior, but is compatible with a plasma at finite η / s . Introducing a suitable freeze-out condition, we see a significant reduction of v 2 ( p T ) especially at intermediate p T and for more peripheral collisions. This causes a breaking of the scaling for both v 2 ( p T ) and the p T -averaged v 2 , while keeping the scaling of v 2 ( p T ) / 〈 v 2 〉 . This is in better agreement with the experimental observations and shows as a first indication that the η / s should be significantly lower than the pQCD estimates. We finally point out the necessity to include the hadronization via coalescence for a definite evaluation of η / s from intermediate p T data.

Phase diagrams in the hadron-Polyakov-Nambu-Jona-Lasinio model

G.Y. Shao, M. Di Toro, 2, ∗ V. Greco, 2 M. Colonna, S. Plumari, 2 B. Liu, 4 and Y.X. Liu 6 INFN-Laboratori Nazionali del Sud, Via S. Sofia 62, I-95123 Catania, Italy Physics and Astronomy Dept., University of Catania, Italy IHEP, Chinese Academy of Sciences, Beijing, 100049 China Theoretical Physics Center for Scientific Facilities, Chinese Academy of Sciences, Beijing, 100049 China Department of Physics and State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, China Center of Theoretical Nuclear Physics, National Laboratory of Heavy Ion Accelerator, Lanzhou 730000, China

Fock exchange terms in nonlinear quantum hadrodynamics

We propose a method to introduce Fock term contributions in relativistic models of fermions coupled to mesons, including self-interactions for the mesonic fields. We show that effects on equilibrium properties and on the dynamical response of the fermionic system can be consistently accounted for. Some implications on equilibrium properties of asymmetric nuclear matter are discussed. In particular an indication is emerging for a reduced contribution of charged mesons to the symmetry term of the nuclear equation of state around normal density.

Photons from the Early Stages of Relativistic Heavy Ion Collisions

We present results about photons production in relativistic heavy ion collisions. The main novelty of our study is the calculation of the contribution of the early stage photons to the photon spectrum. The initial stage is modeled by an ensemble of classical gluon fields which decay to a quark-gluon plasma via the Schwinger mechanism, and the evolution of the system is studied by coupling classical field equations to relativistic kinetic theory; photons production is then computed by including the pertinent collision processes into the collision integral. We find that the contribution of the early stage photons to the direct photon spectrum is substantial for

Collective Flows in a Transport Approach

p_T \approx 2

PROBING THE SYMMETRY ENERGY AT HIGH BARYON DENSITY WITH HEAVY ION COLLISIONS

GeV and higher, the exact value depending on the collision energy; therefore we identify this part of the photon spectrum as the sign of the early stage. Moreover, the amount of photons produced during the early stage is not negligible with respect to those produced by a thermalized quark-gluon plasma: we support the idea that there is no dark age in relativistic heavy ion collisions.

The high-density symmetry energy in heavy ion collisions

We introduce a transport approach at fixed shear viscosity to entropy ratio η/s to study the generation of collective flows in ultra-relativistic heavy-ion collisions. Transport theory supplies a covariant approach valid also at large η/s and at intermediate transverse momentum pT, where deviations from equilibrium is no longer negligible. Such an approach shows that at RHIC energies a temperature dependent η/s enhances significantly the v4/v22 respect to the case of constant η/s. Furthermore if NJL chiral dynamics is self-consistently implemented we show that it does not modify the relation between v2 and η/s.

INVESTIGATION OF LOW-DENSITY SYMMETRY ENERGY VIA NUCLEON AND FRAGMENT OBSERVABLES

The nuclear symmetry energy at densities above saturation density (ρ0 ~ 0.16fm-3) is poorly constrained theoretically and very few relevant experimental data exist. Its study is possible through Heavy Ion Collisions (HIC) at energies E/A > 200 MeV, particularly with beams of neutron-rich radioactive nuclei. The energy range implies that the momentum dependence of the isospin fields, i.e. the difference of the effective masses on protons and neutrons, also has to be investigated before a safe constraint on Esym(ρ) is possible. We discuss the several observables which have been suggested, like n/p emission and their collective flows and the ratio of meson yields with different isospin projection, π-/π+ and K0/K+. We point out several physical mechanisms that should be included in the theoretical models to allow a direct comparison to the more precise experiments which will be able to distinguish the isospin projection of the detected particles: CSR/Lanzhou, FAIR/GSI, RIBF/RIKEN, FRIB/MSU.