H. van Hees

Nonperturbative heavy-quark diffusion in the quark-gluon plasma.

We evaluate heavy-quark (HQ) transport properties in a quark-gluon plasma (QGP) within a Brueckner many-body scheme employing interaction potentials extracted from thermal lattice QCD. The in-medium T matrices for elastic charm- and bottom-quark scattering off light quarks in the QGP are dominated by attractive meson and diquark channels which support resonance states up to temperatures of ~1.5T(c). The resulting drag coefficient increases with decreasing temperature, contrary to expectations based on perturbative QCD scattering. Employing relativistic Langevin simulations we compute HQ spectra and elliptic flow in sqrt[s(NN)]=200 GeV Au-Au collisions. A good agreement with electron decay data supports our nonperturbative computation of HQ diffusion, indicative for a strongly coupled QGP.

Resonance recombination model and quark distribution functions in the quark-gluon plasma

We investigate the consequences of space-momentum correlations in quark phase-space distributions for coalescence processes at the hadronization transition. Thus far it has been proved difficult to reconcile such correlations with the empirically observed constituent quark number scaling (CQNS) at the Relativistic Heavy Ion Collider (RHIC). To address this problem we combine our earlier developed quark recombination model with quark phase-space distributions computed from relativistic Langevin simulations in an expanding quark-gluon plasma(QGP).HadronizationisbasedonresonanceformationwithinaBoltzmannequationthatrecoversthermal equilibrium and obeys energy conservation in the quark-coalescence process, while the fireball background is adjusted to hydrodynamic simulations of semicentral Au-Au collisions at RHIC. To facilitate the applicability of the Langevin process, we focus on strange and charm quarks. Their interactions in the QGP are modeled using leading-order perturbative QCD augmented by effective Lagrangians with resonances that smoothly merge into hadronic states formed at Tc. The interaction strength is adjusted to reproduce the empirical saturation value for the quark-elliptic flow, v sat 2,q � 7‐8%. The resulting φ and J/ ψelliptic flow recover CQNS over a large range in transverse momentum (pT) within a few percent. As a function of transverse kinetic energy, both the quark spectra from the Langevin simulations and the meson spectra generated via resonance recombination recover CQNS from zero to at least 3 GeV.

Renormalization of a gapless Hartree-Fock approximation to a theory with spontaneously broken O ( N ) symmetry

The renormalization of a gapless {phi}-derivable Hartree-Fock approximation to the O(N)-symmetric {lambda}{phi}{sup 4} theory is considered in the spontaneously broken phase. This kind of approach was proposed by three of us in a previous paper [Yu. B. Ivanov, F. Riek, and J. Knoll, Phys. Rev. D 71, 105016 (2005).] in order to preserve all the desirable features of {phi}-derivable Dyson-Schwinger resummation schemes (i.e., validity of conservation laws and thermodynamic consistency) while simultaneously restoring the Nambu-Goldstone theorem in the broken phase. It is shown that unlike for the conventional Hartree-Fock approximation this approach allows for a scale-independent renormalization in the vacuum. However, the scale dependence still persists at finite temperatures. Various branches of the solution are studied. The occurrence of a limiting temperature inherent in the renormalized Hartree-Fock approximation at fixed renormalization scale {mu} is discussed.

Soft Modes, Resonances and Quantum Transport ∗

Effects of the propagation of particles that have a finite lifetime and an according width in their mass spectrum are discussed in the context of transport description. First, the importance of coherence effects (Landau-Pomeranchuk-Migdal effect) on the production and absorption of field quanta in nonequilibrium dense matter is considered. It is shown that classical diffusion and Langevin results correspond to a resummation of certain field-theory diagrams formulated in terms of full nonequilibrium Greens functions. General properties of broad resonances in dense and hot systems are discussed in the framework of a self-consistent and conserving Φ-derivable method of Baym by considering the examples of the ρ meson in hadronic matter and the pion in dilute nuclear matter. Further, we address the problem of a transport description that properly takes into account the damping width of the particles. The Φ-derivable method generalized to the real-time contour provides a selfconsistent and conserving kinetic scheme. We derive a generalized expression for the nonequilibrium kinetic entropy flow, which includes corrections from fluctuations and mass-width effects. In special cases, an H theorem is proven. Memory effects in collision terms contribute to the kinetic entropy flow that, in the Fermi liquid case, reproduces the famous bosonic-type T3lnT correction to the specific heat of liquid 3He. For the example of the pion-condensate phase transition in dense nuclear matter, we demonstrate the important role of the width effects within the quantum transport.

Properties of thermal photons at RHIC and LHC

Abstract We study the emission characteristics of thermal photons at RHIC and LHC as affected by both the space–time evolution of the bulk medium and the thermal emission rates. For the former we compare the results of two evolution models (expanding fireball and hydrodynamics). For the latter, we detail the influence of hadronic emission components and study a speculative scenario by upscaling the default QGP and hadronic rates around the pseudo-critical region.

In-Medium Excitations

1 Introduction 2 Electromagnetic probes and light vector mesons 3 Hadronic resonance spectroscopy 4 Strangeness 5 Open charm probes 6 Charmonium 7 Excitations of color-superconducting matter 8 Summary and relations to observables

Heavy-Quark Spectra at RHIC and Resonances in the QGP

Thermalization and collective flow of charm ( c ) and bottom ( b ) quarks are evaluated from elastic parton scattering via “ D ”- and “ B ”-meson resonances in an expanding, strongly interacting quark-gluon plasma at RHIC. Pertinent drag and diffusion coefficients are implemented into a relativistic Langevin simulation to compute transverse-momentum spectra and azimuthal flow asymmetries ( v 2 ) of c - and b -quarks. Upon hadronization (including coalescence and fragmentation) and semileptonic D - and B -decays, the resulting electron spectra ( R A A and v 2 ) are compared to recent RHIC data.

Dynamics of the Chiral Phase Transition

The intention of this study is the search for signatures of the chiral phase transition in heavy-ion collisions. To investigate the impact of fluctuations, e.g., of the baryon number, at the transition or at a critical point, the linear sigma model is treated in a dynamical (3+1)-dimensional numerical simulation. Chiral fields are approximated as classical mean fields, and quarks are described as quasi particles in a Vlasov equation. Additional dynamics is implemented by quark-quark and quark-sigma-field interactions. For a consistent description of field-particle interactions, a new Monte-Carlo-Langevin-like formalism has been developed and is discussed.

Novel heavy flavour suppression mechanisms in the QGP

We revisit the question of the measured, unexpectedly large, heavy flavour suppression, RAA(pT) 1, in nucleus?nucleus collisions at RHIC and compare two new theoretical approaches to the D- and B-meson quenching. In the first model, radiative energy loss, collisional energy loss and heavy quark?resonance interactions are combined to evaluate the drag and diffusion coefficients in the quark?gluon plasma and the mixed phase. These are applied in a relativistic Fokker?Planck equation to simulate the heavy c- and b-quark suppression rate and elliptic flow v2(pT). In the second model, the fragmentation probability for heavy quarks and the medium-induced decay probability for heavy hadrons are derived. These are implemented in a set of coupled rate equations that describe the attenuation of the observable spectra from the collisional dissociation of heavy mesons in the QGP. An improved description of the non-photonic electron RAA(pT) at RHIC can be obtained. In contrast to previous results, the latter approach predicts suppression of B-mesons comparable to that of D-mesons at transverse momenta as low as pT ~ 10 GeV.

Heavy quark dynamics in the QGP

We assess transport properties of heavy quarks in the Quark-Gluon Plasma (QGP) that show a strong non-perturbative behavior. A T-matrix approach based on a potential taken from lattice QCD hints at the presence of heavy-quark (HQ) resonant scattering with an increasing strength as the temperature, T, reaches the critical temperature, Tc ⋍ 170 MeV for deconfinement from above. The implementation of HQ resonance scattering along with a hadronization via quark coalescence under the conditions of the plasma created in heavy-ion collisions has been shown to correctly describe both the nuclear modification factor, RAA, and the elliptic flow, ν2, of single electrons at RHIC and have correctly predicted the RAA of D mesons at LHC energy.