Mott dissociation of D-mesons at the chiral phase transition and anomalous J/Psi suppression

We investigate the in-medium modification of the charmonium breakup processes due to the Mott-effect for D-mesons at the chiral phase transition. A model calculation for the process J/Psi+pi --> D+D^*+ h.c. is presented which demonstrates that threshold effects in the thermal averaged breakup cross section can be explained as a Mott transition where final state quark-antiquark bound states enter the continuum of resonant states at the QCD phase transition. Applications to heavy-ion collisions within a modified Glauber model scenario and the phenomenon of anomalous J/$\psi$ suppression in the CERN NA50 experiment are addressed.Comment: 5 pages, 4 figures, uses JHEP.cls styl

Pseudorapidity shape of elliptic flow as signature for fast equilibration in relativistic heavy-ion collisions at energies up to sqrt(s) = 200 GeV

The implications of parton recombination processes on the dynamics of ultrarelativistic heavy-ion reactions are investigated. To do so, the quark-gluon string transport model has been extended for partonic recombination and fusion processes. Parton recombination leads to short equilibration times and improves significantly on the theoretical description of measured directed and elliptic flow, i.e., v_1 and v_2, distributions in Au+Au collisions at sqrt(s) = 200 GeV, in particular what concerns their pseudorapidity dependence. The shape of v_2(eta) is found to be closely related to fast thermalization.Comment: 7 pages (revtex4) with 4 figures, v3: substantially extended description and discussion of the model and its results, accepted for publication in Phys. Rev.

Chiral quark model with infrared cut-off for the description of meson properties in hot matter

A simple chiral quark model of the Nambu--Jona-Lasinio (NJL) type with a quark confinement mechanism is constructed for the description of the light meson sector of QCD at finite temperature. Unphysical quark production thresholds in the NJL model are excluded by an infrared cut-off in the momentum integration within quark loop diagrams. This chiral quark model satisfies the low energy theorems. Using the vacuum masses and decay widths of \pi- and \rho-mesons for fixing the model parameters, the properties of the \sigma- meson are derived. Within the Matsubara formalism, the model is systematically extended to finite temperatures where chiral symmetry restoration due to a dropping constituent quark mass entails a vanishing of the infrared cut-off (deconfinement) at the pion Mott temperature T_c=186 MeV. Besides of the pion mass and weak decay constant, the masses, coupling constants and decay widths of \sigma- and \rho-mesons in hot matter are investigated. The quark-antiquark decay channel of the light mesons is opened for T>T_c only and becomes particularly strong for the \rho- meson. The two-pion decay channel below T_c has almost constant width for the \rho- meson up to T_c, but for the \sigma-meson it closes below T_c such that a scalar meson state with vanishing width is obtained as a precursor of the chiral/deconfinement transition.Comment: Latex file, 23 pages, 7 figure

Mott Effect and J/Psi Dissociation at the Quark-Hadron Phase Transition

We investigate the in-medium modification of pseudoscalar and vector mesons in a QCD motivated chiral quark model by solving the Dyson-Schwinger equations for quarks and mesons at finite temperature for a wide mass range of meson masses, from light (pi, rho) to open-charm (D, D*) states. At the chiral / deconfinement phase transition, the quark-antiquark bound states enter the continuum of unbound states and become broad resonances (the hadronic Mott effect). We calculate the in-medium cross sections for charmonium dissociation due to collisions with light hadrons in a chiral Lagrangian approach, and show that the D and D* meson spectral broadening lowers the threshold for charmonium dissociation by pi and rho meson impact. This leads to a step-like enhancement in the reaction rate. We suggest that this mechanism for enhanced charmonium dissociation may be the physical mechanism underlying the anomalous J/Psi suppression observed by NA50.Comment: 3 pages, 3 figures, uses EPJ style (included), contribution to the Proceedings of the International Conference on Quark Nuclear Physics, June 9 - 14, 2002, Juelich, Germany; 1 figure added, text adde

Hadronic Spectral Function and Charm Meson Production

At the chiral restoration/deconfinement transition, most hadrons undergo a Mott transition from being bound states in the confined phase to resonances in the deconfined phase. We investigate the consequences of this qualitative change in the hadron spectrum on final state interactions of charmonium in hot and dense matter, and show that the Mott effect for D-mesons leads to a critical enhancement of the J/Psi dissociation rate. Anomalous J/Psi suppression in the NA50 experiment is discussed as well as the role of the Mott effect for the heavy flavor kinetics in future experiments at the LHC. The status of our calculations of hadron-hadron cross sections using the quark interchange and chiral Lagrangian approaches is reviewed, and an Ansatz for a unification of these schemes is given.Comment: 12 pages, 6 figures, Proceedings of the Budapest'02 Workshop on Quark & Hadron Dynamics, Budapest, Hungary, March 3-7, 200

Workshops Quark Matter in Astro- and Particle Physics & Dynamical Aspects of the QCD Phase Transition

These proceedings contain research results presented during the Workshops "Quark Matter in Astro- and Particle Physics" held at the University of Rostock, November 27-29, 2000 and "Dynamical Aspects of the QCD Phase Transition" held at the ECT* in Trento, March 12-15, 2001