5,142 research outputs found
Non-perturbative Approach to Equation of State and Collective Modes of the QGP
We discuss a non-perturbative -matrix approach to investigate the
microscopic structure of the quark-gluon plasma (QGP). Utilizing an effective
Hamiltonian which includes both light- and heavy-parton degrees of freedoms.
The basic two-body interaction includes color-Coulomb and confining
contributions in all available color channels, and is constrained by
lattice-QCD data for the heavy-quark free energy. The in-medium -matrices
and parton spectral functions are computed selfconsistently with full account
of off-shell properties encoded in large scattering widths. We apply the
-matrices to calculate the equation of state (EoS) for the QGP, including a
ladder resummation of the Luttinger-Ward functional using a matrix-log
technique to account for the dynamical formation of bound states. It turns out
that the latter become the dominant degrees of freedom in the EoS at low QGP
temperatures indicating a transition from parton to hadron degrees of freedom.
The calculated spectral properties of one- and two-body states confirm this
picture, where large parton scattering rates dissolve the parton quasiparticle
structures while broad resonances start to form as the pseudocritical
temperature is approached from above. Further calculations of transport
coefficients reveal a small viscosity and heavy-quark diffusion coefficient.Comment: 10 pages, 8 figures, proceedings of XLVII International Symposium on
Multiparticle Dynamics (ISMD2017
The Influence of Reaction Rates on the Final p-Abundances
The astrophysical p-process is responsible for the origin of the proton rich
nuclei,which are heavier than iron. A huge network involving thousands of
reaction rates is necessary to calculate the final p-abundances. But not all
rates included in the network have a strong influence on the p-nuclei
abundances. The p-process was investigated using a full nuclear reaction
network for a type II supernovae explosion when the shock front passes through
the O/Ne layer. Calculations were done with a multi-layer model adopting the
seed of a pre-explosion evolution of a 25 mass star. In extensive simulations
we investigated the impact of single reaction rates on the final p-abundances.
The results are important for the strategy of future experiments in this field.Comment: 4 page
Quark Recombination and Heavy Quark Diffusion in Hot Nuclear Matter
We discuss resonance recombination for quarks and show that it is compatible
with quark and hadron distributions in local thermal equilibrium. We then
calculate realistic heavy quark phase space distributions in heavy ion
collisions using Langevin simulations with non-perturbative T-matrix
interactions in hydrodynamic backgrounds. We hadronize the heavy quarks on the
critical hypersurface given by hydrodynamics after constructing a criterion for
the relative recombination and fragmentation contributions. We discuss the
influence of recombination and flow on the resulting heavy meson and single
electron R_AA and elliptic flow. We will also comment on the effect of
diffusion of open heavy flavor mesons in the hadronic phase.Comment: Contribution to Quark Matter 2011, submitted to J.Phys.G; 4 pages, 5
figure
Quarkonia and Heavy-Quark Relaxation Times in the Quark-Gluon Plasma
A thermodynamic T-matrix approach for elastic 2-body interactions is employed
to calculate spectral functions of open and hidden heavy-quark systems in the
Quark-Gluon Plasma. This enables the evaluation of quarkonium bound-state
properties and heavy-quark diffusion on a common basis and thus to obtain
mutual constraints. The two-body interaction kernel is approximated within a
potential picture for spacelike momentum transfers. An effective
field-theoretical model combining color-Coulomb and confining terms is
implemented with relativistic corrections and for different color channels.
Four pertinent model parameters, characterizing the coupling strengths and
screening, are adjusted to reproduce the color-average heavy-quark free energy
as computed in thermal lattice QCD. The approach is tested against vacuum
spectroscopy in the open (D, B) and hidden (Psi and Upsilon) flavor sectors, as
well as in the high-energy limit of elastic perturbative QCD scattering.
Theoretical uncertainties in the static reduction scheme of the 4-dimensional
Bethe-Salpeter equation are elucidated. The quarkonium spectral functions are
used to calculate Euclidean correlators which are discussed in light of lattice
QCD results, while heavy-quark relaxation rates and diffusion coefficients are
extracted utilizing a Fokker-Planck equation.Comment: 33 pages, 28 figure
Medium Effects in rho-Meson Photoproduction
We compute dilepton invariant mass spectra from the decays of rho mesons
produced by photon reactions off nuclei. Our calculations employ a realistic
model for the rho photoproduction amplitude on the nucleon which provides fair
agreement with measured cross sections. Medium effects are implemented via an
earlier constructed rho propagator based on hadronic many-body theory. At
incoming photon energies of 1.5 -3 GeV as used by the CLAS experiment at JLAB,
the average density probed for iron targets is estimated at about half
saturation density. At the pertinent rho-meson 3-momenta the predicted medium
effects on the rho propagator are rather moderate. The resulting dilepton
spectra approximately agree with recent CLAS data.Comment: One numerical error corrected, conclusions unchange
Medium Modifications of Charm and Charmonium in High-Energy Heavy-Ion Collisions
The production of charmonia in heavy-ion collisions is investigated within a
kinetic theory framework simultaneously accounting for dissociation and
regeneration processes in both quark-gluon plasma (QGP) and hadron-gas phases
of the reaction. In-medium modifications of open-charm states (c-quarks,
D-mesons) and the survival of J/psi mesons in the QGP are included as inferred
from lattice QCD. Pertinent consequences on equilibrium charmonium abundances
are evaluated and found to be especially relevant to explain the measured
centrality dependence of the psi'/psi ratio at SPS. Predictions for recent
In-In experiments, as well as comparisons to current Au-Au data from RHIC, are
provided.Comment: 4 Latex pages including 4 eps figures and IOP style files. Talk given
at the 17th International Conference on Ultra-Relativistic Nucleus-Nucleus
Collisions, Quark Matter 2004, Oakland, CA USA, 11-17 Jan 2004. To appear in
J. Phys.
Interpretation of Recent SPS Dilepton Data
We summarize our current theoretical understanding of in-medium properties of
the electromagnetic current correlator in view of recent dimuon data from the
NA60 experiment in In(158 AGeV)-In collisions at the CERN-SPS. We discuss the
sensitivity of the results to space-time evolution models for the hot and dense
partonic and hadronic medium created in relativistic heavy-ion collisions and
the contributions from different sources to the dilepton-excess spectra.Comment: To appear in the proceedings of the 19th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2006) v2:
references added, minor typos correcte
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