805 research outputs found
Heavy-Quark Probes of the Quark-Gluon Plasma at RHIC
Thermalization and collective flow of charm (c) and bottom (b) quarks in
ultra-relativistic heavy-ion collisions are evaluated based on elastic parton
rescattering in an expanding quark-gluon plasma (QGP). We show that resonant
interactions in a strongly interacting QGP (sQGP), as well as the effects of
parton coalescence, can play an essential role in the interpretation of recent
data from the Relativistic Heavy-Ion Collider (RHIC), and thus illuminate the
nature of the sQGP and its hadronization. Our main assumption, motivated by
recent findings in lattice computations of Quantum Chromodynamics, is the
existence of D- and B-meson states in the sQGP, providing resonant cross
sections for heavy quarks up to temperatures of sim 2 T_c. Pertinent drag and
diffusion coefficients are implemented into a relativistic Langevin simulation
to compute transverse-momentum spectra and azimuthal asymmetries (v_2) of b-
and c-quarks in Au-Au collisions at RHIC. Hadronization into D- and B-mesons is
calculated from a combination of coalescence with light quarks and
fragmentation, and associated electron-decay spectra and v_2 are compared to
recent RHIC data. We also comment on the relative importance of radiative and
elastic energy loss of heavy quarks in the QGP.Comment: 4 pages, 3 figures, v2: 1 reference updated, v3: replaced comparison
to data to more recent data, references added, contents unchange
Soft Modes, Resonances and Quantum Transport
Effects of the propagation of particles, which have a finite life-time 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 production and absorption of field quanta
in non-equilibrium dense matter is considered. It is shown that classical
diffusion and Langevin results correspond to re-summation of certain
field-theory diagrams formulated in terms of full non-equilibrium Green's
functions. Then the general properties of broad resonances in dense and hot
systems are discussed in the framework of a self-consistent and conserving
Phi-derivable method of Baym at the examples of the rho-meson in hadronic
matter and the pion in dilute nuclear matter. Further we address the problem of
a transport description that properly accounts for the damping width of the
particles. The Phi-derivable method generalized to the real-time contour
provides a self-consistent and conserving kinetic scheme. We derive a
generalized expression for the non-equilibrium kinetic entropy flow, which
includes corrections from fluctuations and mass-width effects. In special cases
an H-theorem is proved. Memory effects in collision terms give contributions to
the kinetic entropy flow that in the Fermi-liquid case recover the famous
bosonic type T^3 ln T correction to the specific heat of liquid Helium-3. At
the example of the pion-condensate phase transition in dense nuclear matter we
demonstrate important part played by the width effects within the quantum
transport.Comment: submitted to Phys. At. Nucl. (Rus.), the volume dedicated to the
memory of A.B. Migdal. 31 pages, 5 figure
Soft Modes, Quantum Transport and Kinetic Entropy
The effects of the propagation of particles which have a finite life-time and
an according width in their mass spectrum are discussed in the context of
transport descriptions. In the first part the coupling of soft photon modes to
a source of charged particles is studied in a classical model which can be
solved completely in analytical terms. The solution corresponds to a
re-summation of certain field theory diagrams. The general properties of broad
resonances in dense finite temperature systems are discussed at the example of
the -meson in hadronic matter. The second part addresses the problem of
transport descriptions which also account for the damping width of the
particles. The Kadanoff--Baym equation after gradient approximation together
with the -derivable method of Baym provides a self-consistent and
conserving scheme. Memory effects appearing in collision term diagrams of
higher order are discussed. We derive a generalized expression for the
nonequilibrium kinetic entropy flow, which includes corrections from
fluctuations and mass-width effects. In special cases an -theorem is proved.
Memory effects in collision terms provide contributions to the kinetic entropy
flow that in the Fermi-liquid case recover the famous bosonic type
correction to the specific heat of liquid Helium-3.Comment: Contribution to Proc. of Int. Workshop "Kadanoff-Baym Equations -
Progress and Perspectives for Many-Body Physics" Rostock (Germany), September
20-24 1999, ed. M.Bonitz, World Scientific (2000
Bottomonium Production at RHIC and LHC
Properties of bottomonia (Upsilon, chi_b and Upsilon') in the Quark-Gluon
Plasma (QGP) are investigated by assessing inelastic reaction rates and their
interplay with open-bottom states (b-quarks or B-mesons) and color-screening.
The latter leads to vanishing quarkonium binding energies at sufficiently high
temperatures (close to the dissolution point), which, in particular, renders
standard gluo-dissociation, g+Upsilon -> b + b-bar, inefficient due to a
substantial reduction in final-state phase space. This problem is overcome by
invoking a "quasifree" destruction mechanism, g,q,q-bar + Upsilon -> g,q,q-bar
+ b + b-bar, as previously introduced for charmonia. The pertinent reaction
rates are implemented into a kinetic theory framework to evaluate the time
evolution of bottomonia in heavy-ion reactions at RHIC and LHC within an
expanding fireball model. While bottom quarks are assumed to be exclusively
produced in primordial nucleon-nucleon collisions, their thermal relaxation
times in the QGP, which importantly figure into Upsilon-formation rates, are
estimated according to a recent Fokker-Planck treatment. Predictions for the
centrality dependence of Upsilon production are given for upcoming experiments
at RHIC and LHC. At both energies, Upsilon suppression turns out to be the
prevalent effect.Comment: 16 Pages, 21 figures, 1 table v2: Manuscript reorganized, several
sections moved to appendices, additional comments included, contents
unchange
Theory and Phenomenology of Heavy Flavor at RHIC
We review the problem of heavy-quark diffusion in the Quark-Gluon Plasma and
its ramifications for heavy-quark spectra in heavy-ion collisions at RHIC. In
particular, we attempt to reconcile underlying mechanisms of several seemingly
different approaches that have been put forward to explain the large
suppression and elliptic flow of non-photonic electron spectra. We also
emphasize the importance of a quantitative description of the bulk medium
evolution to extract reliable values for the heavy-quark diffusion coefficient.Comment: 8 pages latex, including 10 eps figures; plenary talk at SQM08,
Beijing (China), Oct. 06-10, 200
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