871 research outputs found
Thermalization of Heavy Quarks in the Quark-Gluon Plasma
Charm- and bottom-quark rescattering in a Quark-Gluon Plasma (QGP) is
investigated with the objective of assessing the approach towards
thermalization. Employing a Fokker-Planck equation to approximate the collision
integral of the Boltzmann equation we augment earlier studies based on
perturbative parton cross sections by introducing resonant heavy-light quark
interactions. The latter are motivated by recent QCD lattice calculations which
indicate the presence of "hadronic" states in the QGP. We model these states by
colorless (pseudo-) scalar and (axial-) vector D- and B-mesons within a
heavy-quark effective theory framework. We find that the presence of these
states at moderate QGP temperatures substantially accelerates the kinetic
equilibration of c-quarks as compared to using perturbative interactions. We
also comment on consequences for -meson observables in ultra-relativistic
heavy-ion collisions.Comment: 14 pages, 5 figures, v2: Added references, v2: Added further
references, some typos correcte
Thermal Electromagnetic Radiation in Heavy-Ion Collisions
We review the potential of precise measurements of electromagnetic probes in
relativistic heavy-ion collisions for the theoretical understanding of strongly
interacting matter. The penetrating nature of photons and dileptons implies
that they can carry undistorted information about the hot and dense regions of
the fireballs formed in these reactions and thus provide a unique opportunity
to measure the electromagnetic spectral function of QCD matter as a function of
both invariant mass and momentum. In particular we report on recent progress on
how the medium modifications of the (dominant) isovector part of the vector
current correlator ( channel) can shed light on the mechanism of chiral
symmetry restoration in the hot and/or dense environment. In addition, thermal
dilepton radiation enables novel access to (a) the fireball lifetime through
the dilepton yield in the low invariant-mass window , and (b) the early temperatures of the fireball
through the slope of the invariant-mass spectrum in the intermediate-mass
region (). The investigation of
the pertinent excitation function suggests that the beam energies provided by
the NICA and FAIR projects are in a promising range for a potential discovery
of the onset of a first order phase transition, as signaled by a non-monotonous
behavior of both low-mass yields and temperature slopes.Comment: 5 pages, 4 figures; contribution to the NICA White Paper (EPJA
topical issue
Electromagnetic emission from hot medium measured by the PHENIX experiment at RHIC
Electromagnetic radiation has been of interest in heavy ion collisions
because they shed light on early stages of the collisions where hadronic probes
do not provide direct information since hadronization and hadronic interactions
occur later. The latest results on photon measurement from the PHENIX
experiment at RHIC reflect thermodynamic properties of the matter produced in
the heavy ion collisions. An unexpectedly large positive elliptic flow measured
for direct photons can not be explained by any of the current models.Comment: Talk contributed to Rutherford Centennial Conference, Aug 8-12, 2011,
held in Manchester, U
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