1,527 research outputs found
Static quark anti-quark free and internal energy in 2-flavor QCD and bound states in the QGP
We present results on heavy quark free energies in 2-flavour QCD. The
temperature dependence of the interaction between static quark anti-quark pairs
will be analyzed in terms of temperature dependent screening radii, which give
a first estimate on the medium modification of (heavy quark) bound states in
the quark gluon plasma. Comparing those radii to the (zero temperature) mean
squared charge radii of cha rmonium states indicates that the may
survive the phase transition as a bound state, while and are
expected to show significant thermal modifications at temperatures close to the
transition. Furthermore we will analyze the relation between heavy quark free
energies, entropy contributions and internal energy and discuss their relation
to potential models used to analyze the melting of heavy quark bound states
above the deconfinement temperature. Results of different groups and various
potential models for bound states in the deconfined phase of QCD are compared.Comment: 6 pages, 8 figures, Lattice 2005 (Finite temperature and density
Quark antiquark energies and the screening mass in a Quark-Gluon plasma at low and high temperatures
We discuss quark antiquark energies and the screening mass in hot QCD using
the non-perturbative lattice approach. For this purpose we analyze properties
of quark antiquark energies and entropies at infinitely large separation of the
quark antiquark pair at low and high temperatures. In the limit of high
temperatures these energies and entropies can be related perturbatively to the
temperature dependence of the Debye mass and the coupling. On the one hand our
analysis thus suggests that the quark antiquark energies at (infinite) large
distances are rather related to the Debye screening mass and the coupling than
to the temperature dependence of heavy-light meson masses. On the other hand we
find no or only little differences in all mass scales introduced by us when
changing from quenched to 2-flavor QCD at temperatures which are only
moderately above the phase transition.Comment: 5 pages, 2 figures, To appear in the proceedings of Workshop on
Extreme QCD, Swansea, Wales, 2-5 Aug 200
Short distance physics with heavy quark potentials
We present lattice studies of heavy quark potentials in the quenched
approximation of QCD at finite temperatures. Both, the color singlet and color
averaged potentials are calculated. While the potentials are well known at
large distances, we give a detailed analysis of their short distance behavior
(from 0.015 fm to 1 fm) near the critical temperature. At these distances we
expect that the T-dependent potentials go over into the zero temperature
potential. Indeed, we find evidences that the temperature influence gets
suppressed and the potentials starts to become a unique function of the
underlying distance scale. We use this feature to normalize the heavy quark
potentials at short distances and extract the free energy of the quark system
in a gluonic heat bath.Comment: Lattice2001(hightemp), 3 pages, 2 figure
Screening of heavy quark free energies at finite temperature and non-zero baryon chemical potential
We analyze the dependence of heavy quark free energies on the baryon chemical
potential (mu_b) in 2-flavour QCD using improved (p4) staggered fermions with a
bare quark mass of m/T = 0.4. By performing a 6th order Taylor expansion in the
chemical potential which circumvents the sign problem. The Taylor expansion
coefficients of colour singlet and colour averaged free energies are calculated
and from this the expansion coefficients for the corresponding screening masses
are determined. We find that for small mu_b the free energies of a static quark
anti-quark pair decrease in a medium with a net excess of quarks and that
screening is well described by a screening mass which increases with increasing
mu_b. The mu_b-dependent corrections to the screening masses are well described
by perturbation theory for T > 2 T_c. In particular, we find for all
temperatures above T_c that the expansion coefficients for singlet and colour
averaged screening masses differ by a factor 2.Comment: 14 page
Heavy quark free energies, potentials and the renormalized Polyakov loop
We discuss the renormalized free energy of a heavy quark anti-quark pair in
the color singlet channel for quenched and full QCD at finite temperature. The
temperature and mass dependence, as well as its short distance behavior is
analyzed. Using the free energies we calculate the heavy quark potential and
entropy in quenched QCD. The asymptotic large distance behavior of the free
energy is used to define the non-perturbatively renormalized Polyakov loop
which is well behaved in the continuum limit. String breaking is studied in the
color singlet channel in 2-flavor QCD.Comment: 3 pages, Lattice2003(nonzero
Renormalized quark-anti-quark free energy
We present results on the renormalized quark-anti-quark free energy in SU(3)
gauge theory at finite temperatures. We discuss results for the singlet, octet
and colour averaged free energies and comment on thermal relations which allow
to extract separately the potential energy and entropy from the free energy.Comment: 5 pages, 2 figures, To appear in the proceedings of Workshop on
Strong and Electroweak Matter (SEWM 2002), Heidelberg, Germany, 2-5 Oct 200
An new order parameter with renormalized Polyakov loops
It is well established that physical quantities like the heavy quark
potentials get temperature independent at sufficiently short distances. As a
first application of this feature we suggest a new order parameter for the
confinement/deconfinement phase transition. Our investigations are based on
recent lattice studies.Comment: 2 pages, 2 figures, contribution to 'Statistical QCD', Bielefeld,
August 26-30, 200
Heavy Quark Interactions in Finite Temperature QCD
We study the free energy of a heavy quark-antiquark pair in a thermal medium.
We constuct a simple ansatz for the free energy for two quark flavors motivated
by the Debye-H\"uckel theory of screening.Comment: 4 pages, 4 figures, contribution to the proceedings of the
International Conference on Hard and Electromagnetic Probes of High Energy
Nuclear Collisions, Ericeira, Portugal, Nov. 4-10, 200
Free energies of static three quark systems
We study the behaviour of free energies of baryonic systems composed of three
heavy quarks on the lattice in SU(3) pure gauge theory at finite temperature.
For all temperatures above we find that the connected part of the singlet
(decuplet) free energy of the three quark system is given by the sum of the
connected parts of the free energies of -triplets (-sextets). Using
renormalized free energies we can compare free energies in different colour
channels as well as those of - and -systems on an unique energy scale.Comment: 5 pages, 6 figures, Contribution to Strong and Electroweak Matter
2004 (SEWM04), Helsinki, Finland 16-19 June 200
Lattice constraints on the thermal photon rate
We estimate the photon production rate from an SU(3) plasma at temperatures
of about 1.1Tc and 1.3Tc. Lattice results for the vector current correlator at
spatial momenta k ~ (2-6)T are extrapolated to the continuum limit and analyzed
with the help of a polynomial interpolation for the corresponding spectral
function, which vanishes at zero frequency and matches to high-precision
perturbative results at large invariant masses. For small invariant masses the
interpolation is compared with the NLO weak-coupling result, hydrodynamics, and
a holographic model. At vanishing invariant mass we extract the photon rate
which for k \gsim 3T is found to be close to the NLO weak-coupling prediction.
For k \lsim 2T uncertainties remain large but the photon rate is likely to fall
below the NLO prediction, in accordance with the onset of a strongly
interacting behaviour characteristic of the hydrodynamic regime.Comment: 20 pages. v2: clarifications adde
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