Sessions - DPG-Tagungen

Nuclear Physics Tuesday
The linear sigma-model with quarks provides a valid description of
QCD on a scale below approximately 1.3 GeV. It is well suited to describe
the physics of the chiral symmetric phase at the UV scale, as well
as he physics at low energies characterized by chiral symmetry breaking.
Starting with the theory given at the UV scale, in the renormalization
group approach infinitesimal shells of large momentum modes are
integrated out and the couplings of the theory are renormalized. In this
way, an effective low energy theory is obtained by evolving the couplings
towards small momentum scales.
In order to enable a comparison with results from lattice QCD, we
consider a renormalization group treatment of the linear sigma model in
a finite Euclidean volume. The renormalization group flow equations are
derived and solved numerically. Explicit breaking of the chiral symmetry
is considered through the introduction of a finite quark mass.
We obtain results for the volume dependence of the chiral condensate.
In accordance with the results obtained from finite volume partition
functions, the mesonic zero modes are important for the evolution
of the couplings at low renormalization scales.
HK 20.4 Tue 16:45 E
RG analysis of the quark-meson model at finite temperature
and density — •Bernd-Jochen Schaefer and Jochen Wambach
— IKP, Schlossgartenstrasse 9,D-64289 Darmstadt
Renormalization group equations obtained by means of a proper-time
regulator are used in order to analyze the chiral symmetry restoration
at finite temperature and density in the two flavor quark-meson model.
Results for the Nf = 2 QCD phase diagram are presented and compared
with those coming from lattice simulations.
HK 20.5 Tue 17:00 E
Properties of two- and three-quark states in hot and dense matter
— •S. Mattiello 1 , M. Beyer 1 , S. Strauss 1 , T. Frederico 2 ,
and H.J. Weber 3 — 1 FB Physik, U Rostock, Germany — 2 CTA, Sao
Jose dos Campos, Brazil — 3 U of Virginia, Charlottesville, USA
In the framework of the light front field theory at finite temperature
and density we investigate the formation of two- and three-body bound
states in quark matter. This approach leads to the dominant medium
effects, i.e. the Pauli blocking and the self energy corrections. Utilizing
the Nambu-Jona-Lasinio model on the light front we study the chiral
restauration and the dependence of pionic properties (mass and decay
costante) on the temperature and the chemical potential. The threequark
dynamics is investigated using a scalar zero-range interaction and
the results for the dependence on the medium of the three-body mass
are presented. The dissociation of the three-quark state as well as the
critical temperature of the color-superconducting phase are investigated.
Acknowledgement: Work supported by Deutsche Forschungsgemeinschaft.
HK 20.6 Tue 17:15 E
Quasiparticle Description of Hot QCD at Finite Quark Chemical
Potential (∗) — •Michael Thaler 1 , Roland Schneider 1,2 , and
Wolfram Weise 1,2 — 1 Physik Department Technische Universität
München — 2 ECT ∗ , Villa Tambosi, Trento, Italy
We study the extension of a phenomenologically successful quasiparticle
model that describes lattice results of the equation of state of the
deconfined phase of QCD for Tc ≤ T ∼ < 4Tc, to finite quark chemical
potential µ. The phase boundary line Tc(µ), the pressure difference
∆p(T, µ) = (p(T, µ) − p(T, µ = 0))/T 4 and the quark number density
nq(T, µ)/T 3 are calculated and compared to recent lattice results. Good
agreement is found up to quark chemical potentials of order µ ∼ Tc. (∗)
Work supported in part by BMBF and GSI.
HK 20.7 Tue 17:30 E
The effect of quark off-shellness in high energy processes —
•Olena Linnyk, Stefan Leupold, and Ulrich Mosel — Institut
für Theoretische Physik, Universität Giessen, 35392 Giessen, Germany
We study the quark and gluon structure of hadrons going beyond the
well-known picture of collinear non-interacting partons. Calculated are
the effects of an initial quark off-shellness in several high energy processes.
The interaction of the partons missed in the standard perturbative consideration
is taken into account in the spectral functions of the quarks,
and using a generalized factorization. The intrinsic motion of the partons
is consistently treated as well. The quark off-shellness turns out to
be important in the description of semi-exclusive observables such as the
triple differential Drell-Yan cross section. Recent data of the Fermilab
experiment E866 on continuum dimuon production are analyzed and the
width of the quark spectral function in the proton is found to be approximately
150 MeV. The dependence of the width on the hard scale is
investigated. The results of our calculations reveal the important role of
the initial quark virtuality in high energy processes.
Work supported by the European graduate school Giessen–Copenhagen.
HK 20.8 Tue 17:45 E
Stable gapless color superconducting phases of dense quark
matter — •Igor Shovkovy — Institute for Theoretical Physics, Johann
Wolfgang Goethe University, 60325 Frankfurt am Main
I review the zero and finite temperature properties of the recently proposed
gapless color superconducting phase of neutral dense quark matter
in β-equilibrium. This is a stable phase of quark matter that could exist
inside cores of compact stars.
HK 20.9 Tue 18:00 E
ρ −ω splitting and mixing in nuclear matter — •Sven Zschocke
and Burkhard Kämpfer — Forschungszentrum Rossendorf e.V., Institut
für Kern- und Hadronenphysik, D-01314 Dresden,Postfach 51 01
19
We investigate mass splitting and mixing effect of ρ and ω mesons
in nuclear matter within the QCD sum rule approach in zero-width approximation.
In matter, ρ and ω differ only by a scalar flavour mixed
condensate and a twist-4 four-quark condensate as long as one is restricted
to dimension-6 operators. In our sum rule analysis we have
taken into account both condensates and investigate the impact of the
poorly known four-quark condensate. Both effects, mixing and splitting,
are much stronger in a nuclear medium than in vacuum. This triggers
the hope to verify this in-medium effects with experiments like HADES
at GSI.
HK 20.10 Tue 18:15 E
Suppression of high transverse momentum particles at RHIC by
(pre–)hadronic FSI — •Kai Gallmeister, Wolfgang Cassing,
and Carsten Greiner* — Institut für Theoretische Physik, Universität
Giessen, 35392 Giessen, Germany (*present address: Institut für
Theoretische Physik, Universität Frankfurt, 60054 Frankfurt am Main,
Germany)
We investigate transverse hadron spectra from proton+proton,
deuteron+Au and Au+Au collisions at √ s = 200 GeV within the
Hadron–String–Dynamics (HSD) approach which is based on quark, diquark,
string and hadronic degrees of freedom, combined with Pythia
calculations for high p⊥ spectra. The comparison to experimental data
from RHIC shows that pre–hadronic effects of the leading hadrons can
be responsible for both the hardening of the spectra for low transverse
momenta as well as the suppression of high p⊥ hadrons. The interactions
of formed, non–leading hadrons are found to be more or less negligible
for p⊥ ≥ 8 GeV/c and cannot be responsible for the large suppression
seen experimentally, but they have some importance for lower p⊥ values.
These findings are in nice agreement with the hadron attenuation
observed in virtual photon induced reactions on nuclei at HERMES, cf.
Thomas Falter’s talk.
Work supported by BMBF.