Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Wednesday
Group Report HK 23.2 Wed 11:15 A
Renormalization Group Flow in large Nc and beyond — •Kai
Schwenzer for the Rhone-Neckar-Flow collaboration — Institut fuer
Theoretische Physik, Universitaet Heidelberg, Philosophenweg 19, 69120
Heidelberg
We calculate renormalization group flow equations for the bosonized
Nambu–Jona-Lasinio model in large Nc approximation. The flow equations
decouple and can be solved analytically. The solution is equal to
a self consistent solution of the NJL model in the same approximation,
which shows that flow equations are a promising method to solve the
NJL model. Including explicit chiral symmetry breaking, the large Nc
approximation describes physics reasonably well. We further compare
the analytic solution to the usually used polynomial truncation and find
consistency. Further we also discuss the inclusion of meson loops by an
extension to higher orders in 1/Nc.
HK 23.3 Wed 11:45 A
Renormalization in Self-Consistent Approximation schemes at
Finite Temperature — •Hendrik van Hees 1 and Jörn Knoll 2 —
1 Fakultät für Physik, Universität Bielefeld, Universitätsstraße, D-33615
Bielefeld — 2 GSI Darmstadt, Theorie, Planckstraße 1, D-64291 Darmstadt
Within finite temperature field theory, we show that self-consistent
Dyson resummation schemes can be renormalized with all counter terms
defined at the vacuum level (1) provided that the underlying theory is
renormalizable and that the self-consistent scheme follows Baym’s Φderivable
concept. The scheme generates the renormalized self-consistent
equations of motion and the same time the corresponding generating
functional and the thermodynamical potential in consistency with the
equations of motion. This guarantees the standard Φ-derivable properties
like thermodynamic consistency and exact conservation laws also for
the renormalized approximation schemes to hold. First numerical applications
for the φ 4 -theory including the tadpole and the sunset self-energy
diagram are presented in order to show the practicability of the scheme
(2). The question of symmetry violations of such schemes and the concepts
to recover the symmerties (like Goldstone modes) are discussed
(3).
(1) H. van Hees and J. Knoll, Phys. Rev. D, Dec 15 2001; hepph/0107200
(2) H. van Hees and J. Knoll, Phys. Rev. D, submitted; hep-ph/0111193
(3) H. van Hees and J. Knoll, to be submitted to Phys. Rev. D.
HK 23.4 Wed 12:00 A
Evaluation of QCD sum rules for light vector mesons at finite
density and temperature — •Sven Zschocke 1 , Burkhard
Kaempfer 1 ,andOleg Pavlenko 2 — 1 Research Center Rossendorf
e.V., PF 510119, 01314 Dresden, Germany — 2 Institute for Theoretical
Physics, 252143 Kiev-143, Ukraine
The Borel QCD sum rules are evaluated at finite nucleon densities
and temperatures to determine the in–medium behaviour of the lightest
vector mesons ρ, ω and φ. The influence of the poorly known four–
quark condensate is considered. The ρ meson mass drops with increasing
density quite independent of the temperature, while the ω meson experi-
HK24 Nuclear Physics / Spectroscopy III
ences a positive or negative mass shift depending on the parametrization
of the four–quark condensate. On the contrary, the φ meson in–medium
behaviour is mainly determined by the chiral condensate of the strange
quarks and depends on the hidden strangness fraction in the nucleon.
The investigations address a density and temperature region relevant for
the starting experiments of HADES.
HK 23.5 Wed 12:15 A
Chiral Dynamics of the η ′ — •Niklas Beisert, Bugra Borasoy,
and Stefan Wetzel — Physik-Department, Technische Universität
München
We investigate chiral dynamics of the η ′ at low energies based on a
U(3) chiral Lagrangian.
As a first example, the dominant hadronic decay mode of the η ′ ,
η ′ → ηππ, is evaluated up to one-loop order. For the evaluation of loop
integrals we employ infrared regularization which makes 1/Nc counting
rules redundant. Reasonable agreement with data is obtained without
finetuning any parameters.
In the second part of the report, the spectrum of scalar resonances
is analysed by non-pertubative means. The chiral effective Lagrangian
is combined with a coupled-channel Bethe-Salpeter approach which generates
bound state poles of two pseudoscalar mesons. By taking the
next-to-leading order Lagrangian into account we observe a number of
resonances, including exotics, around 1.5 GeV, some of which can be
identified with resonances found in nature.
Work supported in part by the DFG.
HK 23.6 Wed 12:30 A
The case for a large polarized antiquark flavor asymmetry
∆ū(x) − ∆ ¯ d(x) — R.J. Fries 1 , K. Goeke 2 , M. Polyakov 2 , A.
Schäfer 1 ,and•C. Weiss 1 — 1 Institut für Theoretische Physik, Universität
Regensburg, D–93053 Regensburg, Germany — 2 Institut für
Theoretische Physik II, Ruhr–Universität Bochum, D–44780 Bochum,
Germany
The flavor asymmetry of the polarized antiquark distributions in the
proton, ∆ū(x) − ∆ ¯ d(x), is measured in semi-inclusive DISat HER-
MESand in future polarized Drell–Yan / W ± production experiments at
RHIC. Standard explanations for the origin of the antiquark flavor asymmetries
are i) the Pauli blocking effect in a constituent quark picture of
the nucleon, or ii) “meson cloud” contributions to the DISprocess. Estimates
of ∆ū(x) − ∆ ¯ d(x) from rho meson contributions have resulted in
very small values [1]. We show that a sizable polarized flavor asymmetry
is obtained in the meson cloud picture from the interference of πN and
σN contributions to the DISprocess [2]. The value of ∆ū(x) − ∆ ¯ d(x)
expected from this effect is compatible with the Pauli blocking model of
Glück and Reya [3], as well as with the prediction of the chiral quark–
soliton model based on the Nc →∞limit of QCD [4]. We comment on
the experimental consequences of a large polarized flavor asymmetry.
[1] R.J. Fries and A. Schäfer, Phys. Lett. B 443, 40 (1998)
[2]B.Dressler,K.Goeke,M.V.PolyakovandC.Weiss,Eur.Phys.J.C
14, 147 (2000)
[3]M.Glück and E. Reya, Mod. Phys. Lett. A 15, 883 (2000)
[4] D.I. Diakonov et al. Nucl. Phys. B 480, 341 (1996)
Time: Wednesday 10:45–12:45 Room: B
Group Report HK 24.1 Wed 10:45 B
Cluster Knockout from Halo Nuclei — •L.V. Chulkov for the
S174 collaboration — Gesellschaft für Schwerionenforschung, D-64291
Darmstadt, Germany — Russian Research Centre “Kurchatov Institute”,
R-123182 Moscow, Russia
Quasi-elastic scattering of a proton on a cluster inside the halo nuclei
6 He and 8 He has been studied at relativistic energies. The purpose of the
experiment is to determine the spectroscopic factor of the α-cluster in
6 He and in 8 He and the relative contribution of the 6 He ∗ +2n configuration
in the 8 He wave function. These quantities are of vital importance
for understanding the structure of halo nuclei. Additionally, the 4 He projectile
was used as a bench mark nucleus to illustrate the kinematics of
different reaction mechanisms.
The experimental setup consisted of a 600 mg/cm 2 liquid hydrogen
target, a forward spectrometer for tracking and identifying the projectile
fragments and position sensitive detectors for the detection of the recoil
protons. The direction of the fragment has been measured together
with the momentum vector of the recoil proton. The processes of valence
neutron or α-cluster knockout dominate the reaction mechanism.
These processes are well separated by the reaction kinematics through
the correlations in azimuthal and polar angles of the detected particles.
The combination of the relativistic energy beams with the comprehensive
kinematical analysis provides a direct method to determine the
structure of exotic nuclei. The experiment has no analogy with any
other radioactive beam experiments and the experimental data obtained
are unique.