Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Thursday
The effect of final state rescattering on the spin asymmetry for pion
photoproduction on the deuteron is discussed. The corresponding
Gerasimov-Drell-Hearn integrals evaluated up to 550 MeV are also
presented.
It turns out that the inclusion of final state interaction is important
and should be considered in forthcoming theoretical studies.
[1] R. Schmidt et al., Z.Phys.,A355 (1996), 421
[2]J.Haidenbaueret al., Phys.Rev.,C30 (1984), 1822
[3] S. Nozawa et al., Nucl. Phys., A513 (1990) 459
HK 37.5 Thu 15:15 A
Strong two-body decays of baryons in a covariant quark model
— •Dirk Merten, Ulrich Löring, Sascha Migura, Bernard
Metsch, andHerbert-R. Petry — Institut für Theoretische Kernphysik,
Nussallee 14-16, D-53115 Bonn, Germany
HK38 Theory VI
Strong two-body baryon decays are considered in a covariant quark
model for baryons and mesons. The model is based on the Bethe-Salpeter
equation in instantaneous approximation with a phenomenological confinement
potential and a residual interaction induced by instantons. The
parameters have been fixed to the spectra of meson and baryon resonances.
The widths of strong two-body baryon decays are then evaluated
without any additional free parameter in a formally covariant way.
Time: Thursday 14:00–15:30 Room: C
HK 38.1 Thu 14:00 C
Bottom-Antibottom and Quarkonium Hadroproduction in k⊥-
Factorization at High Energies — •Philipp Hägler 1 , Roland
Kirschner 2 , Andreas Schäfer 1 , Lech Szymanowski 3 ,andO.V.
Teryaev 4 — 1 Institut für Theoretische Physik, Universität Regensburg,
D-93040 Regensburg — 2 Institut für Theoretische Physik, Universität
Leipzig, D-04109 Leipzig — 3 Centre de Physique Theorique, Ecole Polytechnique,
91128 Palaiseau Cedex, France — 4 Bogoliubov Laboratory of
Theoretical Physics, JINR, 141980 Dubna
We have studied the hadroproduction of b ¯ b, direct χc and J/ψ in the
framework of the k⊥ factorization approach at high energies. The NLLA
BFKL q¯q-production vertex provides a gauge invariant description of the
processes and plays a central role in our considerations. The calculated b ¯ b
cross sections are significantly larger than in the collinear approach and
give a good description of the Tevatron data. Concerning Quarkonium
production we find that the color-singlet contributions are essentially
larger than in the collinear approach. For the J/ψ the color singlet contribution
is still an order of magnitude below the data. This deficit may
be well described in the framework of NRQCD by color octet contribu-
tions. The value of the color octet matrix element < 0|O J/ψ
8 ( 3 S1)|0 > is
substantially decreased in comparison with fits in the collinear factorization.
This should lead to a reduction of the large transverse polarization,
predicted in the collinear approach.
HK 38.2 Thu 14:15 C
Confinement in the Chromodielectric Model — •Gunnar
Martens, Carsten Greiner, Stefan Leupold, and Ulrich
Mosel — Institut für Theoretische Physik, Universität Gießen,
Germany
The phenomenon of confinement is an open problem and not understood
from first principles. The chromodielectric model [1,2] describes it
as the consequence of the interaction between color electromagnetic fields
and the vacuum having dielectric properties. The vacuum is described
via a scalar field with selfinteraction designed to separate perturbative
from nonperturbative spatial regions. We investigate static properties of
meson and baryon type configurations. For the mesons, we find the linear
rising string potential and reproduce the string tension found in heavy
quark meson spectroscopy. For the three quark system we study the field
configuration to distinguish between the ∆ and the Y type models of the
baryon.
Work supported by BMBF.
[1] R. Friedberg, T.D. Lee; Phys.Rev. D 15 (1977) 1694
[2] C.T. Traxler, U. Mosel, T.S. Biro; Phys.Rev. C 59 (1999) 1620
HK 38.3 Thu 14:30 C
The Spectrum of the Dirac Operator in the linear sigma model
with Quarks — •Thomas Spitzenberg 1 , kai Schwenzer 2 , and
hans juergen pirner 2 for the Chiral dynamics Mainz Heidelberg
collaboration — 1 institut fuer kernphysik, uni-mainz, johann-joachim
becher weg 45, 55099 mainz, germany — 2 institut fuer theoretische
physik, uni heidelberg, phil. weg 19,69120 Heidelberg, germany
The QCD Dirac operator spectrum in the large NC approximation is
derived using renormalization group flow equations. The spectrum is
presented beyond the usual low energy regime.
HK 38.4 Thu 14:45 C
Photoproduction of φ mesons off nuclei — •Pascal Mühlich,
Thomas Falter, Carsten Greiner, Jürgen Lehr, Marcus Post,
and Ulrich Mosel — Institut für Theoretische Physik, Universität
Gießen, Germany
We investigate the consequences of possible medium modifications of
the φ mesoninnuclearmatteronφ photoproduction off nuclei. Various
models predict both a mass-shift and/or a in-medium broadening of the
φ meson at finite nuclear matter density [1][2]. In principle, photoproduction
provides a clean method to learn about the in-medium properties
of the φ meson. Our purpose is to check the feasability of a proposed
experiment [3], in which one tries to observe the φ properties through the
K + K − -invariant mass spectrum, restricting the momentum of the φ to
small values. In our calculation, we use the BUU transport model, which
allows for a detailed analysis of the final state interactions both of the φ
and the kaons. Due to these effects, we find only a small sensitivity of
the K + K − -invariant mass distribution on the in-medium properties of
the φ.
Work supported by DFG and BMBF.
[1] G. E. Brown, M. Rho, PRL 66 (1991), 2720.
[2] E. Oset, A. Ramos, NPA 679 (2001), 616.
[3] T. Nakano et al., NPA 684 (2001), 71.
HK 38.5 Thu 15:00 C
Chiral Dynamics and Nuclear Matter — •Stefan Fritsch 1 , Norbert
Kaiser 1 ,andWolfram Weise 2,1 — 1 Physik Department der
Technischen Universität München, Garching, Germany — 2 ECT*, Villazzano
(Trento), Italy
We calculate the equation of state of isospin-symmetric nuclear matter
in the three-loop approximation of chiral perturbation theory. The
contributions to the energy per particle Ē(kf) from one- and two-pion
exchange diagrams are ordered in powers of the Fermi-momentum kf
) two-pion exchange
(modulo functions of kf/mπ). Already at order O(k4 f
produces realistic nuclear binding. Without inclusion of any further
short-range terms the empirical saturation point and nuclear compressibility
K � 250 MeV are well reproduced at order O(k5 f) with a momentum
cut-off of Λ � 0.65 GeV. In the same framework we calculate the
density-dependent asymmetry energy, reproducing its empirical value of
A0 � 34 MeV. We also evaluate the momentum and density dependent
single particle potential of nucleons in isospin-symmetric nuclear matter.
The contributions from one- and two-pion exchange diagrams give
rise to a potential depth for a nucleon at rest of U(0,kf0) =−53.2MeV
at saturation density. The momentum dependence of the single particle
potential can be translated into a mean effective nucleon mass of
¯M ∗ � 0.8M. Finally, we extend our scheme to small non-zero temperatures
and observe the liquid–gas phase transition of nuclear matter at
Tc � 26 MeV and ρc � 0.5ρ0.
Work supported in part by BMBF, GSI and DFG.