Monday, March 11, 2002 - DPG-Tagungen

Nuclear Physics Tuesday
HK 9.24 Tue 10:30 Foyer Chemie
Quark Loop Calculations of Electroweak Meson Observables in
a Covariant Bethe–Salpeter Model — •Matthias Koll, Ralf
Ricken, Bernard Metsch, andVladimir Hellmann — Institut
für Theoretische Kernphysik, Nußallee 14-16, D–53115 Bonn, Germany
We present recent theoretical results concerning electroweak processes
such as γγ decays of π 0 ,η,η ′ mesons, the so–called π2ℓγ/K2ℓγ decays
or scattering reactions like γπ → γπ and related processes. The basis
of our calculations is a relativistic quark model based on the instantanteous
Bethe–Salpeter equation; as quark–antiquark interactions, we
adopt a linearly rising confinement potential with a suitably chosen spinorial
structure plus a residual force induced by ’t Hooft’s instantons.
First, we present the results for the light meson spectrum where we
ultimately fix the few parameters of our model. We then discuss certain
decays of pseudoscalar mesons into non–hadronic final states and compare
the results with experimental data as well as with other theoretical
calculations. Finally, we study the relevance of pure quark box contributions
to processes like γγ → ππ or Compton scattering off pseudoscalar
mesons at low energies and present our lowest order results concerning
specific scattering reactions.
HK 9.25 Tue 10:30 Foyer Chemie
Coulomb effect in hard-photon proton-proton bremsstrahlung
— •R.G.E. Timmermans and T.D. Penninga — Theory group,
KVI, University of Groningen, Zernikelaan 25, 9747 AA Groningen, The
Netherlands
We study proton-proton bremsstrahlung near the end point of the photon
spectrum. The Coulomb interaction is treated exactly and highquality
pp potential models are used. The effect of the Coulomb force is
shown to be dramatic. Implications for experiment are discussed.
HK 9.26 Tue 10:30 Foyer Chemie
Final State Interaction Effects in Incoherent Photoproduction
of π-Mesons on the Deuteron — •Eed Darwish 1,2 , Hartmuth
Arenhövel 1 ,andMichael Schwamb 1 — 1 Institut für Kernphysik, J.
Gutenberg-Universität, J.-J. Becher-Weg 45, D-55099 Mainz, Germany
— 2 Physics Department, Faculty of Science, South Valley University,
Sohag, Egypt
Incoherent photoproduction of pions on the deuteron in the ∆(1232)
resonance region is investigated with inclusion of nucleon-nucleon (NN)
and pion-nucleon (πN) rescattering. The elementary γN → πN production
amplitude contains besides the standard pseudovector Born terms
the resonance contribution from the ∆(1232) excitation [1].
The major point of concern is the inclusion of NN and πN rescattering
which we limit to contributions of two-particle interactions in the
NN-andπN-subsystems. As models for the interaction of the NN-and
πN-subsystems we use separable interactions from Haidenbauer et al. [2]
and Nozawa et al. [3], respectively.
In general, the inclusion of final state interaction effects is found to
be important in the total and differential cross sections. Moreover, they
lead to an improved agreement with the existing experimental data.
[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 9.27 Tue 10:30 Foyer Chemie
Two and Three Neutron Halos in Helium and Lithium Isotope
— •M. Tomaseli 1,2 , T. Kuehl 2 , P. Egelhof 2 , W. Noertershaeuser
2 , A. Dax 2 , H. Wang 2 , D. Marx 2 , S.R. Neumaier 2 ,
H.-J. Kluge 2 , I. Tanihata 3 , S.Fritzsche 4 ,andM. Muttere 1 —
1 Institute of Nuclear Physics, Darmstadt University, D-64289 Darmstadt,
Germany — 2 Gesellschaft fuer Schwerionenforschung (GSI), D-64291
Darmstadt, Germany — 3 RIKEN 2-1 Hirosawa, Wako-Shi, Saitama 351-
0198, Japan — 4 Institute of Physics, Kassel University, D-34132 Kassel,
Germany
The far reaching shape of the matter distributions (halo) of exotic
nuclei with high isospin components is calculated in the Dynamic Correlation
Model (DCM) which is based on the interaction of valence- and
core-particles. In this model, one, two, or more valence particles and
intrinsic vacuum-clusters (collective-excitations of reference vacuum) are
treated within the same formalism. Matter and charge distributions of
lithium and beryllium isotopes are strongly modulated by the couplig of
the valence particles with the core and the matter radii extracted from
the theoretical distributions are in good agreement with experimental
results. Within the model the core-protons are de facto contributing to
the halo formation. The effect of the core excitation mechanism on the
calculated cross sections for proton scattering on helium and lithium isotopes
is analysed. For the charge radii new experiments based on the
determination of the volume-shift are discussed
HK 9.28 Tue 10:30 Foyer Chemie
Three quark correlations in hot and dense nuclear matter —
•Michael Beyer 1 , Stefano Mattiello 1 , Tobias Frederico 2 ,
and Hans J Weber 3 — 1 FBPhysik,U.Rostock,Germany— 2 Sao
Paulo, Inst. Tech. Aeronautics, Brazil — 3 U of Virginia, Charlottesville,
USA
We investigate the transition region from quark to nuclear matter at
high densities and temperatures as it might be relevant for highly relativistic
heavy ion collisions. To this end, we present a relativistic threebody
equation to investigate three-quark clusters in hot and dense quark
matter. To derive such an equation we use the Dyson equation approach.
The equation systematically includes the Pauli blocking factors as well as
the self energy corrections of quarks. Special relativity is realized through
the light front form. Presently we use a zero-range force and investigate
the Mott transition.
References
M. Beyer, S. Mattiello, T. Frederico, H.J. Weber, Phys. Lett. B521
(2001) 33; S. Mattiello, M. Beyer, T. Frederico, H.J. Weber, Few-Body
Systems in print.
HK 9.29 Tue 10:30 Foyer Chemie
The Jülich pion-nucleon model — •Achot M. Gasparyan , Johann
Haidenbauer, Christoph Hanhart, andJosef Speth —
FZ Jülich, IKP, 52425 Jülich
The coupled channel model of the πN interaction developed by the
Jülich group [1] yields a quite satisfactory description of the πN phase
shifts and inelasticities as well as of the ηN differential and total cross
sections in the energy range from the πN threshold up to about 1600
MeV. Presently we are extending this model to higher energies and we
will report corresponding results at this meeting.
For the extension to higher energies further channels like KΛ, KΣ,
and ωN (which open at center of mass energies within the region 1600-
1700 MeV) have to be included. In addition, contributions from several
pole diagrams, in particular of the S31(1620), P 13(1720) and D33(1700)
resonances, are considered.
[1] O. Krehl et al., Phys. Rev. C 62, 025207 (2000).
HK 9.30 Tue 10:30 Foyer Chemie
The influence of three body cuts on the reaction NN → NNx—a
toy model study — •Andreas Motzke 1 , Charlotte Elster 1,2 ,
Christoph Hanhart 1 ,andJosef Speth 1 — 1 Institut für Kernphysik
(Theorie), Forschungszentrum Jülich, D-52425 Jülich — 2 Department of
Physics and Astronomy, Ohio University, Athens, OH 45701
In recent years there is an increasing interest in meson production reactions
in NN collisions. High quality data is available for a large number
of different mesons. Unfortunately, several theoretical issues are still to
be investigated in detail. One of those is the impact of three body cuts
on the reaction cross sections. In this talk we will study the significance
of NNπ–cuts on the reaction NN → NNx within a toy model
developed in Ref. [1]. We discuss the numerical methods used and compare
the exact results to several approximations used in the literature. [1]
C.Hanhart, G.A.Miller, F.Myhrer, T.Sato, and U.van Kolck, Phys.Rev.C
63(2001)044002.