595 research outputs found
Dilepton Production in Elementary Processes on the Nucleon
We study elementary processes for production of dileptons from nucleons,
either through NN bremsstrahlung or through photon-induced reactions. We
emphasize the dependence of the expected cross-sections on the electromagnetic
formfactor of the nucleon in the time-like regime and point out that the
mentioned reactions can provide important information on the validity of vector
meson dominance for the nucleon. We also study the off-shell dependence of the
formfactors.Comment: Figures available from author by fa
Coupling of Baryon Resonances to the channel
We estimate the resonance coupling strength and
from a Vector Meson Dominance (VMD) analysis. The isoscalar and isovector part
of the photon coupling are obtained separately from helicity amplitudes. The
reliability of this approach is tested by comparing VMD predictions for
with values obtained from fitting the hadronic decay widths into
. A reasonable agreement is found, but VMD tends to underestimate the
coupling constants. In order to confirm consistency with experimental data, we
calculate the cross-sections for photon-and pion induced reactions within a
{\it Breit-Wigner} model. Finally, we study how the properties of
mesons in nuclear matter are affected from the excitation of resonance-hole
loops. For an at rest, we find a broadening of about 40 MeV, while at
higher momenta the effect of resonance excitations is reduced.Comment: 21 pages, 5 ps figures, misprints corrected, discussion added,
improved calculation of gamma N -> omega N, revised version to be published
in Nuclear Physics
The Giessen Model - Vector Meson Production on the Nucleon in a Coupled Channel Approach
In this paper we present the extension of our unitary gauge invariant
effective Lagrangian model to vector meson nucleon final states. This model
already included the final states , , , , , and and was developed for a simultaneous analysis of all
avaible experimental data for photon- and pion-induced reactions on the
nucleon. We discuss how the extension to vector meson nucleon final states is
realized, outline a generalization of the standard partial wave formalism, that
is applicable to any meson-/photon-baryon reaction, and show first results for
production.Comment: 4 pages, talk given at NSTAR 2001, Workshop on the Physics of Excited
Nucleons, University of Mainz, Germany, March 7-10, 2001. To be published in
World Scientifi
- …