Verlag des Forschungszentrums Jülich
JUEL-4004
A detailed theoretical analysis of the different channels of the reaction
NN -> NNη, i .e . pp -> ppη, pn -> pmη and pn -> dη, has been performed in
the near-threshold region, i.e . for the energy not more than 50 MeV above
threshold. The production mechanisms which have been included consist
of re-scattering terms wich M = π, ρ, η, σ meson exchanges and the direct
η production . Effects of the final and initial state interaction between the
nucleons are fully taken into account . The calculation utilizes the Bonn B
and the CCF NN models for the treatment of the FSI and ISI, respectively,
and a realistic coupled-channel model of the πN system developed in Jülich,
which was used for the calculation of the MN -> ηN transition amplitudes .
A quantitative agreement of calculated cross sections wich the experimental
data is achieved for all channels of this reaction .
It is found that the leading role in the process of the η-meson production
near threshold belongs to the re-scattering mechanism wich the intermediate
pion exchange . The contributions from other meson exchanges, specifically
from ρ and η as well as from the direct η production are smaller . However,
they are still important and have to be taken into account because of their
influence an the cross sections due to the interference with the amplitude
corresponding to the π exchange.
NN FSI effects in the reactions NN -> NNM wich production of meson M
but wich different masses are studied in detail . It is demonstrated that the
füll reaction amplitude can not be factorized an the pieces corresponding
the production process and independently the NN FSI if one is interested
in the quantitative predictions for the cross sections . It is shown that the
use of the Jost function for the evaluation of NN FSI effects leads to the results
considerably different from the ones of correct calculation . It is shown
also that NN FSI effects are not universal with respect to the different produced
mesons, i.e. their absolute values definitely depend an the mass of
the produced meson (momentum transfer) .
It is found that ISI effects in the reaction NN -> NNη are not universal
with respect to the different meson exchanges, i.e . to the different production
mechanisms. lt is emphasized that taking into account NN ISI effects affects
the magnitude of the cross sections significantly leading to a reduction of a
factor 10 (or even more) in some cases .
The total and differential cross sections of the ao-meson production in the
reaction pn -> ppa0(-) have been evaluated . The dependence of these cross
sections an the specific parameters of the ao meson such as position of the
resonance, its width, branching ratio is investigated.
Baru, Vadim
Production of the meson in nucleon-nucleon collisions
IV, 126 S., 2003
In conclusion we would like to present a short list of the main results obtained in
the thesis .
Neuerscheinungen
Schriften des Forschungszentrums Jülich
Ihre Ansprechperson
Heike Lexis
+49 2461 61-5367
zb-publikation@fz-juelich.de