Near Threshold Production of eta and eta'
and Charged Kaon Pairs in Proton-Proton Collisions
The near threshold production of mesons in nucleon-nucleon
collisions is of fundamental interest and provides a
possibility to study various theoretical models.
Close to threshold only few partial waves contribute
and due to the low relative momenta of the ejectiles,
final state interactions can be studied in more detail.
At the cooler synchrotron COSY various near threshold measurements
have been performed using the internal installation COSY-11 .
In this contribution data for the eta, eta' and
K+K- meson production in proton-proton
collisions will be presented and discussed in view of possible
1. The reactions pp->pp eta and
In case of the eta meson the production in
NN interaction close to the production threshold has
been studied in several theoretical works using one-boson
exchange models and is assumed to proceed dominant through the
excitation of the S11 nucleon resonance
N*(1535) with a branching ratio
N*(1535)->eta N of about 30-55 %.
However, at energies close to the eta' threshold no
such resonance is known.
Thus, it is not expected that the eta' production via the
excitation of baryonic resonances will be appreciable.
To check different models data especially close to threshold
Therefore, the production of eta and eta' mesons
has been measured at COSY-11 at excess energies of
Q=0-6.8 MeV (eta) and Q=1.5-25.0 MeV (eta'),
2. The reaction pp->K+K-
Nucleon-nucleon production cross sections of kaons and kaon pairs
are of great interest for the understanding of many topics like
the still controversially discussed structure of the
f0(980) or medium effects of kaon production
in nuclear matter.
Different to the K+ meson, which can also be
produced via hyperon resonances, up to now there exist no data
for the production of K- mesons in the
nucleon-nucleon scattering near threshold.
Therefore, measurements of the elementary production process
pp->K+K- have been investigated
at COSY-11 at excess energies between
Q=4.4 MeV and Q=56.1MeV [4,5].
S.Brauksiepe et al.,
Nucl. Instr. & Meth. A 376 (1996) 397
Ph.D. thesis, University Bochum (1998)
P.Moskal et al.,
Phys. Rev. Lett. 80 (1998) 3202
Ph.D. thesis, University Münster (1998)
Ph.D. thesis, University Bonn (1998)
in PostScript format (41kB)
document in PostScript format (122kB)