P.Moskal for the COSY-11-Collaboration
One of the topics investigated at the COSY-Jülich
accelerator is the production of the eta and eta'
mesons in the proton-proton interaction close to the
kinematical threshold.
Similar studies, however, by means of different detection methods,
are performed at the CELSIUS and SATURNE accelerators.
Recent results concerning both eta and eta' mesons
production in the proton-proton collisions enables one besides
the investigations of the primary production mechanism also study
of the eta-proton and eta'-proton
interaction.
The available experimantal data made possible to conclude that
the eta meson is predominantly produced via the excitation
of the S-wave baryonic resonance and that the interaction of
eta meson with proton is attractive.
In contrary, in the case of the eta' meson, production via
excitation of the baryonic resonance seems to be not significant
and the eta'-proton interaction seems to be repulsive,
however, the latter conclusion is still very
uncertain.
A plausible production mechanism of the eta'-proton mesons
can be a fusion of gluons emitted from the two colliding protons,
which is complementary to meson exchange current and would probe
the gluonic content of this meson.
According to the SU(3) classification the eta- and
eta'-mesons together with pions and kaons belong to the
ground pseudoscalar meson nonet.
The hadron-quark mass formula, which describes quite well masses
of the octet members implies that the eta' meson mass
should be about factor of three smaller than the observed
one.
This discrepancy and the anomalous large branching ratio of the
B-mesons decay into eta' suggest other than the
quarkonium components within the eta'
structure.
The structure of the eta' meson enters in the meson
exchange models as the effective coupling constant, which is
still not well known.
The better estimation of this constant and the investigation of
the possible production processes of the eta' meson in
the collisions of protons constitutes the basic motivation for
the performed measurements, which will be presented in this talk.
The discussion of the above issues will be interlaced with the
presentation of the experminetal method used by the COSY-11 group
for the measurement of the pp->pp eta' and
pp->pp eta reactions, which have been performed
at the cooler synchrotron COSY in Jülich.