Verlag des Forschungszentrums Jülich
JUEL-3685
Moskal, Pawel
n meson production in the pp -> ppn reaction near threshold
114 S., 1999
The n' meson belongs to the ground state pseudoscalar meson nonet.
According to the SU(3) classification its quark composition is similar to the structure of
the n meson. However, due to the small pseudoscalar mixing angle ([Theta]ps ~ 15°)
the n' meson is predominantly a flavour singlet state and hence can comprise a
significant amount of gluons. A possible gluon admixture would be reflected in the
production mechanism of the n' meson in the elementary proton-proton reaction,
it would modify an n'pp coupling constant which determines the direct
production amplitude, and it would also influence the potential of the proton-n' meson
interaction. These issues make the investigations of the n' meson very interesting.
The total cross section for the production of the n' meson in the pp -> ppn'
reaction has been measured close to the kinematical threshold. The experiment has
been carried out at the cooler synchrotron COSY using the internal proton beam
and the hydrogen cluster target. The ejected charged particles were registered
using the COSY-11 detection system, which allow for an unique identification of
positively charged particles and determination of their four - momentum vectors.
Events with the creation of the n' meson were identified by means of the missing
mass technique.
The obtained cross sections for the n' meson production are by about a factor
of fifty smaller that the cross section for the production of the n meson at the same
center of mass excess energies. Such large difference suggests that these mesons
are produced in a rather different way.
Comparison of the measured cross section values with calculations based on the
effective Lagrangian approach yields an upper limit for the n'pp coupling constant.
The analysis of the energy dependence of the total cross section for the pp ->
ppn' reaction suggests that either the primary production amplitude decreases
very close to threshold or that the proton-n' interaction is repulsive.
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