Last year, for the first time total cross section measurements
in the proton-proton collision close to the reaction
threshold of the eta' meson production have been published
[1].
Two independent experiments performed at the accelerators SATURNE
and COSY have consistent results.
At a given excess energy the determined values of the total cross
sections for the eta' meson production are about a factor
of fifty smaller than the corresponding ones for the eta
meson.
This observation rather excludes a resonant production of the
eta' meson in the threshold region, whereas, such a
mechanism dominates the close to threshold creation of meson
eta.
The quark content of both these mesons is very similar, however,
due to the small pseudoscalar mixing angle
(ThetaPS ~ -15°) [2], the eta'
meson is predominantly a flavour singlet state and is expected to
contain a significant admixture of gluons. This possibility makes
a comparative study of eta and eta' mesons very
interesting.
Detailed investigations of the production mechanism and of the
proton-eta and proton-eta' interaction constituted
the motivation for the further precise measurements of the
eta' meson production performed with a stochastically
cooled proton beam, and of the eta meson production
performed with a beam momentum changed continuously during each
cycle of data taking [3].
Results of these new measurements carried out by the COSY-11
detection system at the COSY accelerator will be presented and
discussed.
Complete
document in PostScript format (~668kB)
E-print:
http://xxx.lanl.gov/abs/nucl-ex/0007002
Publication:
Conference
Proceedings
512,
Melville, NY, 2000, ISBN 1-56396-928-9, p.65-78