Heavy Meson Production at COSY-11


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.

F.Hibou et al., Phys. Lett. B 438 (1998) 41
P.Moskal et al., Phys. Rev. Lett. 80 (1998) 3202
A.Bramon, R.Escribano, M.D.Scadron, Eur. Phys. J. C 7 (1999) 271
P.Wüstner, PhD thesis, Ruhr-Universität Bochum (1998)

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