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HK: Hadronen und Kerne
HK 49: Hadronic Probes V, Particle Production
HK 49.5: Gruppenbericht
Mittwoch, 18. März 1998, 15:45–16:15, C
η’-meson production in the pp scattering at COSY — •P. Moskal — Institute of Physics, Jagellonian University, Cracow, Poland
Cross sections of production of the η’(958)-meson, which is the heaviest meson of the
pseudoscalar meson nonet, have not been measured at threshold in the pp
scattering so far. Data will be presented at excitation energies
in the range up to 4.1 MeV. They were taken at the internal facility
COSY-11 [1] using a cluster target in front of a regular COSY dipole. For the two exit
protons in the reaction pp —→ pp η’ the four-momentum vectors were
determined by means of drift chambers and scintillators whereas the η’-meson was
identified exclusively via the missing mass method based on energy and momentum
conservation laws.
The absolute normalisation of the total cross section was obtained by comparing the
simultaneously measured rate of elastically scattered protons to data recently published
by the EDDA collaboration [2].
For excitation energies between 1.5 MeV and 4.1 MeV the cross sections range from 2.5 nb
to 25 nb, being about a factor of 50 smaller than the ones for the η and π0
production processes. On the other hand, plotting the cross section as a function of the
η-parameter (η = maximum meson momentum normalized by its mass) the
η’-meson data are on the same curve as the π0 production rate, in contrast to
the η-meson cross section which is much larger. It might be speculated that the
η’-meson production mechanism - as known for the π0 - is not mediated via a
baryon resonance whereas the eta-meson production is dominated by the large
N* (S11(1535)) resonance - η-meson interaction. The experimental data will be
compared with theoretical model predictions.
[1] S. Brauksiepe et al., Nucl. Instr. and Meth. A 376 (1996) 397
[2] D. Alberts et al., Phys. Rev. Lett. 78 (1997) 1652