Bochum 1998 – wissenschaftliches Programm

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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