Total cross section for eta production in the quasi-free pn->pn eta reaction

M.Janusz for the COSY-11-Collaboration
Institute of Physics, Jagellonian University, Cracow, PL-30-059, Poland

The comparison of the total cross sections for the eta and eta' meson production in the p-n and p-p collisions may be a proper tool in studying structure and production mechanism of both mesons. The value of the total cross section for the reaction pp->pp eta was found to be about 6.5 times smaller than that for the pn->pn eta reaction in the excess energy range beetwen 16 MeV and 109 MeV [1] which is explained by a dominant isovector meson (pi, rho) exchange. The corresponding ratio for the eta' production will yield information of the underlying reaction mechanisms which are mediated by the eta' structure.

A feasibility study of the quasi-free pn->pn eta reaction has been carried out at the COSY-11 facility at the cooler synchrotron COSY in Jülich using a proton beam scattered at a deuteron cluster target [2]. The data are still under evaluation but clearly demonstrate the possibility to reconstruct quasi-free pn reactions at COSY-11. Similar investigations for the production of the eta' meson have started. First measurements have been performed and a production run is scheduled for summer 2004 [3].

The detection capabilities of the quasi-free pn->pn eta (eta') reaction at COSY-11 as well as preliminary results in the eta channel will be presented.

[1] H.Calén et al., Phys. Rev. C 58 (1998) 2667.
[2] P.Moskal et al., nucl-ex/0311003.
[3] P.Moskal, COSY Proposal No.133.

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