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The production of $eta$ mesons in the reactions $ppto ppeta$ and $pnto pneta $ at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. The description of cross section and angular distributions of the available data in this kinematical region in the $pp$ channel is accomplished by including meson currents and nucleon currents with the resonances $S_{11}(1650)$, $P_{11}(1710)$ and $P_{13}(1720)$. Predictions for the $pn$ channel are given. The di-electron production from subsequent $eta$ Dalitz decay $eta to gamma gamma^* togamma e^+e^-$ is also calculated and numerical results are presented for intermediate energy and kinematics of possible experiments with HADES, CLAS and KEK-PS.
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The production of eta and eta-prime mesons in nucleon-nucleon collisions near thresholds is considered within a one-boson exchange model. We show the feasibility of an experimental access to transition formfactors.
A comparison of the close-to-threshold total cross section for the eta prime production in pp --> pp eta prime and pn --> pn eta prime reactions constitutes a tool to investigate the eta prime meson structure and the reaction mechanism in the channels of isospin I=0 and I=1 and may provide insight into the flavour-singlet (perhaps also into gluonium) content of the eta prime meson. In this contribution we present preliminary results of measurement of the quasi-free production of the eta prime meson in the proton-neutron collisions conducted using the COSY-11 facility.
A procedure is proposed which accounts for final state interaction corrections for near threshold meson production in nucleon-nucleon scattering. In analogy with the Watson-Migdal approximation, it is shown that in the limit of extremely strong final state effects, the amplitude factorizes into a primary production amplitude and an elastic scattering amplitude describing a $3 to 3$ transition. This amplitude determines the energy dependence of the reaction cross section near the reaction threshold almost solely. The approximation proposed satisfies the Fermi-Watson theorem and the coherence formalism. Application of this procedure to meson production in nucleon-nucleon scattering shows that, while corrections due to the meson-nucleon interaction are small for s-wave pion production, they are crucial for reproducing the energy dependence of the $eta$ production cross section.
The two-step model with pi-, rho- and omega- exchanges taken into account is applied to investigate the reactions pn -> d eta and pn -> d eta-prime. The existing experimental data on the reaction pn -> d eta are analysed and predictions for the cross section of the reaction pn -> d eta-prime are presented. It is found that pi- as well as rho exchange yield significant contributions in both reactions. The effect of the final state interaction is also studied.
According to the quark model, the masses of eta and eta mesons should be almost equal. However, the empirical values of these masses differ by more than the factor of two. Similarly, though the almost the same quark-antiquark content, the total cross section for the creation of these mesons close to the kinematical thresholds in the pp --> ppX reaction differs significantly. Using the COSY-11 detection setup we intend to determine whether this difference will also be so significant in the case of the production of these mesons in the proton-neutron scattering. Additionally, the comparison of the pp --> pp eta and pn --> pn eta total cross sections will allow to learn about the production of the eta meson in the channels of isospin I = 0 and I = 1 and to investigate aspects of the gluonium component of the eta meson.
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