Production of the #eta# meson in nucleon-nucleon collisions

The thesis is structured in the following way. The chapters 2 and 3 are devoted to a detailed theoretical analysis of different channels of the reaction NN#->#NN#eta#, i.e. in pp#->#pp#eta#, pn#->#pn#eta#, and pn#->#d#eta#. In the presented model calculations effects of the NN FSI and ISI are taken into account. Our model analysis suggests that the dominant role in the #eta#-meson production process belongs to the re-scattering mechanism involving the pion exchange. The contributions of other meson exchanges have to be taken into account as well since they have an influence on the magnitude of the cross sections due to interference with the amplitude of the pion exchange. The effects of the nucleon-nucleon final state interaction in the reactions NN#->#NNM are studied in detail in chapter 4. It is shown that the FSI effects are indeed not universal, i.e. they do depend on the mass of the produced meson. This is in contrary to the results of Ref. [19-22] where an universal NN FSI was utilized. Furthermore, it is demonstrated that the reaction amplitude cannot be factorized into the production process and (independent) NN FSI effects if the calculation aims at predicting absolute values of the cross sections. The analysis of ISI effects performed in chapter 2 leads us to the conclusion that ISI effects are not uniform in respect to the exchanges by different mesons. It is stressed that the inclusion of the ISI has a significant impact on the absolute value of the cross sections. It leads to strong reduction of the cross sections. Apart from the investigation of the #eta#-meson production in NN-collisions we present also, in chapter 5, an estimation of the cross sections for a_0(980) meson production in the reaction pn#->#ppa_0"-. (orig.)Available from TIB Hannover: RA 831(4004) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman