Production of a(o)-mesons in the reactions pi N -> a(o)N and pp -> da(o)(+) at GeV energies

We investigate the reactions piN --> a(0)N and pp --> da(0)(+) near thresho ld and at medium energies. An effective Lagragian approach and the Regge po le model are applied to analyze different contributions to the cross-sectio n of the reaction piN --> a(0)N. These results are used to calculate the di fferential and total cross-sections of the reaction pp --> da(0)(+) within the framework of the two-step model in which two nucleons produce an a(0)-m eson via pi -meson exchange and fuse to a deuteron. The necessity of new me asurements on a(0) production and branching fractions (of its decay to the K (K) over bar and pi eta channels) is emphasized for clarifying the a(0) s tructure. Detailed predictions for the reaction pp --> da(0)(+) are present ed for the energy regime of the proton synchrotron COSY-Julich.