Production of $a_0$-mesons in the reactions $\pi N\to a_{0}N$ and $pp\to d{a}_0^{+}$ at GeV energies

We investigate the reactions $\pi N\to a_{0}N$ and $pp\to d{a}_0^{+}$ near threshold and at medium energies. An effective Lagragian approach and the Regge pole model are applied to analyze different contributions to the cross section of the reaction $\pi N\to a_{0}N$. These results are used to calculate the differential and total cross sections of the reaction $pp\to d{a}_0^{+}$ within the framework of the two-step model in which two nucleons produce an $a_0$-meson via $\pi$ -meson exchange and fuse to a deuteron. The necessity of new measurements on $a_0$ production and branching fractions (of its decay to the $K\bar{K}$ and $\pi \eta$ channels) is emphasized for clarifying the $a_0$ structure. Detailed predictions for the reaction $pp\to d{a}_0^{+}$ are presented for the energy regime of the proton synchrotron COSY-J"ulich.