Unitary meson-exchange calculation of NN→NNπ reaction

Within a unitary πNN theory a set of coupled integral equations have been developed for the study of pion production from NN collisions, and have been applied to calculate the coincidence cross sections of pp→pn${\pi }^{+}$ at 800 MeV. The calculation is based on a meson-exchange Hamiltonian which was previously constructed to describe NN elastic scattering up to 1 GeV by extending the Paris potential to include Δ excitation. It involves solving a Faddeev-Alt-Grassberger-Sandhas scattering equation for the final πNN state and a NN⊕NΔ coupled-channel equation for the initial NN state. We present the procedure of using the newly developed spline function method to solve the considered Faddeev-Alt-Grassberger-Sandhas equation directly on the real momentum axis. The importance of using a unitary approach to treat the initial NN and final πNN scattering is analyzed in detail, in order to understand the results obtained in several previous approaches by Betz, Dubach et al., and Verwest. The calculated cross sections reproduce the main features of the data both in magnitude and shape. The main difficulty of the present theory is found to be in reproducing the polarization data $A_y$. Our results provide further evidence that the πNN dynamics cannot be described completely by the conventional meson-exchange model.