Importance of quark interchange in pion production via nucleon-nucleon scattering

We investigate pion production via nucleon-nucleon scattering, i.e., N+N→N+N+π, assuming that pion emission takes place effectively at the quark level and that quark-quark interactions are described to a reasonable approximation by one-gluon exchange plus effective one-pion exchange. The six-quark wave function is totally antisymmetrized. Consequently, reaction mechanisms may be grouped into several categories: (1) one-nucleon mechanism or the nucleon-only impulse approximation, (2) two-nucleon mechanisms or meson-exchange currents, and (3) reaction mechanisms involving quark interchange. Applying the formalism to the reactions p+p→d+${\pi }^{+}$ and n+p→p+p+${\pi }^{\mathrm{-}}$, we find that, for a nucleon radius of greater than 0.8 fm (as measured in the MIT bag model), reaction mechanisms involving quark interchange may be as important as the conventional one-nucleon or two-nucleon reaction mechanisms even near the pion production threshold. This specific result provides a quantitative support of the conclusion reached by Miller and Kisslinger in the hybrid quark-baryon model concerning the necessity of incorporating quark effects in describing pion production or absorption reactions.