Pion-Produktion in Proton-Proton-Stößen

Based on well established models for nucleon-nucleon and pion--nucleon scattering the a modell for pion production in proton proton collisions is presented. The $\Delta$(1232) degree of freedom is explicitly taken into account. For the first time all possible final states (pp $\rightarrow$ pp$\pi^{o}$, pp $\rightarrow$ d$\pi^{+}$ and pp $\rightarrow$ p$\eta \pi^{+}$) are investigated simultanously. We obtain an overall satisfactory agreement with available data on total cross sections as well as polarization observables from pion production threshold up to the Delta resonance region. We discuss the effect of the delta isobar and the sensitivity to off-shell properties of the $\pi$N amplitude. The need for using a microscopic model to treat the $\pi$N subsystem is pointed out. The results are compared to those obtained in tree level chiral perturbation theory. Possible sources of the differences are discussed