Meson exchange and pion rescattering contributions to the cross section for pp → ppπ0

Short range meson-exchange mechanisms such as ϱ → ωπ0 contribute significantly to the amplitude for pp → ppπ0 near threshold in addition to pion rescattering. The uncertainty of the latter contribution, which depends on poorly determined parameters, is estimated. Allowing for this uncertainty and taking the short range meson exchange contributions into account makes it possible to reproduce the measured cross section.