The differential cross section and analyzing power $A_y$ of the ${vec p}p{to}pp{pi}^0$ reaction have been measured at RCNP in coplanar geometry at a beam energy of 390 MeV and the dependence on both the pion emission angle and the relative momentum o
f the final protons have been extracted. The angular variation of Ay for the large values of the relative momentum studied here shows that this is primarily an effect of the interference of pion s- and p-waves and this interference can also explain the momentum dependence. Within the framework of a very simple model, these results would suggest that the pion-production operator has a significant long-range component.
