Total cross section for p+p→p+p+π0 close to threshold

Making use of an electron-cooled beam in the IUCF storage ring, we have measured the total cross section σtot for pp→ppπ0 at 31 bombarding energies between 285 and 325 MeV. At a level of about 5%, the data show no fluctuations that could be associated with the onset of other pion production channels. A calculation of the single-partial-wave cross section σss, including direct production only (no rescattering), falls short of the experiment by a factor of 5.2±0.3, but reproduces the observed energy dependence when scaled. This energy dependence is explained by contributions from the phase-space factor and the final-state interaction between the outgoing nucleons. The relative importance of higher partial waves is deduced from the energy dependence of σtot as well as from the angular distributions of reaction protons. (orig.)