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

Abstract Making use of an electron-cooled beam in the IUCF storage ring, we have measured the total cross section σ tot for pp→pp π 0 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 σ ss , 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 σ tot as well as from the angular distributions of reaction protons.