Study of the reaction pp to ppπ⁰ within 10 MeV above the threshold

Kinematographically complete measurement of the pp to ppc0;⁰ reaction were performed for beam energies in the range 292 - 298 MeV. By detecting both protons in coincidence with the large acceptance COSY-TOF spectrometer set up at an external beam line of the proton synchrotron COSY-Jülich, total and differential cross sections and energy distributions were obtained. A strong enhancement is observed in the Dalitz plots resulting from the final state interaction between the outgoing proton pair; the data are well reproduced by Monte Carlo simulations with standard parameters for scattering lengths a0 = 7.83 fm and effective range r0 = 2.8 fm. The total cross section exceed the ones measured recently in internal target experiments at IUCF and CELSIUS by roughly 50%. Arguments are presented which link this discrepancy with the effect of the final state interaction pushing yield into the very small-angle region and the near-impossibility of an internal target experiment to cover just this range.