Kinematically complete measurements of the $pp\to pp\pi^{0}$ 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-Julich, 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 length $a_0$=-7.83 fm and effective range $r_0$=2.8 fm. The total cross sections 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.
Total P P --> P P PI0 cross section.
The reaction pp → pp π 0 has been measured using electron-cooled protons incident on an internal gas-jet target at seven different incident beam energies, from 280.7 MeV (1 MeV above the reaction threshold) up to 310.2 MeV. The pions were measured by their decay photons. In the overlapping energy region, the measured total cross sections agree with those measured in a recent Indiana experiment. The angular distributions are consistent with a 3 P 0 → 1 S 0 s 0 transition in the full energy range studied. The kinematical distributions are well described when taking into account the final state and the Coulomb interactions.
AN OVERALL 5 PCT ERROR IN NORMALIZATION IS NOT INCLUDED.
The total cross section for the reaction pp→ppπ0 was measured at nine center-of-mass energies from 1.5 to 23 MeV above threshold. The experiment was carried out with the Indiana Cooler, a recently constructed storage ring. The experimental advantages of an electron-cooled proton beam were utilized. The data cover an energy range where only the lowest possible angular momentum state contributes in the exit channel. The measured energy dependence of the total cross section is not compatible with that predicted by models of s-wave pion production and rescattering.
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