Study of the reaction pp$ \to$ pp $\pi^0$ within 10 MeV above the threshold
Kinematically complete measurements of the $pp\to pp\pi^0$ reaction were performed for beam energies in the range 292-298 MeV. We detected both protons in coincidence by using the large-acceptance COSY-TOF spectrometer and an external proton beam at COSY-Jülich; thus, we measured total and differential cross-sections and energy distributions. A strong enhancement was observed in the Dalitz plots due to the final-state interaction between the two outgoing protons; the data are well reproduced by Monte Carlo simulations using a standard scattering length of a 0=-7.83 fm and effective range of r 0=2.8 fm. Our measured total cross-sections are roughly 50% larger than those of recent internal-target experiments at IUCF and CELSIUS. This discrepancy may be due to the final-state interaction pushing some events into the very small-angle region which is almost inaccessible to an internal-target experiment. In the angular distributions we found only very slight deviations from isotropy. The analysis of our momentum distributions yielded a small fraction of $5\pm 5 \%$ for Ps or Pp wave contributions.
© Società Italiana di Fisica and Springer-Verlag, 2003