Total cross section for p+p-->p+p+ pi 0 near threshold measured with the Indiana Cooler.

Abstract

The total cross section for the reaction pp\ensuremath{\rightarrow}pp${\mathrm{\ensuremath{\pi}}}^{0}$ 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.