Positive Pion Production in Proton-Proton Collisions at 450 Mev

Abstract

The external proton beam of the Chicago cyclotron has been used to study the reaction $p+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+n+p$ at 450 Mev. The reaction $p+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+d$ was also measured as a check on the equipment. A double focusing wedge magnet was used to observe the momentum distribution of pions at angles of 14\ifmmode^\circ\else\textdegree\fi{}, 20.5\ifmmode^\circ\else\textdegree\fi{}, and 30\ifmmode^\circ\else\textdegree\fi{} in the laboratory system. The over-all resolution of the magnet system varied from 1.5% to 2.2%. A least squares fit of the $p+p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}+d$ data in the center-of-mass system gives $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}\ensuremath{\alpha}(0.38\ifmmode\pm\else\textpm\fi{}0.20+{cos}^{2}\ensuremath{\theta})}$ with $\ensuremath{\sigma}=1.47\ifmmode\pm\else\textpm\fi{}0.12$ millibarns. The spectra for the unbound reaction were fitted to $\mathrm{Ss}$, $\mathrm{Sp}$, $\mathrm{Ps}$, and $\mathrm{Pp}$ spectrum shapes predicted by the phenomenological theory of pion production. This fit gives $\frac{d\ensuremath{\sigma}}{d\ensuremath{\Omega}}\ensuremath{\propto}(0.40\ifmmode\pm\else\textpm\fi{}0.08+{cos}^{2}\ensuremath{\theta})$ with $\ensuremath{\sigma}=1.80\ifmmode\pm\else\textpm\fi{}0.7$ millibarns. The results of this fit have been compared with the cross section for neutral pion production at 450 Mev. This comparison was found satisfactory for the amounts of the $\mathrm{Ss}$, $\mathrm{Sp}$, and $\mathrm{Pp}$ spectrum shapes found in this experiment, but an excessively large amount of the $\mathrm{Ps}$ shape, 0.38\ifmmode\pm\else\textpm\fi{}0.10 millibarns, was required to fit the data. The results show that ${\ensuremath{\sigma}}_{10}(\mathrm{Pp})$ is much smaller than has been previously reported. An excitation function for the unbound cross section is predicted by this fit in terms of the phenomenological model, and is found to increase too rapidly at high bombarding energies.