A detailed analysis of 7514 $\mathrm{pp}\to \mathrm{pp}{\pi }^{+}{\pi }^{-}$ events at $6.6 \frac{\mathrm{GeV}}{c}$ incident beam momentum is presented. Three types of analyses are presented which argue that a single-pion exchange process is responsible for the dominant peripheral ${\Delta }^{++}p{\pi }^{-}$ production. An angular-correlation analysis is presented in which it appears that the 1450-MeV $\Delta \pi$ Deck enhancement is not a pure $J^P={\frac{1}{2}}^{+}$ state. The demonstration that the absolute magnitude for this enhancement is accounted for by the pion-exchange process indicates that only one process (i.e., pion exchange with diffraction scattering at the ${\pi }^{-}p$ vertex) contributes to the final state, and that a second process need not be added to the pion exchange to account for the observed cross section. Some ad hoc dependence on the $\Delta \pi$ mass must be introduced for a precise fit to the shape of the $\Delta \pi$ mass spectrum, or equivalently to the $\theta ,\phi$ angular distributions in the ${\pi }^{-}p$ c.m. system. The $S\Delta {\pi }^{2\alpha \mathrm{}\left(t\right)\mathrm{}}$ dependence of the Reggeized pion-exchange model of Berger is well known to accomplish this; however, the $\alpha \mathrm{}\left(t\right)\mathrm{}$ with unit slope required by this model is at variance with the apparently rather flat trajectory deduced from data on quasi-two-body pion-exchange-dominated reactions. It is suggested that a $\Delta \pi$ final-state-interaction model may be useful in understanding the reaction.

• Received 31 August 1970

DOI:https://doi.org/10.1103/PhysRevD.3.1063