π−pReactions at 456, 505, and 552 MeV/c

We present the results of an experiment to study the reactions ${\pi }^{-}p\to \pi \pi N$ at incident momenta of 456, 505, and 552 MeV/c in a hydrogen bubble chamber. The most prominent features of the data in the ${\pi }^{+}{\pi }^{-}n$ final state are a high-mass peak in the $M^2\left({\pi }^{+}{\pi }^{-}\right)$ spectrum (which moves upward in mass and becomes less significant as the incident momentum increases), and ${\Delta }^{-}$ production. We show that the ${\pi }^{+}{\pi }^{-}$ enhancement can be explained by the introduction of an $I=J=0\mathrm{}$ $\pi \pi$ interaction, and investigate two forms for this interaction. Within the framework of an isobar model, we derive values of the $\pi N$ partial-wave inelasticities and compare these with the predictions of $\pi N$ elastic phase-shift analyses. It is shown that the branching ratio $\pi N:\pi \Delta :\sigma N$ of the $P_{11}$ partial wave depends strongly on the assumed form of $\pi \pi$ final-state interaction.