Positive-Pion Production in Inelasticπ−pInteractions between 500 and 1300 MeV

The momentum distributions of the ${\pi }^{+}$ in the reaction ${\pi }^{-}p\to {\pi }^{+}{\pi }^{-}n$ were measured at several ${\pi }^{+}$ angles for incident ${\pi }^{-}$ beam energies of 516, 550, 599, 667, and 715 MeV; ${\pi }^{-}n$ mass spectra were calculated from the ${\pi }^{+}$ momentum distributions. Partial data were also obtained at higher energies. The ${\pi }^{-}$ beam was obtained from the Berkeley Bevatron. The momenta of the ${\pi }^{+}$ were measured with a magnetic spectrometer consisting of a $C$ magnet and thin-walled aluminum spark chambers to display the trajectory of the particle entering and leaving the magnet. An array of scintillation counters was used to detect the occurrence of an event. An electronic time-of-flight system was used to distinguish positive pions from protons that passed through the spectrometer. The measured spectra can not be adequately explained by any of the several models with which we tried to fit our spectra, including an isobar model, although production of the (3,3) isobar is prominent.