Pion Production inπ−−pInteractions at Energies 790, 830, and 870 MeV

Single-pion production has been studied in the reactions ${\pi }^{-}p\to {\pi }^{-}{\pi }^{+}n$ and ${\pi }^{-}p\to {\pi }^{-}{\pi }^{0}p$ at 790, 830, and 870 MeV. A total of 4193 events in these two channels, divided approximately equally between the three energies, have been identified. The most interesting feature of the data is the tendency for events to concentrate at high values of $m_{\pi \pi }$ and low values of four-momentum transfer. These effects are discussed in terms of conventional isobar models and a model involving two-pion exchange. Partial cross sections for the reactions studied are reported for each energy.