Single-Pion Production inπ−+pCollisions at 2.14 BeV/c

A bubble-chamber experiment in which the reaction ${\pi }^{-}+p\to \pi +\pi +N$ was studied at a beam momentum of 2.14 BeV/c yielded 1533 and 2234 events of the final states ${\pi }^{-}{\pi }^{0}p$ and ${\pi }^{-}{\pi }^{+}n$, respectively. These events are dominated by the formation of the $\rho$ resonance, which is produced mostly in the forward direction. Both the production and decay angular distributions of the ${\rho }^{-}$ agree very well with the predictions of the one-pion exchange theory modified by absorption effects. The decay angular distribution of the ${\rho }^0$ shows the well-known forward-backward asymmetry. This effect is interpretable as the result of the interference between the ${\rho }^0$ and an isospin-zero $s$-wave $\pi -\pi$ resonance. The production of the ${\rho }^0$, in addition to its forward peak, shows a weak backward peak. Partial cross sections of various final states are also presented.