In ${\pi }^{-}p$ single-pion-production reactions near 4 GeV/c, we observe several interesting features. Backward ${\rho }^0$ production is seen to occur with $\frac{d\sigma }{\mathrm{du}}=63\mathrm{}\pm 21$ μb/${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ at 180°. Backward ${\rho }^{-}$ production is less prominent. We see evidence for production at small $u$ of $N^{*0\mathrm{}}$ ($p{\pi }^{-}$ near 1700 MeV) and ${\Delta }^{-}$ ($n{\pi }^{-}$ at 1236 MeV), and possible evidence for other $n{\pi }^{-}$ structure at about 1800 MeV. The density-matrix elements for peripheral ${\rho }^0$ production are presented in the Jackson and in the helicity frame. The ${\pi }^{+}{\pi }^{-}$ elastic cross section is obtained by extrapolation of the data to the mass shell. The $S$-wave $\pi \pi$ phase shifts are calculated by two methods and compared with previous results. We find evidence in the dipion decay angular distribution for the ${\pi }^{+}{\pi }^{-}$ decay mode of the $S^{*}\mathrm{}\left(1070\right)\mathrm{}$.

• Received 26 July 1968

DOI:https://doi.org/10.1103/PhysRev.176.1651