Spin-Parity Analysis of theA3

A partial-wave analysis of the charged three-pion system in the reaction ${\pi }^{-}p\to p{\pi }^{+}{\pi }^{-}{\pi }^{-}$ for incident ${\pi }^{-}$ momenta from 5 to 25 GeV/c shows the existence of a broad enhancement (∼ 300 MeV) in the $J^P=2^{-}f\pi$ ($S$-wave) state in the region of the $A_3\mathrm{}\left(1650\right)\mathrm{}$. No other state ($J\le 4$) shows structure in this region. Upper bounds for $\rho \pi$ and $\epsilon \pi$ decay modes of the $A_3$ are given. The interference of the $2^{-}f\pi$ ($S$-wave) amplitude with other amplitudes has been observed. The mass variation of the phase of the $2^{-}f\pi$ ($S$-wave) amplitude measured with respect to the phases of other amplitudes does not show the behavior expected for the relative phase between resonant and nonresonant amplitudes. Results are given on the polarization and momentum-transfer dependence of the $A_3$ and on the $A_3$ production cross section as a function of incident ${\pi }^{-}$ momentum.