Four- and Five-Body Final States from 3-GeV/cπ−pInteractions

Abstract

Approximately 3600 four-prong events produced by ${\pi }^{-}p$ interactions at 2.96 GeV/c have been analyzed. The $p{\pi }^{+}{\pi }^{-}{\pi }^{-}$ channel shows production of $N^{*++}\mathrm{}\left(1238\right)\mathrm{}$ [(41±4)%], ${\rho }^0$ [(40±5)%], and ${A_2}^{-}$[(7±2)%]. Some evidence for associated $N^{*0\mathrm{}}{\rho }^0$ production is also observed. The one-pion-exchange mode with form factor is shown to give an adequate description of the $N^{*0\mathrm{}}{\rho }^0$ events. The $N^{*++}{\pi }^{-}{\pi }^{-}$ events are analyzed within the framework of this model, and the $I=2\mathrm{}$ $\pi \pi$ scattering cross section up to $m\left(\pi \pi \right)\simeq 1$ GeV/${\mathit{c}}^2$ is calculated. A value for the $I=2\mathrm{}$ $\pi \pi$ $s$-wave scattering length of $\left|{a_2}^0\right|=0.19\mathrm{}{m_{\pi }}^{-1\mathrm{}}$ is obtained. In a determination of the spin and parity of the $A_2$ meson, the $2^{+}$ assignment is favored throughout the fairly wide range of experimental uncertainties in the estimate of the background in the $A_2$ region. The $p{\pi }^{+}{\pi }^{-}{\pi }^{-}{\pi }^0$ channel is dominated by production of ${\omega }^0$ [(26±2)%] and $N^{*++}\mathrm{}\left(1238\right)\mathrm{}$ [(30±6)%]. ${\rho }^{-}$, ${\rho }^0$, and $N^{*++}\mathrm{}\left(1238\right)\mathrm{}$ are produced much more weakly. Peripherality is much less pronounced than in the four-constraint fits. No $B$ meson is observed in the present data. The observation of enhancements at 2080 and 2190 MeV/${\mathit{c}}^2$ in the $p{\pi }^{+}{\pi }^{-}{\pi }^0$ spectrum has been reported previously. The $n{\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^{-}$ channel shows strong $N^{*-}\mathrm{}\left(1238\right)\mathrm{}$ production [(50±10)%] and some weak ${\rho }^0$ production.