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

Abstract

Approximately 3600 four-prong events produced by ${\ensuremath{\pi}}^{\ensuremath{-}}p$ interactions at 2.96 GeV/c have been analyzed. The $p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ channel shows production of ${N}^{*++}(1238)$ [(41\ifmmode\pm\else\textpm\fi{}4)%], ${\ensuremath{\rho}}^{0}$ [(40\ifmmode\pm\else\textpm\fi{}5)%], and ${{A}_{2}}^{\ensuremath{-}}$[(7\ifmmode\pm\else\textpm\fi{}2)%]. Some evidence for associated ${N}^{*0}{\ensuremath{\rho}}^{0}$ production is also observed. The one-pion-exchange mode with form factor is shown to give an adequate description of the ${N}^{*0}{\ensuremath{\rho}}^{0}$ events. The ${N}^{*++}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ events are analyzed within the framework of this model, and the $I=2$ $\ensuremath{\pi}\ensuremath{\pi}$ scattering cross section up to $m(\ensuremath{\pi}\ensuremath{\pi})\ensuremath{\simeq}1$ GeV/${\mathit{c}}^{2}$ is calculated. A value for the $I=2$ $\ensuremath{\pi}\ensuremath{\pi}$ $s$-wave scattering length of $|{{a}_{2}}^{0}|=0.19{{m}_{\ensuremath{\pi}}}^{\ensuremath{-}1}$ 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 $p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ channel is dominated by production of ${\ensuremath{\omega}}^{0}$ [(26\ifmmode\pm\else\textpm\fi{}2)%] and ${N}^{*++}(1238)$ [(30\ifmmode\pm\else\textpm\fi{}6)%]. ${\ensuremath{\rho}}^{\ensuremath{-}}$, ${\ensuremath{\rho}}^{0}$, and ${N}^{*++}(1238)$ 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 $p{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ spectrum has been reported previously. The $n{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{\ensuremath{-}}$ channel shows strong ${N}^{*\ensuremath{-}}(1238)$ production [(50\ifmmode\pm\else\textpm\fi{}10)%] and some weak ${\ensuremath{\rho}}^{0}$ production.

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