Four- and Five-Body Final States from 6.7-GeV/cπ−pInteractions

We have analyzed approximately 9000 four-prong events produced by ${\pi }^{-}p$ interactions at 6.7 GeV/c. All the effective-mass distributions from final states ${\pi }^{-}{\pi }^{-}{\pi }^{+}p$, ${\pi }^{-}{\pi }^{-}{\pi }^{+}{\pi }^{0}p$, and ${\pi }^{-}{\pi }^{-}{\pi }^{+}{\pi }^{+}n$ are presented, as well as cross sections. Resonances in each final state amount to more than 50% of total events, dominated by $\rho$ mesons and $\Delta \mathrm{}\left(1236\right)\mathrm{}$ baryons. Three-pion mass distributions show strong signals in the $A$-meson region in all three final states, but only a modest enhancement is observed in the $R$-meson region. We rule out $J^P$ of $0^{-}$ and $2^{+}$ for the $A_{1.5}$. A similar analysis for the $A_1$ is consistent with $1^{+}$. In the $\pi \rho$ and $\pi \eta$ mass distributions no evidence for $A_2$ structure is seen. Low-mass enhancements in four-pion mass distributions appear in the region of the $B$ meson and the $\rho \mathrm{}\left(1700\right)\mathrm{}$ meson. There is also possibly some evidence for $f^{\prime }\to 4\pi$. Higher-mass nucleon isobars are found to be closely associated with $\Delta \mathrm{}\left(1236\right)\mathrm{}$ production. There is no significant production of quasi-two-body final states.