Double Resonance Production by 2.77-BeV/cπ+Mesons on Hydrogen

Reactions ${\pi }^{+}+p\to {\pi }^{+}+{\pi }^{+}+{\pi }^{-}+p$, ${\pi }^{+}+p\to {\pi }^{+}+{\pi }^{+}+{\pi }^{-}+p+{\pi }^0$ and ${\pi }^{+}+p\to {\pi }^{+}+{\pi }^{+}+{\pi }^{+}+{\pi }^{-}+n$ were studied at an incident ${\pi }^{+}$ momentum of 2.77 BeV/c. The first reaction is dominated by a quasi-two-body intermediate state $\rho +N^{*}$. The decay distributions of $\rho$ and $N^{*}$ are consistent with the predictions of the single-pion-exchange model. The ${\rho }^0$ decay distributions show the well-known asymmetry, which may be attributed to an interference with a $T=0\mathrm{}$ even-spin background. The second reaction is dominated by a quasi-two-body intermediate state $\omega +N^{*}$. The decay distributions of $\omega$ and $N^{*}$ are not consistent with the unmodified $\rho$-exchange model, but could be made to be consistent by including the absorptive effects in the input and output channels. The last reaction shows no prominent resonance production.