Inelasticπ+nInteractions in the Center-of-Mass Energy Range 1.40-1.65 GeV

The reactions ${\pi }^{+}+n\to p+{\pi }^{+}+{\pi }^{-}$ and ${\pi }^{+}+n\to p+\eta$ have been studied as a function of the ${\pi }^{+}n$ center-of-mass energy in the range 1.40-1.65 GeV, using ${\pi }^{+}$ interactions in deuterium and the impulse approximation. Within specified limits, the data are shown to be consistent with this approximation. The relative cross sections for ${\pi }^{+}+n\to p+{\pi }^{+}+{\pi }^{-}$ have been obtained at 13 points in the energy range, with a standard deviation of 4% at the center, rising to 10% at the extreme energies. There is a clear enhancement in the region of the $N^{*}\mathrm{}\left(1470\right)\mathrm{}$ and $N^{*}\mathrm{}\left(1518\right)\mathrm{}$ and the cross section rises steeply at the higher energies. The rapid rise and subsequent decay of the $\eta$-production cross section is confirmed. From the $\eta$-production angular distributions, evidence for the decay of the $N^{*}\mathrm{}\left(1680\right)\mathrm{}$ and $N^{*}\mathrm{}\left(1688\right)\mathrm{}$ into $\eta p$ is found, together with an indication that the $N^{*}\mathrm{}\left(1470\right)\mathrm{}$ may decay in this mode.