π−pTwo-Prong Interactions at 4.16 GeV/c

Abstract

An analysis of ${\pi }^{-}p$ two-prong interactions at 4.16 GeV/c is presented. The total two-prong cross section is 19.11±0.40 mb, based on 33 672 events. The elastic-scattering differential cross section shows an exponential behavior, $K\exp (-A{\Delta }^2)$. With $A=7.36\mathrm{}\pm 0.14$ Ge${\mathrm{V}}^{-2\mathrm{}}$, the "absorption parameters" are derived as $C_{+}=0.846\mathrm{}\pm 0.017$ and ${\gamma }_{+}=0.040\mathrm{}\pm 0.001$. The final-state ${\pi }^{-}{\pi }^{0}p$ exhibits a strong ${\rho }^{-}$, and the ${\pi }^{-}{\pi }^{+}n$ a strong ${\rho }^0$ and $f^0$. The partial cross sections for the dominant resonant channels $p{\rho }^{-}$, ${\pi }^{-}{\Delta }^{+}\mathrm{}\left(1236\right)\mathrm{} (\to p{\pi }^0)$, ${\rho }^{0}n$, and $f^{0}n$ are 0.59±0.03, 0.17±0.01, 1.15±0.05, and 0.53±0.06 mb, respectively. The ${\rho }^{-}$ production and decay angular distributions do not agree with the predictions of the absorption-modified one-pion-exchange model. However, an inclusion of the contribution from $\omega$ exchange adequately accounts for the discrepancy. The ${\rho }^0$ asymmetry is interpreted as a result of an interference of the resonant $P$ wave and isospin-zero $S$ wave, and the corresponding spin-density matrix elements are obtained. In the final state ${\pi }^{-}p$+neutrals, a clear peak for the $\eta$ meson and some evidence for the $\omega$ meson are seen.