Final States with a Single Charged Particle and VisibleΛfromK−nInteractions at 4.5 GeV/c

Abstract

The results presented in this paper were obtained from an analysis of 372 000 $K^{-}d$ bubble-chamber pictures at an incident $K^{-}$ momentum of 4.48 GeV/c. This paper reports the results on two-body final states, such as ${\pi }^{-}\Lambda$, ${\pi }^{-}{\Sigma }^0$, ${\rho }^{-}\Lambda$, ${\pi }^{-}{\Sigma }^0\mathrm{}\left(1385\right)\mathrm{}$, ${\pi }^0{\Sigma }^{-}\mathrm{}\left(1385\right)\mathrm{}$, ${{\pi }_N}^{-}\mathrm{}\left(980\right)\mathrm{}\Lambda$, $\eta {\Sigma }^{-}\mathrm{}\left(1385\right)\mathrm{}$. The polarization of the $\Lambda$ hyperon in the reaction $K^{-}n\to {\pi }^{-}\Lambda$ has been determined and compared with the double-Regge-pole model of Reeder and Sarma. The polarization is large and remains more or less constant. No change in sign was observed, in contrast with the prediction of the model of Reeder and Sarma. A common feature of the observed two-body final states is that their production process is dominated by a peripheral mechanism which arises from meson exchange processes. The exchange mechanism for the reaction $K^{-}n\to {\rho }^{-}\Lambda$ was investigated in terms of the density matrix formalism. It was found that more than one exchange contributes to the production of this final state. The ${{\pi }_N}^{-}\mathrm{}\left(980\right)\mathrm{}$ meson was observed in the reaction $K^{-}n\to {{\pi }_N}^{-}\Lambda$. The decay mode observed was ${{\pi }^{-}}_N\to {\pi }^{-}\eta$. The mass observed is 0.98±0.01 GeV with a width of 0.06±0.03 GeV.