Capture ofK−Mesons by Nuclei

Abstract

Seventy events of $K^{-}$ capture at rest have been analyzed in emulsion stacks exposed to the Berkeley Bevatron. The distribution of prong numbers and energy release of stars is given. The average prong number was 3.3 and the maximum prong number was 10. The small average energy release was found to be consistent with the assumption that in many events a large fraction of the $K^{-}$ rest energy is carried away by neutral particles. The energy distribution of emitted nucleons was found to include energies up to 200 Mev. The energy distribution of emitted pions falls into two groups, one with a sharp upper limit corresponding to the expected pion energy of $\Sigma$-hyperon reactions and the other corresponding to ${\Lambda }^0$-hyperon reactions. The energy release in $\Sigma \pi$ events was found to be consistent with the assumption that the capture process takes place on bound nucleons. A small difference in the energy release of ${\Sigma }^{+}{\pi }^{-}$ compared with ${\Sigma }^{-}{\pi }^{+}$ events was found, indicating a possible mass difference $M\left({\Sigma }^{-}\right)>M\left({\Sigma }^{+}\right)$. An estimate of the ratio of production of $\Sigma$ to ${\Lambda }^0$ hyperons, based on pion energies, gave $\frac{\Sigma }{{\Lambda }^0}$ about 2. The ratio $\frac{{\Sigma }^{-}}{{\Sigma }^{+}}$ was found to be $\ge \frac{7}{3}$. The emission of pions with energies of more than 100 Mev was found, providing evidence for the direct production of ${\Lambda }^0$ hyperons. Hyperfragments were observed in four events. In one event two fast particles of nucleonic mass were emitted, one of them disappearing in flight, providing evidence for the existence of two-nucleon reactions.