High-EnergyK−-Meson Interactions and Decays

The interactions of 20 to 300 Mev $K^{-}$ mesons on free protons and on emulsion nuclei have been studied and their decays analyzed. The $K^{-}$-meson mean lifetime is found to be (1.38±0.24)×${10}^{-8\mathrm{}}$ sec. Examples of the decay modes $K_{\mu 2}$, $K_{\pi 2}$, $K_{\mu 3}$, $\tau$, and ${\tau }^{\prime }$ are identified. The branching ratios are found to be in agreement with those for $K^{+}$ mesons. The ($K^{-}p, K^{-}p$) elastic scattering cross section is found to be 35±16 mb and the ($K^{-}p, {\Sigma }^{\pm }{\pi }^{\mp }$) cross section 27±13 mb in the energy region of 150 to 300 Mev. The mean free path for $K^{-}$-meson captures and inelastic scatters on emulsion nuclei, except hydrogen, can be represented by $\Lambda \left(\mathrm{cm}\right)=(17.2\mathrm{}\pm 3.4)+(0.081\pm 0.027)T_K$, where $T_K$ is the laboratory $K^{-}$-meson kinetic energy, for $K^{-}$-meson energies from 20 to 300 Mev. This increase in the mean free path with $K^{-}$-meson energy is explained in terms of the decreasing nucleon cross section. The fraction of the interactions of $K^{-}$ mesons on nuclei which are inelastic scatters increases from 2% at low $K^{-}$-meson energies to about 15% at 150 Mev. This increase in inelastic scattering with energy is additional evidence that the nucleus is becoming partially transparent to $K^{-}$ mesons at about 150 Mev. Data are presented for the fraction of events with observed $\pi$ mesons, $\Sigma$ hyperons, and $\pi$ meson-$\Sigma$ hyperon pairs. The data are discussed in terms of the model which was previously presented to explain $K^{-}$ meson captures at rest on nucleons bound in nuclei.