We have observed an intense high-energy component in an inclusive ${}^4\mathrm{He}$(stopped $K^{-},d$) spectrum. For back-to-back $\Lambda d$ pairs a prominent event cluster has been found just below the $m_{{}^4\mathrm{He}}+m_{K^{-}}-m_n$ mass threshold in the $\Lambda d$ invariant mass spectrum of $\Lambda \mathit{dn}$ events, which is evidence for a three-nucleon absorption process of $K^{-}$ in ${}^4\mathrm{He}$. In addition, an appreciable strength is revealed below $~3220$ MeV/$c^2$. Well separated ${\Sigma }^0\mathit{dn}$ events show a peak similar to the case of $\Lambda \mathit{dn}$.

• Received 5 September 2007

DOI:https://doi.org/10.1103/PhysRevC.76.068202