We examine phenomenologically the inclusive and exclusive 4 He (K − ,π − ) reactions from a stopped K − within a distorted-wave impulse approximation by using a coupled ( 3N – Λ ) + ( 3N – Σ ) model with a spreading potential. We discuss these spectra from various atomic orbits of K − – 4 He atoms in order to explain the reaction mechanism quantitatively. The results show that the spectra are in excellent agreement with the available data from Λ to Σ regions simultaneously, including the in-flight reactions; the capture probabilities per stopped K − for Λ 4 He and Σ 4 He are 1.7% and 9.5%, respectively. It is established that there exists the Σ 4 He unstable bound state, of which pole resides on the second Riemann sheet of the complex energy plane in the 3N – Y system.
