⁴He(K ⁻,π⁻) Spectra and the ⁴_Σ He Bound State

Abstract

We examine phenomenologically the ⁴He(K ⁻,π⁻) spectra in flight and at rest within the distorted-wave impulse approximation by using a coupled (3N−Λ)+(3N−Σ) model with a spreading potential. The resultant spectra can explain consistently all the available data. We show that there exists a pole of the ⁴_Σ He unstable bound state on the second Riemann sheet of the complex energy plane.