Calculation of the _Σ⁴He Bound State in the ⁴He(K^-,π^-) Reaction at 600MeV/c

We examine phenomenologically the 4He(in-flight K-,π-) spectrum at pK- = 600MeV/c and θKπ = 4° within distorted-wave impulse approximation calculations by using a coupled (3N-Λ)+(3N-Σ) model. The result shows that there exists a pole of the Σ4He unstable bound state on the second Riemann sheet of the complex energy plane, and its complex eigenvalue is EΣ+(pole) = -1.1-i6.2 MeV near the Σ threshold. Because of the Σ branch cut associated with opening the Σ channel, an asymmetric peak for Σ4He appears with lying at 3.7 MeV below the Σ+3H threshold and the width of about 10 MeV, which is in good agreement with the recent observation.