Calculation of the Σ4He bound state in the 4He(K-,π-) reaction at 600 MeV/c

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