On the structure in the ΛN cross section at the ΣN threshold

The complexity of threshold phenomena is exemplified on a prominent and long-known case - the structure in the Lambda p cross section (invariant mass spectrum) at the opening of the Sigma N channel. The mass splitting between the Sigma baryons together with the angular momentum coupling in the S-3(1) - D-3(1) partial wave imply that, in principle, up to six channels are involved. Utilizing hyperon-nucleon potentials that provide an excellent description of the available low-energy Lambda p and Sigma N scattering data, the shape of the resulting Lambda p cross section is discussed and the poles near the Sigma N threshold are determined. Evidence for a strangeness S = -1 dibaryon is provided, in the form of a (unstable) Sigma N bound state in the vicinity of the Sigma N threshold. Predictions for level shifts and widths of Sigma(-)p atomic states are given.

Automated summary

The complexity of threshold phenomena is exemplified by the structure in the Lambda p cross section at the opening of the Sigma N channel. The mass splitting between the Sigma baryons and angular momentum coupling in the S-3(1) - D-3(1) partial wave imply the involvement of up to six channels. Evidence for a strangeness S = -1 dibaryon is provided with predictions for level shifts and widths of Sigma(-)p atomic states.