New insights into the pole parameters of the Λ(1380), the Λ(1405) and the Σ(1385)

A coupled-channel S- and P-wave next-to-leading order chiral-unitary approach for strangeness S = -1 meson-baryon scattering is extended to include the new data from the KLOE and AMADEUS experiments as well as the Lambda pi mass distribution of the Sigma(1385). The positions of the poles on the second Riemann sheet corresponding to the S(1385) pole and the Lambda(1380) and Lambda(1405) poles as well as the couplings of these states to various channels are calculated. We find that the resonance positions and branching ratios are on average determined with about 20% higher precision when including the KLOE and AMADEUS data. Additionally, for the first time, the correlations between the parameters of the poles are investigated and shown to be relevant. We also find that the Sigma(1385) has negligible influence on the properties of the Lambda states given the available data. Still, we identify isospin-1 cusp structures in the present solution in light of new measurements of pi +/-(Lambda) line-shapes by the Belle collaboration.

Automated summary

By extending the coupled-channel S- and P-wave next-to-leading order chiral-unitary approach, we have successfully incorporated the new data from the KLOE and AMADEUS experiments as well as the Lambda pi mass distribution of the Sigma(1385) into the strangeness S = -1 meson-baryon scattering. We have calculated the positions of the poles on the second Riemann sheet corresponding to the S(1385) pole and the Lambda(1380) and Lambda(1405) poles, as well as the couplings of these states to various channels. The inclusion of KLOE and AMADEUS data has improved the average precision for determining resonance positions and branching ratios by about 20%.