New insights into the pole parameters of the $\Lambda(1380)$, the $\Lambda(1405)$ and the $\Sigma(1385)$

TL;DR

This study refines the understanding of the pole parameters of the $\Lambda(1380)$, $\Lambda(1405)$, and $\Sigma(1385)$ resonances using an extended chiral-unitary approach with new experimental data, revealing improved precision and parameter correlations.

Contribution

The paper extends a coupled-channel chiral-unitary model to include new experimental data, providing more precise pole positions and couplings for strange baryon resonances, and investigates parameter correlations for the first time.

Findings

Resonance positions and branching ratios determined with ~20% higher precision.

Correlations between pole parameters are significant and analyzed.

$\Sigma(1385)$ has negligible influence on $\Lambda$ states with current data.

Abstract

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 $\Sigma(1385)$ 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 $\pi^\pm\Lambda$ line-shapes by the Belle collaboration.