Dynamical coupled-channels model of $K^- p$ reactions (II): Extraction of $\Lambda^*$ and $\Sigma^*$ hyperon resonances

TL;DR

This paper extracts hyperon resonance parameters using a dynamical coupled-channels model, confirming known resonances, proposing new ones, and highlighting the need for more precise data to resolve analysis discrepancies.

Contribution

We developed a comprehensive coupled-channels analysis to extract hyperon resonance parameters, identifying new resonances and emphasizing the importance of polarization data.

Findings

Confirmed most four-star hyperon resonances

Proposed a new narrow J^P=3/2^+ Lambda resonance

Highlighted discrepancies with other analyses and the need for better data

Abstract

Resonance parameters (pole masses and residues) associated with the excited states of hyperons, Lambda^* and Sigma^*, are extracted within a dynamical coupled-channels model developed recently by us [Phys. Rev. C 90, 065204 (2014)] through a comprehensive partial-wave analysis of the K^- p --> barK N, pi Sigma, pi Lambda, eta Lambda, K Xi data up to invariant mass W = 2.1 GeV. We confirm the existence of resonances corresponding to most, if not all, of the four-star resonances rated by the Particle Data Group. We also find several new resonances, and in particular propose a possible existence of a new narrow J^P=3/2^+ Lambda resonance that couples strongly to the eta Lambda channel. The J^P=1/2^- Lambda resonances located below the barK N threshold are also discussed. Comparing our extracted pole masses with the ones from a recent analysis by the Kent State University group, some significant differences in the extracted resonance parameters are found, suggesting the need of more extensive and accurate data of K^- p reactions including polarization observables to eliminate such an analysis dependence of the resonance parameters. In addition, the determined large branching ratios of the decays of high-mass resonances to the pi Sigma^* and barK^* N channels also suggest the importance of the data of 2 --> 3 reactions such as K^- p --> pi pi Lambda and K^- p --> pi barK N. Experiments on measuring cross sections and polarization observables of these fundamental reactions are highly desirable at hadron beam facilities such as J-PARC for establishing the Lambda^* and Sigma^* spectrum.