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 Λπ mass distribution of the Σ(1385). The positions of the poles on the second Riemann sheet corresponding to the Σ(1385) pole and the Λ(1380) and Λ(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 Σ(1385) has negligible influence on the properties of the Λ states given the available data. Still, we identify isospin-1 cusp structures in the present solution in light of new measurements of π ±Λ line-shapes by the Belle collaboration.

Received 1 January 2021DOI:https://doi.org/10.1103/PhysRevD.103.019901© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFew-body systemsParticle & resonance productionResonance reactionsParticles & FieldsNuclear Physics

We formulate the final state interaction of the $a_1(1260)$ resonance decay in a manifestly three-body unitary parameterization and fit it to the $a_1(1260)$ lineshape measured by the ALEPH experiment. Dalitz plots calculated from this fit are presented. The work demonstrates the feasibility to numerically solve a previously derived amplitude and its generalization to isobars with spin and coupled channels. The model can also be applied to other meson decays and modified for the finite-volume problem as it arises in lattice QCD due to its manifest unitarity.

We perform a simultaneous analysis of s- and p-waves of the S=−1 meson–baryon scattering amplitude using all low-energy experimental data. For the first time, differential cross section data are included for chiral unitary coupled-channel models. From this model s- and p-wave amplitudes are extracted and we observe both well-known I(JP)=0(1/2−) s-wave states as well as a new I(JP)=1(1/2+) state absent in quark models and lattice QCD results. Multiple statistical and phenomenological tests suggest that, while the data clearly require an I=1 p-wave resonance, the new state just accounts for the absence of the decuplet Σ(1385)3/2+ in the model.

The helicity couplings at Q(2) = 0 for excited baryonic states have been determined in the past, but no information is available regarding their correlations that are relevant for comparison to theory. We present here our calculation of such correlations between the helicity couplings. They contain information for quantitative comparisons with theoretical values, they can be used to quantify the impact of polarization observables, and can help design new experiments.

Measurements of the linearly-polarized photon beam asymmetry Sigma for photoproduction from the proton of eta and eta ' mesons are reported. A linearly-polarized tagged photon beam produced by coherent bremsstrahlung was incident on a cryogenic hydrogen target within the CEBAF Large Acceptance Spectrometer. Results are presented for the gamma p -> eta p reaction for incident photon energies from 1.070 to 1.876 GeV, and from 1.516 to 1.836 GeV for the gamma p -> eta ' p reaction. For gamma p -> eta p, the data reported here considerably extend the range of measurements to higher energies, and are consistent with the few previously published measurements for this observable near threshold. For gamma p -> eta ' p, the results obtained are consistent with the few previously published measurements for this observable near threshold, but also greatly expand the incident photon energy coverage for that reaction. Initial analysis of the data reported here with the Bonn-Gatchina model strengthens the evidence for four nucleon resonances - the N(1895)1/2(-), N(1900)3/2(+), N(2100)1/2(+) and N(2120)3/2(-) resonances which presently lack the "four-star" status in the current Particle Data Group compilation, providing examples of how these new measurements help refine models of the photoproduction process. (C) 2017 The Authors. Published by Elsevier B.V.