Four-star Resonances Research Articles

Erratum: Dynamical coupled-channels model of K−p reactions. II. Extraction of Λ* and Σ* hyperon resonances [Phys. Rev. C 92 , 025205 (2015)

Resonance parameters (pole masses and residues) associated with the excited states of hyperons, Λ* and Σ*, are extracted within a dynamical coupled-channels model developed recently by us [Phys. Rev. C 90, 065204 (2014)]PRVCAN0556-281310.1103/PhysRevC.90.065204 through a comprehensive partial-wave analysis of the K−p→K¯N,πΣ,πΛ,ηΛ,KΞ 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 JP=3/2+Λ resonance that couples strongly to the ηΛ channel. The JP=1/2−Λ resonances located below the K¯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 πΣ* and K¯*N channels also suggest the importance of the data of 2→3 reactions such as K−p→ππΛ and K−p→πK¯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 Λ* and Σ* spectrum.

Dynamical coupled-channels model ofK−preactions. II. Extraction ofΛ*andΣ*hyperon resonances

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.

Production and Dalitz decays of baryon resonances in proton-proton interaction at = 3.16 GeV with HADES

One of the physics goals of HADES is to investigate spectral modifications of light vector mesons in strongly interacting matter via their dielectron (e+e−) decay channel. Theoretical models predict such modifications due to strong meson-baryon resonance coupling which can be also probed in elementary collisions. In 2007 electron-positron pair production has been measured in p+p reactions at a beam kinetic energy of 3.5 GeV. We present analysis results of the exclusive channels ppπ0, pnπ+, ppe+e−, which indicate contributions of higher resonances. In order to estimate production cross sections of the baryonic resonances, the results have been compared to Monte Carlo calculations based on a resonance model assuming an incoherent sum of various four-star resonances. To obtain the corresponding e+e− yields, two models of the width parametrization are applied in the simulation.

Effects of a spin-flavour-dependent interaction on light-flavoured baryon helicity amplitudes

This paper is a continuation of a previous work about the effects of a phenomenological flavour-dependent force in a relativistically covariant constituent quark model based on the Salpeter equation on the structure of light-flavoured baryon resonances. Here the longitudinal and transverse helicity amplitudes as studied experimentally in the electro-excitation of nucleon- and Δ-resonances are calculated. In particular the amplitudes for the excitation of three- and four-star resonances as calculated in a previous model A are compared to those of the novel model C as well as to existing and partially new experimental data such as, e.g., determined by the CB-ELSA Collaboration. A brief discussion on some improvements to model C is given after the introduction.

Baryon resonance analysis from MAID

The unitary isobar model MAID2007 has been used to analyze the recent data of pion electroproduction. The model contains all four-star resonances in the region below W = 2 GeV and both single-Q2 and Q2 dependent transition form factors could be obtained for the Delta, Roper, D13(1520), S11(1535), S31(1620), S11(1650), D15(1675), F15(1680) and P13(1720). From the complete world data base, including also π− data on the neutron, also Q2 dependent neutron form factors are obtained. For all transition form factors we also give convenient numerical parameterizations that can be used in other reactions. Furthermore, we show how the transition form factors can be used to obtain empirical transverse charge densities and our first results are given for the Roper, the S11 and D13 resonances.

Unitary isobar model --MAID2007

The unitary isobar model MAID2007 has been developed to analyze the world data of pion photo- and electroproduction. The model contains both a common background and several resonance terms. The background is unitarized according to the K-matrix prescription, and the 13 four-star resonances with masses below 2 GeV are described by appropriately unitarized Breit-Wigner forms. The data have been analyzed by both single-energy and global fits, and the transverse and longitudinal helicity amplitudes have been extracted for the four-star resonances below 2 GeV. Because of its inherent simplicity, MAID2007 is well adopted for predictions and analysis of the observables in pion photo- and electroproduction.