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Register a new userCovariant calculation of nonstrange decays of strange baryon resonances
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We report on a study of pi and eta decays of strange baryon resonances within relativistic constituent-quark models based on one-gluon-exchange and Goldstone-boson-exchange dynamics. The investigations are performed in the point form of Poincare-invariant relativistic quantum mechanics with a spectator-model decay operator. The covariant predictions of the constituent-quark models underestimate the experimental data in most cases. These findings are congruent with an earlier study of nonstrange baryon decays in the light-flavor sector. We also consider a nonrelativistic reduction of the point-form spectator model, which leads to the decay operator of the elementary emission model. For some decays the nonrelativistic results differ substantially from the relativistic ones and they exhibit no uniform behavior as they scatter above and below the experimental decay widths.
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We present results for kaon decay widths of baryon resonances from a relativistic study with constituent quark models. The calculations are done in the point-form of Poincare-invariant quantum mechanics with a spectator-model decay operator. We obtain covariant predictions of the Goldstone-boson-exchange and a variant of the one-gluon-exchange constituent quark models for all kaon decay widths of established baryon resonances. They are generally characterized by underestimating the available experimental data. In particular, the widths of kaon decays with increasing strangeness in the baryon turn out to be extremely small. We also consider the nonrelativistic limit, leading to the familiar elementary emission model, and demonstrate the importance of relativistic effects. It is found that the nonrelativistic approach evidently misses sensible influences from Lorentz boosts and some essential spin-coupling terms.
The description of baryon resonance decays represents a major challenge of strong interaction physics. We will report on a relativistic approach to mesonic decays of light and strange baryon resonances within constituent quark models. The calculations are performed in the point-form of relativistic quantum mechanics, specifically focussing on the strange sector. It is found that the relativistic predictions generally underestimate the experimental data. The nonrelativistic approximation of the approach leads to the decay operator of the elementary emission model. It is seen that the nonrelativistic reduction has considerable effects on the decay widths.
Constituent quark models provide a reasonable description of the baryon mass spectra. However, even in the light- and strange-flavor sectors several intriguing shortcomings remain. Especially with regard to strong decays of baryon resonances no consistent picture has so far emerged, and the existing experimental data cannot be explained in a satisfactory manner. Recently first covariant calculations with modern constituent quark models have become available for all pi, eta, and K decay modes of the low-lying light and strange baryons. They generally produced a remarkable underestimation of the experimental data for partial decay widths. We summarize the main results and discuss their impact on the classification of baryon resonances into flavor multiplets. These findings are of particular relevance for future efforts in the experimental investigation of baryon resonances.
Given presently known empirical information about the exotic Theta+ baryon, we analyze possible properties of its SU(3)F partners, paying special attention to the nonstrange member of the antidecuplet N*. The modified PWA analysis presents two candidate masses, 1680 MeV and 1730 MeV. In both cases the N* should be highly inelastic. The theoretical analysis, based on the soliton picture and assumption of Gamma(Theta+) < 5 MeV, shows that most probably Gamma(N*) < 30 MeV. Similar analysis for Xi3/2 predicts its width to be not more than about 10 MeV. Our results suggest several directions for experimental studies that may clarify properties of the antidecuplet baryons, and structure of their mixing with other baryons.
Longitudinal and transverse transition form factors for most of the four-star nucleon resonances have been obtained from high-quality cross section data and polarization observables measured at MAMI, ELSA, BATES, GRAAL and CEBAF. As an application, we further show how the transition form factors can be used to obtain empirical transverse charge densities. Contour plots of the thus derived densities are shown and compared for the Roper and S11 nucleon resonances.
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