Model Dependence of the Properties of S11 Baryon Resonances

The properties of baryon resonances are extracted from a complicated process of fitting sophisticated, empirical models to data. The reliability of this process comes from the quality of data and the robustness of the models employed. With the large of amount of data coming from recent experiments, this is an excellent time for a study of the model dependence of this extraction process. A test case is chosen where many theoretical details of the model are required, the S11 partial wave. The properties of the two lowest N* resonances in this partial wave are determined using various models of the resonant and non-resonant amplitudes.Comment: 24 pages, 10 figures; revised fits with error estimates, expanded comparison between CMB and K-matrix model

Longitudinal response function of 4He with a realistic force

The longitudinal response function of 4He is calculated with the Argonne V18 potential. The comparison with experiment suggests the need of a three-body force. When adding the Urbana IX three-body potential in the calculation of the lower longitudinal multipoles, the total strength is suppressed in the quasi-elastic peak, towards the trend of the experimental data.Comment: 3 pages, 3 figures, proceedings of the 20th European Conference on Few-Body Problems in Physics (EFB20

Evidence for the fourth P11 resonance predicted by the constituent quark model

It is pointed out that the third of five low-lying P11 states predicted by a constituent quark model can be identified with the third of four states in a solution from a three-channel analysis by the Zagreb group. This is one of the so-called ``missing'' resonances, predicted at 1880 MeV. The fit of the Zagreb group to the pi N -> eta N data is the crucial element in finding this fourth resonance in the P11 partial wave.Comment: 8 pages, revtex; expanded acknowledgement

Covariant calculation of mesonic baryon decays

We present covariant predictions for pi and eta decay modes of N and Delta resonances from relativistic constituent-quark models based on one-gluon-exchange and Goldstone-boson-exchange dynamics. The results are calculated within the point-form approach to Poincare-invariant relativistic quantum mechanics applying a spectator-model decay operator. The direct predictions of the constituent-quark models for covariant pi and eta decay widths show a behaviour completely different from previous ones calculated in nonrelativistic or so-called semirelativistic approaches. It is found that the present theoretical results agree with experiment only in a few cases but otherwise always remain smaller than the experimental data (as compiled by the Particle Data Group). Possible reasons for this behaviour are discussed with regard to the quality of both the quark-model wave functions and the mesonic decay operator.Comment: 10 pages, 2 figures, accepted for publication in Phys. Rev.

Unquenching the Quark Model and Screened Potentials

The low-lying spectrum of the quark model is shown to be robust under the effects of `unquenching'. In contrast, the use of screened potentials is shown to be of limited use in models of hadrons. Applications to unquenching the lattice Wilson loop potential and to glueball mixing in the adiabatic hybrid spectrum are also presented.Comment: 6 pages, 3 ps figures, revtex. Version to appear in J. Phys.

Pseudoscalar meson photoproduction: from known to undiscovered resonances

The role of dynamics in spin observables for pseudoscalar meson photoproduction is investigated using a density matrix approach in a multipole truncated framework. Extraction of novel rules for $\gamma p \rightarrow \pi^+ n,~ K^+ \Lambda$ and $\eta p$ reactions based on resonance dominance, and on other broad and reasonable dynamical assumptions, are discussed. Observables that are particularly sensitive to missing nucleonic resonances predicted by quark-based approaches, are singled out.Comment: 22 pages, latex, 3 figure