Quark Models of Baryon Masses and Decays

The description of baryon resonance masses and decays in the constituent quark model is outlined, with emphasis on the potential-model approach combined with the 3P0 pair-creation model of strong decays. This approach allows the estimation of branching fractions for baryon states missing in pion nucleon elastic scattering analyses but expected to be present in electromagnetic production. Prospects for the discovery of hybrid baryons are discussed. A subjective list of the most important corrections required to this approach is presented.Comment: 10 pages, 5 figures. Invited contribution to the COSY Workshop on Baryon Excitations, Juelich, 2-3 May 200

Interpretation of the Theta+ as an isotensor pentaquark with weakly decaying partners

The Theta+(1540), recently observed at LEPS, DIANA and CLAS, is hypothesized to be an isotensor resonance. This implies the existence of a multiplet where the Theta++, Theta+ and Theta0 have isospin-violating strong decays, and the Theta+++ and Theta- have weak decays and so are long-lived. Production mechanisms for these states are discussed. The J^P assignment of the Theta is most likely 1/2^- or 3/2^-.Comment: references added, section on pentaquark model revised, 11 pages, LaTeX, accepted for publication in Physics Letters

Kutovi miješanja u barionima S11 i D13

The nature of the short-range interactions between quarks in baryons is of fundamental importance to our understanding of the nature of nuclear matter in the soft-QCD regime. Models of the structure of the negative-parity excited baryons in the S11 and D13 partial waves in Nπ scattering differ in their predictions for the amount by which states of different quark spin but the same total spin are mixed. It may be possible to distinguish among these models by an accurate determination of the mixing angles in these states. A study of the dependence on these mixing angles of their decay branching fractions to Nπ, Nη, and ΛK, using a constituent quark model and the 3P0 decay model, allows conclusions to be drawn about the values of the mixing angles.Priroda kratkodosežnih međudjelovanja među kvarkovima u barionima ima osnovnu važnost za razumijevanje značajki nuklearne tvari u uvjetima mekog QCD. Modeli strukture uzbuđenih bariona negativne parnosti s parcijalnim valovima S11 i D13 u raspršenju Nπ razlikuju se prema svojim predviđanjima ovisno o miješaju stanja s istim ukupnim spinom ali različitih kvarkovskih spinova. Možda će se ti modeli moći razlikovati točnim određivanjem kutova miješanja u tim stanjima. Proučavanje ovisnosti kutova miješanja preko omjera grananja u raspadima Nπ, Nη i ΛK, primjenom modela sastavnih kvarkova i modela raspada 3P0, omogućuje izvođenje zaključaka o iznosima kutova miješanja

Quasi-Two-Body Decays of Nonstrange Baryons

We examine the decays of nonstrange baryons to the final states $\Delta\pi$, $N\rho$, $N\eta$, $N\eta^\prime$, $N\omega$, $N1/2^+(1440)\pi$, and $\Delta3/2^+(1600)\pi$, in a relativized pair-creation($^3P_0$) model which has been developed in a previous study of the $N\pi$ decays of the same baryon states. As it is our goal to provide a guide for the possible discovery of new baryon states at CEBAF and elsewhere, we examine the decays of resonances which have already been seen in the partial-wave analyses, along with those of states which are predicted by the quark model but which remain undiscovered. The level of agreement between our calculation and the available widths from the partial-wave analyses is encouraging.Comment: 41 pages, CEBAF-TH-93-1