295 research outputs found
Extra S11 and P13 in the Hypercentral Constituent Quark Model
We report on the recent results of the hypercentral Constituent Quark Model
(hCQM). The model contains a spin independent three-quark interaction which is
inspired by Lattice QCD calculations and reproduces the average energy values
of the SU(6) multiplets. The splittings within each multiplet are obtained with
a SU(6)-breaking interaction, which can include also an isospin dependent term.
All the 3- and 4-stars resonances are well reproduced. Moreover, as all the
Constituent Quark models, the hCQM predicts ``missing'' resonances ({\em e.g.}
extra and states) which can be of some help for the experimental
identification of new resonances. The model provides also a good description of
the medium -behavior of the electromagnetic transition form factors. In
particular the calculated helicity amplitude for the
resonance agrees very well with the recent CLAS data. More recently, the
elastic nucleon form factors have been calculated using a relativistic version
of the hCQM and a relativistic quark current.Comment: 7 pages,3 figures, Talk given at NStar 2002 workshop on the physics
of excited nucleons, Pittsburgh, Pennsylvania, October 9-12, 200
Masses and magnetic moments of pentaquarks
We discuss the spectroscopy of pentaquarks. The quantum numbers of the ground
state depend on the interplay between spin-flavor and orbital contributions to
the energy. The magnetic moments of the lowest pentaquark state with negative
and positive parity are found to be 0.382 \mu_N and 0.089 \mu_n, respectively.Comment: 15 pages, 4 figures, 3 tables (text rewritten, extra figure added,
essential results unchanged
Mass spectrum of pentaquarks
We discuss the properties of the pentaquark in a collective stringlike model
with a nonplanar configuration of the four quarks and the antiquark. In an
application to the mass spectrum of exotic Theta baryons, we find that the
ground state pentaquark has angular momentum and parity J(p)=1/2(-) and a small
magnetic moment of 0.382 nuclear magnetons. The decay width is suppressed by
the spatial overlap with the decay products.Comment: 8 pages, 3 figures, 1 table, invited talk at 23rd International
Workshop on Nuclear Theory, June 14-19, 2004, Rila, Bulgari
Hypercentral constituent quark model and isospin dependence
The constituent quark model based on a hypercentral approach takes into
account three-body force effects and standard two-body potential contributions.
The quark potential contains a hypercentral interaction, to which a hyperfine
term is added. While the hypercentral potential supplies good values for the
centroid energies of the resonance multiplets and a realistic set of quark wave
functions, the hyperfine splittings are sometimes not sufficient to account for
the observed masses.
In this work we have introduced an improved form of the hyperfine interaction
and an isospin dependent quark potential. The resulting description of the
baryon spectrum is very good, also for the Roper resonance, specially thanks to
the flavour dependent interaction.Comment: 12 pages, 2 figures, accepted by Eur. Phys. J.
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