123 research outputs found
Does the quark cluster model predict any isospin two dibaryon resonance?
We analyze the possible existence of a resonance in the channel
with isospin two by means of nucleon- interactions based on the
constituent quark model. We solve the bound state and the scattering problem
using two different potentials, a local and a non-local one. The non-local
potential results to be the more attractive, although not enough to generate
the experimentally predicted resonance.Comment: 9 pages in Latex (revtex), 2 eps figures available under reques
Mass and width of the resonance in nuclei
We calculated the mass and width of the resonance inside nuclei within a
nucleon- model by including the self-energy of the in the
propagator. We found that in the nuclear medium the width of the
is increased by one order of magnitude while its mass changes only by a few
MeV. This broadening of the width of the resonance embedded in nuclei is
consistent with the experimental observations so that the can be
understood as a resonance. Thus, given the freedom between either
isospin 0 or isospin 2 for the , our results give weigth to the isospin-2
assignment.Comment: 14 pages, RevteX type, 2 eps figures. To be published in Phys. Rev. C
(September
Microscopic transition potential: Determination of and coupling constants
A transition potential, based on an effective
quark-quark interaction and a constituent quark cluster model for baryons, is
derived in the Born-Oppenheimer approach. The potential shows significant
differences with respect to those obtained by a direct scaling of the
nucleon-nucleon interaction. From its asymptotic behavior we extract the values
of and coupling constants in a
particular coupling schemeComment: 15 eps figures, Accepted for publication in Phys. Rev.
Covariant equations for the three-body bound state
The covariant spectator (or Gross) equations for the bound state of three
identical spin 1/2 particles, in which two of the three interacting particles
are always on shell, are developed and reduced to a form suitable for numerical
solution. The equations are first written in operator form and compared to the
Bethe-Salpeter equation, then expanded into plane wave momentum states, and
finally expanded into partial waves using the three-body helicity formalism
first introduced by Wick. In order to solve the equations, the two-body
scattering amplitudes must be boosted from the overall three-body rest frame to
their individual two-body rest frames, and all effects which arise from these
boosts, including the Wigner rotations and rho-spin decomposition of the
off-shell particle, are treated exactly. In their final form, the equations
reduce to a coupled set of Faddeev-like double integral equations with
additional channels arising from the negative rho-spin states of the off-shell
particle.Comment: 57 pages, RevTeX, 6 figures, uses epsf.st
Effective Lagrangian Approach to pion photoproduction from the nucleon
We present a pion photoproduction model on the free nucleon based on an
Effective Lagrangian Approach (ELA) which includes the nucleon resonances
(, N(1440), N(1520), N(1535), , N(1650), and
), in addition to Born and vector meson exchange terms. The
model incorporates a new theoretical treatment of spin-3/2 resonances, first
introduced by Pascalutsa, avoiding pathologies present in previous models.
Other main features of the model are chiral symmetry, gauge invariance, and
crossing symmetry. We use the model combined with modern optimization
techniques to assess the parameters of the nucleon resonances on the basis of
world data on electromagnetic multipoles. We present results for
electromagnetic multipoles, differential cross sections, asymmetries, and total
cross sections for all one pion photoproduction processes on free nucleons. We
find overall agreement with data from threshold up to 1 GeV in laboratory
frame.Comment: Misprints corrected. 60 pages. 33 figures.5 tables. Accepted for
publication in Annals of Physics (NY
Assignments of Baryons
The "good" diquark is employed to study baryons within a mass
loaded flux tube model. The study indicates that all baryons
candidates in the 2008 review by the Particle Data Group (PDG) are well
described in the mass loaded flux tube model. The quantum numbers of
these candidates are assigned. If is an
orbitally excited , it is likely the one. If
is an orbitally excited , there ought to be
another with mass MeV. In the
model, there exists no predicted
in existing literature. is very possible the orbitally
excited baryon with .Comment: 4 pages, 3 tables, RevTex, Two typos correcte
Deuteron NN*(1440) components from a chiral quark model
We present a nonrelativistic coupled-channel calculation of the deuteron
structure including Delta Delta and NN^*(1440) channels, besides the standard
NN S and D-wave components. All the necessary building blocks to perform the
calculation have been obtained from the same underlying quark model. The
calculated NN^*(1440) probabilities find support in the explanation given to
different deuteron reactions.Comment: 4 pages; revtex4, Accepted for publication in Phys. Rev. C (Brief
Report
Polarization observables of the gamma d --> PiNN reaction in the Delta(1232)-resonance region
Polarization observables of the three charge states of the pion for the
reaction with polarized photon beam and/or oriented
deuteron target are evaluated over the whole (1232)-resonance region
adopting a nonrelativistic model based on time-ordered perturbation theory.
Results for the -meson spectra, linear photon asymmetry, vector and tensor
target asymmetries are presented. Particular attention is given, for the first
time, to double polarization asymmetries for which we present results for
and . We found that all other double
polarization asymmetries of photon and deuteron target are vanished.Comment: 17 Pages, 8 Figures, accepted for publication in Int. J. Mod. Phys.
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.
Elastic Scattering of Pions From the Three-nucleon System
We examine the scattering of charged pions from the trinucleon system at a
pion energy of 180 MeV. The motivation for this study is the structure seen in
the experimental angular distribution of back-angle scattering for pi+ 3He and
pi- 3H but for neither pi- 3He nor pi+ 3H. We consider the addition of a double
spin flip term to an optical model treatment and find that, though the
contribution of this term is non-negligible at large angles for pi+ 3He and pi-
3H, it does not reproduce the structure seen in the experiment.Comment: 15 pages + 5 figure
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