370 research outputs found
ESTABLISHING PRIORITIES AMONG MULTIPLE MANAGEMENT GOALS
Institutional and Behavioral Economics,
Extraction of the Ratio of the N^*(1535) Electromagnetic Helicity Amplitudes from Eta Photoproduction off Neutrons and Protons
Using the recent precise measurements of eta photopro- duction in proton and
deuteron targets, we extract the ratio of the helicity amplitudes A^n_1/2 /
A^p_1/2, for the excitation of N^*(1535), in the effective Lagrangian approach,
It is fairly model-independent, free from the final-state interaction effects,
and negative as predicted by the quark models. We stress the importance of
polarization observables in further elucidation of the N^*(1520)
photoexcitation amplitudes.Comment: 4 figures. It will be published in Phys. Lett.
A (p/E) Calculation of Strong Pionic Decays of Baryons
Strong pionic decays of baryons are studied in a non-relativistic quark model
framework via a convergent (p/E) expansion of the transition operator. Results
are compared to the ones obtained within a more conventional (p/m) expansion.Comment: 16 pages, LaTeX, using amssymb.st
Baryon Current Matrix Elements in a Light-Front Framework
Current matrix elements and observables for electro- and photo-excitation of
baryons from the nucleon are studied in a light-front framework. Relativistic
effects are estimated by comparison to a nonrelativistic model, where we use
simple basis states to represent the baryon wavefunctions. Sizeable
relativistic effects are found for certain transitions, for example, to radial
excitations such as that conventionally used to describe to the Roper
resonance. A systematic study shows that the violation of rotational covariance
of the baryon transition matrix elements stemming from the use of one-body
currents is generally small.Comment: 32 pages, LaTeX, 10 postscript figures, uses epsf.sty; figures
uuencoded with uufiles (or available by request in .ps or hardcopy form
Semi-relativistic charge-current density operator
The charge-current density and two-photon operators consistent with a
single-particle semi-relativistic Hamiltonian are derived within a suitable
functional derivative formalism which preserves gauge invariance. An
application to electron scattering is presented and results are compared with a
fully relativistic case and the non-relativistic cases corrected through fourth
order in M^{-1}.Comment: 20 pages, 3 postscript figures, typos correcte
Light-front CQM calculations of baryon electromagnetic form factors
The parameter-free predictions for the and electromagnetic transition form factors, obtained within our
light-front constituent quark model using eigenfunctions of a baryon mass
operator which includes a large amount of configuration mixing, are reported.
The effects due to small components in the baryon wave functions, such as S'-
and D-wave, are also investigated.Comment: to appear in the Proceedings of the International Workshop on Hadron
Dynamics with the new DAPHNE and CEBAF facilities, Frascati, Italy, 11-14
November 199
Delta isobar masses, large N_c relations, and the quark model
Motivated by recent remarks on the Delta+ mass and comparisons between the
quark model and relations based on large-N_c with perturbative flavor breaking,
two sets of Delta masses consistent with these constraints are constructed.
These two sets, based either on an experimentally determined mass splitting or
a quark model of isospin symmetry breaking, are shown to be inconsistent. The
model dependence of this inconsistency is examined, and suggestions for
improved experiments are made. An explicit quark model calculation and mass
relations based on the large-N_c limit with perturbative flavor breaking are
compared. The expected level of accuracy of such relations is realized in the
quark model, except for mass relations spanning more than one SU(6)
representation. It is shown that the Delta0 and Delta++ pole masses and Delta0
- Delta+ = (Delta- - Delta++)/3 about 1.5 MeV are more consistent with model
expectations than the analogous Breit-Wigner masses and their splittings.Comment: 10 pages, including 1 eps figure, revte
Algebraic Models of Hadron Structure II. Strange Baryons
The algebraic treatment of baryons is extended to strange resonances. Within
this framework we study a collective string-like model in which the radial
excitations are interpreted as rotations and vibrations of the strings. We
derive a mass formula and closed expressions for strong and electromagnetic
decay widths and use these to analyze the available experimental data.Comment: 60 pages, 8 figures, 30 tables, Annals of Physics (N.Y.), in pres
Electromagnetic Form Factors of the Nucleon in a Relativistic Quark Pair Creation Model
We study the effects of the | qqq q\bar{q} > component of the hadronic wave
function on the description of the electromagnetic structure of the nucleon.
Starting with a qqq baryonic wave function which describes the baryonic and
mesonic low energy spectrum, the extra q\bar{q} pair is generated through a
relativistic version of the 3P_0 model. It is shown that this model leads to a
renormalization of the quark mass that allows one to construct a conserved
electromagnetic current. We conclude that these dynamical relativistic
corrections play an important role in reproducing the Q2 dependence of the
electromagnetic form factors at low Q^2.Comment: 15 pages, 3 figures. Minor change
A consistent explanation of the Roper phenomenology
We study the electromagnetic transitions of the Roper N(1440) resonance. Our
results, when combined with the previously obtained for the mass and the pionic
strong decay widths of the Roper, show that within a non-relativistic
constituent quark model scheme, a comprehensible understanding of the Roper
phenomenology can be achieved. They also seem to support the view of the Roper
as a radial excitation of the nucleon, though more experimental data are needed
to reach a definitive conclusion.Comment: 14 pages, 4 figures (7 postscript files). Some referencess adde
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