364 research outputs found
New Baryons in the Delta eta and Delta omega Channels
The decays of excited nonstrange baryons into the final states Delta eta and
Delta omega are examined in a relativized quark pair creation model. The
wavefunctions and parameters of the model are fixed by previous calculations of
N pi and N pi pi, etc., decays through various quasi-two body channels
including N eta and N omega. Our results show that the combination of
thresholds just below the region of interest and the isospin selectivity of
these channels should allow the discovery of several new baryons in such
experiments.Comment: 10 pages, RevTe
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
Strange Decays of Nonstrange Baryons
The strong decays of excited nonstrange baryons into the final states Lambda
K, Sigma K, and for the first time into Lambda(1405) K, Lambda(1520) K,
Sigma(1385) K, Lambda K*, and Sigma K*, are examined in a relativized quark
pair creation model. The wave functions and parameters of the model are fixed
by previous calculations of N pi and N pi pi, etc., decays. Our results show
that it should be possible to discover several new negative parity excited
baryons and confirm the discovery of several others by analyzing these final
states in kaon production experiments. We also establish clear predictions for
the relative strengths of certain states to decay to Lambda(1405) K and
Lambda(1520) K, which can be tested to determine if a three-quark model of the
Lambda(1405) K is valid. Our results compare favorably with the results of
partial wave analyses of the limited existing data for the Lambda K and Sigma K
channels. We do not find large Sigma K decay amplitudes for a substantial group
of predicted and weakly established negative-parity states, in contrast to the
only previous work to consider decays of these states into the strange final
states Lambda K and Sigma K.Comment: 25 pages, 8 figures, RevTe
Constructing Hybrid Baryons with Flux Tubes
Hybrid baryon states are described in quark potential models as having
explicit excitation of the gluon degrees of freedom. Such states are described
in a model motivated by the strong coupling limit of Hamiltonian lattice gauge
theory, where three flux tubes meeting at a junction play the role of the glue.
The adiabatic approximation for the quark motion is used, and the flux tubes
and junction are modeled by beads which are attracted to each other and the
quarks by a linear potential, and vibrate in various string modes. Quantum
numbers and estimates of the energies of the lightest hybrid baryons are
provided.Comment: 4 pages, RevTeX. Submitted to Physical Review Letter
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
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
Meson decay in an independent quark model
Leptonic decay widths and leptonic decay constants of light vector mesons and
weak leptonic decay widths and weak decay constants of light and heavy
pseudoscalar mesons have been studied in a field- theoretic framework based on
the independent quark model with a scalar- vector power-law potential. The
results are in very good agreement with the experimental data.Comment: 13 page
Distinguishing Among Strong Decay Models
Two competing models for strong hadronic decays, the and
models, are currently in use.
Attempts to rule out one or the other have been hindered by a poor
understanding of final state interactions and by ambiguities in the treatment
of relativistic effects.
In this article we study meson decays in both models, focussing on certain
amplitude ratios for which the relativistic uncertainties largely cancel out
(notably the ratios in and
), and using a Quark Born Formalism to estimate the
final state interactions.
We find that the model is strongly favoured.
In addition, we predict a amplitude ratio of for the decay
.
We also study the parameter-dependence of some individual amplitudes (as
opposed to amplitude ratios), in an attempt to identify a ``best'' version of
the model.Comment: 20 pages, uuencoded postscript file with 7 figures, MIT-CTP-2295;
CMU-HEP94-1
Nucleonic resonance excitations with linearly polarized photon in
In this work, an improved quark model approach to the meson
photo-production with an effective Lagrangian is presented. The {\it t}-channel
{\it natural}-parity exchange is taken into account through the Pomeron
exchange, while the {\it unnatural}-parity exchange is described by the
exchange. With a very limited number of parameters, the available experimental
data in the low energy regime can be consistently accounted for. We find that
the beam polarization observables show sensitivities to some {\it s}-channel
individual resonances in the quark model symmetry limit.
Especially, the two resonances and , which belong
to the representation , have dominant contributions
over other excited states. Concerning the essential motivation of searching for
"missing resonances" in meson photo-production, this approach provides a
feasible framework, on which systematic investigations can be done.Comment: 16 pages, Revtex, 9 eps figures, to appear in PR
Meson-like Baryons and the Spin-Orbit Puzzle
I describe a special class of meson-like \Lambda_Q excited states and present
evidence supporting the similarity of their spin-independent spectra to those
of mesons. I then examine spin-dependent forces in these baryons, showing that
predicted effects of spin-orbit forces are small for them for the same reason
they are small for the analogous mesons: a fortuitous cancellation between
large spin-orbit forces due to one-gluon-exchange and equally large inverted
spin-orbit forces due to Thomas precession in the confining potential. In
addition to eliminating the baryon spin-orbit puzzle in these states, this
solution provides a new perspective on spin-orbit forces in all baryons.Comment: 24 pages, 4 figure
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