109 research outputs found
Electromagnetic properties of strange baryons in a relativistic quark model
We present some of our results for the electromagnetic properties of excited ÎŁ hyperons, computed within the framework of the Bonn constituent-quark model, which is based on the Bethe-Salpeter approach. The seven parameters entering the model are fitted against the best-known baryon masses. Accordingly, the results for the form factors and helicity amplitudes are genuine predictions. We compare with the scarce experimental data available and discuss the processes in which ÎŁ
*'s may play an important role
Electromagnetic KY production from the proton in a Regge-plus-resonance approach
A Regge-plus-resonance (RPR) description of the p(\gamma,K)Y and p(e,e'K)Y
processes (Y = \Lambda, \Sigma^{0,+}) is presented. The proposed reaction
amplitude consists of Regge-trajectory exchanges in the t channel, supplemented
with a limited selection of s-channel resonance diagrams. The RPR framework
contains a considerably smaller number of free parameters than a typical
effective-Lagrangian model. Nevertheless, it provides an acceptable overall
description of the photo- and electroproduction observables over an extensive
photon energy range. It is shown that the electroproduction response functions
and polarization observables are particularly useful for fine-tuning both the
background and resonance parameters.Comment: 4 pages, 3 figures, Proceedings for IX International Conference on
Hypernuclear and Strange Particle Physics (HYP2006), October 10-14 2006,
Main
Bridging Two Ways of Describing Final-State Interactions in A(e,e'p) Reactions
We outline a relativistic and unfactorized framework to treat the final-state
interactions in quasi-elastic A(e,e'p) reactions for four-momentum transfers
Q (GeV/c). The model, which relies on the eikonal
approximation, can be used in combination with optical potentials, as well as
with the Glauber multiple-scattering method. We argue that such a model can
bridge the gap between a typical ``low'' and ``high-energy'' description of
final-state interactions, in a reasonably smooth fashion. This argument is made
on the basis of calculated structure functions, polarization observables and
nuclear transparencies for the target nuclei C and O.Comment: revised versio
Electromagnetic form factors of hyperons in a relativistic quark model
The relativistically covariant constituent quark model developed by the Bonn
group is used to compute the EM form factors of strange baryons. We present
form-factor results for the ground-state and some excited hyperons. The
computed magnetic moments agree well with the experimental values and the
magnetic form factors follow a dipole dependence.Comment: 4 pages, 1 figure, Proceedings for NSTAR '04 conference in Grenoble,
France, March 24-27, 2004 (World Scientific
Probing the infrared quark mass from highly excited baryons
We argue that three-quark excited states naturally group into quartets, split
into two parity doublets, and that the mass splittings between these parity
partners decrease higher up in the baryon spectrum. This decreasing mass
difference can be used to probe the running quark mass in the mid-infrared
power-law regime. A measurement of masses of high-partial wave Delta*
resonances should be sufficient to unambiguously establish the approximate
degeneracy. We test this concept with the first computation of excited high-j
baryon masses in a chirally invariant quark model.Comment: 4 pages, 4 figures. submitted to Phys Rev Letter
Using highly excited baryons to catch the quark mass
Chiral symmetry in QCD can be simultaneously in Wigner and Goldstone modes,
depending on the part of the spectrum examined. The transition regime between
both, exploiting for example the onset of parity doubling in the high baryon
spectrum, can be used to probe the running quark mass in the mid-IR power-law
regime. In passing we also argue that three-quark states naturally group into
same-flavor quartets, split into two parity doublets, all splittings decreasing
high in the spectrum. We propose that a measurement of masses of high-partial
wave Delta* resonances should be sufficient to unambiguously establish the
approximate degeneracy and see the quark mass running. We test these concepts
with the first computation of the spectrum of high-J excited baryons in a
chiral-invariant quark model.Comment: 6 pages, 9 figures, To appear in the proceedings of the 19th
International IUPAP Conference on Few-Body Problems in Physics; added
acknowledgment, hyphenized author nam
Helicity amplitudes and electromagnetic decays of strange baryon resonances
We present results for the helicity amplitudes of the lowest-lying hyperon
resonances Y*, computed within the framework of the Bonn constituent-quark
model, which is based on the Bethe-Salpeter approach. The seven parameters
entering the model are fitted against the best known baryon masses.
Accordingly, the results for the helicity amplitudes are genuine predictions.
Some hyperon resonances are seen to couple more strongly to a virtual photon
with finite Q^2 than to a real photon. Other Y*'s, such as the S_{01}(1670)
Lambda resonance or the S_{11}(1620) Sigma resonance, have large
electromagnetic decay widths and couple very strongly to real photons. The
negatively-charged and neutral members of a Sigma* triplet may couple only
moderately to the Sigma(1193), while the positively-charged member of the same
Sigma* triplet displays a relatively large coupling to the Sigma^+(1193) state.
This illustrates the necessity of investigating all isospin channels in order
to obtain a complete picture of the hyperon spectrum.Comment: 4 pages, 1 figure, 1 table, Proceedings of the Conference
"International Workshop on the Physics of Excited Baryons NSTAR 05",
Tallahassee, Florida (USA), Oct. 2005, contributed tal
Regge-model predictions for K+Sigma photoproduction from the nucleon
We present Regge-model predictions for the p(gamma,K+)Sigma0 and
n(gamma,K+)Sigma- differential cross sections and photon-beam asymmetries in
the resonance region. The reaction amplitude encompasses the exchange of
K+(494) and K*+(892) Regge-trajectories, introducing a mere three free
parameters. These are fitted to the available p(gamma,K+)Sigma0 data beyond the
resonance region. The n(gamma,K+)Sigma- amplitude is obtained from the
p(gamma,K+)Sigma0 one through SU(2) isospin symmetry considerations.Comment: 4 pages, 2 figures; Proceedings Tenth Conference on the Intersections
of Particle and Nuclear Physics, San Diego, 200
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