11,119 research outputs found
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.
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
Acquisition of ownership illusion with self-disownership in neurological patients
The multisensory regions in frontoparietal cortices play a crucial role in the sense of body and self. Disrupting this sense may lead to a feeling of disembodiment, or more generally, a sense of disownership. Experimentally, this altered consciousness disappears during illusory own-body perceptions, increasing the intensity of perceived ownership for an external virtual limb. In many clinical conditions, particularly in individuals with a discontinuous or absent sense of bodily awareness, the brain may effortlessly create a convincing feeling of body ownership over a surrogate body or body part. The immediate visual input dominates the current bodily state and induces rapid plastic adaptation that reconfigures the dynamics of bodily representation, allowing the brain to acquire an alternative sense of body and self. Investigating strategies to deconstruct the lack of a normal sense of bodily ownership, especially after a neurological injury, may aid the selection of appropriate clinical treatment
Disentangling instrumental broadening
A new procedure aiming at disentangling the instrumental profile broadening
and the relevant X-ray powder diffraction (XRPD) profile shape is presented.
The technique consists of three steps: denoising by means of wavelet
transforms, background suppression by morphological functions and deblurring by
a Lucy--Richardson damped deconvolution algorithm. Real XRPD intensity profiles
of ceria samples are used to test the performances. Results show the robustness
of the method and its capability of efficiently disentangling the instrumental
broadening affecting the measurement of the intrinsic physical line profile.
These features make the whole procedure an interesting and user-friendly tool
for the pre-processing of XRPD data.Comment: 9 pages, 1 table, 1 figure; typos correcte
Electromagnetic Form Factors and the hCQM
We briefly report on results about the electromagnetic form factors of the
nucleon obtained with different models and then we concentrate our attention on
recent results obtained with the hypercentral constituent quark model (hCQM).Comment: 12 pages, 5 figures, Invited talk at 27th Symposium on Nuclear
Physics, Taxco, Guerrero, Mexico, 5-8 Jan 200
On the relation between the Deuteron Form Factor at High Momentum Transfer and the High Energy Neutron-Proton Scattering Amplitude
A non-relativistic potential-model version of the factorization assumption,
used in perturbative QCD calculations of hadronic form factors, is used, along
with the Born approximation valid at high energies, to derive a remarkably
simple relationship between the impulse approximation contribution to the
deuteron form factor at high momentum transfer and the high energy
neutron-proton scattering amplitude. The relation states that the form factor
at a given value of is proportional to the scattering amplitude at a
specific energy and scattering angle. This suggests that an accurate
computation of the form factors at large requires a simultaneous
description of the phase-shifts at a related energy, a statement that seems
reasonable regardless of any derivation. Our form factor-scattering amplitude
relation is shown to be accurate for some examples. However, if the potential
consists of a strong short distance repulsive term and a strong longer ranged
attractive term, as typically occurs in many realistic potentials, the relation
is found to be accurate only for ridiculously large values of . More general
arguments, using only the Schroedinger equation, suggest a strong, but
complicated, relationship between the form factor and scattering amplitude.
Furthermore, the use of recently obtained soft potentials, along with an
appropriate current operator, may allow calculations of form factors that are
consistent with the necessary phase shifts.Comment: 14 pages, 4 figures, The discussion has been extended by including
numerical examples and general argument
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