44,584 research outputs found
Strangeness magnetic form factor of the proton in the extended chiral quark model
Background: Unravelling the role played by nonvalence flavors in baryons is
crucial in deepening our comprehension of QCD. Strange quark, a component of
the higher Fock states in baryons, is an appropriate tool to investigate
nonperturbative mechanisms generated by the pure sea quark.
Purpose: Study the magnitude and the sign of the strangeness magnetic moment
and the magnetic form factor () of the proton.
Methods: Within an extended chiral constituent quark model, we investigate
contributions from all possible five-quark components to and in the four-vector momentum range (GeV/c). Probability
of the strangeness component in the proton wave function is calculated
employing the model.
Results: Predictions are obtained without any adjustable parameters.
Observables and are found to be small and negative,
consistent with the lattice-QCD findings as well as with the latest data
released by the PVA4 and HAPPEX Collaborations.
Conclusions: Due to sizeable cancelations among different configurations
contributing to the strangeness magnetic moment of the proton, it is
indispensable to (i) take into account all relevant five-quark components and
include both diagonal and non-diagonal terms, (ii) handle with care the
oscillator harmonic parameter and the component
probability.Comment: References added, typos corrected, accepted for publication by Phys.
Rev.
Intrinsic charm content of the nucleon and charmness-nucleon sigma term
In the extended chiral constituent quark model, the intrinsic
content of the nucleon is investigated. The probabilities of the
quark-antiquark components in the nucleon wave functions are calculated by
taking the nucleon to be admixtures of three- and five-quark components, with
the relevant transitions handled {\it via} the P mechanism.
Predictions for the probability of the in the nucleon wave function
and the charmness-nucleon sigma term are presented. Our numerical results turn
out to be consistent with the predictions from various other approaches
reported in the literature.Comment: Accepted for publication in Phys. Rev.
Strong decays of in an extended chiral quark model
The strong decays of the resonance are investigated in an
extended chiral quark model by including the low-lying components
in addition to the component. The results show that these five-quark
components in contribute significantly to the and decays. The contributions to the decay
come from both the lowest energy and the next-to-lowest energy five-quarks
components, while the contributions to the decay come from only the
latter one. Taking these contributions into account, the description for the
strong decays of is improved, especially, for the puzzling large
ratio of the decays to and .Comment: 6 pages, 1 figur
production off the proton in a Regge-plus-chiral quark approach
A chiral constituent quark model approach, embodying s- and u-channel
exchanges,complemented with a Reggeized treatment for t-channel is presented. A
model is obtained allowing data for and to be describe satisfactorily. For the latter reaction, recently released
data by CLAS and CBELSA/TAPS Collaborations in the system total energy range
GeV are well reproduced due to the inclusion of
Reggeized trajectories instead of simple and poles.
Contribution from "missing" resonances is found to be negligible in the
considered processes.Comment: 23 pages.4 figures,4 tables, to appear in Phys.Rev.
Sea flavor content of octet baryons and intrinsic five-quark Fock states
Sea quark contents of the octet baryons are investigated by employing an
extended chiral constituent quark approach, which embodies higher Fock
five-quark components in the baryons wave-functions. The well-known flavor
asymmetry of the nucleon sea , is used as input to predict the
probabilities of , and in the nucleon, ,
and baryons, due to the intrinsic five-quark components in the
baryons wave functions.Comment: 22 page
The role of the components in the electromagnetic transition
The helicity amplitudes and for the
electromagnetic transition are calculated in the
quark model that is extended to include the lowest lying
components in addition to the component. It is found that with admixture
of 5-quark components with a proportion of 20% in the nucleon and 25-65% in the
resonance the calculated helicity amplitude
decreases at the photon point, to the empirical range. The
components contain pairs, which is consistent with the
substantial width for decay of the . The best description
of the momentum dependence of the empirical helicity amplitudes is obtained by
assuming that the components are more compact than the
component. However, this version of extended quark model still does not lead to
a satisfactory simultaneous description of both and
although with significant improvement.Comment: version to appear in Eur. Phys. J.
Mean free paths and in-medium scattering cross sections of energetic nucleons in neutron-rich nucleonic matter within the relativistic impulse approximation
The mean free paths and in-medium scattering cross sections of energetic
nucleons in neutron-rich nucleonic matter are investigated using the nucleon
optical potential obtained within the relativistic impulse approximation with
the empirical nucleon-nucleon scattering amplitudes and the nuclear densities
obtained in the relativistic mean field model. It is found that the
isospin-splitting of nucleon mean free paths, sensitive to the imaginary part
of the symmetry potential, changes its sign at certain high kinetic energy. The
in-medium nucleon-nucleon cross sections are analytically and numerically
demonstrated to be essentially independent of the isospin asymmetry of the
medium and increase linearly with density in the high energy region where the
relativistic impulse approximation is applicable.Comment: 13 pages, 6 figure
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