Search results for "Constituent quark"
showing 10 items of 85 documents
NN Interaction in Chiral Constituent Quark Models
2003
We review the actual state in the description of the nucleon-nucleon (NN) interaction by means of chiral constituent quark models. We present a series of relevant features that are nicely explained within the quark model framework.
Polarized Structure Functions and the Nucleon Spin
1995
The link between the light-cone momentum distributions of constituent quark models and their corresponding parton distributions is used to study the polarized structure functions g 1 of proton and neutron. The formalism allows to analyze the effects of the structure of the quark model wave function and thus we discuss the SU (6) breaking mechanism associated with the One Gluon Exchange and large D-state admixtures originated in pionic models. We analyze the contribution to these structure functions of the gluon polarization arising from the anomaly.
Power-law running of the effective gluon mass
2007
The dynamically generated effective gluon mass is known to depend non-trivially on the momentum, decreasing sufficiently fast in the deep ultraviolet, in order for the renormalizability of QCD to be preserved. General arguments based on the analogy with the constituent quark masses, as well as explicit calculations using the operator-product expansion, suggest that the gluon mass falls off as the inverse square of the momentum, relating it to the gauge-invariant gluon condensate of dimension four. In this article we demonstrate that the power-law running of the effective gluon mass is indeed dynamically realized at the level of the non-perturbative Schwinger-Dyson equation. We study a gauge…
Model calculations of the Sivers function satisfying the Burkardt sum rule
2009
9 pages, 4 figures.-- ISI article identifier:000266408300028.-- ArXiv pre-print avaible at:http://arxiv.org/abs/0811.1191
Sivers Asymmetry for the proton and the neutron
2008
A formalism is presented to evaluate the Sivers function in constituent quark models. A non-relativistic reduction of the scheme is performed and applied to the Isgur-Karl model. The results obtained are consistent with a sizable Sivers effect and the signs for the u and d flavor contributions turn out to be opposite. The Burkardt Sum Rule is fulfilled to a large extent. After the estimate of the QCD evolution of the results from the momentum scale of the model to the experimental one, a reasonable agreement with the available data is obtained. A calculation of nuclear effects in the extraction of neutron single spin asymmetries in semi-inclusive deep inelastic scattering off 3He is also de…
Constituent quarks and parton distributions
1997
Abstract The high energy parton distribution when evolved to a low energy scale appears to indicate that a valence picture of hadron structure arises. We have developed a formalism based on a laboratory partonic description which connects the parton distributions with the momentum distributions of a quark model. The formalism uses Next to Leading Order evolution and has been defined to produce the right support for the parton distributions. In this scheme we have analyzed the polarized and unpolarized data and shown that well-known Quark Models lead to a qualitative description of the data. However, if one aims at a quantitative agreement, these conventional low energy models have to be cha…
Double parton correlations in constituent quark models
2013
Double parton correlations, having effects on the double parton scattering processes occurring in high-energy hadron-hadron collisions, for example at the LHC, are studied in the valence quark region by means of constituent quark models. In this framework, two particle correlations are present without any additional prescription, at variance with what happens, for example, in independent particle models, such as the MIT bag model in its simplest version. From the present analysis, conclusions similar to the ones obtained recently in a modified version of the bag model can be drawn: correlations in the longitudinal momenta of the active quarks are found to be sizable, while those in transver…
Higher Order Polarizabilities of the Proton
1999
Compton scattering results are used to probe proton structure via measurement of higher order polarizabilities. Values for $\alpha_{E2}^p,\beta_{E2}^p,\alpha_{E\nu}^p,$ $\beta_{E\nu}^p$ determined via dispersion relations are compared to predictions based upon chiral symmetry and from the constituent quark model. Extensions to spin-polarizabilities are also discussed.
Four-quark spectroscopy within the hyperspherical formalism
2006
We present a generalization of the hyperspherical harmonic formalism to study systems made of quarks and antiquarks of the same flavor. This generalization is based on the symmetrization of the $N-$body wave function with respect to the symmetric group using the Barnea and Novoselsky algorithm. The formalism is applied to study four-quark systems by means of a constituent quark model successful in the description of the two- and three-quark systems. The results are compared to those obtained by means of variational approaches. Our analysis shows that four-quark systems with exotic $0^{+-}$ and non-exotic $2^{++}$ quantum numbers may be bound independently of the mass of the quark. $2^{+-}$ …
One-photon decay of the tetraquark stateX(3872)→γ+J/ψin a relativistic constituent quark model with infrared confinement
2011
We further explore the consequences of treating the $X(3872)$ meson as a tetraquark bound state by analyzing its one-photon decay $X\ensuremath{\rightarrow}\ensuremath{\gamma}+J/\ensuremath{\psi}$ in the framework of our approach developed in previous papers which incorporates quark confinement in an effective way. To introduce electromagnetism we gauge a nonlocal effective Lagrangian describing the interaction of the $X(3872)$ meson with its four constituent quarks by using the $P$-exponential path-independent formalism. We calculate the matrix element of the transition $X\ensuremath{\rightarrow}\ensuremath{\gamma}+J/\ensuremath{\psi}$ and prove its gauge invariance. We evaluate the $X\ens…