The strangeness form factors of the proton within nonrelativistic constituent quark model revisited (original) (raw)

Proton Strangeness form Factors in (4,1) Clustering Configuration

Few-Body Systems, 2013

We reexamine a recent result within a nonrelativistic constituent quark model (NRCQM) which maintains that the uudss component in the proton has its uuds subsystem in P state, with itss in S state (configuration I). When the result are corrected, contrary to the previous result, we find that all the empirical signs of the form factors data can be described by the lowest-lying uudss configuration withs in P state that has its uuds subsystem in S state (configuration II). Further, it is also found that the removal of the center-of-mass (CM) motion of the clusters will enhance the contributions of the transition current considerably. We also show that a reasonable description of the existing form factors data can be obtained with a very small probability P ss = 0.025% for the uudss component. We further see that the agreement of our prediction with the data for G s A at low-q 2 region can be markedly improved by a small admixture of configuration I. It is also found that by not removing CM motion, P ss would be overestimated by about a factor of four in the case when transition dominates over direct currents. Then, we also study the consequence of a recent estimate reached from analyzing the existing data on quark distributions that P ss lies between 2.4 − 2.9% which would lead to a large size for the five-quark (5q) system, as well as a small bump in both G s E + ηG s M and G s E in the region of q 2 ≤ 0.1 GeV 2 .

Towards a unified picture of constituent and current quarks

Physics Letters B, 1998

Using a simple picture of the constituent quark as a composite system of point-like partons, we construct the parton distributions by a convolution between constituent quark momentum distributions and constituent quark structure functions. We evaluate the latter at a low hadronic scale with updated phenomenological information, and we build the momentum distributions using well-known quark models. The resulting parton distributions and structure functions are evolved to the experimental scale and good agreement with the available DIS data is achieved. When compared with a similar calculation using non-composite constituent quarks, the accord with experiment of the present calculation becomes impressive. We therefore conclude that DIS data are consistent with a low energy scenario dominated by composite, mainly non-relativistic constituents of the nucleon.

Quark model predictions for the SU(6)-breaking ratio of the proton momentum distributions

Physics Letters B - PHYS LETT B, 2003

The ratio between the anomalous magnetic moments of proton and neutron has recently been suggested to be connected to the ratio of proton momentum fractions carried by valence quarks. This ratio is evaluated using different constituent quark models, starting from the CQM density distributions and calculating the next-to-leading order distributions. We show that this momentum fraction ratio is a sensitive test for SU(6)-breaking effects and is a useful observable to distinguish among different CQMs. We investigate also the possibility of getting constraints on the formulation of quark structure models.

On the flavour structure of the constituent quark

Journal of Physics G: Nuclear and Particle Physics, 1996

We discuss the dressing of constituent quarks with a pseudoscalar meson cloud within the effective chiral quark model. SU (3) f symmetry breaking effects are included explicitly. Our results are compared with those of the traditional meson cloud approach in which pions are coupled to the nucleon. The pionic dressing of the constituent quarks explains the experimentally observed violation of the Gottfried Sum Rule and leads to an enhanced nonperturbative sea of qq pairs in the constituent quark and consequently in the nucleon. We find 2.5 times more pions and 10-15 times more kaons in the nucleon than in the traditional picture. Thed −ū asymmetry obtained here is concentrated at somewhat smaller x and theū/d ratio is somewhat different than in the traditional meson cloud model of the nucleon.

Strangeness content and structure function of the nucleon in a statistical quark model

European Physical Journal C, 1999

The strangeness content of the nucleon is determined from a statistical model using confined quark levels, and is shown to have a good agreement with the corresponding values extracted from experimental data. The quark levels are generated in a Dirac equation that uses a linear confining potential (scalar plus vector). With the requirement that the result for the Gottfried sum rule violation, given by the New Muon Collaboration (NMC), is well reproduced, we also obtain the difference between the structure functions of the proton and neutron, and the corresponding sea quark contributions.

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 (e.g. extra S11 and P 13 states) which can be of some help for the experimental identification of new resonances. The model provides also a good description of the medium Q 2 -behavior of the electromagnetic transition form factors. In particular the calculated helicity amplitude A 1 2 for the S 11 (1535) 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.