The spin structure of constituent quarks

We review the theory and present status of the proton spin problem and discuss how the spin structure of constituent quarks is manifest in polarised deep inelastic scattering.     

The spin structure of the constituent quarks and of the nucleon

We define a constituent quark within QCD. It is shown that the spin of such a quark and hence also the spin of the nucleon is a complex phenomenon. We discuss it in view of the experimental data.Received: 31 March 2005, Revised: 13 May 2005, Published online: 28 July 2005     

Shares of sea and valence quarks in the proton spin puzzle

The first moments of the polarized valence parton distribution functions truncated to the wide Bjorken x region 0.004 < x < 0.7 are directly (without any fitting procedure) extracted in NLO QCD from the combined COMPASS and HERMES semi-inclusive deep inelastic scattering data. Applying the proposed original procedure to these results, we estimate the contributions of light sea quarks to the proton spin, which occur just zero within the errors.     

Pionic transitions as tests of the connection between current and constituent quarks

A proposed connection between current and constituent quarks is discussed and tested through comparison with the magnitudes and signs of amplitudes for pionic transitions between hadrons.     

Proton–proton interaction in constituent quarks model at LHC energies

In this paper we consider soft processes at LHC energies in the framework of the constituent quark model. We show that this rather naive model is able to describe all available soft process data at lower energies and to predict the behavior of the total cross section, the elastic and diffractive cross sections at LHC energy. It turns out that the “input” pomeron that has been used in this approach has parameters that are close to the so called “hard” pomeron with rather large intercept Δ≈0.12 and small value of the slope α^′ _P≈0.08 GeV^-2. We show that the elastic amplitude has a minimum at impact parameter b=0 and a maximum at b≈2 GeV^-1. Such a behavior is the result of overlapping of the parton clouds that belong to the different quarks in the hadron.     

Thermodynamics of constituent quarks

We investigate the thermal behavior of quarks and antiquarks interacting via a temperature-dependent linear potential. The quarks are constituent quarks with dynamically generated masses from the background linear σ model.     

Test of amplitude signs in pion photoproduction predicted by the transformation from current to constituent quarks

The transformation from current to constituent quark basis states is discussed as it applies to relating amplitudes for photon-nucleon decays of baryon resonances. The predictions for the relative signs of pion photoproduction amplitudes through baryon resonances in the $\text{70}\text{L = 1}$ and $\text{56}\text{L = 2}$ multiplets are presented and compared with experiment. Theory and experiment are found to be completely, with the pion-nucleom decay amplitudes of resonances in the $\text{70}\text{L = 1}$ having the signs characteristic of the $\text{3,}\text{3}\text{)?(}\text{3}\text{, 3)}$ rather than (8, 1)?(1, 8) term in the transformation axial-vector charge.     

Chiral quarks and proton decay

In this paper we calculate the hadronic matrix elements of baryon decay operators using a chiral effective lagrangian with quarks, gluons and Goldstone boson fields. We study in detail the cases where the ΔB = 1 operators arise from supersymmetric SU(5) GUT as well as the minimal SU(5) GUT model. In each model the results depend on two parameters. In particular there is a range of values for the two parameters, where the dominant decay modes in the minimal SU(5) GUT are: p → ηe⁺ and n → π^? e⁺.     

Distributions and correlations of constituent quarks in jets

In the frame of the quark recombination model, we study the momentum distributions and correlations of constituent quarks in jets by analyzing the final state hadrons generated by PYTHIA for the hard parton fragmentation processes in vacuum. Parameterizations for the distributions are tabulated.     

Distributions and correlations of constituent quarks in jets

In the frame of the quark recombination model, we study the momentum distributions and cor- relations of constituent quarks in jets by analyzing the final state hadrons generated by PYTHIA for the hard parton fragmentation processes in vacuum. Parameterizations for the distributions are tabulated.     

Distribution of charmed constituent quarks in hadrons

By using a statistical approach within noncovariant perturbation theory, the distributions of light and charmed quarks in hadrons are derived with allowance for the charmed-quark mass. The parameters of the model are extracted from a comparison with NA3 data on the hadroproduction of J/ψ particles. A reanalysis of EMC data on charm production in muon-nucleon scattering is performed. In relation to the conventional source of charmed quarks from photon-gluon fusion, the EMC data are found to suggest the presence of an additional contribution from deep-inelastic scattering on charmed quarks at large x. The resulting admixture of Fock states that contain charmed quarks in the decomposition of the proton wave function is about 1%. The approach presented for the excitation of Fock states involving charmed quarks can also be applied to states featuring beauty quarks, as well as to the hadronic component of the virtual photon (resolved photon component).     

From three nucleons to three quarks

Some short history of three-body methods originated from the famous Skornyakov-Ter-Martirosyan equation is given, including the latest development of Faddeev formalism and Efimov states. The 3q system is shown to require an alternative, which is provided by the hyperspherical method (K harmonics), highly successful for baryons.     

Neutrino and antineutrino proton scattering data and the ratio of down to up quarks in the proton

New data on the x-dependence of the ratio of down to up quarks in the proton are presented from neutrino and antineutrino experiments using the Fermilab 15-foot bubble chamber filled with hydrogen. The new data are in good agreement with existing data from electron scattering experiments performed at SLAC but are not accurate enough at large x to discriminate between the QCD prediction and a (1 ? x) behavior as x → 1.     

Model of a hybrid chiral bag involving constituent quarks

A three-phase modification of the hybrid quark-bag model is considered. In addition to the asymptotic-freedom and the hadronization phase, it includes the intermediate phase of constituent quarks. In the (1+1)-dimensional version of this model, a self-consistent solution is found with allowance for fermion-vacuum-polarization effects. Within this solution, the total bag energy, including the one-loop contribution from the Dirac sea, is investigated as a function of parameters that characterize bag geometry, the condition of a nonvanishing boson-condensate density in the internal region being imposed. It is shown that the ground-state bag configuration that is constructed on the basis of the solution found here, which minimizes the total energy, and which includes all three phases exists and is unique.     

Measuring the transverse polarization of quarks in the proton

The transverse spin polarization distribution of quarks in a proton contributes at leading twist to the angular distribution of lepton pair production in doubly polarized proton-proton collisions. Although this distribution is straightforward to define in the QCD-improved parton model and represents a fundamental quark degree of freedom, it has never been measured. Moreover, deeply inelastic electroproduction experiments are only sensitive to this distribution at the higher twist level, and then mix this contribution with others, including the one coming from multiparton initial states. Reviewing this, we conclude that the Drell-Yan process is the best way to measure the quark transverse spin polarization distribution.Unité propre du CNRS