Narrow Results

To obtain the improved QCD predictions for the moments of the xF₃ structure function in νN scattering, three-loop Wilson coefficients with the corresponding NNLO anomalous dimension coefficients is used. A comparison between QCD predictions and the xF₃ data of the CCFR collaboration has been done in which the Bernstein Polynomial method is used in the complete renormalization group improvement approach. A direct fits for over the corresponding range of Q² with five effective quark flavours, is performed.

Sea quark distributions in the NLO approximation, based on the phenomenological valon model or constituent quark model are analyzed. We use the parametrized inverse Mellin transform technique to perform a direct fit with available experimental data and obtain the unknown parameters of the distributions. We try to extend the calculation to the NLO approximation for the singlet and nonsinglet cases in DIS phenomena. We do also the same calculation for electron–positron annihilation. The resulting sea distributions are effectively independent of the process used. The approach of complete RG improvement (CORGI) is employed and the results are compared with the standard approach of perturbative QCD in the scheme with a physical scale. The comparisons with data are in good agreement. As is expected, the results in the CORGI approach indicate a better agreement to the data than the NLO calculation in the standard approach.

Sea quark densities in the nucleon, based on the constituent quark model are analyzed. To model the asymmetry of these densities, the meson cloud or alternatively chiral quark model (χQM) is used. Valence quark densities of the meson which are required to extract the sea quark densities in the constituent quarks are obtained using the phenomenological valon model. In addition to the standard perturbative QCD approach which uses the scheme with a physical choice of renormalization scale, the calculations are also performed using the complete RG-improvement (CORGI) approach. To avoid a physically unacceptable Q² behavior of the sea densities inside the constituent quarks, we assume that the free parameter which exists in the vertex function of the boson–quark splitting function, is Q²-dependent. Using the unsymmetrized sea densities of the nucleon which result from convoluting the constituent density in a nucleon with the quark density in the constituent quark, the Gottfried sum rule (GSR) is calculated using the standard perturbative and CORGI approaches. The CORGI result is closer to the reported experimental value for the GSR. The extracted sea and valence quark density in a nucleon, using χQM and also the CORGI approach, have been compared with available experimental data and what was obtained, based on χQM in the standard approach. This comparison confirms the anticipated better agreement of the CORGI approach with the data.