Polarized Parton Distribution Functions Reexamined

Abstract

The hard-gluonic contribution to the first moment of the polarized proton structure function $g_1^p(x)$ is dependent of the factorization convention chosen in defining the quark spin density and the hard cross section for photon-gluon scattering. Two extremes of interest, namely gauge-invariant and chiral-invariant factorization schemes, are considered. We show that in order to satisfy the positivity constraint for sea and gluon polarizations, the polarized valence quark distributions should fully account for the observed $g_1^p(x)$ at $x\gsim 0.2\,$. This together with the first-moment and perturbative QCD constraints puts a pertinent restriction on the shape of $\Delta u_v(x)$ and $\Delta d_v(x)$. The spin-dependent sea distribution in the gauge-invariant factorization scheme is extracted from the data of $g_1^p(x)$. It is shown in the chiral invariant scheme that it is possible to interpret the $g_1^p(x)$ data with anomalous gluonic contributions, yet a best least ${\chi }^2$ fit to the data implies a gluon spin distribution which violates the positivity condition $|\Delta G(x)|\le G(x)$. We then propose a more realistic set of parton spin distributions with sea polarization and with a moderate value of $\Delta G$. The polarized parton distributions in this work are presented in the next-to-leading order of QCD at the scale $Q^2=10{\mathrm{GeV}}^2$. Predictions for the polarized structure functions $g_1^n(x)$ of the neutron and $g_1^d(x)$ of the deuteron are given.

17 pages, 9 figures. Main changes: (i) all polarized parton distributions are parametrized and determined in the MS scheme, (ii) all figures are modified

References in corpus (11)

• Measurement of the Spin-Dependent Structure Function $g_1(x)$ of the Proton
• QCD Constrains on the Shape of Polarized Quark and Gluon Distributions
• Pinning down the Glue in the Proton
• Parton Distributions of the Proton
• Determination of ${\alpha }_s$ and the Nucleon Spin Decomposition Using Recent Polarized Structure Function Data
• FLAVOR-SINGLET g_A FROM LATTICE QCD
• Proton Spin Structure from Lattice QCD
• Spin-dependent Parton Distributions from Polarized Structure Function Data
• Scale Dependence and Small-x Behaviour of Polarized Parton Distributions
• The spin content of the proton in quenched QCD
• Matrix Elements of the Singlet Axial Current in the Proton

Cited by in corpus (4)

• QCD Analysis of Polarized Deep Inelastic Data and Parton Distributions
• Testing various polarized parton distributions at RHIC
• Contribution superstring Z' boson on the polarization effects in proton-proton collisions
• The next-to-leading order of the differential cross-section of the subprocess of Compton scattering of quark-gluon of prompt photon production in proton-proton collisions at NICA energies