A statistical approach for polarized parton distributions

TL;DR

This work develops a statistical, thermodynamics-inspired approach to generating polarized and unpolarized parton distributions, fitting a compact set of eight parameters to extensive DIS data at NLO. By tying quark/antiquark distributions through chiral QCD relations and enforcing a universal temperature with helicity-dependent potentials, the authors achieve a coherent description of F2, xF3, and g1 across a wide kinematic range while making concrete predictions for W/Z production and related spin observables at RHIC. Key outcomes include flavor asymmetries in the light sea, positive Δ¯u and negative Δ¯d at moderate x, and testable predictions for W^±, Z helicity asymmetries that can probe antiquark polarization with high precision. The framework also provides a direct, experimentally accessible check on the proposed antiquark flavor structure via RHIC measurements, linking DIS phenomenology to hadronic collider spin programs.

Abstract

A global next-to-leading order QCD analysis of unpolarized and polarized deep-inelastic scattering data is performed with parton distributions constructed in a statistical physical picture of the nucleon. The chiral properties of QCD lead to strong relations between quarks and antiquarks distributions and the importance of the Pauli exclusion principle is also emphasized. We obtain a good description, in a broad range of $x$ and $Q^2$, of all measured structure functions in terms of very few free parameters. We stress the fact that at RHIC-BNL the ratio of the unpolarized cross sections for the production of $W^+$ and $W^-$ in $pp$ collisions, will directly probe the behavior of the $\bar d(x) / \bar u(x)$ ratio for $x \geq 0.2$, a definite and important test for the statistical model. Finally, we give specific predictions for various helicity asymmetries for the $W^{\pm}, Z$ production in $pp$ collisions at high energies, which will be measured with forthcoming experiments at RHIC-BNL and are sensitive tests of the statistical model for $Δ\bar u(x)$ and $Δ\bar d(x)$.

Figures (27)

• Figure 1: The isovector structure functions $2x g_1^{(p-n)}(x)$ and $F_2^{(p-n)}(x)$. Data is taken from Refs. NMCE155.
• Figure 2: The Fermi-Dirac functions for quarks $F_q^h = X^h_{0q}/ (\exp[(x-X_{0q}^h)/{\overline{x}}]+1)$ at the input energy scale $Q_0^2=4\hbox{GeV}^2$, as a function of $x$.
• Figure 3: The Fermi-Dirac functions for antiquarks $F_{\overline{q}}^h = 1/X^h_{0\overline{q}}(\exp[(x+X_{0\overline{q}}^h)/{\overline{x}}]+1)$ at the input energy scale $Q_0^2=4\hbox{GeV}^2$, as a function of $x$.
• Figure 4: The different helicity components of the light quark distributions after NLO evolution, at $Q^2=20\hbox{GeV}^2$, as a function of $x$.
• Figure 5: The different helicity components of the light antiquark distributions after NLO evolution, at $Q^2=20\hbox{GeV}^2$, as a function of $x$.