Perspective on polarised parton distribution functions and proton spin
Peng Cheng, Y. Yu, H. Xing, Chen Chen, Zhu-Fang Cui, Craig D. Roberts
Abstract
Supposing there exists an effective charge which defines an evolution scheme for both unpolarised and polarised parton distribution functions (DFs) that is all-orders exact and using Ansätze for hadron-scale proton polarised valence quark DFs, constrained by flavour-separated axial charges and insights from perturbative quantum chromodynamics, predictions are delivered for all proton polarised DFs at the scale ζC2=3 GeV2. The pointwise behaviour of the predicted DFs and, consequently, their moments, compare favourably with results inferred from data. Notably, flavour-separated singlet polarised DFs are small. On the other hand, the polarised gluon DF, ΔG(x;ζC), is large and positive. Using our result, we predict ∫0.051dxΔG(x;ζC)=0.214(4) and that experimental measurements of the proton flavour-singlet axial charge should return a0E(ζC)=0.33(2).