All-Orders Evolution of Parton Distributions: Principle, Practice, and Predictions

• Published in: Chinese physics letters Vol. 40; no. 9; pp. 91201 - 31
• Main Authors: Yin, Pei-Lin, Xu, Yin-Zhen, Cui, Zhu-Fang, Roberts, Craig D., Rodríguez-Quintero, José
• Format: Journal Article
• Language: English
• Published: Chinese Physical Society and IOP Publishing Ltd 01.08.2023; Dpto.Sistemas Físicos,Químicos y Naturales,Univ.Pablo de Olavide,E-41013 Sevilla,Spain%School of Physics,Nanjing University,Nanjing 210093,China; Institute for Nonperturbative Physics,Nanjing University,Nanjing 210093,China%Dpto.Ciencias Integradas,Centro de Estudios Avanzados en Fis.,Mat.y Comp.,Fac.Ciencias Experimentales,Universidad de Huelva,Huelva 21071,Spain; College of Science,Nanjing University of Posts and Telecommunications,Nanjing 210023,China%Dpto.Ciencias Integradas,Centro de Estudios Avanzados en Fis.,Mat.y Comp.,Fac.Ciencias Experimentales,Universidad de Huelva,Huelva 21071,Spain
• ISSN: 0256-307X; 1741-3540
• DOI: 10.1088/0256-307X/40/9/091201

Parton distribution functions (PDFs) are defining expressions of hadron structure. Exploiting the role of effective charges in quantum chromodynamics, an algebraic scheme is described which, given any hadron's valence parton PDFs at the hadron scale, delivers predictions for all its PDFs (unpolarized and polarized) at any higher scale. The scheme delivers results that are largely independent of both the value of the hadron scale and the pointwise form of the charge; and, inter alia , enables derivation of a model-independent identity that relates the strength of the proton's gluon helicity PDF, Δ G p ζ , to that of the analogous singlet polarized quark PDF and valence quark momentum fraction. Using available data fits and theory predictions, the identity yields Δ G p ( ζ C = 3 GeV ) = 1.48 ( 10 ) . It furthermore entails that the measurable quark helicity contribution to the proton spin is a ∼ 0 p ζ C = 0.32 ( 3 ) , thereby reconciling contemporary experiment and theory.