Bjorken polarized sum rule and infrared-safe QCD couplings

• Published in: The European physical journal. C, Particles and fields Particles and fields, 2018-12, Vol.78 (12), p.1-25, Article 1002
• Main Authors: Ayala, César, Cvetič, Gorazd, Kotikov, Anatoly V., Shaikhatdenov, Binur G.
• Format: Article
• Language: English
• Subjects: Astronomy; Astrophysics and Cosmology; Couplings; Elementary Particles; Hadrons; Heavy Ions; Measurement Science and Instrumentation; Nuclear Energy; Nuclear Physics; Perturbation methods; Perturbation theory; Physics; Physics and Astronomy; Quantum Field Theories; Quantum Field Theory; Regular Article - Theoretical Physics; Singularities; String Theory
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-018-6490-9

Experimental data obtained for the polarized Bjorken sum rule (BSR) Γ 1 p - n ( Q 2 ) are fitted by using predictions derived within a truncated operator product expansion (OPE) approach to QCD. Four QCD versions are considered: perturbative QCD (pQCD) in the MS ¯ scheme, Analytic Perturbation Theory (APT), and 2 δ and 3 δ analytic QCD versions. In contrast to pQCD, these QCD variants do not have Landau singularities at low positive Q 2 , which facilitates the fitting procedure significantly. The fitting procedure is applied first to the experimental data of the inelastic part of BSR, and the known elastic contributions are added after the fitting. In general, when 2 δ and 3 δ QCD coupling is used the fitted curves give the best results, within the Q 2 -range of the fit as well as in extended Q 2 -intervals. When the fitting procedure is applied to the total BSR, i.e., to the sum of the experimental data and the elastic contribution, the quality of the results deteriorates significantly.