Evaluation of Bjorken polarised sum rule with a renormalon-motivated approach
César Ayala, Camilo Castro-Arriaza, Gorazd Cvetič
Abstract
We use the known renormalon structure of Bjorken polarised sum rule (BSR) Γ‾1p−n(Q2) to evaluate the leading-twist part of that quantity. In addition, we include D=2 and D=4 Operator Product Expansion (OPE) terms and fit this expression to available experimental data for inelastic BSR. Since we use perturbative QCD (pQCD) coupling, which fails at low squared spacelike momenta Q2≲1GeV2 due to Landau singularities, the fit is performed for Q2≥Qmin2 where Qmin2≈(1.7±0.3)GeV2. Due to large BSR experimental uncertainties, the extracted value of the pQCD coupling has very large uncertainties, especially when Qmin2 is varied. However, when we fix the pQCD coupling to the known world average values, the D=2 and D=4 residue parameters can be determined within large but reasonable uncertainties.