Determination of αs and the nucleon spin decomposition using recent polarized structure function data

Abstract

New data on polarized μ− p and e− p scattering permit a first determination of α s using the Bjorken sum rule, as well as higher precision in determining the nucleon spin decomposition. Using perturbative QCD calculations to ▪ for the non-singlet combination of structure functions, we find α s (2.5 GeV 2) = 0.375 −0.081 +0.062, corresponding to α s ( M Z 2) = 0.122 −0.009 +0.005, and using calculations to ▪ for the singlet combination we find Δu = 0.83 ± 0.03, Δd = −0.43 ± 0.03, Δs = −0.10±0.03, ΔΣ  Δu + Δd + Δs = 0.31 ± 0.07, at a renormalization scale Q 2 = 10 GeV 2. Perturbative QCD corrections play an essential role in reconciling the interpretations of data taken using different targets. We discuss systematic uncertainties in the above numbers, which are dominated by higher-twist effects and lead, we estimate, to α s ( M Z 2) = 0.118 −0.014 +0.007. The Δ q determinations are used to update predictions for the couplings of massive Cold Dark Matter particles and axions to nucleons.