/ Phenomenology-HEP arXiv:0911.3297

Nucleon spin structure and pQCD frontier on the move

Pasechnik, Roman S. (Uppsala U.) ; Shirkov, Dmitry V. (Dubna, JINR) ; Teryaev, Oleg V. (Dubna, JINR) ; Solovtsova, Olga P. (Gomel State Tech. U.) ; Khandramai, Vyacheslav L. (Gomel State Tech. U.)

Published in: Phys.Rev.
Year: 2010
Vol.: D81
Page No: 016010
Pages: 21

Abstract: We discuss the interplay between higher orders of the perturbative QCD expansion and higher twist contributions in the analysis of recent Jefferson Lab (JLab) data on the lowest moments of spin-dependent proton and neutron structure functions $\Gamma_1^{p,n} (Q^2)$ and Bjorken sum rule function $\Gamma_1^{p-n}(Q^2)$ at $0.05<Q^2< 3 {\rm GeV}^2$. We demonstrate that the values of the higher twist coefficients $\mu^{p,n}_{2k}$ extracted from the mentioned data by using the singularity-free analytic perturbation theory provide a better convergence of the higher-twist series than with the standard pQCD. From the high-precision proton data, we extract the value of the singlet axial charge $a_0(1 \GeV^2)=0.33\pm0.05$. We observe a slow $Q^2$-dependence of fitted values of the twist coefficient $\mu_4$ and $a_0$ when going to lower energy scales, which can be explained by the well-known RG evolution of $\mu_4(Q^2)$ and $a_0(Q^2)$. As the main result, a good quantitative description of all the JLab data sets down to $Q \simeq 350 \MeV$ is achieved.

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