A New Evaluation of Polarized Parton Densities in the Nucleon
E. Leader, A. V. Sidorov, D. B. Stamenov
TL;DR
The paper tackles the spin decomposition of the nucleon by performing a global NLO QCD analysis of inclusive polarized DIS data to extract polarized parton densities in the $\overline{MS}$ and JET schemes, incorporating SLAC/E155p data and MRST$99$ unpolarized densities. It updates the non-singlet axial charges $a_3$ and $a_8$, and uses a simple input parametrization with a flavor-symmetric sea to fit $A_1^N(x,Q^2)$ across 185 data points. The results show $\Delta G( Q^2=1~{\rm GeV}^2)\approx 0.68\pm0.32$, and $\Delta\Sigma(Q^2)\approx 0.37\pm0.07$, with $\Delta s+\Delta\bar{s}\approx -0.07\pm0.02$, while $(\Delta u+\Delta\bar{u})$ and $(\Delta d+\Delta\bar{d})$ are well constrained; $\Delta G$ and $\Delta s$ remain weakly constrained, and the analysis emphasizes that inclusive DIS data primarily determine the non-strange quark polarizations. A FORTRAN package with the densities is provided for practical applications.
Abstract
We present a new leading and next-to-leading QCD analysis of the world data on inclusive polarized deep inelastic scattering. A new set of polarized parton densities is extracted from the data and the sensitivity of the results to the newly incorporated SLAC/E155 proton data is discussed.