Global Analysis of Helicity Parton Densities and their Uncertainties

We present a new analysis of the helicity parton distributions of the nucleon. The analysis takes into account the available data from inclusive and semi-inclusive polarized deep inelastic scattering, as well as from polarized proton-proton ($p\mathrm{\text{−}}p$) scattering at RHIC. For the first time, all theoretical calculations are performed fully at next-to-leading order (NLO) of perturbative QCD, using a method that allows incorporation of the NLO corrections in a very fast and efficient way in the analysis. We find evidence for a rather small gluon polarization in the nucleon, over a limited region of momentum fraction, and for interesting flavor patterns in the polarized sea.

Figure 1

Comparison of RHIC data [4] and our fit. The shaded bands correspond to $\Delta {\chi }^2=1$ and $\Delta {\chi }^2/{\chi }^2=2\%$ (see text).

Figure 2

Our DSSV polarized sea and gluon densities compared to previous fits [6, 8]. The shaded bands correspond to alternative fits with $\Delta {\chi }^2=1$ and $\Delta {\chi }^2/{\chi }^2=2\%$ (see text).

Figure 3

The ${\chi }^2$ profile (a) and partial contributions $\Delta {\chi }_i^2$ (b) of the data sets for variations of $\Delta g^{1,[0.05\to 0.2]}$ at $Q^2=10{\mathrm{GeV}}^2$.