Spin Content of the Proton at Higher Orders

We study the scale evolution of the quark and gluon spin contributions to the proton spin, using the recently derived three-loop results for the helicity evolution kernels. We find that the evolution of the quark spin contribution may actually be extended to four-loop order. We investigate the scale dependence of Δ∑ and ΔG numerically, both to large and down to lower “hadronic” scales.