Determination of the Bjorken sum and strong coupling from polarized structure functions

We present an NLO perturbative analysis of all available data on the polarized structure function g1(x,Q2) with the aim of making a quantitative test of the validity of the Bjorken sum rule, of measuring αs, and of deriving helicity fractions. We take particular care over the small x extrapolation, since it is now known that Regge behaviour is unreliable at perturbative scales. For fixed αs we find that if all the most recent data are included gA=1.19±0.09, confirming the Bjorken sum rule at the 8% level. We further show that the value of αs is now reasonably well constrained by scaling violations in the structure function data, despite the fact that it cannot yet be reliably fixed by the value of the Bjorken sum: our final result is αs(mZ) =0.120+0.010-0.008. We also confirm earlier indications of a sizeable positive gluon polarization in the nucleon. (orig.)