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

Abstract

We present an NLO perturbative analysis of all available data on the polarized structure function g 1 ( x, Q 2) with the aim of making a quantitative test of the validity of the Bjorken sum rule, of measuring α s 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 α 5, we find that if all the most recent data are included g A = 1.19 ± 0.09, confirming the Bjorken sum rule at the 8% level. We further show that the value of α s 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 a s ( m z ) = −0.008 +0.010. We also confirm earlier indications of a sizeable positive gluon polarization in the nucleon.