The spin structure of the nucleon

Abstract

We present the final results of the spin asymmetries A 1 and the spin structure functions g 1 of the proton and the deuteron from the SMC. In the region ξ < 0.02 we use a new method for the determination of A 1. The usual method employs inclusive scattering events and includes a large radiative background at low ξ, while the new method minimises the radiative background by selecting events with at least one hadron as well as a muon in the final state. Using these data and other presently available data we performed a next-to-leading order QCD analysis of the spin structure function g 1. We present results for the first moments of the proton, deuteron and neutron structure functions, and determine singlet and non-singlet parton distributions. We also test the Bjorken sum rule and find agreement with the theoretical prediction at the level of 10%.