Spin dependent structure function $g_{1}$: Recent experimental results

In the last two years new measurements of the structure functions $g_{1}^{p}, g_{1}^{n}, g_{1}^{d}$ have been performed by experiments at CERN, SLAC and DESY. A complete review of these experimental results is presented. Perturbative QCD evolution in next-to-leading order is used to evolve $g_{1}$ to a common $Q^{2}$, at which the first moment or the structure function is evaluated. Results from different experiments show consistently a violation of the Ellis-Jaffe sum rule. A preliminary combined analysis of all the available data gives at 5 GeV$^{2}: \Gamma_{1}^{p} − \Gamma_{1}^{n} = \int_{0}^{1}g_{1}^{p}(x) − \int_{0}^{1}g_{1}^{n}(x) = 0.189 \pm 0.018$, in agreement with the theoretical prediction given by the Bjorken sum rule $0.181 \pm 0.03$.