Experimental study of isovector spin sum rules

We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for 0.05 < Q(2)< 2.92 GeV2. The integral is fit to extract the twist-4 element f(2)(p-n) which appears to be relatively large and negative. Systematic studies of this higher twist analysis establish its legitimacy at Q(2) around 1 GeV2. We also performed an isospin decomposition of the generalized forward spin polarizability gamma(0). Although its isovector part provides a reliable test of the calculation techniques of chiral perturbation theory, our data disagree with the calculations.