Experimental study of isovector spin sum rules

We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for 0.05<Q²<2.92 GeV². The integral is fit to extract the twist-4 element f₂^p-n which appears to be relatively large and negative. Systematic studies of this higher twist analysis establish its legitimacy at Q² around 1 GeV². We also performed an isospin decomposition of the generalized forward spin polarizability γ₀. Although its isovector part provides a reliable test of the calculation techniques of chiral perturbation theory, our data disagree with the calculations.