Experimental study of isovector spin sum rules

Abstract

We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for $0.05l{Q}^{2}l2.92\text{ }\text{ }{\mathrm{GeV}}^{2}$. The integral is fit to extract the twist-4 element ${f}_{2}^{p\ensuremath{-}n}$ which appears to be relatively large and negative. Systematic studies of this higher twist analysis establish its legitimacy at ${Q}^{2}$ around $1\text{ }\text{ }{\mathrm{GeV}}^{2}$. We also performed an isospin decomposition of the generalized forward spin polarizability ${\ensuremath{\gamma}}_{0}$. Although its isovector part provides a reliable test of the calculation techniques of chiral perturbation theory, our data disagree with the calculations.