Experimental study of isovector spin sum rules

Abstract

We present the Bjorken integral extracted from Jefferson Lab experiment EG1b for $0.05<Q^2<2.92$ GeV${}^2$. 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 GeV${}^2$. We also performed an isospin decomposition of the generalized forward spin polarizability ${\hat{I}}_0^3$. Although its isovector part provides a reliable test of the calculation techniques of Chiral Perturbation Theory, our data disagree with the calculations.

7 pages, 4 figures. Version changed to longer version published in PRD