The Shape and Experimental Tests of the Q^2-Invariant Polarized Gluon Asymmetry

Abstract

The absence of "valence-gluon" degrees of freedom combined with an examination of radiative QCD diagrams leads to an implication that the gluon spin asymmetry in a proton, defined as A_G(x,Q^2) = (Delta G)/G, should be approximately Q^2 invariant. The condition for scale invariance completely determines the x-dependence of this asymmetry, which satisfies the constituent counting rules and reproduces the basic results of the Bremsstrahlung model originated by Close and Sivers. This asymmetry can be combined with the measured unpolarized gluon density, G(x,Q^2) to provide a prediction for Delta G(x,Q^2). Existing and proposed experiments can test both the prediction of scale invariance for A_G and the nature of Delta G itself.