FIXING THE RENORMALIZATION SCHEME IN NNLO PERTURBATIVE QCD USING CONFORMAL LIMIT ARGUMENTS

We discuss how the renormalization scheme ambiguities in QCD can be fi xed, when two observables are related, by requiring the coefficients i n the perturbative expansion relating the two observables to have thei r conformal limit values, i.e., to be independent of the beta function of the renormalized coupling. We show how the next-to-leading order B LM automatic scale-fixing method can be extended to next-to-next-to-le ading order to fix both the renormalization scale and beta(2) in a uni que way. As an example we apply the method to the relation between Bjo rken's sum rule and R(e+e-) and compare with experimental data as well as other scheme-fixing methods.