QCD contributions to the b → ul − v l decay rate, which are known to two-loop order in the MS scheme, exhibit sufficient dependence on the renormalization mass μ to compromise phenomenological predictions for inclusive semileptonic B → X u processes. Such scale dependence is ameliorated by the renormalization-group (RG) extraction and summation of all leading and RG-accessible subleading logarithms occurring subsequent to two-loop order in the perturbative series. This optimal RG-improvement of the known portion of the perturbative series virtually eliminates μ-dependence as a source of theoretical uncertainty in the predicted semileptonic B → X u inclusive rate.
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