We discuss the use of the optimization procedure based on the Principle of Minimal Sensitivity to the third-order calculation of { \mbox{ ${ R_{ e^+e^-}}$}}. The effective coupling constant remains finite allowing us to apply the Poggio-Quinn-Weinberg smearing method down to energies below 1 GeV, where we find good agreement between theory and experiment. The couplant freezes to a value of $\alpha_s/\pi = 0.26$ at zero energy which is in remarkable concordance with values obtained phenomenologically.
Categories: hep-ph