Ac. Mattingly et Pm. Stevenson, OPTIMIZATION OF R(E-) AND FREEZING OF THE QCD COUPLANT AT LOW ENERGIES(E), Physical review. D. Particles and fields, 49(1), 1994, pp. 437-450
The new result for the third-order QCD corrections to R(e+e-), unlike
the old, incorrect result, is nicely compatible with the principle-of-
minimal-sensitivity optimization method. Moreover, it leads to infrare
d fixed-point behavior: the optimized couplant alpha(s)/pi for R(e+e-)
does not diverge at low energies, but ''freezes'' to a value 0.26 bel
ow about 300 MeV. This provides some direct theoretical evidence, pure
ly from perturbation theory, for the ''freezing'' of the couplant-an i
dea that has long been a popular and successful phenomenological hypot
hesis. We use the ''smearing'' method of Poggio, Quinn, and Weinberg t
o compare the resulting theoretical prediction for R(e+e-) with experi
mental data down to the lowest energies, and find excellent agreement.