A Modification of Contour-Improved Perturbation Theory

We present a modification of the standard method of evaluating the semihadronic tau decay width. The method is based on a derivative expansion for the Adler function rather than the standard series in powers of the strong coupling. The extracted QCD coupling at the tau mass scale is by 2% lower than the “contour improved” value. We find αs(MZ2)=0.1211±0.0010.