Analysis of the renormalization scheme ambiguities in the QCD corrections to hadronic decays of the $\tau$ lepton

The QCD corrections to the R_{\tau}^{12} moment of the invariant mass distribution in hadronic decays of the tau lepton are discussed. The next-to-next-to-leading order prediction is shown to be stable with respect to change of the renormalization scheme, provided that the contour integral expression is used. The optimized predictions are obtained using the principle of minimal sensitivity to select the preferred renormalization scheme. The optimized predictions for R_{\tau}^{12} and R_{\tau} are used in a simplified fit to the experimental data to determine the strong coupling constant and the parameter characterizing the nonperturbative contribution