Measurement of the strong coupling constant αs and the vector and axial-vector spectral functions in hadronic tau decays the opal collaboration

Abstract

The spectral functions of the vector current and the axial-vector current have been measured in hadronic τ decays using the OPAL detector at LEP. Within the framework of the Operator Product Expansion a simultaneous determination of the strong coupling constant αs, the non-perturbative operators of dimension 6 and 8 and of the gluon condensate has been performed. Different perturbative descriptions have been compared to the data. The Contour Improved Fixed Order Perturbation Theory gives αs(mτ2) = 0.348 ± 0.009exp ± 0.019theo at the τ-mass scale and αs(mZ2) = 0.1219 ± 0.0010exp ± 0.0017theo at the Z°- mass scale. The values obtained for αs(mZ2) using Fixed Order Perturbation Theory or Renorm..