Experimental physics

The European Physical Journal C - Particles and Fields

, Volume 4, Issue 3, pp 409-431

First online:

Measurement of the axial-vector \(\tau\) spectral functions and determination of \(\alpha_s(M_\tau^2)\) from hadronic \(\tau\) decays

  • ALEPH Collaboration
  • , R. Barate et al.Affiliated with Laboratoire de Physique des Particules (LAPP), IN2P3-CNRS, F-74019 Annecy-le-Vieux Cedex, France

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An analysis based on 124 000 selected \(\tau\) pairs recorded by the ALEPH detector at LEP provides the vector \((V)\) and axial-vector \((A)\) spectral functions of hadronic \(\tau\) decays together with their total widths. This allows the evaluation of finite energy chiral sum rules that are weighted integrals over the \((V-A)\) spectral functions. In addition, a precise measurement of \(\alpha_s\) along with a determination of nonperturbative contributions at the \(\tau\) mass scale is performed. The experimentally and theoretically most robust determination of \(\alpha_s(M_\tau^2)\) is obtained from the \((V+A)\) fit that yields \(\alpha_s(M_\tau^2)=0.334\pm 0.022\) giving \(\alpha_s(M_{\rm Z}^2)=0.1202\pm 0.0027\) after the extrapolation to the mass of the Z boson. The approach of the Operator Product Expansion (OPE) is tested experimentally studying the evolution of the \(\tau\) hadronic widths to masses smaller than the \(\tau\) mass.