The physics of hadronic tau decays

By M. Davier, A. Höcker, Zhi-qing Zhang. 2005

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Hadronic {tau} decays provide a clean laboratory for the precise study of quantum chromodynamics (QCD). Observables based on the spectral functions of hadronic {tau} decays can be related to QCD quark-level calculations to determine fundamental quantities like the strong-coupling constant, parameters of the chiral Lagrangian |V{sub us}|, the mass of the strange quark, and to simultaneously test the concept of quark-hadron duality. Using the best available measurements and a revisited analysis of the theoretical framework, the value {alpha}{sub s}(m{sub {tau}}{sup 2})=0.345{+-}0.004{sub exp}{+-}0.009{sub th} is obtained. Taken together with the determination of {alpha}{sub s}(M{sub Z}{sup 2}) from the global electroweak fit, this result leads to the most accurate test of asymptotic freedom: the value of the logarithmic slope of {alpha}{sub s}{sup -1}(s) is found to agree with QCD at a precision of 4%. The {tau} spectral functions can also be used to determine hadronic quantities that, due to the nonperturbative nature of long-distance QCD, cannot be computed from first principles. An example for this is the contribution from hadronic vacuum polarization to loop-dominated processes like the anomalous magnetic moment of the muon. This article reviews the measurements of nonstrange and strange {tau} spectral functions and their phenomenological applications.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/496b9d7f6b5c530ffa1035c5b0a61fa9092538de