The European Physical Journal C

, Volume 56, Issue 3, pp 305–322

The determination of αS from τ decays revisited

  • M. Davier
  • S. Descotes-Genon
  • A. Höcker
  • B. Malaescu
  • Z. Zhang
Regular Article - Experimental Physics

DOI: 10.1140/epjc/s10052-008-0666-7

Cite this article as:
Davier, M., Descotes-Genon, S., Höcker, A. et al. Eur. Phys. J. C (2008) 56: 305. doi:10.1140/epjc/s10052-008-0666-7

Abstract

We revisit the determination of αS(mτ2) using a fit to inclusive τ hadronic spectral moments in light of (1) the recent calculation of the fourth-order perturbative coefficient K4 in the expansion of the Adler function, (2) new precision measurements from BABAR of e+e annihilation cross sections, which decrease the uncertainty in the separation of vector and axial-vector spectral functions, and (3) improved results from BABAR and Belle on τ branching fractions involving kaons. We estimate that the fourth-order perturbative prediction reduces the theoretical uncertainty, introduced by the truncation of the series, by 20% with respect to earlier determinations. We discuss to some detail the perturbative prediction of two different methods: fixed-order perturbation theory (FOPT) and contour-improved perturbative theory (CIPT). The corresponding theoretical uncertainties are studied at the τ and Z mass scales. The CIPT method is found to be more stable with respect to the missing higher order contributions and to renormalization scale variations. It is also shown that FOPT suffers from convergence problems along the complex integration contour. Nonperturbative contributions extracted from the most inclusive fit are small, in agreement with earlier determinations. Systematic effects from quark-hadron duality violation are estimated with simple models and found to be within the quoted systematic errors. The fit based on CIPT gives αS(mτ2)=0.344±0.005±0.007, where the first error is experimental and the second theoretical. After evolution to MZ we obtain αS(MZ2)=0.1212±0.0005±0.0008±0.0005, where the errors are respectively experimental, theoretical and due to the evolution. The result is in agreement with the corresponding N3LO value derived from essentially the Z width in the global electroweak fit. The αS(MZ2) determination from τ decays is the most precise one to date.

Copyright information

© Springer-Verlag / Società Italiana di Fisica 2008

Authors and Affiliations

  • M. Davier
    • 1
  • S. Descotes-Genon
    • 2
  • A. Höcker
    • 3
  • B. Malaescu
    • 1
  • Z. Zhang
    • 1
  1. 1.Laboratoire de l’Accélérateur LinéaireIN2P3/CNRS et Université Paris-Sud 11 (UMR 8607)Orsay CedexFrance
  2. 2.Laboratoire de Physique ThéoriqueCNRS et Université Paris-Sud 11 (UMR 8627)Orsay CedexFrance
  3. 3.CERNGenevaSwitzerland