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On the Extraction of the Strong Coupling from Hadronic Tau Decay

The finite energy sum rule extraction of the strong coupling α_s from hadronic τ decay data provides one of its most precise experimental determinations. As precision improves, small non-perturbative effects become increasingly relevant to both the central value and error. Here we present a new framework for this extraction employing a physically motivated model to accommodate violations of quark-hadron duality and enforcing a consistent treatment of higher-dimension operator product expansion contributions. Using 1998 OPAL data for the non-strange vector and axial-vector spectral functions, we find the n_f=3 values for α_s(m_τ^2) of 0.307(19) for fixed-order perturbation theory and 0.322(26) for contour-improved perturbation theory, corresponding to n_f=5 values for α_s(M_Z^2) of 0.1169(25) and 0.1187(32), respectively.