$α_s$ from an improved $τ$ vector isovector spectral function

After discussing difficulties in determining $α_s$ from tau decay due to the existence of Duality Violations and the associated asymptotic nature of the OPE, we describe a new determination based on an improved vector isovector spectral function, now based solely on experimental input, obtained by (i) combining ALEPH and OPAL results for $2π+4π$ and (ii) replacing $K^-K^0$ and higher-multiplicity exclusive-mode contributions, both previously estimated using Monte Carlo, with new experimental BaBar results for $K^-K^0$ and results implied by $e^+ e^-$ cross sections and CVC for the higher-multiplicity modes. We find $α_s(m_τ)=0.3077\pm 0.0075$, which corresponds to $α_s(m_Z)=0.1171\pm 0.0010$. Finally, we comment on some of the shortcomings in the criticism of our approach by Pich and Rodriguez-Sanchez.

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