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Full LEP-I data collected by the ALEPH detector during 1991-1995 running are analyzed in order to measure the $\tau$ decay branching fractions. The analysis follows the global method used in the published study based on 1991-1993 data, with several improvements, especially concerning the treatment of photons and $\pi^0$'s. Extensive systematic studies are performed, in order to match the large statistics of the data sample corresponding to 327148 measured and identified $\tau$ decays. Preliminary values for the branching fractions are obtained for the 2 leptonic channels and 11 hadronic channels defined by their respective numbers of charged particles and $\pi^0$'s. Using previously published ALEPH results on final states with charged and neutral kaons, corrections are applied so that branching ratios for exclusive final states without...
The Standard Model preciction for the muon anomalous magnetic moment is reviewed. Recent updates of QED, electroweak and hadronic contributions are described. Comparison of theory and experiment suggests a $2.4\sigma$ difference if $e^+e^- \rightarrow$ hadrons data are used to evaluate the main hadronic effects, but a smaller discrepancy if hadronic $\tau$ decay data are employed. Implications of a deviation for "new physics" contributions along with an outlook for future improvements in theory and experiment are briefly discussed.
In a recent paper \cite{benayoun} M.Benayoun {\it et al.} use a specific model to compare results on the existing data for the cross section of the process $e^+e^-\rightarrow \pi^+\pi^-$ and state conclusions about the inconsistency of the BABAR results with those from the other experiments. We show that a direct model-independent comparison of the data at hand contradicts this claim. Clear discrepancies with the results of Ref. \cite{benayoun} are pointed out. As a consequence we do not believe that the lower value and the smaller uncertainty obtained for the prediction of the muon magnetic anomaly are reliable results.
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