The Hadronic Contribution to (g-2)μ

The evaluation of the hadronic contribution to the muon magnetic anomaly aμ is revisited, taking advantage of new experimental data on e+e- annihilation into hadrons: SND and CMD-2 for the π+π- channel, and BABAR for multihadron final states. Discrepancies are observed between KLOE and CMD-2/SND data, preventing one from averaging all the e+e- results. The long-standing disagreement between spectral functions obtained from τ decays and e+e- annihilation is still present, and not accounted by isospin-breaking corrections, for which new estimates have been presented. The updated Standard Model value for aμ based on e+e- annihilation data is now reaching a precision better than experiment, and it disagrees with the direct measurement from BNL at the 3.3σ level, while the τ-based estimate is in much better agreement. The τ/e+e- discrepancy, best revealed when comparing the measured branching fraction for τ-→π-π0ντ to its prediction from the isospin-breaking-corrected e+e- spectral function, remains a serious problem to be understood