The Hadronic Contribution to (g−2)μ

The evaluation of the hadronic contribution to the niuon magnetic anomaly aμ is reviewed, including a new estimate using precise results on the π+π− spectral function from the KLOE Collaboration. It is found that the KLOE data confirm to some extent the previous e+e− annihilation data in this channel, and accentuate the disagreement with the isospin-breaking-corrected spectral function from τ−→π+π0ντ decays. Correcting for the empirical difference in the mass of the charged and the neutral ρ locally improves, but does not resolve this discrepancy. A preliminary reevaluation (including the KLOE data) of the e+e−-based Standard Model prediction of aμ results in a deviation of 2.7 standard deviations from the BNL measurement.