THE HADRONIC CONTRIBUTION TO (g - 2)_μ

摘要

The evaluation of the hadronic contribution to the muon magnetic anomaly a_μ 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~- π~0 v_τ 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 a_μ results in a deviation of 2.7 standard deviations from the BNL measurement.