The Hadronic Contribution to the Muon g-2

Abstract

The evaluation of the hadronic contribution to the muon magnetic anomaly a_mu is reviewed, including a new estimate using precise results on the pi+pi- 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 tau- -> pi-pi0 nu decays. Correcting for the empirical difference in the mass of the charged and the neutral rho 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_mu results in a deviation of 2.7 standard deviations from the BNL measurement.

Comments: Invited talk given at the 32nd International Conference on High-Energy Physics (ICHEP'04), Beijing, China, August 2004; 6 pages LaTeX, 3 eps figures