Status of the Hadronic Contribution to the Muon (g-2) Value

Abstract

With the recent interest in the measured and standard model values of the muon anomalous magnetic moment, a_mu, some confusion has arisen concerning our knowledge of the hadronic contribution to a_mu. In the dispersion integral approach to hadronic vacuum polarization effects, low energy contributions must be evaluated from data or in a model-dependent approach tested by data. At higher energies perturbative QCD has been used, sometimes in conjunction with data. The history of such evaluations is reviewed, and the prospects for further improvement are discussed. We conclude that not all published evaluations are on an equal footing or up-to-date. One must critically examine which, and how much information went into each analysis in order to determine which are more complete, and reliable.