Resolving the tau versus electroproduction discrepancy for the I=1 vector spectral function and implications for the SM prediction for a_mu

Abstract

Using only independent high-scale OPE input, we investigate QCD sum rule constraints on two currently incompatible versions of the I=1 vector spectral function, one obtained from electroproduction data, the other from hadronic tau decay data. Sum rules involving weighted integrals over the spectral functions, from threshold to a variable upper endpoint, s_0,are employed. It is shown that both the normalization and slope with respect to s_0 of the EM spectral integrals disagree with the corresponding OPE expectations, while both the normalization and slope are in good agreement when hadronic tau decay data is used instead. These results favor determinations of the leading order hadronic vacuum polarization contribution to a_mu obtained using the tau decay data, and hence Standard Model predictions for a_mu compatible with the current experimental determination.

4 pages, prepared for the proceedings of the International Conference on QCD and Hadronic Physics, Beijing, June 16-20, 2005