Lowest order hadronic contribution to the muong−2value with systematic error correlations

We have performed a new evaluation of the hadronic contribution to $a_{\mu }=\frac{\mathrm{}(g-2\mathrm{})\mathrm{}}{2}$ of the muon with explicit correlations of systematic errors among the experimental data on $\sigma (e^{+}{e}^{-}\to \mathrm{hadrons})$. Our result for the lowest order hadronic vacuum polarization contribution is $a_{\mu }^{\mathrm{had}}=702.6\mathrm{}\left(7.8\right)\mathrm{}\left(14.0\right)\mathrm{}\times {10}^{-10\mathrm{}}$ where the first error is statistical and the second is systematic. The total systematic error contributions from below and above $\sqrt{s}=1.4\mathrm{}$ GeV are (13.1)×${10}^{-10\mathrm{}}$ and (5.1)×${10}^{-10\mathrm{}}$, respectively, and are hence dominated by the low energy region. Therefore, new measurements on $\sigma (e^{+}{e}^{-}\to \mathrm{hadrons})$ below 1.4 GeV can significantly reduce the total error on $a_{\mu }^{\mathrm{had}}$. In particular, the effect on the total errors of new hypothetical data with 3% statistical and 0.5-1.0% systematic errors is presented.