e+e− results from BABAR and implications for the muon g-2

Abstract

The BaBar collaboration has nearly completed a program of precise measurements of the cross sections for the dominant channels of $e^{+}{e}^{-}\to \mathrm{hadrons}$ from threshold to an energy of 3–5 GeV using the initial-state radiation (ISR) method, i.e. the measurement of the cross sections $e^{+}{e}^{-}\to \gamma \mathrm{hadrons}$ with the energetic γ detected at large angle to the beams. These data are used as input to vacuum polarization dispersion integrals, in particular the hadronic contribution to the muon $g-2$ anomaly. In addition to the recently measured ${\pi }^{+}{\pi }^{-}$ cross section, giving the dominant contibution, many multihadronic channels have been investigated, with some recent examples presented here. We give preliminary results for the process $e^{+}{e}^{-}\to K^{+}{K}^{-}\left(\gamma \right)$ using $232{\text{fb}}^{-1}$ of data collected with the BaBar detector at $e^{+}{e}^{-}$ center-of-mass energies near 10.6 GeV. The lowest-order contribution to the hadronic vacuum polarization term in the muon magnetic anomaly is obtained for this channel: $a_{\mu }^{KK,LO}=(22.95\pm {0.14}_{\text{(stat)}}\pm {0.22}_{\text{(syst)}})\times {10}^{-10}$, which is about a factor of three more precise than the previous world average value.