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

The BaBar collaboration has nearly completed a program of precise measurements of the cross sections for the dominant channels of e+e−→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 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 π+π− 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−→K+K−(γ) using 232fb−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: , which is about a factor of three more precise than the previous world average value.