Precise measurement of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>e</mml:mi><mml:mo mathvariant="bold">+</mml:mo></mml:msup><mml:msup><mml:mi>e</mml:mi><mml:mo mathvariant="bold">−</mml:mo></mml:msup><mml:mo>→</mml:mo><mml:msup><mml:mi>π</mml:mi><mml:mo mathvariant="bold">+</mml:mo></mml:msup><mml:msup><mml:mi>π</mml:mi><mml:mo mathvariant="bold">−</mml:mo></mml:msup><mml:mo mathvariant="bold" stretchy="false">(</mml:mo><mml:mi>γ</mml:mi><mml:mo mathvariant="bold" stretchy="false">)</mml:mo></mml:math>cross section with the initial-state radiation method at<i>BABAR</i>

A precise measurement of the cross section of the process e^+e^-→π^+π^-(γ) from threshold to an energy of 3 GeV is obtained with the initial-state radiation (ISR) method using 232 fb^(-1) of data collected with the BABAR detector at e^+e^- center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process e^+e^-→μ^+μ^-(γ)γ_(ISR), which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process e^+e^-→π^+π^-(γ) is obtained with a systematic uncertainty of 0.5% in the dominant ρ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured ππ cross section from threshold to 1.8 GeV is (514.1±2.2(stat)±3.1(syst))×10^(-10).