Precise Measurement of the e+e-→π+π-(γ) Cross Section with the Initial State Radiation Method at BABAR

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). The leading-order hadronic contribution to the muon magnetic anomaly calculated using the ππ cross section measured from threshold to 1.8 GeV is (514.1±2.2(stat)±3.1(syst))×10-10.