Measurement of $e^+e^- \to$ hadron cross-section at low energy with ISR events at BaBar

Abstract : The precise measurement of the cross section e(+)e(-) -> pi(+)pi(-)(gamma) from threshold to an energy of 3 GeV, using events with Initial State Radiation (ISR) collected with the BABAR detector, is presented. The ISR luminosity is determined from a study of the leptonic process e(+)e(-) -> mu(+)mu(-)gamma(gamma), and the method is tested by the comparison with the next-to-leading order (NLO) QED prediction. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the BABAR pi pi cross section measured from threshold to 1.8 GeV is (514.1 +/- 2.2(stat) +/- 3.1(syst)) x 10(-10). Other results on ISR multihadronic cross sections from BABAR are presented.