Measurement of the e+e−→π+π−(γ) Cross Section with the ISR Method with BaBar

Abstract : A precision measurement of the cross section for the process e+e−→π+π−(γ) is presented with the radiative return method with the high statistics data accumulated by BaBar at the Upsilon(4S). The luminosity is determined from the study of the corresponding leptonic process e+e−→μ+μ−(γ), thus cancelling several factors and reducing the overall systematic uncertainty. Trigger, tracking, particle identification, and kinematic-fit χ2 efficiencies are evaluated from data in the same environment. Additional radiation from the initial and the final states is studied in both processes. The analysis covers the mass range between threshold and 5 GeV. Preliminary results are presented here between 0.5 and 3 GeV, with data samples of 513183 pion events and 445631 muon events. The systematic uncertainty in the main ρ resonance region is 5.6×10−3. The measured mass dependent pion-pair cross section is compared with measurements from earlier experiments and used to compute the hadronic vacuum polarization contribution from the dominant ππ channel to the muon magnetic anomaly.
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M. Davier. Measurement of the e+e−→π+π−(γ) Cross Section with the ISR Method with BaBar. 10th International Workshop on Tau Lepton Physics (TAU'08), Sep 2008, Novosibirsk, Russia. Elsevier, 189, pp.222-232, 2009, 〈10.1016/j.nuclphysbps.2009.03.038〉. 〈in2p3-00381257〉



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