Study of the Process e⁺ e⁻ → <i>π</i> ⁺ <i>π</i> ⁻ <i>π</i>⁰ Using Initial State Radiation with BABAR

Abstract

The process e+e−→ π+π−π0γ is studied at a center-of-mass energy near the ϒ(4S) resonance using a data sample of 469 fb−1 collected with the BABAR detector at the PEP-II collider. We have performed a precise measurement of the e+e−→ π+π−π0 cross section in the center-of-mass energy range from 0.62 to 3.5 GeV. In the energy regions of theω and ϕ resonances, the cross section is measured with a systematic uncertainty of 1.3%. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured e+e− → π+π−π0 cross section from threshold to 2.0 GeV is (45.86 plusmn; 0.14 plusmn; 0.58) × 10−10. From the fit to the measured 3π mass spectrum we have determined the resonance parameters Γ(ω → e+e−)B(ω → π+π-π0)= (0.5698 plusmn; 0.0031 plusmn; 0.0082) keV, Γ(ϕ → e+e−) B(ϕ → π+π+π0) = (0.1841 plusmn; 0.0021 plusmn; 0.0080) keV, and B(ρ → 3π)=(0.88 plusmn;0.23 plusmn; 0.30) × 10−4. The significance of the ρ → 3π signal is greater than 6σ. For the J=ψ resonance we have measured the product Γ(J /ψ →e+e−)B(J/ψ→3π)=(0.1248±0.0019±0.0026) keV.