Study of the Reaction e⁺e⁻ -→ J/ψ π⁺π⁻ via Initial-State Radiation at BABAR

We study the process e⁺e⁻ → J/ψ π⁺π⁻ with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BABAR detector at center-of-mass energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454 fb⁻¹. We investigate the J/ψ π⁺π⁻ mass distribution in the region from 3.5 to 5.5 GeV/c². Below 3.7 GeV/c² the ψ(2S) signal dominates, and above 4 GeV/c² there is a significant peak due to the Y(4260). A fit to the data in the range 3.74-5.50 GeV/c² yields a mass value 4245 ±5(stat) ±4(syst) MeV/c² and a width value 114{_-15 ^{+16}} (stat) ±7(syst) MeV for this state. We do not confirm the report from the Belle Collaboration of a broad structure at 4.01 GeV/c². In addition, we investigate the π⁺π⁻ system which results from Y(4260) decay.