Study of the reaction e^+e^- → J/ψ π^+π^- via initial-state radiation at BABAR

Abstract

We study the process e^+e^- → J/ψπ^+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/c^2. Below 3.7  GeV/c^2 the ψ(2S) signal dominates, and above 4  GeV/c^2 there is a significant peak due to the Y(4260). A fit to the data in the range 3.74–5.50  GeV/c^2 yields a mass value 4245±5(stat)±4(syst)  MeV/c^2 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/c^2. In addition, we investigate the π^+π^- system which results from Y(4260) decay.

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