Observation of a Broad Structure in the π+π-J/ψ Mass Spectrum around 4.26 GeV/c2

We study initial-state radiation events, e+e-→γISRπ+π-J/ψ, with data collected with the BABAR detector. We observe an accumulation of events near 4.26  GeV/c2 in the invariant-mass spectrum of π+π-J/ψ. Fits to the mass spectrum indicate that a broad resonance with a mass of about 4.26  GeV/c2 is required to describe the observed structure. The presence of additional narrow resonances cannot be excluded. The fitted width of the broad resonance is 50 to 90  MeV/c2, depending on the fit hypothesis.