Observation of a broad structure in the π+π-J/ψ mass spectrum around 4.26 GeV/c2 -: art. no. 142001

We study initial-state radiation events, e(+)e(-)->gamma(ISR)pi(+)pi(-)J/psi, with data collected with the BABAR detector. We observe an accumulation of events near 4.26 GeV/c(2) in the invariant-mass spectrum of pi(+)pi(-)J/psi. Fits to the mass spectrum indicate that a broad resonance with a mass of about 4.26 GeV/c(2) 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/c(2), depending on the fit hypothesis.