ISSN - 00319007, EISSN - 10797114, Physical Review Letters, 2005, vol. 95, p. -
Observation of a broad structure in the n+n-J/ψ mass spectrum around 4.26GeV/c2
We study initial-state radiation events, e+e- â†'ÎISRÏ€+Ï€-J/Ï, with data collected with the BABAR detector. We observe an accumulation of events near 4.26GeV/c2 in the invariant-mass spectrum of Ï€+Ï€-J/Ï. Fits to the mass spectrum indicate that a broad resonance with a mass of about 4.26GeV/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 90MeV/c2, depending on the fit hypothesis. © 2005 The American Physical Society.