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Updated: Jul 28, 2026

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation
Published on: October 30, 2012
Observation of a broad structure in the pi+ pi- J/psi mass spectrum around 4.26 GeV/c2
B Aubert1, R Barate, D Boutigny
1Laboratoire de Physique des Particules, F-74941 Annecy-le-Vieux, France.
Abstract:
We study initial-state radiation events, e+ e- --> gammaISR pi+ pi- J/psi, with data collected with the BABAR detector. We observe an accumulation of events near 4.26 GeV/c2 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/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.
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