Observation of a Broad Structure in the ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}J/\ensuremath{\psi}$ Mass Spectrum around $4.26\text{ }\text{ }\mathrm{GeV}/{c}^{2}$

Observation of a Broad Structure in the $π^{+} π^{-} J / ψ$ Mass Spectrum around $4.26 GeV / c^{2}$

B. Aubert et al. (BABAR Collaboration)

Phys. Rev. Lett. 95, 142001 – Published 28 September 2005

Abstract

We study initial-state radiation events, $e^{+} e^{-} \to γ_{ISR} π^{+} π^{-} J / ψ$ , 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 $π^{+} π^{-} J / ψ$ . 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.