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

The BABAR Collaboration, B. Aubert

We study initial-state radiation events, $e^{+}{e}^{-}\to {\gamma }_{ISR}{\pi }^{+}{\pi }^{-}J/\psi$, with data collected with the BaBar detector. We observe an accumulation of events near 4.26 GeV/$c^2$ in the…