Observation of a threshold enhancement in the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ spectrum in $\ddot{I}ˆ(3686)\to \ddot{I}{€}^{+}\ddot{I}{€}^{-}J/\ddot{I}ˆ$ decays

BESIII Collaboration, M. Ablikim, M. N. Achasov +677

The BESIII experiment analyzed over 2.7 billion ψ(3686) decays and observed a clear resonance-like enhancement near the π⁺π⁻ mass threshold in ψ(3686)→π⁺π⁻J/ψ decays, measuring its…