Y(4260) and Y(4360) as mixed hadrocharmonium

Understand

Recent BESIII data indicate a significant rate of the process $e^+e^- \to h_c \pi^+ \pi^-$ at the Y(4260) and Y(4360) resonances, implying a substantial breaking of the heavy quark spin symmetry.

• We consider these resonances within the picture of hadrocharmonium, i.e.
• of (relatively) compact charmonium embedded in a light quark mesonic excitation.
• We suggest that the resonances Y(4260) and Y(4360) are a mixture, with mixing close to maximal, of two states of hadrochamonium, one containing a spin-triplet $c \bar c$ pair and the other containing a spin-singlet heavy quark pair.