Observation of the Charged Hadron $Z_c^{\pm}(3900)$ and Evidence for the Neutral $Z_c^0(3900)$ in $e^+e^-\to \pi\pi J/\psi$ at $\sqrt{s}=4170$ MeV

Understand

Using 586 pb$^{-1}$ of $e^+e^-$ annihilation data taken with the CLEO-c detector at $\sqrt{s}=4170$ MeV, the peak of the charmonium resonance $\psi(4160)$, we analyze the decay $\psi(4160)\to \pi^+\pi^- J/\psi$, and report observation of the charged state $Z_c^\pm(3900)$ decaying into $\pi^\pm J/\psi$ at a significance level of $>5 \sigma$.

• We obtain $M(Z_c^\pm)=3886\pm4(\text{stat})\pm 2(\text{syst})$ MeV and $\Gamma(Z_c^\pm)=37\pm4(\text{stat})\pm 8(\text{syst})$ MeV, which are in good agreement with the results for this resonance obtained by the BES III and Belle Collaborations in the decay of the resonance Y(4260).
• We also present first evidence for the production of the neutral member of this isospin triplet, $Z_c^0(3900)$ decaying into $\pi^0J/\psi$ at a $3.5\sigma$ significance level.