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

Abstract

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.