Observation of $Z_c(3900)$ both by BESIII and Belle

Using $525$ pb${}^{-1}$ data collected with the BESIII detector at $e^{+}{e}^{-}$ central-of-mass energy 4.26 GeV, the BESIII Collaboration observed a charged charmoniumlike state $Z_c(3900)\to {\pi }^{\pm }J\mathrm{/}\psi$ with mass $M[Z_c(3900)]=3899.0\pm 3.6\pm 4.9$ MeV/c${}^2$, and width $\mathrm{\Gamma }[Z_c(3900)]=46\pm 10\pm 20$ MeV. The significance of this state was estimated to be $>8\sigma$ in all kinds of systematic tests. Using $967$ fb${}^{-1}$ data recorded by the Belle detector on or near $\mathrm{{\rm Y}}(nS)$, n=1, 2, $\cdots$, 5 resonances, the $e^{+}{e}^{-}\to {\pi }^{+}{\pi }^{-}J\mathrm{/}\psi$ process has been studied through initial-state-radiation (ISR) method. Except for the $Y(4260)$ resonance, an intermediate state $Z(3900{)}^{\pm }$ has been observed in the ${\pi }^{\pm }J\mathrm{/}\psi$ mass spectrum, with significance $>5.2\sigma$. The measured mass $M[Z(3900{)}^{\pm }]=3894.5\pm 6.6\pm 4.5$ MeV/c${}^2$ and width $\mathrm{\Gamma }[Z(3900{)}^{\pm }]=63\pm 24\pm 26$ MeV, shows good agreement with the BESIII measurement within errors, which means $Z_c(3900)$ and $Z(3900{)}^{\pm }$ is the same state.