E. Oset, Ju-Jun Xie, M. Albaladejo, F. Aceti, M. Bayar, A. Martinez Torres, K. P. Khemchandani, F. S. Navarra, M. Nielsen, J. M. Dias

The BES data on the $J/\psi\to\etaK^0\bar{K}^0$ reaction show a clear enhancement in the $K^0\bar{K}^0$ mass distribution close to the threshold of this channel. Such an enhancement is usually a signature of a L=0 resonance around threshold, which in this case would correspond to an h1 state with quantum numbers $I^G(J^{PC})=0^-(1^{+−})$. A state around 1800 MeV results from the interaction of the $K\bar{K}$ using the local hidden gauge approach. We show that the peak observed in $J/\psi\to\etaK^0\bar{K}^0$ naturally comes from the creation of this h1 state with mass and width around 1830 MeV and 110 MeV, respectively. A second analysis, model independent, corroborates the first result, confirming the relationship of the enhancement in the invariant mass spectrum with the h1 resonance. After discussing the OZI suppression of one light meson exchange in the interaction of $D^ \bar{D}^$ with isospin I=1, we study the contribution of two pion exchange to the interaction and the exchange of a heavy vector $J/\psi$. We find this latter mechanism weak but enough to barely bind the system in J=2 with a mass around 4000 MeV, while the effect of the two pion exchange is a net attraction but weaker than that from $J/\psi$ exchange. We discuss this state and try to relate it to the $Z_c(4025)$ state, above the $D^ \bar{D}^$ threshold, claimed in an experiment at BES from and enhancement of the $D^\bar{D}^$ distribution close to threshold. Together with the results from a recent reanalysis of the BES experiment showing that it is compatible with a J=2 state below threshold around 3990 MeV, we conclude that the BES experiment could be showing the existence of the state that we find in our approach. At the same time we study the interaction of $D \bar{D}^$ in the isospin I=1 channel in the light of recent theoretical advances that allow to combine elements of the local hidden gauge approach with heavy quark spin symmetry. We find that the exchange of light qqbar is OZI suppressed and, thus, we concentrate on the exchange of heavy vectors and of two pion exchange. The latter is found to be small compared to the exchange of heavy vectors, which then determines the strength of the interaction. A barely $D \bar{D}^$ bound state decaying into $\eta_c\rho$ and $\pi J/\psi$ is found. At the same time we reanalyze the data of the BESIII experiment on $e^+e^−\rightarrow\pi^\pm (D \bar{D}^)^\pm$, from where a $Z_c(3885)$ state was claimed, associated to a peak in the $(D \bar{D}^)^\pm$ invariant mass distribution close to threshold, and we find the data compatible with a resonance with mass around 3875 MeV and width around 30 MeV. We discuss the possibility that this and the $Z_c(3900)$ state found at BESIII, reconfirmed at 3896 MeV at Belle, or 3885 MeV at CLEO, could all be the same state and correspond to the one that we find theoretically.