The $Z_c(3900)$ peak does not come from the "triangle singularity"

Abstract

We compare contributions from the triangle diagram and the $D{\bar{D}}^{\ast }$ bubble chain to the processes of $e^{+}{e}^{-}\to J/\psi {\pi }^{+}{\pi }^{-}$ and $e^{+}{e}^{-}\to (D{\bar{D}}^{\ast }{)}^{\mp }{\pi }^{\pm }$. By fitting the $J/\psi \pi$ maximum spectrum and the $D{\bar{D}}^{\ast }$ spectrum, we find that the triangle diagram cannot explain the new data from BESIII Collaboration at center of mass at 4.23GeV and 4.26GeV, simultaneously. On the contrary, the molecular assignment of $Z_c(3900)$ gives a much better description.