Analysis of the $Z(4430)$ as the first radial excitation of the   $Z_c(3900)$
  In this article, we take the $Z_c(3900)$ and $Z(4430)$ as the ground state and the first radial excited state of the axial-vector tetraquark states with $J^{PC}=1^{+-}$, respectively, and study their masses and pole residues with the QCD sum rules by calculating the contributions of the vacuum condensates up to dimension-10 in a consistent way in the operator product expansion. The numerical result favors assigning the $Z_c(3900)$ and $Z(4430)$ as the ground state and first radial excited state of the axial-vector tetraquark states, respectively. 
Zhi-Gang Wang
hep-ph