  Experimentally several charged axial-vector hidden-charm states were
reported. Within the framework of the color-magnetic interaction, we have
systematically considered the mass spectrum of the hidden-charm and
hidden-bottom tetraquark states. It is impossible to accommodate all the three
charged states $Z_c(3900)$, $Z_c(4025)$ and $Z_c(4200)$ within the axial vector
tetraquark spectrum simultaneously. Not all these three states are tetraquark
candidates. Moreover, the eigenvector of the chromomagnetic interaction
contains valuable information of the decay pattern of the tetraquark states.
The dominant decay mode of the lowest axial vector tetraquark state is $J/\psi
\pi$ while its $D^*\bar{D}$ and $\bar{D}^*D^*$ modes are strongly suppressed,
which is in contrast with the fact that the dominant decay mode of $Z_c(3900)$
and $Z_c(4025)$ is $\bar{D}D^*$ and $\bar{D}^*D^*$ respectively. We emphasize
that all the available experimental information indicates that $Z_c(4200)$ is a
very promising candidate of the lowest axial vector hidden-charm tetraquark
state.
