Reanalysis of the $Y(3940)$, $Y(4140)$, $Z_c(4020)$, $Z_c(4025)$ and $Z_b(10650)$ as molecular states with QCD sum rules

Abstract

In this article, we calculate the contributions of the vacuum condensates up to dimension-10 in the operator product expansion, and study the $J^{PC}=0^{++}$, $1^{+-}$, $2^{++}$ $D^*\bar{D}^*$, $D_s^*\bar{D}_s^*$, $B^*\bar{B}^*$, $B_s^*\bar{B}_s^*$ molecular states with the QCD sum rules. In calculations, we use the formula $\mu=\sqrt{M^2_{X/Y/Z}-(2{\mathbb{M}}_Q)^2}$ to determine the energy scales of the QCD spectral densities. The numerical results favor assigning the $Z_c(4020)$ and $Z_c(4025)$ as the $J^{PC}=0^{++}$, $1^{+-}$ or $2^{++}$ $D^*\bar{D}^*$ molecular states, the $Y(4140)$ as the $J^{PC}=0^{++}$ $D^*_s{D}_s^*$ molecular state, the $Z_b(10650)$ as the $J^{PC}=1^{+-}$ $B^*\bar{B}^*$ molecular state, and disfavor assigning the $Y(3940)$ as the ($J^{PC}=0^{++}$) molecular state. The present predictions can be confronted to the experimental data in the futures.