Relating $D^* \bar{D}^*$ currents with $J^\pi= 0^+,1^+$ and $2^+$ to $Z_c$ states

Abstract

In this work we study the $D^* \bar{D}^*$ current with QCD sum rules. We write the correlation function using the general current corresponding to the $D^* \bar{D}^*$ system and then use spin projectors to obtain the correlation function in the $0^+, 1^+$ and $2^+$ spin-parity configurations. The purpose of the present work is to investigate the possibility of explaining the recently reported $Z_c(4025)$ as a $D^* \bar{D}^*$ moleculelike state. As a result we find a state for each spin case with a very similar mass: $M^{S=0} = \left(3943 \pm 104\right)$ MeV, $M^{S=1} = \left(3950 \pm 105\right)$ MeV, $M^{S=2} = \left(3946 \pm 104 \right)$ MeV. We discuss that our mass results, within error bars, for $1^+$ or $2^+$ are both compatible with $Z_c(4025)$. However, our results are also compatible with a possible $D^* \bar{D}^*$ bound state, in agreement with predictions of some previous works. We have also calculated the current-state coupling which turns out to be larger in the $2^+$ case.