## Estimating the Mass of Hidden Charm $1^+(1^{+})$ Tetraquark State via QCD Sum Rules    [PDF]

Cong-Feng Qiao, Liang Tang
By virtue of the QCD Sum Rules, we estimate the mass of hidden charm tetraquark $[cu][\bar{c}\bar{d}]$ state with $I^{G} (J^{P}) = 1^+ (1^{+})$ (HCTV), which presumably to be the newly observed charmonium-like resonance $Z_c^+(3900)$. In our calculation, the contributions up to dimension eight in the Operator Product Expansion(OPE) are taken into account. We find $m_{1^+}^c = (3912^{+106}_{-103}) \, \text{MeV}$, which is consistent, within the errors, with the experimental data of the $Z_c^+(3900)$. Extending to the b-quark sector, we obtain $m_{1^+}^b = (10561^{+185}_{-95}) \,\text{MeV}$. Our results strongly support the tetraquark picture for the "exotic" states $Z_c^+(3900)$ and $Z_b^+(10610)$.
View original: http://arxiv.org/abs/1307.6654