Estimating the mass of the hidden charm 1+(1+) tetraquark state via QCD sum rules

By using QCD sum rules, the mass of the hidden charm tetraquark [cu][c¯d¯] state with IG(JP)=1+(1+) (HCTV) is estimated, which presumably will turn out to be the newly observed charmonium-like resonance Zc+(3900) . In the calculation, contributions up to dimension eight in the operator product expansion (OPE) are taken into account. We find m1+c=(3912-153+306)MeV , which is consistent, within the errors, with the experimental observation of Zc+(3900) . Extending to the b-quark sector, m1+b=(10561-163+395)MeV is obtained. The calculational result strongly supports the tetraquark picture for the “exotic” states of Zc+(3900) and Zb+(10610)