Mass Predictions for Pseudoscalar $J^{PC}=0^{-+}$ Charmonium and   Bottomonium Hybrids in QCD Sum-Rules
  Masses of the pseudoscalar $(J^{PC}=0^{-+})$ charmonium and bottomonium hybrids are determined using QCD Laplace sum-rules. The effects of the dimension-six gluon condensate are included in our analysis and result in a stable sum-rule analysis, whereas previous studies of these states were unable to optimize mass predictions. The pseudoscalar charmonium hybrid is predicted to have a mass of approximately 3.8 GeV and the corresponding bottomonium prediction is 10.6 GeV. Calculating the full correlation function, rather than only the imaginary part, is shown to be necessary for accurate formulation of the sum-rules. The charmonium hybrid mass prediction is discussed within the context of the X Y Z resonances. 
R. Berg, D. Harnett, R. T. Kleiv, T. G. Steele
hep-ph