The Mass and Decay Properties of the $1^{-+}$ Light Hybrid Meson

We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the ($1^{-+}$,$0^{++}$) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of $langle g^3G^3rangle$ increase the QCD sum rule mass prediction for the $1^{-+}$ light hybrid. The obtained conservative mass range 1.72--2.60 GeV does not favor the $pi_1(1400)$ and the $pi_1(1600)$ to be pure hybrid states and suggests the $pi_1(2015)$ observed by E852 is more likely to have much of a hybrid constituent. We also study the $b_1pi$ and $rhopi$ decay patterns of the $1^{-+}$ light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the $b_1pi$ mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the $rhopi$ mode is small due to the absence of the leading twist contribution in the light-cone expansion of the correlation function.