Heavy quarkonium production in double Pomeron exchange processes in perturbative QCD

We calculate the heavy quarkonium production in double pomeron exchange processes in perturbative QCD by using two-gluon exchange model. For the $P$-wave $\chi_J$ productions, we find $\chi_1$ and $\chi_2$ production amplitudes which vanish in the forward scattering limit. We also calculate direct $J/\psi(\Upsilon)+\gamma$ production in the same approach, and these direct contributions are much smaller than the feeddown contributions from the $P$-wave states.