Diffractive charm jet production at hadron colliders in the two-gluon   exchange model
  We present a calculation of diffractive charm jet production at hadron colliders in perturbative QCD based on the two-gluon exchange model. Differing from the previous calculations, we abandon the use of the effective color-singlet vitual gluon simplification, and use the real gluon in the calculations for the partonic process. We find the final result is free of the linear singularities due to the small transverse momenta of the exchanged two gluons. In the leading logarithmic approximation (LLA) in QCD, this process is related to the off-diagonal gluon density in the proton. As a result, this process may provide a wide window for testing the two-gluon exchange model, and may be particularly useful in studying the small $x$ physics. In comparison, the diffractive bottom jet production is also discussed, and is found to be important only for large transverse momentum of the jet. 
Feng Yuan, Kuang-Ta Chao (PKU)