Diffractive J/ψJ/\psi production through color-octet mechanism in resolved photon processes at HERA

We use the color-octet mechanism combined with the two gluon exchange model for the diffractive $J/\psi$ production in resolved photon processes. In the leading logarithmic approximation in QCD, we find that the diffractive $J/\psi$ production cross section is related to the off-diagonal gluon density of the proton, the gluon density of the photon and to the nonperturbative color-octet $^3 S_{1}^{(8)}$ matrix element of $J/\psi$. The cross section is found to be very sensitive to the gluon density of the photon. As a result, this process may provide a wide window for testing the two-gluon exchange model, studying the nature of hard diffractive factorization breaking and may be particularly useful in studying the gluon distribution of the photon. And it may also be a golden place to test the color-octet mechanism proposed by solving the $\psi'(J/\psi)$ surplus problem at the Tevatron.Comment: Revtex, 10 pages, 4 PS figure