Leading twist nuclear shadowing and suppression of hard coherent diffraction in proton-nucleus scattering

We use the theory of leading twist shadowing to develop a method for the calculation of hard leading twist coherent diffraction in hadron-nucleus processes. We demonstrate that soft multiple rescatterings lead to the factorization breaking of hard diffraction in proton-nucleus scattering, which is larger than in hadron-nucleon scattering. At the LHC and RHIC kinematics, we compare the contribution of hard diffraction into two jets to the e.m. contribution, when the two-jet diffractive final state is produced by the coherent nuclear Coulomb field. We study the x_{\Pomeron}, \beta and A-dependence of the ratio of the two effects, R. We demonstrate that in proton-heavy nucleus hard coherent diffraction at the LHC, R is small, which offers a clean method to study hard photon-proton scattering at the energies exceeding the HERA energies by the factor of ten. On the other hand, the use of lighter nuclei, such as Ca-40, will allow to study the screened nuclear diffractive parton distribution. Moreover, a comparison of the dijet diffractive production to the heavy-quark-jet diffractive production will estimate the screened nuclear diffractive gluon PDF, which will be measured in nucleus-nucleus ultraperipheral collisions at the LHC