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

We use the Glauber-Gribov multiple scattering formalism and the theory of leading-twist nuclear shadowing to develop a method for the calculation of leading-twist hard 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 that in hadron-nucleon scattering. For the kinematics encountered at the CERN Large Hadron Collider (LHC) and at the BNL Relativistic Heavy Ion Collider (RHIC), we compare the hard diffractive to electromagnetic (e.m.) mechanisms of hard coherent production of two jets in proton-nucleus scattering. We study the x(IP),beta, and A dependence of the ratio of the dijet production cross sections due to the two effects, R, at the LHC and RHIC kinematics. 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 energies exceeding those available at the DESY Hadron Electron Ring Accelerator (HERA) by a factor of ten. In contrast, the use of lighter nuclei, such as Ca-40, allows the study of the screened nuclear diffractive parton distribution. Moreover, a comparison of the dijet diffractive production to the heavy-quark-jet diffractive production will estimate the scree-ned nuclear diffractive gluon PDF, which will be measured in nucleus-nucleus ultraperipheral collisions at the LHC.