Azimuthal angle correlations in hadron-nucleus scattering: enhanced   diagrams
  In this paper we calculate the contribution to rapidity and angular correlations of the first Pomeron loop diagram in the dense partonic environment. This diagram is expected to give the largest contribution to the density variation mechanism of the angular correlations. We show that this diagrams leads to sizable contributions to the rapidity correlation functions of the order of $\sigma_{in} /\Lb \pi R^2\Rb$ where $\sigma_{in}$ is the inelastic cross section and $R$ is the size of the typical dipole inside the proton saturation scale. Therefore, the correlations do not depend on the saturation scale. We demonstrated that density variation mechanism does not lead to suppression of the angular dependance of the double inclusive cross section generating the coefficient in front of $\cos^2 \varphi$ in $A^{1/3}$ larger in the case of hadron-nucleus collision than in hadron-hadron interaction. The angular correlations are suppressed in comparison with the rapidity ones but only due to large multiplicity of the produced gluons. We consider this paper as the first attempt of quantitative description of the density variation mechanism in CGC/saturation approach. 
Eugene Levin (Tel Aviv U./UTFSM) and Sebastian Tapia (UTFSM)
hep-ph nucl-th