We show that the long-range rapidity correlations between the produced charged-hadron pairs from two Balitsky-Fadin-Kuraev-Lipatov parton showers generate considerable azimuthal angle correlations. These correlations have no $1/N_c$ suppression. The effect of gluon saturation on these correlations are discussed and we show that it is important. We show that a pronounced ridgelike structure emerges by going from the Balitsky-Fadin-Kuraev-Lipatov to the saturation region. We show that the ridge structure at high-energy proton-proton and nucleus-nucleus collisions has the same origin and its main feature can be understood due to initial-state effects. Although the effects of final-state interactions in the latter case can be non-negligible.

• Received 24 May 2011

DOI:https://doi.org/10.1103/PhysRevD.84.034031