We study quantitatively angular correlations in the two-particle spectrum produced by an energetic probe scattering off a dense hadronic target with sizable saturation momentum. To this end, two-parton inclusive cross sections for arbitrary projectiles with small color charge density are derived in the eikonal formalism. Our results are the following: For large momenta of the observed particles, the perturbative limit with characteristic back-to-back correlation is recovered. As the trigger momenta get closer to the saturation scale $Q_s$, the angular distribution broadens. When the momenta are significantly smaller than $Q_s$, the azimuthal distribution is broad but still peaked back-to-back. However, in a narrow momentum range $(0.5÷1.5)Q_s$, we observe that the azimuthal correlation splits into a double peak with maxima displaced away from $180°$. We argue that it is the soft multiple scattering physics that is responsible for the appearance of this shift in the angle of maximal correlation. We also point out that when the physical size of the projectile is particularly small, the double peak structure persists in a significantly wider range of final state momenta.

• Received 24 June 2005

DOI:https://doi.org/10.1103/PhysRevD.72.094013