Forward dihadron back-to-back correlations in pA collisions

Abstract

We study the disappearance of the away-side peak of the di-hadron correlation function in p + A vs p + p collisions at forward rapidities, when the scaterring process presents a manifest dilute-dense asymmetry. We improve the state-of-the-art description of this phenomenon in the framework of the color glass condensate (CGC), for hadrons produced nearly back to back. In that case, the gluon content of the saturated nuclear target can be described with transverse-momentum-dependent gluon distributions, whose small-x evolution we calculate numerically by solving the Balitsky-Kovchegov equation with running coupling corrections. We first show that our formalism provides a good description of the disappearance of the away-side azimuthal correlations in d + Au collisions observed at BNL Relativistic Heavy Ion Collider (RHIC) energies. Then, we predict the away-side peak of upcoming p + Au data at root s = 200 GeV to be suppressed by about a factor 2 with respect to p + p collisions, and we propose to study the rapidity dependence of that suppression as a complementary strong evidence of gluon saturation in experimental data.