Probing gluon saturation with forward di-hadron correlations in proton-nucleus collisions

TL;DR

This paper investigates forward di-hadron production in proton-nucleus collisions using the Color Glass Condensate theory, incorporating non-linear evolution, Sudakov resummation, and initial condition modeling, comparing with experimental data and making future predictions.

Contribution

It introduces a comprehensive numerical framework combining small-x gluon evolution, Sudakov effects, and phenomenological modeling, applied to forward di-hadron correlations in proton-nucleus collisions.

Findings

Good agreement with STAR data on azimuthal correlations.

Quantified uncertainties related to saturation scales and hadronization.

Predicted di-hadron correlation patterns for future LHC measurements.

Abstract

We present a detailed numerical investigation of semi-inclusive forward di-hadron production in proton-nucleus collisions employing the Color Glass Condensate effective theory. We focus on the regime where di-hadrons are produced nearly back-to-back in the transverse plane, thereby justifying a transverse-momentum-dependent factorization approach in terms of small-$x$ gluon distributions. Our computation integrates several key elements: i) non-linear rapidity evolution via the Balitsky-Kovchegov equation with running coupling, ii) both perturbative and non-perturbative Sudakov resummation, and iii) a phenomenologically constrained model for the initial conditions for small-$x$ gluon distributions. We compare this phenomenological framework to experimental data from the STAR Collaboration on azimuthal correlations in forward di-pion production in both proton-proton and proton-gold collisions. We analyze the systematic theoretical uncertainties associated with the saturation scales of nuclei at the initial scale for rapidity evolution and with those associated with the hadronization process. Finally, we make predictions for the kinematics anticipated to be covered by the ALICE Forward Calorimeter (FoCal) upgrade at the Large Hadron Collider.