Semi-inclusive photon-hadron production in pp and pA collisions at RHIC and LHC

TL;DR

This paper studies semi-inclusive photon-hadron production in proton-proton and proton-nucleus collisions at RHIC and LHC energies within the color glass condensate framework, revealing unique azimuthal correlation structures linked to QCD saturation effects.

Contribution

It introduces a detailed analysis of azimuthal correlations in photon-hadron production, highlighting the conditions for double-peak and single-peak structures and providing new predictions for nuclear modification factors.

Findings

Double-peak and single-peak azimuthal correlation structures depend on kinematic variables.

The ratio p_T^hadron/p_T^photon controls the correlation structure.

Predictions for photon-to-hadron production ratios and nuclear modification factors.

Abstract

We investigate semi-inclusive photon-hadron production in the color glass condensate (CGC) framework at RHIC and the LHC energies in proton-proton (pp) and proton-nucleus (pA) collisions. We calculate the coincidence probability for azimuthal correlation of pairs of photon-hadron and show that the away-side correlations have a double-peak or a single-peak structure depending on trigger particle selection and kinematics. This novel feature is unique for semi-inclusive photon-hadron production compared to a similar measurement for double inclusive dihadron production in pA collisions. We obtain necessary conditions between kinematics variables for the appearance of a double-peak or a single peak structure for the away-side photon-hadron correlations in pp and pA collisions at forward rapidities and show that this feature is mainly controlled by the ratio p_T^hadron/p_T^photon. Decorrelation of away-side photon-hadron production by increasing the energy, rapidity and density, and appearance of double-peak structure can be understood by QCD saturation physics. We also provide predictions for the ratio of single inclusive prompt photon to hadron production, and two-dimensional nuclear modification factor for the semi-inclusive photon-hadron pair production at RHIC and the LHC at forward rapidities.