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

We investigate semi-inclusive photon-hadron production in the color-glass-condensate 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 production 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 kinematic 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 z(T) = 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 the two-dimensional nuclear modification factor for the semi-inclusive photon-hadron pair production at RHIC and the LHC at forward rapidities.