Constraining unintegrated gluon distributions from inclusive photon production in proton-proton collisions at the LHC

Sanjin Benić; Kenji Fukushima; Oscar Garcia-Montero; Raju Venugopalan

doi:10.1016/j.physletb.2019.02.007

paper

Constraining unintegrated gluon distributions from inclusive photon production in proton-proton collisions at the LHC

arXiv:1807.03806 · doi:10.1016/j.physletb.2019.02.007

Abstract

We compute the leading order (LO) $q g \to q γ$ and next-to-leading order (NLO) $g g \to q q ˉ γ$ contributions to inclusive photon production in proton-proton (p+p) collisions at the LHC. These channels provide the dominant contribution at LO and NLO for photon transverse momenta $k_{γ ⊥}$ corresponding to momentum fractions of $x \leq 0.01$ in the colliding protons. Our computations, performed in the dilute-dense framework of the Color Glass Condensate effective field theory (CGC EFT), show that the NLO contribution dominates at small- $x$ because it is sensitive to $k_{⊥}$ -dependent unintegrated gluon distributions in both of the protons. We predict a maximal $10%$ modification of the cross section at low $k_{γ ⊥}$ as a direct consequence of the violation of $k_{⊥}$ -factorization. The coherence effects responsible for this modification are enhanced in nuclei and can be identified from inclusive photon measurements in proton-nucleus collisions. We provide numerical results for the isolated inclusive photon cross section for $k_{γ ⊥} \leq 20$ GeV in p+p collisions that can be tested in the future at the LHC.

9 pages, 5 figures

Constraining unintegrated gluon distributions from inclusive photon production in proton-proton collisions at the LHC

Abstract

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