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

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

doi:10.1016/j.physletb.2019.02.007

Title: Constraining unintegrated gluon distributions from inclusive photon production in proton–proton collisions at the LHC

Journal Article · 11 February 2019 · Physics Letters. B

DOI: https://doi.org/10.1016/j.physletb.2019.02.007 · OSTI ID:1507120

Benić, Sanjin ^[1]; Fukushima, Kenji ^[2]; Garcia-Montero, Oscar ^[3]; Venugopalan, Raju ^[4]

Kyoto Univ., Kyoto (Japan); Univ. of Zagreb, Zagreb (Croatia)
The Univ. of Tokyo, Tokyo (Japan)
Univ. Heidelberg, Heidelberg (Germany)
Brookhaven National Lab. (BNL), Upton, NY (United States)

We compute the leading order (LO) qg → qγ and next-to-leading order (NLO) gg → qq¯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 ≤ 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_γ⟂-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⟂ ≤ 20 GeV in p+p collisions that can be tested in the future at the LHC.

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Research Organization:: Brookhaven National Laboratory (BNL), Upton, NY (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)

Grant/Contract Number:: SC0012704

OSTI ID:: 1507120

Report Number(s):: BNL--211546-2019-JAAM

Journal Information:: Physics Letters. B, Journal Name: Physics Letters. B Journal Issue: C Vol. 791; ISSN 0370-2693

Publisher:: ElsevierCopyright Statement

Country of Publication:: United States

Language:: English

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