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arXiv · 1807.03806

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

Sanjin Benić·Kenji Fukushima·Oscar Garcia-Montero·Raju Venugopalan
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Abstract

We compute the leading order (LO) $qg\to q γ$ and next-to-leading order (NLO) $gg\to q{\bar q} γ$ 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 $k_{γ\perp}$ 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 $k_\perp$-dependent unintegrated gluon distributions in both of the protons. We predict a maximal $10\%$ modification of the cross section at low $k_{γ\perp}$ as a direct consequence of the violation of $k_\perp$-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 $k_{γ\perp}\leq 20$ GeV in p+p collisions that can be tested in the future at the LHC.

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Sanjin Benić, Kenji Fukushima, Oscar Garcia-Montero, Raju Venugopalan. 2019-02-26. Constraining unintegrated gluon distributions from inclusive photon production in proton-proton collisions at the LHC. https://doi.org/10.1016/j.physletb.2019.02.007

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