How large is the diffractive contribution to inclusive dijet photoproduction in ultraperipheral collisions at the LHC?

Using next-to-leading order perturbative QCD, we calculate the diffractive contribution to inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions (UPCs) at the LHC and find that it does not exceed 5-10% in small-xA bins in the ATLAS kinematics at ffiffiffiffiffiffiffi restricted kinematics (pT1 > 20 GeV and xA > 0.001), the large nuclear suppression of nuclear diffractive parton distribution functions predicted in the leading twist model of nuclear shadowing, and additional suppression due to QCD factorization breaking in diffraction. At the same time, using looser pT cuts, e.g., pT1 > 10 GeV and pTi not equal 1 > 5-7 GeV, we find that (do-diff/dxA)/(do-inc/dxA) can reach 10-20% at x 5 x 10-4. Also, applying our framework to proton-proton UPCs at ffiffiffiffiffiffiffi ratio of the diffractive and inclusive cross sections of dijet photoproduction (do-diff/dxp)/(do-inc/dxp) is as large as 10-15% for xp similar to 5 x 10-4. An account of the contribution of Pomeron-Pomeron scattering, which is not included in our analysis, should make this ratio somewhat larger.

Automated summary

Utilizing next-to-leading order perturbative QCD, the diffractive contribution to inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions at the LHC was calculated, showing it does not exceed 5-10% under specific conditions. Under looser conditions, the ratio of diffractive to inclusive cross sections can reach 10-20% at specific xA values, while in proton-proton UPCs, the ratio can reach 10-15% for specific xp values, with room for an increase when accounting for Pomeron-Pomeron scattering.