Transverse-momentum resummation for photon pair production at NNLL+NLO

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We are interested in the transverse-momentum (qₜ) distribution of a diphoton pair produced in hadron collisions. We resum the logarithmically-enhanced perturbative QCD contributions at small values of qₜ up to next-to-next-to-leading logarithmic accuracy. We consistently combine resummation with the known next-to-leading order perturbative result at intermediate and large values of qₜ. We include all perturbative terms up to order αₛ² in our computation which, after integration over qₜ, reproduces the known next-to-next-to-leading order result for the diphoton pair production total cross section. A comparison with LHC data is presented. We estimate the perturbative accuracy of the theoretical calculation by performing the corresponding variation of scales. We anticipate that the effect of the transverse momentum resummation is not only to recover the predictivity of the calculation at small qₜ, but also to improve substantially the agreement with the experimental data.