Abstract
We present a new calculation for the production of isolated photon pairs at the LHC with {mathrm{NNLL}}_{{mathcal{T}}_0}^{prime } +NNLO accuracy. This is the first implementation within the Geneva Monte Carlo framework of a process with a nontrivial Born-level definition which suffers from QED singularities. Throughout the computation we use a smooth-cone isolation algorithm to remove such divergences. The higher-order resummation of the 0-jettiness resolution variable {mathcal{T}}_0 is based on a factorisation formula derived within Soft-Collinear Effective Theory which predicts all of the singular, virtual and real NNLO corrections. Starting from this precise parton-level prediction and by employing the Geneva method, we provide fully showered and hadronised events using Pythia8, while retaining the NNLO QCD accuracy for observables which are inclusive over the additional radiation. We compare our final predictions to LHC data at 7 TeV and find good agreement.
Highlights
Be suppressed by isolating the photons from the final-state hadrons with either the fixedcone or the smooth-cone
This is the first implementation within the Geneva Monte Carlo framework of a process with a nontrivial Born-level definition which suffers from QED singularities
We have presented the first calculation for the production of isolated photon pairs at the LHC resummed in the 0-jettiness resolution variable to next-to-next-to-leading logarithmic (NNLL) accuracy and matched to the NNLO calculation
Summary
In this paper we consider the process pp → γγ +X, where the photon pair is produced through the hard scattering interaction (i.e. direct photon production). The fixed-cone isolation procedure is currently used in all experimental measurements of processes involving photons This method has the theoretical drawback of being sensitive to the fragmentation contributions since configurations with a photon collinear to a final-state parton are still allowed. Where the isolation function χ(r; Riso) must be a smooth and monotonic function which vanishes when r → 0 This requirement implies that the hadronic activity is reduced in a smooth way when approaching the photon direction, and the parton radiation collinear to the photon is completely absent at r = 0. One initially applies very loose smooth-cone isolation cuts which are tightened by the fixed-cone procedure This makes the resulting events directly suitable for experimental analyses..
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