Precise predictions for photon pair production matched to parton showers in GENEVA

Abstract: We present a new calculation for the production of isolated photon pairs at the LHC with NNLL$'_{\mathcal{T}_0}$+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.