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

TL;DR

This paper introduces a highly precise calculation method for photon pair production at the LHC, combining NNLL' and NNLO accuracy within the GENEVA framework, and validates it against experimental data.

Contribution

It is the first implementation of a process with nontrivial Born-level definitions and QED singularities in GENEVA, using a smooth-cone isolation and NNLO resummation based on Soft-Collinear Effective Theory.

Findings

Good agreement with LHC 7 TeV data

First NNLO+NNLL' prediction for photon pairs in GENEVA

Effective removal of QED singularities with smooth-cone isolation

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.