Diphoton production at the LHC: a QCD study up to NNLO

TL;DR

This paper presents a comprehensive QCD analysis of diphoton production at the LHC, including NNLO corrections and a comparison of isolation criteria, providing insights into theoretical uncertainties and data agreement.

Contribution

It introduces a detailed NNLO QCD calculation for diphoton production with a comparison of isolation methods and discusses the impact on theoretical predictions and experimental data.

Findings

Large radiative corrections at NLO for both isolation criteria

Smooth cone isolation is reliable for higher-order QCD calculations

NNLO corrections reduce uncertainties and improve data agreement

Abstract

We consider the production of prompt-photon pairs at the LHC and we report on a study of QCD radiative corrections up to the next-to-next-to-leading order (NNLO). We present a detailed comparison of next-to-leading order (NLO) results obtained within the standard and smooth cone isolation criteria, by studying the dependence on the isolation parameters. We highlight the role of different partonic subprocesses within the two isolation criteria, and we show that they produce large radiative corrections for both criteria. Smooth cone isolation is a consistent procedure to compute QCD radiative corrections at NLO and beyond. If photon isolation is sufficiently tight, we show that the NLO results for the two isolation procedures are consistent with each other within their perturbative uncertainties. We then extend our study to NNLO by using smooth cone isolation. We discuss the impact of the NNLO corrections and the corresponding perturbative uncertainties for both fiducial cross sections and distributions, and we comment on the comparison with some LHC data. Throughout our study we remark the main features that are produced by the kinematical selection cuts that are applied to the photons. In particular, we examine soft-gluon singularities that appear in the perturbative computations of the invariant mass distribution of the photon pair, the transverse-momentum spectra of the photons, and the fiducial cross section with asymmetric and symmetric photon transverse-momentum cuts, and we present their behaviour in analytic form.