Predictions for diphoton production at the LHC through NNLO in QCD

TL;DR

This paper presents a detailed NNLO QCD calculation for diphoton production at the LHC, including new effects and comparing predictions with experimental data for background estimation.

Contribution

The paper provides the first implementation of NNLO corrections for diphoton production in a Monte Carlo framework, including some $ ext{O}( ext{α}_s^3)$ effects, and highlights discrepancies with previous calculations.

Findings

NNLO predictions agree with data-driven fits for diphoton mass spectrum shape.

Inclusion of $ ext{O}( ext{α}_s^3)$ effects improves theoretical accuracy.

Discrepancies found with previous calculations in the literature.

Abstract

In this paper we present a next-to-next-to-leading order (NNLO) calculation of the process $pp\rightarrow \gamma\gamma$ that we have implemented into the parton level Monte Carlo code MCFM. We do not find agreement with the previous calculation of this process in the literature. In addition to the $\mathcal{O}(\alpha_s^2)$ corrections present at NNLO, we include some effects arising at $\mathcal{O}(\alpha_s^3)$, namely those associated with gluon-initiated closed fermion loops. We investigate the role of this process in the context of studies of QCD at colliders and as a background for searches for new physics, paying particular attention to the diphoton invariant mass spectrum. We demonstrate that the NNLO QCD prediction for the shape of this spectrum agrees well with functional forms used in recent data-driven fits.