Scale and isolation sensitivity of diphoton distributions at the LHC

TL;DR

This paper investigates the theoretical uncertainties in diphoton distribution predictions at the LHC, focusing on isolation and scale choices, and finds that these factors significantly affect the agreement with experimental data.

Contribution

It provides a detailed analysis of how isolation and scale choices impact diphoton distribution predictions, highlighting their importance in theoretical uncertainty estimation.

Findings

Variations due to isolation and scale choices are substantial.

Alternative scale and isolation prescriptions improve data agreement.

Infrared sensitivity affects cone-based isolation distributions.

Abstract

Precision measurements of diphoton distributions at the LHC display some tension with theory predictions, obtained at next-to-next-to-leading order (NNLO) in QCD. We revisit the theoretical uncertainties arising from the approximation of the experimental photon isolation by smooth-cone isolation, and from the choice of functional form for the renormalisation and factorisation scales. We find that the resulting variations are substantial overall, and enhanced in certain regions. We discuss the infrared sensitivity at the cone boundaries in cone-based isolation in related distributions. Finally, we compare predictions made with alternative choices of dynamical scale and isolation prescriptions to experimental data from ATLAS at 8 TeV, observing improved agreement. This contrasts with previous results, highlighting that scale choice and isolation prescription are potential sources of theoretical uncertainty that were previously underestimated.