Measurement of the production cross section of pairs of isolated photons in $pp$ collisions at 13 TeV with the ATLAS detector

Abstract

A measurement of prompt photon-pair production in proton-proton collisions at $\sqrt{s}=13$ TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity of 139 fb${}^{-1}$. Events with two photons in the well-instrumented region of the detector are selected. The photons are required to be isolated and have a transverse momentum of $p_{\mathrm{T},{\gamma }_{1(2)}}>40(30)$ GeV for the leading (sub-leading) photon. The differential cross sections as functions of several observables for the diphoton system are measured and compared with theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The QCD predictions from next-to-next-to-leading-order calculations and multi-leg merged calculations are able to describe the measured integrated and differential cross sections within uncertainties, whereas lower-order calculations show significant deviations, demonstrating that higher-order perturbative QCD corrections are crucial for this process. The resummed predictions with parton showers additionally provide an excellent description of the low transverse-momentum regime of the diphoton system.

52 pages in total, author list starting page 36, 12 figures, 5 tables, published in JHEP. All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-30/

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