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.
Highlights
Background estimationReconstructed photon pairs can appear in the detector from a variety of sources beyond prompt production processes
Samples were generated using the NNPDF3.0 next-to-next-to-leading-order (NNLO) set [23] of parton distribution functions (PDF), along with the dedicated set of tuned parton-shower parameters developed by the Sherpa authors
The background from jets misidentified as prompt photons is estimated using a data-driven method, extrapolating the amount from multiple control regions enriched in background to the signal region, i.e. the region defined by the nominal event selection
Summary
The ATLAS experiment [8] at the LHC is a multipurpose particle detector with a forwardbackward symmetric cylindrical geometry and a near 4π coverage in solid angle. It consists of an inner tracking detector surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer. The ATLAS experiment [8] at the LHC is a multipurpose particle detector with a forwardbackward symmetric cylindrical geometry and a near 4π coverage in solid angle.. The ATLAS experiment [8] at the LHC is a multipurpose particle detector with a forwardbackward symmetric cylindrical geometry and a near 4π coverage in solid angle.1 It consists of an inner tracking detector surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer. Within the region |η| < 3.2, electromagnetic (EM) calorimetry is provided by a lead/liquid-argon (LAr) sampling calorimeter with accordion geometry It is divided into a barrel section covering |η| < 1.475 and two endcap sections covering 1.375 < |η| < 3.2. An extensive software suite [10] is used for the reconstruction and analysis of real and simulated data, for detector operations, and in the trigger and data acquisition systems of the experiment
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