Measurement of $Z\gamma\gamma$ production in $pp$ collisions at $\sqrt{s}= 13$ TeV with the ATLAS detector

TL;DR

This paper reports precise measurements of Z boson production with two photons at 13 TeV using the ATLAS detector, testing Standard Model predictions and setting limits on new physics via effective field theory operators.

Contribution

First measurement of Z+2 photon production cross-sections at 13 TeV with detailed differential analysis and EFT limits using ATLAS data.

Findings

Measured integrated cross-section with 12% precision.

Compared data with NLO QCD predictions.

Set limits on dimension-8 operator couplings.

Abstract

Cross-sections for the production of a $Z$ boson in association with two photons are measured in proton$-$proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the $Z$ boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated $Z(\rightarrow\ell\ell)\gamma\gamma$ cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the $Z\gamma\gamma$ system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.