Measurement of the cross-sections of the electroweak and total production of a $Z\gamma$ pair in association with two jets in $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

Abstract

This Letter presents the measurement of the fiducial and differential cross-sections of the electroweak production of a $Z\gamma$ pair in association with two jets. The analysis uses 140 fb${}^{-1}$ of LHC proton-proton collision data taken at $\sqrt{s}$=13 TeV recorded by the ATLAS detector during the years 2015-2018. Events with a $Z$ boson candidate decaying into either an $e^{+}{e}^{-}$ or ${\mu }^{+}{\mu }^{-}$ pair, a photon and two jets are selected. The electroweak component is extracted by requiring a large dijet invariant mass and a large rapidity gap between the two jets and is measured with an observed and expected significance well above five standard deviations. The fiducial $pp\to Z\gamma jj$ cross-section for the electroweak production is measured to be 3.6 $\pm$ 0.5 fb. The total fiducial cross-section that also includes contributions where the jets arise from strong interactions is measured to be $16.8_{-1.8}^{+2.0}$ fb. The results are consistent with the Standard Model predictions. Differential cross-sections are also measured using the same events and are compared with parton-shower Monte Carlo simulations. Good agreement is observed between data and predictions.

44 pages in total, author list starting page 27, 6 figures, 3 tables, submitted to PLB. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2018-36/

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• Electroweak, QCD and flavour physics studies with ATLAS data from Run 2 of the LHC
• Constraints on Anomalous Quartic Gauge Couplings via Electroweak Production of $\gamma \gamma jj$ at Future Proton-Proton Colliders