Observation of Single-Top-Quark Production in Association with a Photon Using the ATLAS Detector

Abstract

This Letter reports the observation of single top quarks produced together with a photon, which directly probes the electroweak coupling of the top quark. The analysis uses 139 fb${}^{-1}$ of 13 TeV proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. Requiring a photon with transverse momentum larger than 20 GeV and within the detector acceptance, the fiducial cross section is measured to be 688 $\pm$ 23 (stat.) ${}_{-71}^{+75}$ (syst.) fb, to be compared with the standard model prediction of 515 ${}_{-42}^{+36}$ fb at next-to-leading order in QCD.

33 pages in total, author list starting page 18, 5 figures, 0 tables, published in Phys. Rev. Lett. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2018-44/

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• Towards a test of the Born rule in high-energy collisions
• Photon production in top quark events at ATLAS and CMS