Aad, G.Abbott, B.Abbott, D. C.Abeling, K.Abidi, S. H.Aboulhorma, A.Çetin, Serkant Ali2024-05-192024-05-1920230031-90071079-7114https://doi.org10.1103/PhysRevLett.131.181901https://hdl.handle.net/20.500.12713/5869This 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 +/- 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.eninfo:eu-repo/semantics/openAccessPair ProductionPlus PlusArticle1311837977601WOS:0010943219000012-s2.0-85179841715N/A10.1103/PhysRevLett.131.181901Q1