Observation of top-quark pair production in association with a photon and measurement of the t(t)over-bar gamma production cross section in pp collisions at root s=7 TeV using the ATLAS detector
2015 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 7, 072007Article in journal (Refereed) Published
A search is performed for top-quark pairs (tt¯) produced together with a photon (γ) with transverse energy greater than 20 GeV using a sample of tt¯ candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb−1 of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 tt¯γ candidate events are observed in the electron and muon channels, to be compared to the expectation of 79±26 and 120±39 non-tt¯γ background events, respectively. The production of tt¯γ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The tt¯γ production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is σfidtt¯γ×BR=63±8(stat)+17−13(syst)±1(lumi) fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48±10 fb.
Place, publisher, year, edition, pages
2015. Vol. 91, no 7, 072007
IdentifiersURN: urn:nbn:se:uu:diva-256565DOI: 10.1103/PhysRevD.91.072007ISI: 000353545500001OAI: oai:DiVA.org:uu-256565DiVA: diva2:825807
ATLAS Collaboration, for complete list of authors see dx.doi.org/10.1103/PhysRevD.91.0720072015-06-242015-06-242016-04-28Bibliographically approved