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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
Department of Physics, Humboldt University, Berlin, Germany.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
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2015 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 91, no 7, 072007Article in journal (Refereed) Published
Abstract [en]

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
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-256565DOI: 10.1103/PhysRevD.91.072007ISI: 000353545500001OAI: diva2:825807

ATLAS Collaboration, for complete list of authors see

Available from: 2015-06-24 Created: 2015-06-24 Last updated: 2016-04-28Bibliographically approved

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Bergeås Kuutmaan, ElinBrenner, RichardBuszello, Claus P.Ekelöf, TordEllert, MattiasFerrari, ArnaudIsaksson, CharlieMadsen, AlexanderÖhman, HenrikPelikan, DanielRangel Smith, Camila
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