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Observation of top-quark pair production in association with a photon and measurement of the $t\bar{t}\gamma$ production cross section in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector

G. Aad 1 S. Albrand 2 J. Brown 2 J. Collot 2 S. Crépé-Renaudin 2 B. Dechenaux 2 P.A. Delsart 2 C. Gabaldon 2 M.H. Genest 2 J.Y. Hostachy 2 B.T. Le 2 F. Ledroit-Guillon 2 A. Lleres 2 A. Lucotte 2 F. Malek 2 C. Monini 2 J. Stark 2 B. Trocmé 2 M. Wu 2 G. Rahal 3 S. Abdel Khalek 4 A. Bassalat 4 C. Becot 4 S. Binet 4 C. Bourdarios 4 D. Charfeddine 4 J.B. de Vivie De Regie 4 L. Duflot 4 M. Escalier 4 L. Fayard 4 D. Fournier 4 E.L. Gkougkousis 4 J.-F. Grivaz 4 T. Guillemin 4 F. Hariri 4 S. Henrot-Versillé 4 J. Hrivnac 4 L. Iconomidou-Fayard 4 M. Kado 4 A. Lounis 4 N. Makovec 4 C. Nellist L. Poggioli 4 P. Puzo 4 A. Renaud 4 D. Rousseau 4 G. Rybkin 4 A.C. Schaffer 4 E. Scifo 4 L. Serin 4 S. Simion 4 R. Tanaka 4 H.L. Tran 4 D. Zerwas 4 Zhen Zhang 4 D. Boumediene 5 Emmanuel Busato 5 D. Calvet 5 S. Calvet 5 J. Donini 5 E. Dubreuil 5 N. Ghodbane 5 G. Gilles 5 Ph. Gris 5 C. Guicheney 5 H. Liao 5 D. Pallin 5 Daniela Paredes Hernández 5 F. Podlyski 5 C. Santoni 5 Timothée Theveneaux-Pelzer 5 Loïc Valery 5 F. Vazeille 5 Z. Barnovska 6 N. Berger 6 M. Delmastro 6 L. Di Ciaccio 6 T.K.O. Doan 6 S. Elles 6 C. Goy 6 T. Hryn’ova 6 S. Jézéquel 6 I. Koletsou 6 R. Lafaye 6 J. Leveque 6 V.P. Lombardo 6 N. Massol 6 G. Sauvage 6 E. Sauvan 6 O. Simard 6 T. Todorov 6 I. Wingerter-Seez 6 L. Alio 1 M. Barbero 1 J. C. Clémens 1 Y. Coadou 1 S. Diglio 1 F. Djama 1 L. Feligioni 1 J. Gao 1 D. Hoffmann 1 F. Hubaut 1 E. B. F. G. Knoops 1 E. Le Guirriec 1 B. Li 1 D. Madaffari 1 K. Mochizuki 1 E. Monnier 1 S. Muanza 1 Y. Nagai 1 P. Pralavorio 1 A. Rozanov 1 T. Serre 1 M. Talby 1 S. Tisserant 1 J. Toth 1 F. Touchard 1 M. Ughetto 1 L. Vacavant 1 C. Bertella 1 E. Tiouchichine 1
Abstract : A search is performed for top-quark pairs ($t\bar{t}$) produced together with a photon ($\gamma$) with transverse momentum $>20$ GeV using a sample of $t\bar{t}$ candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The dataset 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 $t\bar{t}\gamma$ candidate events are observed in the electron and muon channels, to be compared to the expectation of $79\pm 26$ and $120\pm 39$ non-$t\bar{t}\gamma$ background events respectively. The production of $t\bar{t}\gamma$ events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The $t\bar{t}\gamma$ 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 $\sigma_{t\bar{t}\gamma}^{fid} = 63 \pm 8 (stat.) ^{+17}_{-13} (syst.) \pm 1 (lumi.)$ fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of $48\pm 10$ fb.
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http://hal.in2p3.fr/in2p3-01112466
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Submitted on : Tuesday, February 3, 2015 - 8:43:20 AM
Last modification on : Wednesday, September 16, 2020 - 4:28:11 PM

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G. Aad, S. Albrand, J. Brown, J. Collot, S. Crépé-Renaudin, et al.. Observation of top-quark pair production in association with a photon and measurement of the $t\bar{t}\gamma$ production cross section in pp collisions at $\sqrt{s}=7$ TeV using the ATLAS detector. Physical Review D, American Physical Society, 2015, 91 (7), pp.072007. ⟨10.1103/PhysRevD.91.072007⟩. ⟨in2p3-01112466⟩

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