Articulo
Observation of top-quark pair production in association with a photon and measurement of the tt¯γ production cross section in pp collisions at √s = 7 TeV using the ATLAS detector
Registro en:
issn:1550-7998
Autor
Alconada Verzini, María Josefina
Alonso, Francisco
Anduaga, Xabier Sebastián
Dova, María Teresa
Monticelli, Fernando Gabriel
Wahlberg, Hernán Pablo
The ATLAS Collaboration
Institución
Resumen
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<sup>-1</sup> 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 σ<sup>fid</sup><sub>tt¯γ</sub>×BR=63±8(stat)<sup>+17</sup><sub>-13</sub>(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. La lista completa de autores que integran el documento puede consultarse en el archivo. Facultad de Ciencias Exactas Instituto de Física La Plata