PT Journal
AU ATLAS Collaboration (Aad, Gea
   Cabrera Urban, S
   Castillo Gimenez, V
   Costa, MJ
   Ferrer, A
   Fiorini, L
   Fuster, J
   Garcia, C
   Garcia Navarro, JE
   Gonzalez de la Hoz, S
   Hernandez Jimenez, Y
   Higon-Rodriguez, E
   Irles Quiles, A
   Kaci, M
   King, M
   Lacasta, C
   Lacuesta, VR
   Marti-Garcia, S
   Mitsou, VA
   Moles-Valls, R
   Oliver Garcia, E
   Pedraza Lopez, S
   Perez Garcia-Estañ, MT
   Romero Adam, E
   Ros, E
   Salt, J
   Sanchez Martinez, V
   Soldevila, U
   Sanchez, J
   Torro Pastor, E
   Valero, A
   Valladolid Gallego, E
   Valls Ferrer, JA
   Vos, M
TI 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
SO Physical Review D
JI Phys. Rev. D
PY 2015
BP 072007
EP 28pp
VL 91
IS 7
DI 10.1103/PhysRevD.91.072007
LA English
AB A search is performed for top-quark pairs (t (t) over bar) produced together with a photon (gamma) with transverse energy greater than 20 GeV using a sample of t (t) over bar 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 t (t) over bar gamma candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 +/- 26 and 120 +/- 39 non-t (t) over bar gamma background events, respectively. The production of t (t) over bar gamma events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The t (t) over bar 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(fid)(t (t) over bar gamma) x BR = 63 +/- 8(stat)(-13)(+17) (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.
ER