Measurement of the top quark pair production cross-section with ATLAS in pp collisions at sqrt(s) = 7 TeV in dilepton final states

A measurement is presented of the production cross section of top quark pairs (ttbar) in proton-proton (pp) collisions at √s = 7 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. Using a data sample of 35.3 pb−1, candidate events are selected in the dilepton topology with large missing transverse energy, ETmiss, and at least two jets. A baseline analysis employing the kinematic properties of the candidate events to separate the signal from background results in a measurement of sigma(ttbar) = 174 ± 23(stat.)+19/−17(syst.) ± 7(lum.) pb, where the three uncertainties are from statistics, systematics and integrated luminosity, respectively. Additional studies are performed to corroborate this measurement; a technique that normalizes the ttbar signal yield to the measured rate of Z decays, and a two-dimensional template shape fit using the ETmiss vs Njets variables to simultaneously measure the production cross sections of ttbar, WW and Ztautau final states. We also perform a cross section measurement requiring at least one b-tagged jet and a looser kinematic selection to optimize the overall measurement uncertainty, yielding sigma(ttbar) = 170 +22/−21(stat.) +24/−17(syst.) +7/−5(lum.) pb. We perform a further cross-check of this measurement by simultaneously measuring sigma(ttbar) and the b-tagging efficiency using the distribution of the number of tagged jets in each event. These measurements a re in good agreement with each other and the Standard Model prediction.