eng Hawkings, R Measurement of the $t\bar{t}$ production cross-section in $pp$ collisions at $\sqrt{s}=$7-8 TeV using $e\mu$ events with $b$-tagged jets Detectors and Experimental Techniques ATL-COM-PHYS-2014-017 This note describes measurements of the inclusive $t\bar{t}$ production cross-section $\sigma_{t\bar{t}}$ with the complete 2011-2012 ATLAS data sample of 4.59 fb$^{-1}$ of $pp$ collision data at $\sqrt{s}=7$ TeV and 20.3 fb$^{-1}$ at $\sqrt{s}=8$ TeV using dilepton $t\bar{t}$ events with an opposite-sign $e\mu$ pair in the final state. Jets containing $b$ quarks were tagged using the MV1 tagging algorithm exploiting the long lifetime, high decay multiplicity and high mass of $b$ hadrons. The numbers of events with exactly one and exactly two $b$-tagged jets were counted and used to simultaneously determine $\sigma_{t\bar{t}}$ and the efficiency to reconstruct and $b$-tag a $b$-jet from a top quark decay, minimising the associated systematic uncertainties. The cross-section was measured to be $182.9\pm 3.1\pm 4.2\pm 3.6\pm 3.3$ pb at $\sqrt{s}=7$ TeV and $242.4\pm 1.7\pm 5.5 \pm 7.5\pm 4.2$ pb at $\sqrt{s}=8$ TeV, where the four uncertainties are due to data statistics, internal systematic effects and the knowledge of the integrated luminosity and LHC beam energy, giving a total relative uncertainty of 3.9 % at 7 TeV and 4.3% at 8 TeV. The results are consistent with recent theoretical calculations. Fiducial measurements corresponding to the experimental acceptance of the leptons are also reported, together with the ratio of cross-sections measured at the two centre-of-mass energies. Finally, the results are used to place limits on the pair-production of supersymmetric top squarks $\tilde{t_1}$ with masses close to $m_{\rm top}$ decaying via $\tilde{t_1}\rightarrow t\tilde{\chi}^0_1$. 2014-01-14 http://cds.cern.ch/record/1642806 Physics http://cds.cern.ch/record/1642806 Requesting INT approval as corresponding paper TOPQ-2013-04 has been accepted by journal for publication. eng Ferrando, J Wendland, D Giuli, Francesco Reference $t\bar{t}$ production cross sections for use in ATLAS analyses Detectors and Experimental Techniques ATL-COM-PHYS-2014-112 Reference cross sections for inclusive $t\bar{t}$ production in ATLAS analyses are presented. The references are given as a function of top mass and centre-of-mass energy. The major theoretical uncertainties are also given. 2014-02-19 http://cds.cern.ch/record/1662536 Physics http://cds.cern.ch/record/1662536 eng Abi, B Khanov, A Rizatdinova, F Saleem, M Measurements of the top pair production cross-section in 8 TeV proton-proton collisions using kinematic information: Top cross-section measurement in lepton + jets channels using 8TeV data Detectors and Experimental Techniques ATL-COM-PHYS-2013-522 This note presents the measurement of the $t\bar{t}$ inclusive production cross-section in pp collisions at a centre-of-mass energy $\sqrt s=8$ TeV using data collected by the ATLAS detector at the CERN Large Hadron Collider. The measurement has been done in a data set corresponding to an integrated luminosity of 20.3 fb$^{-1}$ in the lepton+jets final state. Two methods were used to extract the cross-section, the likelihood fit technique and cut-and-count. In both cases $b$-jet identification was used to improve the signal-to-background ratio. The inclusive $t\bar{t}$ production cross-section $\sigma_{t\bar{t}}$ obtained with the likelihood fit approach is found to be $ 258\pm 1{\rm (stat.)}\pm ^{21}_{22} {\rm (syst.)}\pm 8{\rm (lumi.)}$ pb with a top mass of 172.5 GeV in a good agreement with the theoretical prediction $253^{+13}_{-15}$ pb. The $t\bar{t}$ production cross-section in the fiducial region measured with the likelihood fit approach is found to be $\sigma_{t\bar{t}\to e+jets}^{fiducial} = 11.3\pm 0.1{\rm (stat.)} \pm 1.1 {\rm (syst.)}\pm 0.3{\rm (lumi.)}~{\rm pb}$, $\sigma_{t\bar{t}\to \mu+jets}^{fiducial} = 11.5\pm 0.1{\rm (stat.)} \pm 0.9 {\rm (syst.)}\pm 0.3{\rm (lumi.)}$ pb and $\sigma_{t\bar{t}\to e/\mu+jets}^{fiducial} = 22.8\pm 0.1{\rm (stat.)}^{+1.8}_{-1.9}{\rm (syst.)}\pm 0.7{\rm (lumi.)}$ pb. 2013-04-29 http://cds.cern.ch/record/1544535 Physics http://cds.cern.ch/record/1544535 eng Argyropoulos, S Asbah, N Grohsjean, A Keller, John Stakely Katzy, Judith Measurement of the $t\bar{t}b\bar{b}$ production cross-section using a cut-and-count method with 8 TeV ATLAS data Particle Physics - Experiment ATL-COM-PHYS-2014-637 This note describes the measurement of the $t\bar{t}b\bar{b}$ production cross-section $\sigma_{t\bar{t}b\bar{b}}$ using the complete 2012 dataset of 20.3 fb$^{-1}$ of $pp$ collision data collected with the ATLAS detector at $\sqrt{s}=$8 TeV. The measurement is based on a cut-and-count method, exploiting the most precise jet energy scale and $b$-tagging calibrations and is performed in a fiducial volume using dilepton final states. The fiducial cross-section is measured to be $\sigma_{t\bar{t}b\bar{b}}^{\mathrm{fid}}=18.9\pm 3.5\mathrm{\ (stat)} ^{+5.6}_{-5.5} \mathrm{\ (sys)}\pm 0.6\mathrm{\ (Lumi)\ fb} and is found to agree within uncertainties with NLO QCD predictions. 2014 http://cds.cern.ch/record/1710370 Physics http://cds.cern.ch/record/1710370 eng Arguin, Jean-Francois Berta, Peter Calvet, Samuel Fabbri, Federica Ferreira de Lima, Danilo Enoque Franchini, Matteo Gabizon, Ofir Heck, Tobias Kvita, Jiri Leitner, Rupert Massa, Lorenzo Mengarelli, Alberto Negrini, Matteo Ovcharova, A Pollard, Christopher Samuel Shapiro, Marjorie Spano, Francesco Veatch, Jason Zhong, Jiahang Yao, Weiming Measurement of the top-antitop pair differential fiducial cross-section as a function of the top quark $p_{T}$ in the boosted topology Detectors and Experimental Techniques ATL-COM-PHYS-2013-1093 The differential cross-section for boosted top quark pair production is measured in 20.3~\ifb\ of proton-proton collisions at a center-of-mass energy of 8 TeV. The measurement is performed for $t\bar{t}$ events in the lepton+jets channel, where the hadronically decaying top quark has a transverse momentum above 300 GeV. Jet substructure techniques are employed to identify top quarks, which are reconstructed with an anti-$k_t$ jet with radius parameter $R=1.0$. The cross-section is reported as a function of the hadronically decaying top quark transverse momentum. The observed yield is corrected for detector effects to obtain a cross-section at particle-level in a fiducial region close to the event selection. A parton-level cross-section extrapolated to the full phase-space is also reported for top quarks with transverse momentum above 300 GeV. The predictions of next-to-leading-order and leading-order matrix element plus parton shower Monte Carlo generators are found to generally overestimate the measured cross-sections. 2013-08-09 http://cds.cern.ch/record/1570997 Physics http://cds.cern.ch/record/1570997 eng Lefebvre, G Malaescu, B Ridel, M Trincaz-Duvoid, S Varouchas, D Measurement of the inclusive tt ̄ cross section in pp collisions at √s =8 TeV with ATLAS using the hadronic decays of the top quark pairs Particle Physics - Experiment ATL-COM-PHYS-2014-783 This note describes a measurement of the inclusive tt ̄ production cross√section σtt ̄ with the 2012 ATLAS data sample of 20.3 fb−1at the centre-of-mass energy of s =8 TeV using fully hadronic tt ̄ events. The cross-section was measured to be σtt ̄ = 208 ± 8 (stat) ± 56 (syst) ± 6 (lumi), in agreement with the theoretical predictions at NNLO+NNLL. 2014 http://cds.cern.ch/record/1741524 Physics http://cds.cern.ch/record/1741524 eng Errede, S M Lie, K Vichou, I Measurement of top quark pair differential cross sections in the di-lepton channel with ATLAS in $pp$ collisions at $\sqrt{s}$ = 7 TeV Detectors and Experimental Techniques ATL-COM-PHYS-2013-1567 This note documents measurements of differential cross sections of top quark pair ($t\bar t$) production as a function of the mass, the transverse momentum and the rapidity of the $t\bar t$ system using $\sqrt{s}$ = 7TeV proton-proton collision data corresponding to an integrated luminosity of \lumitot collected by the ATLAS detector at the Large Hadron Collider. Events with top quark pair signatures are selected in the dilepton channel. Distributions of $t\bar t$ system variables are reconstructed at the detector level, and are corrected for estimated backgrounds, detector response, kinematic acceptance and selection efficiency to the parton level. Statistical and systematic effects are estimated as uncertainties of the measurements. The measured differential cross sections are compared with different Monte Carlo generators and theory calculations of top quark pair production. The results are also compared with the measurements in the lepton+jets channel previously reported by ATLAS at $\sqrt{s}$=7TeV. 2013-11-22 http://cds.cern.ch/record/1630813 Physics http://cds.cern.ch/record/1630813 eng Danninger, M Lister, A vanRossem, M Measurement of ttb cross section in the lepton plus jets channel using a fit to the MV1c distribution Particle Physics - Experiment ATL-COM-PHYS-2014-939 A fiducial measurement of the cross-section for the production of $t\bar{t}$ events with exactly 1 lepton and at least five jets, at least three of which have to contain a $B$-hadron is presented, referred to as $t\bar{t}$+$b$ events. Events with one lepton and five or more jets, two or more of them passing the b-jet identification criteria are selected from 20.3 fb$^{-1}$ of $pp$ collision data at $\sqrt{s} = 8$ TeV are used, collected with the ATLAS detector at the Large Hadron Collider. A profile likelihood fit to the distribution of a multivariate $b$-jet discriminant of the jet with the third highest weight is used to extract the number of $t\bar{t}$+$b$ events, from which the cross section is derived. The measured fiducial cross section is found to be $945\,^{+66}_{\,\,\,\,\,\,\,-66}\,\mathrm{(stat.)} \,^{+244}_{\,\,\,\,\,\,\,-188} \,\mathrm{(sys.)} \mathrm{fb}$. 2104 http://cds.cern.ch/record/1747005 Physics http://cds.cern.ch/record/1747005 eng Aldaya, M Shabalina, E Combination of ATLAS and CMS top quark pair cross section measurements in the $e\mu$ final state using proton-proton collisions at $\sqrt{s}$ = 8 TeV Particle Physics - Experiment ATLAS-COM-CONF-2014-063 A combination of top-quark pair production cross-section ($\sigma_{\rm t\bar t}$) measurements at a centre-of-mass energy of 8 TeV performed by the ATLAS and CMS experiments at the LHC in the di-lepton channels is presented. The $\sigma_{\rm t\bar t}$ measurements use between 5.3 and 20.3 fb$^{-1}$ of proton-proton collisions. The combined preliminary LHC measurement of the top-quark pair production cross-section is $\sigma_{\rm t\bar t} = 241.4 \pm 1.4~\mathrm{(stat.)} \pm 5.7~\mathrm{(syst.)} \pm 6.2~\mathrm{(lumi.)}~\mathrm{pb} = 241.4 \pm 8.5~\mathrm{pb}$ for a top-quark mass of $172.5\mathrm{\ GeV}$, corresponding to a total uncertainty of 3.5%. The result is in agreement with the standard model prediction. 2014 http://cds.cern.ch/record/1744692 Conference talks on ATLAS http://cds.cern.ch/record/1744692