The first measurement of the cross section for top-quark pair production in pp collisions at the LHC at center-of-mass energy sqrt(s)= 7 TeV has been performed using 3.1 {\pm} 0.3 inverse pb of data recorded by the CMS detector. This result utilizes the final state with two isolated, highly energetic charged leptons, large missing transverse energy, and two or more jets. Backgrounds from Drell-Yan and non-W/Z boson production are estimated from data. Eleven events are observed in the data with 2.1 {\pm} 1.0 events expected from background. The measured cross section is 194 {\pm} 72 (stat.) {\pm} 24 (syst.) {\pm} 21 (lumi.) pb, consistent with next-to-leading order predictions.
Total cross section. The second systematic error represents the uncertainty on the luminosity.
Measurements are presented of differential cross-sections for top quark pair production in pp collisions at sqrt(s) = 7 TeV relative to the total inclusive top quark pair production cross-section. A data sample of 2.05/fb recorded by the ATLAS detector at the Large Hadron Collider is used. Relative differential cross-sections are derived as a function of the invariant mass, the transverse momentum and the rapidity of the top quark pair system. Events are selected in the lepton (electron or muon) + jets channel. The background-subtracted differential distributions are corrected for detector effects, normalized to the total inclusive top quark pair production cross-section and compared to theoretical predictions. The measurement uncertainties range typically between 10% and 20% and are generally dominated by systematic effects. No significant deviations from the Standard Model expectations are observed.
Relative differential cross-section (1/SIG)*D(SIG)/DM(ttbar) measured in the e+jets, mu+jets and the combined lepton+jets channel.
Relative differential cross-section (1/SIG)*D(SIG)/DPT(ttbar) measured in the e+jets, mu+jets and the combined lepton+jets channel.
Relative differential cross-section (1/SIG)*D(SIG)/DYRAP(ttbar) measured in the e+jets, mu+jets and the combined lepton+jets channel.
A measurement of the t t-bar production cross section in pp collisions at sqrt(s) = 7 TeV is presented. The results are based on data corresponding to an integrated luminosity of 2.3 inverse femtobarns collected by the CMS detector at the LHC. Selected events are required to have one isolated, high transverse momentum electron or muon, large missing transverse energy, and hadronic jets, at least one of which must be consistent with having originated from a b quark. The measured cross section is 158.1 +/- 2.1 (stat.) +/- 10.2 (syst.) +/- 3.5 (lum.) pb, in agreement with standard model predictions.
Measured cross section for t-tbar production for the combined result as well as the electron+jets and muon+jets channels separately.
Results of the fit to the combined electron + jets and muon + jets sample, and each channel individually. The contributions from the background processes are quoted as scale factors with respect to their theoretical predictions. The scale factors do not account for a full treatment of the systematic uncertainties and are strictly valid only in the context of the fit. For brevity, the QCD parameters are not shown.
Correlation matrix of the combined fit to the electron + jets plus muon + jets samples. Only non-QCD parameters are shown.
A measurement of jet shapes in top-quark pair events using 1.8 fb$^{-1}$ of $\sqrt{s}$ = 7 TeV pp collision data recorded by the ATLAS detector is presented. Samples of top-quark pair events are selected in both the single-lepton and dilepton final states. The differential and integrated shapes of the jets initiated by bottom-quarks from the top-quark decays are compared with those of the jets originated by light-quarks from the hadronic W-boson decays $W \to q\bar{q}'$ in the single-lepton channel. The light-quark jets are found to have a narrower distribution of the momentum flow inside the jet area than b-quark jets.
Differential jet shape as a function of the radius r for the PT range 30-40 GeV.
Integrated jet shape as a function of the radius r for the PT range 30-40 GeV.
Differential jet shape as a function of the radius r for the PT range 40-50 GeV.
Searches for anomalous top quark-antiquark production are presented, based on pp collisions at sqrt(s) = 8 TeV. The data, corresponding to an integrated luminosity of 19.7 inverse femtobarns, were collected with the CMS detector at the LHC. The observed ttbar invariant mass spectrum is found to be compatible with the standard model prediction. Limits on the production cross section times branching fraction probe, for the first time, a region of parameter space for certain models of new physics not yet constrained by precision measurements.
Comparison between data and SM prediction for reconstructed M(ttbar) distributions for the boosted semi-leptonic analysis with 0 b-tagged jets.
Comparison between data and SM prediction for reconstructed M(ttbar) distributions for the boosted semi-leptonic analysis with 1 or more b-tagged jets.
Comparison between data and SM prediction for reconstructed M(ttbar) distributions for the all-hadronic analysis.
A search for baryon number violation (BNV) in top-quark decays is performed using pp collisions produced by the LHC at sqrt(s) = 8 TeV. The top-quark decay considered in this search results in one light lepton (muon or electron), two jets, but no neutrino in the final state. Data used for the analysis were collected by the CMS detector and correspond to an integrated luminosity of 19.5 inverse femtobarns. The event selection is optimized for top quarks produced in pairs, with one undergoing the BNV decay and the other the standard model hadronic decay to three jets. No significant excess of events over the expected yield from standard model processes is observed. The upper limits at 95% confidence level on the branching fraction of the BNV top-quark decay are calculated to be 0.0016 and 0.0017 for the muon and the electron channels, respectively. Assuming lepton universality, an upper limit of 0.0015 results from the combination of the two channels. These limits are the first that have been obtained on a BNV process involving the top quark.
Muon channel: expected and observed yields in the tight selections for an assumed BNV decay branching fraction of zero. The uncertainties include both statistical and systematic contributions.
Electron channel: expected and observed yields in the tight selections for an assumed BNV decay branching fraction of zero. The uncertainties include both statistical and systematic contributions.
Expected and observed 95% CL upper limits on the BNV decay branching fraction.
The top-antitop quark (t t-bar) production cross section is measured in proton-proton collisions at sqrt(s) = 8 TeV with the CMS experiment at the LHC, using a data sample corresponding to an integrated luminosity of 5.3 inverse femtobarns. The measurement is performed by analysing events with a pair of electrons or muons, or one electron and one muon, and at least two jets, one of which is identified as originating from hadronisation of a bottom quark. The measured cross section is 239 +/- 2 (stat.) +/- 11 (syst.) +/- 6 (lum.) pb, for an assumed top-quark mass of 172.5 GeV, in agreement with the prediction of the standard model.
The total efficiencies etotal, i.e. the products of event acceptance, selection efficiency and branching fraction for the respective TOP TOPBAR final states, as estimated from simulation for a top-quark mass of 172.5 GeV, and the measured TOP TOPBAR production cross sections, where the uncertainties are from statistical, systematic and integrated luminosity components, respectively.
The TOP TOPBAR cross section obtained by combining all final states.
The t t-bar charge asymmetry in proton-proton collisions at sqrt(s) = 7 TeV is measured using the dilepton decay channel (ee, e mu, or mu mu). The data correspond to a total integrated luminosity of 5.0 inverse femtobarns, collected by the CMS experiment at the LHC. The t t-bar and lepton charge asymmetries, defined as the differences in absolute values of the rapidities between the reconstructed top quarks and antiquarks and of the pseudorapidities between the positive and negative leptons, respectively, are measured to be Ac = -0.010 +/- 0.017 (stat.) +/- 0.008 (syst.) and Ac[lep] = 0.009 +/- 0.010 (stat.) +/- 0.006 (syst). The lepton charge asymmetry is also measured as a function of the invariant mass, rapidity, and transverse momentum of the t t-bar system. All measurements are consistent with the expectations of the standard model.
The unfolded ASYMC and ASYMC(LEPTON) measurements.
Measurements of the unfolded ASYMC(LEPTON) values in bins of M(TOP TOPBAR).
Measurements of the unfolded ASYMC(LEPTON) values in bins of ABS(YRAP(TOP TOPBAR)).
The ratio of the top-quark branching fractions $R = B(t \to Wb)/B(t \to Wq)$, where the denominator includes the sum over all down-type quarks (q = b, s, d), is measured in the $t\bar{t}$ dilepton final state with proton-proton collision data at $\sqrt{s}$ = 8 TeV from an integrated luminosity of 19.7 inverse-femtobarns, collected with the CMS detector. In order to quantify the purity of the signal sample, the cross section is measured by fitting the observed jet multiplicity, thereby constraining the signal and background contributions. By counting the number of b jets per event, an unconstrained value of R = 1.014 $\pm$ 0.003 (stat) $\pm$ 0.032 (syst) is measured, in good agreement with the standard model prediction. A lower limit R greater than 0.955 at the 95% confidence level is obtained after requiring R lower than one, and a lower limit on the Cabibbo-Kobayashi-Maskawa matrix element |$V_tb$| greater than 0.975 is set at 95% confidence level. The result is combined with a previous CMS measurement of the t-channel single-top-quark cross section to determine the top-quark total decay width, $\Gamma_t$ = 1.36 $\pm$ 0.02 (stat)$^{+0.14}_{-0.11}$ (syst) GeV.
The measured TOP TOPBAR production cross section.
The measured ratio of branching fractions, R = BR(TOP --> W BOTTOM) / BR(TOP --> W QUARK) where the denominator includes the sum over all down-type quarks (QUARK = BOTTOM, STRANGE, DOWN). The combined measurement and the individual measurements from the three channels considered are presented.
An indirect measurement of the top-quark total decay width.
The normalised differential top quark-antiquark production cross section is measured as a function of the jet multiplicity in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC with the CMS detector. The measurement is performed in both the dilepton and lepton + jets decay channels using data corresponding to an integrated luminosity of 5.0 inverse femtobarns. Using a procedure to associate jets to decay products of the top quarks, the differential cross section of the t t-bar production is determined as a function of the additional jet multiplicity in the lepton + jets channel. Furthermore, the fraction of events with no additional jets is measured in the dilepton channel, as a function of the threshold on the jet transverse momentum. The measurements are compared with predictions from perturbative quantum chromodynamics and no significant deviations are observed.
Normalised differential TOP TOPBAR production cross section as a function of the jet multiplicity for jets with PT(JET) > 30 GeV in the dilepton channel. The statistical and main experimental and model systematic uncertainties are displayed.
Normalised differential TOP TOPBAR production cross section as a function of the jet multiplicity for jets with PT(JET) > 60 GeV in the dilepton channel. The statistical and main experimental and model systematic uncertainties are displayed.
Normalised differential TOP TOPBAR production cross section as a function of the jet multiplicity for jets with PT(JET) > 35 GeV in the lepton+jets channel. The statistical and main experimental and model systematic uncertainties are displayed.
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