Spin Correlations in tt Events from pp Collisions

Spin Correlations in tt Events from pp Collisions
Author: Boris Lemmer
Publisher: Springer
Total Pages: 246
Release: 2015-06-24
Genre: Science
ISBN: 3319189328

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This thesis introduces readers to the Standard Model, the top quark and its properties, before explaining the concept of spin correlation measurement. The first measurement of top quark spin correlations at the LHC in the lepton+jets decay channel is presented. As the heaviest elementary particle, the top quark plays an essential role in the Standard Model of elementary particle physics. In the case of top quarks being produced in pairs at hadron colliders, the Standard Model predicts their spins to be correlated. The degree of correlation depends on both the production mechanism and properties of the top quark. Any deviation from the Standard Model prediction can be an indicator for new physics phenomena. The thesis employs an advanced top quark reconstruction algorithm including dedicated identification of the up- and down-type quarks from the W boson decay.

Measurement of the T T-bar Production Cross Section in Pp Collisions at 7 TeV in Lepton + Jets Events Using B-quark Jet Identification

Measurement of the T T-bar Production Cross Section in Pp Collisions at 7 TeV in Lepton + Jets Events Using B-quark Jet Identification
Author:
Publisher:
Total Pages: 39
Release: 2011
Genre:
ISBN:

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A new measurement of the inclusive production cross section for pp to t t-bar is performed at a center-of-mass energy of 7 TeV using data collected by the CMS experiment at the LHC. The analysis uses a data sample corresponding to an integrated luminosity of 36 inverse picobarns, and is based on the final state with one isolated, high transverse momentum muon or electron, missing transverse energy, and hadronic jets. The ttbar content of the selected events is enhanced by requiring the presence of at least one jet consistent with b-quark hadronization. The measured cross section is 150 +/- 9 (stat.) +/- 17 syst.) +/- 6 (lumi.) pb and is in agreement with higher-order QCD calculations. The combination of this measurement with a previous CMS result based on dileptons gives 154 +/- 17 (stat.+syst.) +/- 6 (lumi.) pb.

Measurement of the Ttbar Production Cross Section in the All-jets Final State in Pp Collisions at $\sqrt{s}$

Measurement of the Ttbar Production Cross Section in the All-jets Final State in Pp Collisions at $\sqrt{s}$
Author:
Publisher:
Total Pages: 34
Release: 2015
Genre:
ISBN:

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The cross section for tt production in the all-jets final state is measured in pp collisions at a centre-of-mass energy of 8 TeV at the LHC with the CMS detector, in data corresponding to an integrated luminosity of 18.4 fb-1. The inclusive cross section is found to be 275.6 ±6.1 (stat) ± 37.8 (syst) ± 7.2 (lumi) pb. The normalized differential cross sections are measured as a function of the top quark transverse momenta, pT, and compared to predictions from quantum chromodynamics. The results are reported at detector, parton, and particle levels. In all cases, the measured top quark pT spectra are significantly softer than theoretical predictions.

Measurement of the Top Pair Production Cross Section in the Lepton + Jets Channel Using a Jet Flavor Discriminant

Measurement of the Top Pair Production Cross Section in the Lepton + Jets Channel Using a Jet Flavor Discriminant
Author:
Publisher:
Total Pages: 7
Release: 2011
Genre:
ISBN:

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We present a new method to measure the top quark pair production cross section and the background rates with data corresponding to an integrated luminosity of 2.7 fb−1 from p{bar p} collisions at √s = 1.96 TeV collected with the CDF II Detector. We select events with a single electron or muon candidate, missing transverse energy, and at least one b-tagged jet. We perform a simultaneous fit to a jet flavor discriminant across nine samples defined by the number of jets and b-tags. An advantage of this approach is that many systematic uncertainties are measured in situ and inversely scale with integrated luminosity. We measure a top cross section of [sigma]{sub t{bar t}} = 7.64 ± 0.57 (stat + syst) ± 0.45 (luminosity) pb.

Measurement of Differential and Integrated Fiducial Cross Sections for Higgs Boson Production in the Four-lepton Decay Channel in Pp Collisions at $ \sqrt{s}

Measurement of Differential and Integrated Fiducial Cross Sections for Higgs Boson Production in the Four-lepton Decay Channel in Pp Collisions at $ \sqrt{s}
Author:
Publisher:
Total Pages: 46
Release: 2016
Genre:
ISBN:

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Integrated fiducial cross sections for the production of four leptons via the H → 4l decays (l = e, [mu]) are measured in pp collisions at $ \sqrt{s}=7 $ and 8TeV. Measurements are performed with data corresponding to integrated luminosities of 5.1 fb$^{-1}$ at 7TeV, and 19.7 fb$^{-1}$ at 8 TeV, collected with the CMS experiment at the LHC. Differential cross sections are measured using the 8 TeV data, and are determined as functions of the transverse momentum and rapidity of the four-lepton system, accompanying jet multiplicity, transverse momentum of the leading jet, and difference in rapidity between the Higgs boson candidate and the leading jet. A measurement of the Z → 4l cross section, and its ratio to the H → 4l cross section is also performed. All cross sections are measured within a fiducial phase space defined by the requirements on lepton kinematics and event topology. Here, the integrated H → 4l fiducial cross section is measured to be 0.56$_{-0.44}^{+0.67}$ (stat)$_{-0.06}^{+0.21}$ (syst) fb at 7 TeV, and 1.11$_{-0.35}^{+0.41}$ (stat)$_{-0.10}^{+0.14}$ (syst) fb at 8 TeV. The measurements are found to be compatible with theoretical calculations based on the standard model.

Measurement of the T Anti-t Production Cross Section in P Anti-p Collisions at S**(1/2)

Measurement of the T Anti-t Production Cross Section in P Anti-p Collisions at S**(1/2)
Author: Salvatore Rocco Rappoccio
Publisher:
Total Pages: 377
Release: 2005
Genre:
ISBN:

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We present the measurement of the t{bar t} cross section in the lepton plus jets channel with {ge} 1 and {ge} 2 secondary vertex tags. We use the scalar sum of transverse energies of the event (H{sub T}) to discriminate t{bar t} from the other backgrounds. We also use the transverse mass of the leptonic W-boson (M{sub T}{sup W}) to further reduce the Non-W backgrounds. We use a combination of data and Monte Carlo to estimate the backgrounds from electroweak processes, single top, fake leptons, W+ Light Flavor fake tags, and real W+ Heavy Flavor production. We obtain a value of {sigma} {sub {ge}1} = 8.7{sub -0.9}{sup +0.9}(stat){sub -0.9}{sup +1.2}(sys) pb for the {ge}1 tag cross section, and {sigma}{sub {ge}2} = 8.7{sub -1.6}{sup +1.8}(stat){sub -1.3}{sup +1.9}(sys) pb for the {ge}2 tag cross section. The authors also present a measurement of the t{bar t} cross section by fitting the N{sub jet} spectrum. They combine the =1 and {ge}2 tag cross sections to obtain {sigma}{sub t{bar t}} = 8.9{sub -0.9}{sup +0.9}(stat){sub -1.3}{sup +1.4}(syst)pb.