Determination of the Width of the Top Quark

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Precise measurement of the top-quark mass from lepton plus jets events at D0

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Precise Measurement of the Top Quark Mass in the Dilepton Channel at D0

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Improved determination of the width of the top quark

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the top-quark mass in p(p)over-bar collisions using events with two leptons

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the t(t)over-bar production cross section and the top quark mass in the dilepton channel in pp collisions at root s=7 Tev

The t (t) over bar production cross section and top quark mass are measured in proton-proton collisions at root s = 7 TeV in a data sample corresponding to an integrated luminosity of 36 pb(-1) collected by the CMS experiment. The measurements are performed in events with two leptons (electrons or muons) in the final state. Results of the cross section measurement in events with and without b-quark identification are obtained and combined. The measured value is sigma(tt) - 168 +/- 18 (stat:) +/- 14 (syst:) +/- 7 (lumi:) pb, consistent with predictions from the standard model. The top quark mass m(top) is reconstructed with two different methods, a full kinematic analysis and a matrix weighting technique. The combination yields a measurement of m(top) = 175.5 +/- 4.6 (stat:) +/- 4: 6 (syst:) GeV/c(2).

Search for violation of Lorentz invariance in top quark pair production and decay

Using data collected with the D0 detector at the Fermilab Tevatron Collider, corresponding to 5.3fb -1 of integrated luminosity, we search for violation of Lorentz invariance by examining the tt̄ production cross section in lepton+jets final states. We quantify this violation using the standard-model extension framework, which predicts a dependence of the tt̄ production cross section on sidereal time as the orientation of the detector changes with the rotation of the Earth. Within this framework, we measure components of the matrices (c Q) μν33 and (c U) μν33 containing coefficients used to parametrize violation of Lorentz invariance in the top quark sector. Within uncertainties, these coefficients are found to be consistent with zero. © 2012 American Physical Society.

Search for a light charged Higgs boson in top quark decays in pp collisions at √s = 7 TeV

Results are presented on a search for a light charged Higgs boson that can be produced in the decay of the top quark t → H +b and which, in turn, decays into τ +ν t. The analysed data correspond to an integrated luminosity of about 2 fb -1 recorded in protonproton collisions at √s = 7 TeV by the CMS experiment at the LHC. The search is sensitive to the decays of the top quark pairs tt̄ → H ±W ∓bb̄ and tt̄ → H ±H ∓bb̄. Various final states have been studied separately, all requiring presence of a τ lepton from H + decays, missing transverse energy, and multiple jets. Upper limits on the branching fraction B(t → H +b) in the range of 2-4% are established for charged Higgs boson masses between 80 and 160 GeV, under the assumption that B(H + → τ +ν τ) = 1.

Search for flavor changing neutral currents in top quark decays in pp collisions at 7 TeV

The results of a search for flavor changing neutral currents in top quark decays t→Zq in events with a topology compatible with the decay chain tt̄→Wb+Zq→ℓνb+ℓℓq are presented. The search is performed with a data sample corresponding to an integrated luminosity of 5.0 fb-1 of proton-proton collisions at a center-of-mass energy of 7 TeV, collected with the CMS detector at the LHC. The observed number of events agrees with the standard model prediction and no evidence for flavor changing neutral currents in top quark decays is found. A t→Zq branching fraction greater than 0.21% is excluded at the 95% confidence level. © 2012 CERN.

Measurement of differential top-quark-pair production cross sections in pp collisions at √s = 7TeV

Normalised differential top-quark-pair production cross sections are measured in pp collisions at a centre-of-mass energy of 7 TeVat the LHC with the CMS detector using data recorded in 2011 corresponding to an integrated luminosity of 5. 0 fb-1. The measurements are performed in the lepton+jets decay channels (e+jets and μ+jets) and the dilepton decay channels (e+}e-, μ+μ-, and μ±e∓). The tt̄ differential cross section is measured as a function of kinematic properties of the final-state charged leptons and jets associated to b quarks, as well as those of the top quarks and the tt̄ system. The data are compared with several predictions from perturbative QCD calculations up to approximate next-to-next-to-leading-order precision. No significant deviations from the standard model are observed. © 2013 CERN for the benefit of the CMS collaboration.

Estudo de percolação de clusters de Monte Carlo para o modelo de Ising bidimensional

Pós-graduação em Física - IFT

Estudo de Monte Carlo da produção de nova ressonância neutra decaindo em dois bósons vetoriais no experimento CMS

Pós-graduação em Física - IFT

Search for baryon number violation in top-quark decays

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for Flavor-Changing Neutral Currents in Top-Quark Decays t -> Zq in pp Collisions at root s=8 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for the associated production of the Higgs boson with a top-quark pair

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)