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 WH associated production in pp̄ collisions at √s=1.96TeV

This report describes a search for associated production of W and Higgs bosons based on data corresponding to an integrated luminosity of L≈5.3fb -1 collected with the D0 detector at the Fermilab Tevatron pp̄ Collider. Events containing a W→ν candidate (with corresponding to e or μ) are selected in association with two or three reconstructed jets. One or two of the jets are required to be consistent with having evolved from a b quark. A multivariate discriminant technique is used to improve the separation of signal and backgrounds. Expected and observed upper limits are obtained for the product of the WH production cross section and branching ratios and reported in terms of ratios relative to the prediction of the standard model as a function of the mass of the Higgs boson (M H). The observed and expected 95% C.L. upper limits obtained for an assumed M H=115GeV are, respectively, factors of 4.5 and 4.8 larger than the value predicted by the standard model. © 2012 American Physical Society.

Observation of a narrow mass state decaying into Υ(1S)+γ in pp̄ collisions at s=1.96 TeV

Using data corresponding to an integrated luminosity of 1.3fb -1, we observe a narrow mass state decaying into Υ(1S)+γ, where the Υ(1S) meson is detected by its decay into a pair of oppositely charged muons, and the photon is identified through its conversion into an electron-positron pair. The significance of this observation is 5.6 standard deviations. The mass of the state is centered at 10.551±0.014(stat) ±0.017(syst)GeV/c2, which is consistent with that of the state recently observed by the ATLAS Collaboration. © 2012 American Physical Society.

Search for Higgs boson production in oppositely charged dilepton and missing energy events in pp̄ collisions at √s=1.96TeV

We present a search for the standard model Higgs boson using events with two oppositely charged leptons and large missing transverse energy as expected in H→WW decays. The events are selected from data corresponding to 8.6fb -1 of integrated luminosity in pp̄ collisions at √s=1.96TeV collected with the D0 detector at the Fermilab Tevatron Collider. No significant excess above the standard model background expectation in the Higgs boson mass range this search is sensitive to is observed, and upper limits on the Higgs boson production cross section are derived. © 2012 American Physical Society.

Combined search for the standard model Higgs boson decaying to bb̄ using the D0 run II data set

We present the results of the combination of searches for the standard model Higgs boson produced in association with a W or Z boson and decaying into bb̄ using the data sample collected with the D0 detector in pp̄ collisions at √s=1.96TeV at the Fermilab Tevatron Collider. We derive 95% C.L. upper limits on the Higgs boson cross section relative to the standard model prediction in the mass range 100GeV≤M H≤150GeV, and we exclude Higgs bosons with masses smaller than 102 GeV at the 95% C.L. In the mass range 120GeV≤M H≤145GeV, the data exhibit an excess above the background prediction with a global significance of 1.5 standard deviations, consistent with the expectation in the presence of a standard model Higgs boson. © 2012 American Physical Society.

Search for the standard model Higgs boson in ZH→ + -bb̄ production with the D0 detector in 9.7fb -1 of pp̄ collisions at √s=1.96TeV

We present a search for the standard model (SM) Higgs boson produced in association with a Z boson in 9.7fb -1 of pp̄ collisions collected with the D0 detector at the Fermilab Tevatron Collider at √s=1.96TeV. Selected events contain one reconstructed Z→e +e - or Z→μ +μ - candidate and at least two jets, including at least one jet identified as likely to contain a b quark. To validate the search procedure, we also measure the cross section for ZZ production in the same final state. It is found to be consistent with its SM prediction. We set upper limits on the ZH production cross section times branching ratio for H→bb̄ at the 95% C.L. for Higgs boson masses 90≤M H≤150GeV. The observed (expected) limit for M H=125GeV is 7.1 (5.1) times the SM cross section. © 2012 American Physical Society.

Search for the standard model Higgs boson in associated WH production in 9.7fb -1 of pp̄ collisions with the D0 detector

We present a search for the standard model Higgs boson in final states with a charged lepton (electron or muon), missing transverse energy, and two or three jets, at least one of which is identified as a b-quark jet. The search is primarily sensitive to WH→ νbb̄ production and uses data corresponding to 9.7fb -1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp̄ Collider at √s=1.96TeV. We observe agreement between the data and the expected background. For a Higgs boson mass of 125 GeV, we set a 95% C.L. upper limit on the production of a standard model Higgs boson of 5.2×σ SM, where σ SM is the standard model Higgs boson production cross section, while the expected limit is 4.7×σ SM. © 2012 American Physical Society.

Search for Zγ events with large missing transverse energy in pp̄ collisions at √s=1.96TeV

We present the first search for new phenomena in Zγ final states with large missing transverse energy using data corresponding to an integrated luminosity of 6.2fb -1 collected with the D0 experiment in pp̄ collisions at √s=1.96TeV. This signature is predicted in gauge-mediated supersymmetry-breaking models, where the lightest neutralino χ 10 is the next-to-lightest supersymmetric particle and is produced in pairs, possibly through decay from heavier supersymmetric particles. The χ 10 can decay either to a Z boson or a photon and an associated gravitino that escapes detection. We exclude this model at the 95% C.L. for supersymmetry-breaking scales of Λ<87TeV. © 2012 American Physical Society.

Measurement of the semileptonic charge asymmetry in B0 meson mixing with the D0 detector

We present a measurement of the semileptonic mixing asymmetry for B0 mesons, asld, using two independent decay channels: B0→μ +D -X, with D -→K +π -π -; and B0→μ +D *-X, with D * -→D ̄0π -, D ̄0→ K +π - (and charge conjugate processes). We use a data sample corresponding to 10.4fb -1 of pp̄ collisions at √s=1.96TeV, collected with the D0 experiment at the Fermilab Tevatron collider. We extract the charge asymmetries in these two channels as a function of the visible proper decay length of the B0 meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The final measurement combines four signal visible proper decay length regions for each channel, yielding asld=[0.68±0.45(stat)±0.14(syst)]%. This is the single most precise measurement of this parameter, with uncertainties smaller than the current world average of B factory measurements. © 2012 American Physical Society.

Combination of the top-quark mass measurements from the Tevatron collider

The top quark is the heaviest known elementary particle, with a mass about 40 times larger than the mass of its isospin partner, the bottom quark. It decays almost 100% of the time to a W boson and a bottom quark. Using top-antitop pairs at the Tevatron proton-antiproton collider, the CDF and D0 Collaborations have measured the top quark's mass in different final states for integrated luminosities of up to 5.8fb -1. This paper reports on a combination of these measurements that results in a more precise value of the mass than any individual decay channel can provide. It describes the treatment of the systematic uncertainties and their correlations. The mass value determined is 173.18±0.56(stat)±0.75(syst)GeV or 173.18±0.94GeV, which has a precision of ±0.54%, making this the most precise determination of the top-quark mass. © 2012 American Physical Society.

Measurement of angular correlations of jets at s=1.96 TeV and determination of the strong coupling at high momentum transfers

We present a measurement of the average value of a new observable at hadron colliders that is sensitive to QCD dynamics and to the strong coupling constant, while being only weakly sensitive to parton distribution functions. The observable measures the angular correlations of jets and is defined as the number of neighboring jets above a given transverse momentum threshold which accompany a given jet within a given distance δR in the plane of rapidity and azimuthal angle. The ensemble average over all jets in an inclusive jet sample is measured and the results are presented as a function of transverse momentum of the inclusive jets, in different regions of δR and for different transverse momentum requirements for the neighboring jets. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 fb -1 collected with the D0 detector at the Fermilab Tevatron Collider in pp- collisions at s=1.96 TeV. The results are well described by a perturbative QCD calculation in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects. From these results, we extract the strong coupling and test the QCD predictions for its running over a range of momentum transfers of 50-400 GeV. © 2012 Elsevier B.V.

Study of the decay Bs0→J/ψf2′(1525) in μ +μ -K +K - final states

We investigate the decay Bs0→J/ψK +K - for invariant masses of the K +K - pair in the range 1.35

Algoritmos de detecção de bordas implementados em FPGA

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Measurement of the p(p)over-bar -> W plus b plus X production cross section at root s=1.96 TeV D0 Collaboration

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the combined rapidity and p(T) dependence of dijet azimuthal decorrelations in p(p)over-bar collisions at root s=1.96 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)