Search for Higgs Boson Production in Dilepton and Missing Energy Final States with 5.4 fb(-1) of p(p)over-bar Collisions at root s=1.96 TeV

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Search for CP violation in B-s(0) -> mu(+) D-s(-) X decays in p(p)over-bar collisions at root s=1.96 TeV

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Measurement of the t(t)over-bar cross section using high-multiplicity jet events

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Observing Higgs dark matter at the CERN LHC

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Model-independent measurement of the W-boson helicity in top-quark decays at D0

We present the first model-independent measurement of the helicity of W bosons produced in top quark decays, based on a 1 fb(-1) sample of candidate t (t) over bar events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron p (p) over bar Collider. We reconstruct the angle theta(*) between the momenta of the down-type fermion and the top quark in the W boson rest frame for each top quark decay. A fit of the resulting cos theta(*) distribution finds that the fraction of longitudinal W bosons f(0)=0.425 +/- 0.166(stat)+/- 0.102(syst) and the fraction of right-handed W bosons f(+)=0.119 +/- 0.090(stat)+/- 0.053(syst), which is consistent at the 30% C.L. with the standard model.

Measurement of the forward-backward charge asymmetry in top-quark pair production

We present the first measurement of the integrated forward-backward charge asymmetry in top-quark-top-antiquark pair (t (t) over bar) production in proton-antiproton (p (p) over bar) collisions in the lepton+jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming t (t) over bar +X production and decay, a sample of 0.9 fb(-1) of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on t (t) over bar +X production via a Z' resonance.

Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.96 TeV

We measure the t (t) over bar production cross section in p (p) over bar collisions at root s = 1.96 TeV in the lepton + jets channel. Two complementary methods discriminate between signal and background: b tagging and a kinematic likelihood discriminant. Based on 0.9 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure sigma(t (t) over bar) = 7.62 +/- 0.85 pb, assuming the current world average m(t) = 172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top-quark mass of 170 +/- 7 GeV.

Search for excited electrons in p(p)over-bar collisions at root s=1.96 TeV

We present the results of a search for the production of an excited state of the electron, e(*), in proton-antiproton collisions at root s = 1.96 TeV. The data were collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 1 fb(-1). We search for e(*) in the process p (p) over bar -> e(*)e, with the e(*) subsequently decaying to an electron plus photon. No excess above the standard model background is observed. Interpreting our data in the context of a model that describes e(*) production by four-fermion contact interactions and e(*) decay via electroweak processes, we set 95% C.L. upper limits on the production cross section ranging from 8.9 to 27 fb, depending on the mass of the excited electron. Choosing the scale for contact interactions to be Lambda = 1 TeV, excited electron masses below 756 GeV are excluded at the 95% C.L.

New signature for color octet pseudoscalars at the CERN LHC

Color octet (pseudo)scalars, if they exist, will be copiously produced at the CERN Large Hadron Collider (LHC). However, their detection can become a very challenging task. In particular, if their decay into a pair of top quarks is kinematically forbidden, the main decay channel would be into two jets, with a very large background. In this brief report we explore the possibility of using anomaly-induced decays of the color octet pseudoscalars into gauge bosons to find them at the LHC.

Search for W ' boson resonances decaying to a top quark and a bottom quark

We search for the production of a heavy W ' gauge boson that decays to third generation quarks in 0: 9 fb(-1) of p (p) over bar collisions at root s = 1: 96 TeV, collected with the D0 detector at the Fermilab Tevatron collider. We find no significant excess in the final-state invariant mass distribution and set upper limits on the production cross section times branching fraction. For a left-handed W ' boson with SM couplings, we set a lower mass limit of 731 GeV. For right-handed W ' bosons, we set lower mass limits of 739 GeV if the W ' boson decays to both leptons and quarks and 768 GeV if the W ' boson decays only to quarks. We also set limits on the coupling of the W ' boson to fermions as a function of its mass.

Search for scalar neutrino superpartners in e+mu final states in p(p)over-bar collisions at root s=1.96 TeV

We report a search for R-parity-violating production and decay of sneutrino particles in the e mu final state with 1.04 +/- 0.06 fb(-1) of data collected with the D(0) detector at the Fermilab Tevatron Collider in 2002-2006. Good agreement between the data and the standard model prediction is observed. With no evidence for new physics, we set limits on the R-parity-violating couplings lambda'(311) and lambda(312) as a function of the sneutrino mass.

Measurement of the Polarization of the Upsilon(1S) and Upsilon(2S) States in pp Collisions at s=1.96 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of B-s(0) Mixing Parameters from the Flavor-Tagged Decay B-s(0)-> J/psi phi

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Search for Large Extra Spatial Dimensions in the Dielectron and Diphoton Channels in p(p)over-bar Collisions at root s=1.96 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the W Boson Mass

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)