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Adams, Todd

Publications and source records attributed to Adams, Todd.

At least 55 records · Page 3
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DOE OSTI2011

Measurement of spin correlation in ttbar production using dilepton final states

We measure the correlation between the spin of the top quark and the spin of the anti-top quark in t{bar t} {yields} W{sup +}bW{sup -}{bar b} {yields} {ell}{sup +}{nu}b{ell}{sup -}{bar {nu}}{bar b} final states produced in p{bar p} collisions at a center of mass energy {radical}s = 1.96 TeV, where {ell} is an electron or muon. The data correspond to an integrated luminosity of 5.4 fb{sup -1} and were collected with the D0 detector at the Fermilab Tevatron collider. The correlation is extracted from the angles of the two leptons in the t and {bar t} rest frames, yielding a correlation strength C = 0.10{sub -0.45}{sup +0.45}, in agreement with the NLO QCD prediction within two standard deviations, but also in agreement with the no correlation hypothesis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of color flow in $\mathbf{t\bar{t}}$ events from $\mathbf{p\bar{p}}$ collisions at $\mathbf{\sqrt{s}=1.96}$ TeV

We present the first measurement of the color representation of the hadronically decaying W boson in t{bar t} events, from 5.3 fb{sup -1} of integrated luminosity collected with the D0 experiment. A novel calorimeter-based vectorial variable, 'jet pull,' is used, sensitive to the color-flow structure of the final state. We find that the fraction of uncolored W bosons is 0.56 {+-} 0.42(stat+syst), in agreement with the standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Azimuthal decorrelations and multiple parton interactions in photon+2 jet and photon+3 jet events in ppbar collisions at sqrt{s}=1.96 TeV

Samples of inclusive {gamma} + 2 jet and {gamma} + 3 jet events collected by the D0 experiment with an integrated luminosity of about 1 fb{sup -1} in p{bar p} collisions at {radical}s = 1.96 TeV are used to measure cross sections as a function of the angle in the plane transverse to the beam direction between the transverse momentum (p{sub T}) of the {gamma} + leading jet system (jets are ordered in p{sub T}) and p{sub T} of the other jet for {gamma} + 2 jet, or p{sub T} sum of the two other jets for {gamma} + 3 jet events. The results are compared to different models of multiple parton interactions (MPI) in the pythia and sherpa Monte Carlo (MC) generators. The data indicate a contribution from events with double parton (DP) interactions and are well described by predictions provided by the pythia MPI models with p{sub T}-ordered showers and by sherpa with the default MPI model. The {gamma} + 2 jet data are also used to determine the fraction of events with DP interactions as a function of the azimuthal angle and as a function of the second jet p{sub T}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Search for $WH$ associated production in 5.3 fb$^{-1}$ of $p\bar{p}$ collisions at the Fermilab Tevatron

We present a search for associated production of Higgs and W bosons in p{bar p} collisions at a center of mass energy of {radical}s = 1.96 TeV in 5.3 fb{sup -1} of integrated luminosity recorded by the D0 experiment. Multivariate analysis techniques are applied to events containing one lepton, an imbalance in transverse energy, and one or two b-tagged jets to discriminate a potential WH signal from standard model backgrounds. We observe good agreement between data and background, and set an upper limit of 4.5 (at 95% confidence level and for m{sub H} = 115 GeV) on the ratio of the WH cross section multiplied by the branching fraction of H {yields} b{bar b} to its standard model prediction. A limit of 4.8 is expected from simulation.

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DOE OSTI2010

Search for Diphoton Events with Large Missing Transverse Energy in 6.3 fb{sup -1} of pp Collisions at {radical}(s)=1.96 TeV

We report a search for diphoton events with large missing transverse energy produced in pp collisions at {radical}(s)=1.96 TeV. The data were collected with the D0 detector at the Fermilab Tevatron Collider and correspond to 6.3 fb{sup -1} of integrated luminosity. The observed missing transverse energy distribution is well described by the standard model prediction, and 95% C.L. limits are derived on two realizations of theories beyond the standard model. In a gauge-mediated supersymmetry breaking scenario, the breaking scale {Lambda} is excluded for {Lambda}<124 TeV. In a universal extra dimension model including gravitational decays, the compactification radius R{sub c} is excluded for R{sub c}{sup -1}<477 GeV.

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DOE OSTI2010

Search for Events with Leptonic Jets and Missing Transverse Energy in pp Collisions at {radical}(s)=1.96 TeV

We present the first search for pair production of isolated jets of charged leptons in association with a large imbalance in transverse energy in pp collisions using 5.8 fb{sup -1} of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider. No excess is observed above the standard model background, and the result is used to set upper limits on the production cross section of pairs of supersymmetric chargino and neutralino particles as a function of ''dark-photon'' mass, where the dark photon is produced in the decay of the lightest supersymmetric particle.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Search for resonant WW and WZ production in ppbar collisions at ?s = 1.96 TeV

The standard model of particle physics is expected to be a low energy effective theory valid for particle interactions below the TeV scale. Above this scale, extensions to the standard model (SM) augment the existing particle content, leading to enhanced production of many final states at colliders. Specifically, the production and decay of massive charged or neutral particles can produce an excess of W boson pairs for neutral particles or W and Z boson pairs for charged particles. We search for resonant WW or WZ production using up to 5.4 fb{sup -1} of integrated luminosity collected by the D0 experiment in Run II of the Fermilab Tevatron Collider. The data are consistent with the standard model background expectation, and we set limits on a resonance mass using the sequential standard model (SSM) W{prime} boson and the Randall-Sundrum model graviton G as benchmarks. We exclude an SSM W{prime} boson in the mass range 180-690 GeV and a Randall-Sundrum graviton in the range 300-754 GeV at 95% CL.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Measurement of the W boson helicity in top quark decays using 5.4 fb$^{\boldsymbol{-1}}$ of $\boldsymbol{p\bar{p}}$ collision data

We present a measurement of the helicity of the W boson produced in top quark decays using t{bar t} decays in the {ell}+jets and dilepton final states selected from a sample of 5.4 fb{sup -1} of collisions recorded using the D0 detector at the Fermilab Tevatron p{bar p} collider. We measure the fractions of longitudinal and right-handed W bosons to be f{sub 0} = 0.669 {+-} 0.102 [{+-}0.078 (stat.) {+-} 0.065 (syst.)] and f{sub +} = 0.023 {+-} 0.053 [{+-}0.041 (stat.){+-}0.034 (syst.)], respectively. This result is consistent at the 98% level with the standard model. A measurement with f{sub 0} fixed to the value from the standard model yields f{sub +} = 0.010 {+-} 0.037 [{+-}0.022 (stat.) {+-} 0.030 (syst.)].

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Search for neutral Higgs bosons in the multi-$b$-jet topology in 5.2fb$^{-1}$ of $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV

Data recorded by the D0 experiment at the Fermilab Tevatron Collider are analyzed to search for neutral Higgs bosons produced in association with b quarks. The search is performed in the three-b-quark channel using multijet-triggered events corresponding to an integrated luminosity of 5.2 fb{sup -1}. In the absence of any significant excess above background, limits are set on the cross section multiplied by the branching ratio in the Higgs boson mass range 90 to 300 GeV, extending the excluded regions in the parameter space of the minimal supersymmetric standard model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Search for single vector-like quarks in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV

We present a search for hypothetical vector-like quarks in p{bar p} collisions at {radical}s = 1.96 TeV. The data were collected by the D0 detector at the Fermilab Tevatron Collider and correspond to an integrated luminosity of 5.4 fb{sup -1}. We select events with a final state composed of a W or Z boson and a jet consistent with a heavy object decay. We observe no significant excess in comparison to the background prediction and set limits on production cross sections for vector-like quarks decaying to W+jet and Z+jet. Assuming a vector-like quark to standard model quark coupling parameter {tilde {kappa}}{sub qQ} of unity, we exclude vector-like quarks with mass below 693 GeV for decays to W+jet and mass below 449 GeV for decays to Z+jet. These are the most stringent mass limits for electroweak single vector-like quark production at hadron colliders.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Precise study of the $Z/\gamma^*$ boson transverse momentum distribution in $p\bar{p}$ collisions using a novel technique

Using 7.3 fb{sup -1} of p{bar p} collisions collected by the D0 detector at the Fermilab Tevatron, we measure the distribution of the variable {phi}*{sub {eta}}, which probes the same physical effects as the Z/{gamma}* boson transverse momentum, but is less susceptible to the effects of experimental resolution and efficiency. A QCD prediction is found to describe the general features of the {phi}*{sub {eta}} distribution, but is unable to describe its detailed shape or dependence on boson rapidity. A prediction that includes a broadening of transverse momentum for small values of the parton momentum fraction is strongly disfavored.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

A measurement of the ratio of inclusive cross sections $\sigma(p\bar{p}\rightarrow Z+b{\rm\, jet})/ \sigma(p\bar{p}\rightarrow Z+{\rm jet})$ at $\sqrt{s}=1.96$ TeV

The ratio of the cross section for p{bar p} interactions producing a Z boson and at least one b quark jet to the inclusive Z+jet cross section is measured using 4.2 fb{sup -1} of p{bar p} collisions collected with the D0 detector at the Fermilab Tevatron collider at {radical}s = 1.96 TeV. The Z {yields} {ell}{sup +}{ell}{sup -} candidate events with at least one b jet are discriminated from Z+ charm and light jet(s) events by a novel technique that exploits the properties of the tracks associated to the jet. The measured ratio is 0.0193 {+-} 0.0027 for events having a jet with transverse momentum p{sub T} > 20 GeV and pseudorapidity |{eta}| {le} 2.5, which is the most precise to date and is consistent with theoretical predictions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Determination of the width of the top quark

We extract the total width of the top quark, {Lambda}{sub t}, from the partial decay width {Lambda}(t {yields} Wb) measured using the t-channel cross section for single top quark production and from the branching fraction B(t {yields} Wb) measured in t{bar t} events using up to 2.3 fb{sup -1} of integrated luminosity collected by the D0 Collaboration at the Tevatron p{bar p} Collider. The result is {Lambda}{sub t} = 1.99{sub -0.55}{sup +0.69} GeV, which translates to a top-quark lifetime of {tau}{sub t} = (3.3{sub -0.9}{sup +1.3}) x 10{sup -25} s. Assuming a high mass fourth generation b{prime} quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |V{sub tb{prime}}| < 0.63 at 95% C.L.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Evidence for an anomalous like-sign dimuon charge asymmetry

We measure the charge asymmetry A of like-sign dimuon events in 6.1 fb{sup -1} of pp collisions recorded with the D0 detector at a center-of-mass energy {radical}(s)=1.96 TeV at the Fermilab Tevatron collider. From A, we extract the like-sign dimuon charge asymmetry in semileptonic b-hadron decays: A{sub sl}{sup b}=-0.00957{+-}0.00251 (stat){+-}0.00146 (syst). This result differs by 3.2 standard deviations from the standard model prediction A{sub sl}{sup b}(SM)=(-2.3{sub -0.6}{sup +0.5})x10{sup -4} and provides first evidence of anomalous CP violation in the mixing of neutral B mesons.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Measurement of $\boldsymbol{\ttb}$ production in the tau + jets channel using $\boldsymbol{p\bar{p}}$ collisions at $\boldsymbol{\sqrt{s} = 1.96}$~TeV

We present a measurement of the t{bar t} production cross section multiplied by the branching ratio to tau lepton decaying semi-hadronically ({tau}{sub h}) plus jets, {sigma}(p{bar p} {yields} t{bar t} + X) {center_dot} BR(t{bar t} {yields} {tau}{sub h} + jets), at a center of mass energy {radical}s = 1.96 TeV using 1 fb{sup -1} of integrated luminosity collected with the D0 detector. Assuming a top quark mass of 170 GeV, we measure {sigma}{sub t{bar t}} {center_dot} BR{sub {tau}{sub h}+j} = 0.60{sub -0.22}{sup +0.23}(stat){sub -0.14}{sup +0.15}(syst){+-}0.04 (lumi) pb. In addition, we extract the t{bar t} production cross section using the t{bar t} {yields} {tau}{sub h} + jets topology, with the result {sigma}{sub t{bar t}} = 6.9{sub -1.2}{sup +1.2}(stat){sub -0.7}{sup +0.8}(syst) {+-} 0.4 (lumi) pb. These findings are in good agreement with standard model predictions and measurements performed using other top quark decay channels.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Search for $ZH \rightarrow \ell^+\ell^-b\bar{b}$ production in $4.2$~fb$^{-1}$ of $p\bar{p}$ collisions at $\sqrt{s}=1.96~\TeV$

We present a search for the standard model Higgs boson produced in association with a Z boson in 4.2 fb{sup -1} of p{bar p} collisions, collected with the D0 detector at the Fermilab Tevatron at {radical}s = 1.96 TeV. Selected events contain one reconstructed Z {yields} {ell}{sup +}{ell}{sup -} candidate and at least two jets, including at least one b-tagged jet. In the absence of an excess over the background expected from other standard model processes, limits on the ZH cross section multiplied by the branching ratios are set. The limit at M{sub H} = 115 GeV is a factor of 5.9 larger than the standard model prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Search for a heavy neutral gauge boson in the dielectron channel with 5.4~fb$^{-1}$ of $\mathbf{p\bar{p}}$ collisions at $\mathbf{\sqrt{s} = 1.96}$~TeV

We report the results of a search for a heavy neutral gauge boson Z' decaying into the dielectron final state using data corresponding to an integrated luminosity of 5.4 fb{sup -1} collected by the D0 experiment at the Fermilab Tevatron Collider. No significant excess above the standard model prediction is observed in the dielectron invariant-mass spectrum. We set 95% C.L. upper limits on {sigma}(p{bar p} {yields} Z') x BR(Z' {yields} ee) depending on the dielectron invariant mass. These cross section limits are used to determine lower mass limits for Z' bosons in a variety of models with standard model couplings and variable strength.

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