98 research outputs found

    Search for Higgs boson production in oppositely charged dilepton and missing energy final states in 9.7 fbβˆ’1^{-1} of ppΛ‰p\bar{p} collisions at s=1.96\sqrt{s} = 1.96 TeV

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    We present a search for Higgs boson in final states with two oppositely charged leptons and large missing transverse energy as expected in H -> WW -> lvlv decays. The events are selected from the full Run II data sample of 9.7 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt s = 1.96 TeV. To validate our search methodology, we measure the non-resonant W W production cross section and find sigma_WW = 11.6 +/- 0.7 pb, in agreement with the standard model prediction. In the Higgs boson search, no significant excess above the background expectation is observed. Upper limits at the 95% confidence level on the Higgs boson production cross section are therefore derived. Within the standard model, the Higgs boson mass range 159 < MH < 176 GeV is excluded while the expected exclusion sensitivity is 156 < MH < 172 GeV. For a mass hypothesis of MH = 125 GeV, we exclude Higgs boson production cross sections 4.1 times larger than the standard model expectation, which is compatible with the presence of a Higgs boson at this mass. Within a theoretical framework with a fourth generation of fermions, the mass range 125 < MH < 218 GeV is excluded. The search results are also interpreted in the context of fermiophobic Higgs boson couplings, which yields an exclusion of fermiophobic Higgs boson production cross sections 3.1 times larger than the expectation for MH = 125 GeV

    Search for the standard model Higgs boson in β„“Ξ½\bm{\ell\nu}+jets final states in 9.7~fbβˆ’1\bm{^{-1}} of ppΛ‰\bm{p\bar{p}} collisions with the D0 detector

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    We present, in detail, a search for the standard model Higgs boson, HH, in final states with a charged lepton (electron or muon), missing energy, and two or more jets in data corresponding to 9.7 fbβˆ’1^{-1} of integrated luminosity collected at a center of mass energy of s\sqrt{s} = 1.96 TeV with the D0 detector at the Fermilab Tevatron ppΛ‰p\bar{p} Collider. The search uses bb-jet identification to categorize events for improved signal versus background separation and is sensitive to associated production of the HH with a WW boson, WHβ†’β„“Ξ½bbΛ‰WH\to\ell\nu b\bar{b}; gluon fusion with the Higgs decaying to WW boson pairs, Hβ†’WWβ†’β„“Ξ½jjH\to WW\to\ell\nu jj; and associated production with a vector boson where the Higgs decays to WW boson pairs, VHβ†’VWWβ†’β„“Ξ½jjjjVH\to VWW \to \ell\nu jjjj production (where V=WV = W or ZZ). We observe good agreement between data and expected background. We test our method by measuring WZWZ and ZZZZ production with Zβ†’bbΛ‰Z\to b\bar{b} and find production rates consistent with the standard model prediction. 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 \obslimAΓ—ΟƒSM\times\sigma_{\rm SM}, where ΟƒSM\sigma_{\rm SM} is the standard model Higgs boson production cross section, while the expected limit is \explimAΓ—ΟƒSM\times\sigma_{\rm SM}. We also interpret the data considering models with fourth generation fermions, or a fermiophobic Higgs boson

    Search for Higgs boson production in oppositely charged dilepton and missing energy events in ppˉ{p\bar{p}} collisions at s={\sqrt{s} =}1.96 TeV}

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    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→WWH\rightarrow WW decays. The events are selected from data corresponding to 8.6 \ifb\ of integrated luminosity in ppˉp \bar{p} collisions at s=1.96\sqrt{s}=1.96 TeV 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

    Measurement of the ratio of differential cross sections σ(ppˉ→Z+bjet)/σ(ppˉ→Z+jet){\sigma}(p\bar{p} \to Z + b jet)/{\sigma}(p\bar{p} \to Z + jet) in ppˉp\bar{p} collisions at (s)=1.96\sqrt(s)=1.96 TeV

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    We measure the ratio of cross sections, {\sigma}(ppbar -> Z + b jet)/{\sigma}(ppbar -> Z + jet), for associated production of a Z boson with at least one jet. The ratio is also measured as a function of the jet transverse momentum, jet pseudorapidity, Z boson transverse momentum, and the azimuthal angle between the Z boson and the closest jet for events with at least one b jet. These measurements use data collected by the D0 experiment in Run II of Fermilab's Tevatron ppbar Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of 9.7 fbβˆ’1^{-1}. The results are compared to predictions from next-to-leading order calculations and various Monte Carlo event generators

    Measurement of the combined rapidity and pTp_T dependence of dijet azimuthal decorrelations in ppΛ‰p\bar{p} collisions at s=1.96 \sqrt{s}=1.96\,TeV

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    We present the first combined measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations, based on the recently proposed quantity RΔϕR_{\Delta \phi}. The variable RΔϕR_{\Delta \phi} measures the fraction of the inclusive dijet events in which the azimuthal separation of the two jets with the highest transverse momenta is less than a specified value for the parameter Δϕmax\Delta \phi_{\rm max}. The quantity RΔϕR_{\Delta \phi} is measured in ppΛ‰p\bar{p} collisions at s=1.96 \sqrt{s}=1.96\,TeV, as a function of the dijet rapidity interval, the total scalar transverse momentum, and Δϕmax\Delta \phi_{\rm max}. The measurement uses an event sample corresponding to an integrated luminosity of 0.7 0.7\,fbβˆ’1^{-1} collected with the D0 detector at the Fermilab Tevatron Collider. The results are compared to predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for non-perturbative effects. The theory predictions describe the data, except in the kinematic region of large dijet rapidity intervals and large Δϕmax\Delta \phi_{\rm max}

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

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    Using data collected with the D0 detector at the Fermilab Tevatron Collider, corresponding to 5.3 fbβˆ’1^{-1} of integrated luminosity, we search for violation of Lorentz invariance by examining the \ttbar production cross section in lepton+jets final states. We quantify this violation using the standard-model extension framework, which predicts a dependence of the \ttbar 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 (cQ)ΞΌΞ½33(c_Q)_{\mu\nu 33} and (cU)ΞΌΞ½33(c_U)_{\mu\nu 33} 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

    Search for a Higgs boson in diphoton final states with the D0 detector in 9.6 fb-1 of p-pbar collisions at sqrt(s)=1.96 TeV

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    We present a search for a Higgs boson decaying into a pair of photons based on 9.6 fb-1 of p-pbar collisions at sqrt(s)=1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The search employs multivariate techniques to discriminate signal from the non-resonant background and is separately optimized for a standard model and a fermiophobic Higgs boson. No significant excess of data above the background prediction is observed and upper limits on the product of the cross section and branching fraction are derived at the 95% confidence level as a function of Higgs boson mass. For a standard model Higgs boson with mass of 125 GeV, the observed (expected) upper limits are a factor of 12.8 (8.7) above the standard model prediction. The existence of a fermiophobic Higgs boson with mass in the 100-113 GeV range is excluded at the 95% confidence level

    Study of the decay Bs0β†’J/ψf2β€²(1525)B_s^0 \rightarrow J/\psi f_2^{\prime}(1525) in ΞΌ+ΞΌβˆ’K+Kβˆ’\mu^+ \mu^- K^+K^- final states

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    We investigate the decay Bs0β†’J/ψK+Kβˆ’B_s^0 \rightarrow J/\psi K^+ K^- for invariant masses of the K+Kβˆ’K^+K^- pair in the range 1.35<M(K+Kβˆ’)<21.35<M(K^+K^-)<2 GeV. The data sample corresponds to an integrated luminosity of 10.4 fbβˆ’1^{-1} of ppΛ‰p \bar{p} collisions at s=1.96\sqrt{s} = 1.96 TeV accumulated with the D0 detector at the Fermilab Tevatron collider. From the study of the invariant mass and spin of the K+Kβˆ’K^+K^- system, we find evidence for the two-body decay \bsf\ and measure the relative branching fraction of the decays \bsf\ and \bsdec\ to be Rf2β€²/Ο•=0.22Β±0.05 (stat)Β±0.04 (syst)R_{f_2^{\prime}/\phi} = 0.22 \pm 0.05 \rm \thinspace{(stat)} \pm 0.04 \rm \thinspace{(syst)}

    Measurement of the ratio of three-jet to two-jet cross sections in ppˉp\bar{p} collisions at s=1.96\sqrt{s}=1.96 TeV

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    We present a measurement of the ratio of multijet cross sections in pp-bar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron Collider. The measurement is based on a data set corresponding to an integrated luminosity of 0.7 fb-1 collected with the D0 detector. The ratio of the inclusive three-jet to two-jet cross sections, R3/2, has been measured as a function of the jet transverse momenta. The data are compared to QCD predictions in different approximations. Popular tunes of the PYTHIA event generator do not agree with the data, while SHERPA provides a reasonable description of the data. A perturbative QCD prediction in next-to-leading order in the strong coupling constant, corrected for non-perturbative effects, gives a good description of the data