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  • 201.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of color flow in tt̅ events from pp̅ collisions at √s=1.96  TeV2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 83, nr 9, s. 092002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the first measurement of the color representation of the hadronically decaying W boson in tt̅ events, from 5.3  fb-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.

  • 202.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of Dijet Angular Distributions at $\sqrt{s}=1.96$ and Searches for Quark Compositeness and Extra Spatial Dimensions2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, s. 191803-Artikkel i tidsskrift (Fagfellevurdert)
  • 203.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of Direct Photon Pair Production Cross Sections in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 690, s. 108-117Artikkel i tidsskrift (Fagfellevurdert)
  • 204.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of Spin Correlation in $t\bar{t}$ Production Using a Matrix Element Approach2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 3, s. 032001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We determine the fraction of t (t) over bar events with spin correlation, assuming that the spin of the top quark is either correlated with the spin of the top antiquark as predicted by the standard model or is uncorrelated. For the first time we use a matrix-element-based approach to study t (t) over bar spin correlation. We use t (t) over bar -> W(+)bW(-)(b) over bar -> l(+)nu bl(-)(nu) over bar(b) over bar final states produced in p (p) over bar collisions at a center- of- mass energy root s = 1: 96 TeV, where l denotes an electron or a muon. The data correspond to an integrated luminosity of 5: 4 fb(-1) and were collected with the D0 detector at the Fermilab Tevatron collider. The result agrees with the standard model prediction. We exclude the hypothesis that the spins of the t (t) over bar are uncorrelated at the 97.7% C.L.

  • 205.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of Spin Correlation in $t\bar{t}$ Production Using Dilepton Final States2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 702, nr 1, s. 16-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We measure the correlation between the spin of the top quark and the spin of the anti-top quark in final states produced in collisions at a center of mass energy , where is an electron or muon. The data correspond to an integrated luminosity of 5.4 fb−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 rest frames, yielding a correlation strength , in agreement with the NLO QCD prediction within two standard deviations, but also in agreement with the no correlation hypothesis.

  • 206.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of $t\bar{t}$ Production in the $\tau+$jets Channel Using $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2010Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 82, nr 7, s. 071102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a measurement of the tt̅ production cross section multiplied by the branching ratio to tau lepton decaying semihadronically (τh) plus jets, σ(pp̅ →tt̅ +X)·BR(tt̅ →τh+jets), at a center of mass energy √s=1.96  TeV using 1  fb-1 of integrated luminosity collected with the D0 detector. Assuming a top quark mass of 170 GeV, we measure σtt̅ ·BRτh+j=0.60-0.22+0.23(stat)-0.14+0.15(syst)±0.04(lumi)  pb. In addition, we extract the tt̅ production cross section using the tt̅ →τh+jets topology, with the result σtt̅ =6.9-1.2+1.2(stat)-0.7+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.

  • 207.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the Anomalous Like-Sign Dimuon Charge Asymmetry with 9 fb-1 of $p\bar{p}$ Collisions2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 5, s. 052007-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present an updated measurement of the anomalous like-sign dimuon charge asymmetry A(sl)(b) for semileptonic b-hadron decays in 9.0 fb(-1) of p (p) over bar collisions recorded with the D0 detector at a center-of-mass energy of root s = 1.96 TeV at the Fermilab Tevatron collider. We obtain A(sl)(b) = (-0.787 +/- 0.172(stat) +/- 0.093(syst)%. This result differs by 3.9 standard deviations from the prediction of the standard model and provides evidence for anomalously large CP violation in semileptonic neutral B decay. The dependence of the asymmetry on the muon impact parameter is consistent with the hypothesis that it originates from semileptonic b-hadron decays.

  • 208.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the CP-violating phase ϕsJ/ψϕ using the flavor-tagged decay Bs0→J/ψϕ in 8  fb-1 of pp̅  collisions2012Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 85, nr 3, s. # 032006-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report an updated measurement of the CP-violating phase, ϕsJ/ψϕ, and the decay-width difference for the two mass eigenstates, ΔΓs, from the flavor-tagged decay Bs0→J/ψϕ. The data sample corresponds to an integrated luminosity of 8.0  fb-1 accumulated with the D0 detector using pp̅        collisions at √s=1.96  TeV produced at the Fermilab Tevatron collider. The 68% Bayesian credibility intervals, including systematic uncertainties, are ΔΓs=0.163-0.064+0.065  ps-1 and ϕsJ/ψϕ=-0.55-0.36+0.38. The p-value for the Standard Model point is 29.8%.

  • 209.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the Dijet Invariant Mass Cross Section in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 693, nr 5, s. 531-538Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The inclusive dijet production double differential cross section as a function of the dijet invariant mass and of the largest absolute rapidity of the two jets with the largest transverse momentum in an event is measured in collisions at using 0.7 fb−1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. The measurement is performed in six rapidity regions up to a maximum rapidity of 2.4. Next-to-leading order perturbative QCD predictions are found to be in agreement with the data.

  • 210.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the Normalized $Z/\gamma^*\to\mu^+\mu^-$ Transverse Momentum Distribution in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 693, nr 5, s. 522-530Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a new measurement of the Z/γ transverse momentum distribution in the range 0–330 GeV, in proton–antiproton collisions at . The measurement uses 0.97 fb−1 of integrated luminosity recorded by the D0 experiment and is the first using the Z/γμ+μ+X channel at this center-of-mass energy. This is also the first measurement of the Z/γ transverse momentum distribution that presents the result at the level of particles entering the detector, minimizing dependence on theoretical models. As any momentum of the Z/γ in the plane transverse to the incoming beams must be balanced by some recoiling system, primarily the result of QCD radiation in the initial state, this variable is an excellent probe of the underlying process. Tests of the predictions of QCD calculations and current event generators show they have varied success in describing the data. Using this measurement as an input to theoretical predictions will allow for a better description of hadron collider data and hence it will increase experimental sensitivity to rare signals.

  • 211.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the Relative Branching Ratio of $B^0_s\to J/\psi f_0(980)\to B_s^0\to J/\psi\phi$2012Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 85, nr 1, s. # 011103-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a measurement of the relative branching fraction, Rf0, of Bs0→J/ψf0(980), with f0(980)→π+π-, to the process Bs0→J/ψϕ, with ϕ→K+K-. The J/ψf0(980) final state corresponds to a CP-odd eigenstate of Bs0 that could be of interest in future studies of CP violation. Using 8  fb-1 of data recorded with the D0 detector at the Fermilab Tevatron Collider, we find Rf0=0.275±0.041(stat)±0.061(syst).

  • 212.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the $t\bar{t}$ Production Cross Section Using Dilepton Events in $p\bar{p}$ Collisions2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 704, nr 5, s. 403-410Artikkel i tidsskrift (Fagfellevurdert)
  • 213.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the t-channel Single Top Quark Production ross Section2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 682, s. 363-369Artikkel i tidsskrift (Fagfellevurdert)
  • 214.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the top quark pair production cross section in the lepton plus jets channel in proton-antiproton collisions at root s=1.96 TeV2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 1, s. 012008-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a measurement of the inclusive top quark pair production cross section in p (p) over bar collisions at root s = 1.96 TeV utilizing data corresponding to an integrated luminosity of 5.3 fb(-1) collected with the D0 detector at the Fermilab Tevatron Collider. We consider final states containing one high-p(T) isolated electron or muon and at least two jets, and we perform three analyses: one exploiting specific kinematic features of t (t) over bar events, the second using b-jet identification, and the third using both techniques to separate the t (t) over bar signal from the background. In the third case, we determine simultaneously the t (t) over bar cross section and the ratio of the production rates of W + heavy flavor jets and W + light flavor jets, which reduces the impact of the systematic uncertainties related to the background estimation. Assuming a top quark mass of 172.5 GeV, we obtain sigma(t (t) over bar) = 7.78(-0.64)(-0.77)pb. This result agrees with predictions of the standard model

  • 215.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the W Boson Helicity in Top Quark Decays Using 5.4 fb-1 of $p\bar{p}$ Collision Data2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 83, nr 3, s. 032009-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a measurement of the helicity of the W boson produced in top quark decays using tt̅ decays in the ℓ+jets and dilepton final states selected from a sample of 5.4  fb-1 of collisions recorded using the D0 detector at the Fermilab Tevatron pp̅ collider. We measure the fractions of longitudinal and right-handed W bosons to be f0=0.669±0.102[±0.078(stat.)±0.065(syst.)] and f+=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 f0 fixed to the value from the standard model yields f+=0.010±0.037[±0.022(stat.)±0.030(syst.).].

  • 216.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the W Boson Mass2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, s. 141801-Artikkel i tidsskrift (Fagfellevurdert)
  • 217.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of the $WZ\rightarrow \ell\nu\ell\ell$ Cross Section and Limits on Anomalous Triple Gauge Couplings in $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 695, nr 1-4, s. 67-73Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a new measurement of the WZν (=e,μ) cross section and limits on anomalous triple gauge couplings. Using 4.1 fb−1 of integrated luminosity of collisions at , we observe 34 WZ candidate events with an estimated background of 6.0±0.4 events. We measure the WZ production cross section to be , in good agreement with the standard model prediction. We find no evidence for anomalous WWZ couplings and set 95% C.L. limits on the coupling parameters, −0.077<λZ<0.093 and −0.029<ΔκZ<0.080 in the HISZ parameterization for a Λ=2 TeV form factor scale. These are the best limits to date obtained from the direct measurement of the WWZ vertex.

  • 218.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of Three-Jet Differential Cross Sections $d\sigma_{3jet}/dM_{3jet}$ in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 704, nr 5, s. 434-441Artikkel i tidsskrift (Fagfellevurdert)
  • 219.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of Trilinear Gauge Boson Couplings from $WW+WZ\to\ell\nu jj$  in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2009Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 80, s. 053012-Artikkel i tidsskrift (Fagfellevurdert)
  • 220.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurement of $Z/gamma^*$+jet+X Angular Distributions in p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV}2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 682, s. 370-380Artikkel i tidsskrift (Fagfellevurdert)
  • 221.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurements of Inclusive $W$+jets Production Rates as a Function of Jet Transverse Momentum in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, nr 3, s. 200-207Artikkel i tidsskrift (Fagfellevurdert)
  • 222.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Measurements of single top quark production cross sections and vertical bar V(tb)vertical bar in p(p)over-bar collisions at root s=1.96 TeV2011Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 84, nr 11, s. 112001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present measurements of production cross sections of single top quarks in p (p) over bar collisions at root s = 1.96 TeV in a data sample corresponding to an integrated luminosity of 5.4 fb(-1) collected by the D0 detector at the Fermilab Tevatron Collider. We select events with an isolated electron or muon, an imbalance in transverse energy, and two, three, or four jets, with one or two of them containing a bottom hadron. We obtain an inclusive cross section of sigma(p (p) over bar -> tb + X, tqb + X) = 3.43(-0.74)(+0.73) pb and use it to extract the CKM matrix element 0.79 < vertical bar V(tb)vertical bar <= 1 at the 95% C.L. We also measure sigma(p<(p)over bar> -> tb + X) = 0.68(-0.35)(+0.38) pb and sigma(p (p) over bar -> tqb + X) = 2.86(-0.63)(+0.69) pb when assuming, respectively, tqb and tb production rates as predicted by the standard model.

  • 223.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Model-independent Measurement of $t$-channel Single Top Quark Production in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, nr 4, s. 313-319Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a model-independent measurement of t-channel electroweak production of single top quarks in p collisions at root s = 1.96 TeV. Using 5.4 fb(-1) of integrated luminosity collected by the DO detector at the Fermilab Tevatron Collider, and selecting events containing an isolated electron or muon, missing transverse energy and one or two jets originating from the fragmentation of b quarks, we measure a cross section sigma (p (p) over bar -> tqb + X) = 2.90 +/- 0.59 (stat + syst) pb for a top quark mass of 172.5 GeV. The probability of the background to fluctuate and produce a signal as large as the one observed is 1.6 x 10(-8), corresponding to a significance of 5.5 standard deviations.

  • 224.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Precise Measurement of the Top Quark Mass in the Dilepton Channel at D02011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 8, s. 082004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We measure the top quark mass (m(t)) in p (p) over bar collisions at a center of mass energy root s = 1.96 TeV using dilepton t (t) over bar -> W(+)bW(-)b(-) -> l(+)nu(l)bl(-)(nu) over bar (l)(b) over bar events, where l denotes an electron, a muon, or a tau that decays leptonically. The data correspond to an integrated luminosity of 5.4 fb(-1) collected with the D0 detector at the Fermilab Tevatron Collider. We obtain m(t) = 174.0 +/- 1.8(stat) +/- 2.4(syst) GeV, which is in agreement with the current world average m(t) = 173.3 +/- 1.1 GeV. This is currently the most precise measurement of mt in the dilepton channel.

  • 225.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Precise Measurement of the Top-Quark Mass from Lepton+Jets events at DØ2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 3, s. 032004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a measurement of the mass of the top quark in lepton + jets final states of p (p) over bar -> t (t) over bar data corresponding to 2.6 fb(-1) of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. A matrix-element method is developed that combines an in situ jet energy calibration with our standard jet energy scale derived from studies of gamma + jet and dijet events. We then implement a flavor-dependent jet-response correction through a novel approach. This method is used to measure a top-quark mass of m(t) = 176.01 +/- 1.64 GeV. Combining this result with our previous result obtained on an independent data set, we measure a top-quark mass of m(t) = 174.94 +/- 1.49 GeV for a total integrated luminosity of 3.6 fb(-1).

  • 226.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Precise study of the $Z/gamma^\ast$ Boson Transverse Momentum Distribution in $p\bar{p}$ Collisions Using a Novel Technique2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 106, s. 122001-Artikkel i tidsskrift (Fagfellevurdert)
  • 227.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Precision Measurement of the Ratio ${\cal B}(t\to Wb)/{\cal B}(t\to Wq)$ and Extraction of $V_{tb}$2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 12, s. 121802-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a measurement of the ratio of top quark branching fractions R = B(t -> Wb)/B(t -> Wq), where q can be a d, s, or b quark, in the lepton + jets and dilepton t (t) over bar final states. The measurement uses data from 5: 4 fb(-1) of p (p) over bar collisions collected with the D0 detector at the Fermilab Tevatron Collider. We measure R = 0.90 +/- 0.04, and we extract the Cabibbo-Kobayashi-Maskawa (CKM) matrix element vertical bar V(tb)vertical bar as vertical bar V(tb)vertical bar = 0.95 +/- 0.02, assuming unitarity of the 3 x 3 CKM matrix.

  • 228.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for a Fermiophobic and Standard Model Higgs Boson in Diphoton Final States2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 15, s. 151801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a search for the standard model Higgs boson and a fermiophobic Higgs boson in the diphoton final states based on 8.2 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. No excess of data above background predictions is observed and upper limits at the 95% C.L. on the cross section multiplied by the branching fraction are set which are the most restrictive to date. A fermiophobic Higgs boson with a mass below 112.9 GeV is excluded at the 95% C.L.

  • 229.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for a Fourth Generation $t^\prime$ Quark in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 8, s. 082001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a search for pair production of a fourth generation t' quark and its antiparticle, followed by their decays to a W boson and a jet, based on an integrated luminosity of 5: 3 fb(-1) of proton-antiproton collisions at root s = 1.96 TeV collected by the D0 Collaboration at the Fermilab Tevatron Collider. We set upper limits on the t'(t) over bar' production cross section that exclude at the 95% C. L. a t' quark that decays exclusively to W + jet with a mass below 285 GeV. We observe a small excess in the mu + jets channel which reduces the mass range excluded compared to the expected limit of 320 GeV in the absence of a signal.

  • 230.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for a Heavy Neutral Gauge Boson in the Dielectron Channel with 5.4 fb$^{-1}$ of $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 695, nr 1-4, s. 88-94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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−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 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. For the sequential standard model Z boson a lower mass limit of 1023 GeV is obtained.

  • 231.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for a Resonance Decaying into WZ Boson Pairs in $p\bar{p}$ Collisions2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, nr 6, s. 061801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present the first search for an electrically charged resonance W decaying to a WZ boson pair using 4.1  fb-1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron pp̅ collider. The WZ pairs are reconstructed through their decays into three charged leptons (ℓ=e, μ). A total of 9 data events is observed in good agreement with the background prediction. We set 95% C.L. limits on the WWZ coupling and on the W production cross section multiplied by the branching fractions. We also exclude W masses between 188 and 520 GeV within a simple extension of the standard model and set the most restrictive limits to date on low-scale technicolor models.

  • 232.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Anomalous $Wtb$ Couplings in Single Top Quark Production in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2012Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 708, s. 21-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present new direct constraints on a general Wtb interaction using data corresponding to an integrated luminosity of 5.4 fb−1 collected by the D0 detector at the Tevatron collider. The standard model provides a purely left-handed vector coupling at the Wtb vertex, while the most general, lowest dimension Lagrangian allows right-handed vector and left- or right-handed tensor couplings as well. We obtain precise limits on these anomalous couplings by comparing the data to the expectations from different assumptions on the Wtb coupling

  • 233.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Associated Higgs Boson Production Using Like Charge Dilepton Events in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2011Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 84, s. 092002-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a search for associated Higgs boson production in the process pp̅ →W/ZH→ℓ±′±+X in ee, eμ, and μμ final states. The search is based on data collected by the D0 experiment at the Fermilab Tevatron Collider at √s=1.96  TeV corresponding to 5.3  fb-1 of integrated luminosity. We require two isolated leptons (electrons or muons) with the same electric charge and additional kinematic requirements. No significant excess above background is observed, and we set 95% C.L. observed (expected) upper limits on ratio of the production cross section to the standard model prediction of 6.4 (7.3) for a Higgs boson mass of 165 GeV and 13.5 (19.8) for a mass of 115 GeV.

  • 234.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Charged Higgs Bosons in Decays of Top Quarks2009Inngår i: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 80, s. 051107-Artikkel i tidsskrift (Fagfellevurdert)
  • 235.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Charged Higgs Bosons in Top Quark Decays2009Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 682, s. 278-286Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a search for charged Higgs bosons in top quark decays. We analyze the e+jets, μ+jets, ee, , μμ, τe and τμ final states from top quark pair production events, using data from about 1 fb−1 of integrated luminosity recorded by the DØ experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a τ lepton and a τ neutrino and a third one where both decays appear. We extract limits on the branching ratio B(tH+b) for all these models. We use two methods, one where the

    production cross section is fixed, and one where the cross section is fitted simultaneously with B(tH+b). Based on the extracted limits, we exclude regions in the charged Higgs boson mass and tanβ parameter space for different scenarios of the minimal supersymmetric standard model

  • 236.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Dark Photons from Supersymmetric Hidden Valleys2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, s. 081802-Artikkel i tidsskrift (Fagfellevurdert)
  • 237.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Diphoton Events with Large Missing Transverse Energy in 6.3 fb$^{-1}$ of $p\bar{p}$ Collisions at $\sqrt{s} = 1.96$ TeV2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, s. 221802-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report a search for diphoton events with large missing transverse energy produced in pp̅ collisions at √s=1.96  TeV. The data were collected with the D0 detector at the Fermilab Tevatron Collider and correspond to 6.3  fb-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 Λ is excluded for Λ<124  TeV. In a universal extra dimension model including gravitational decays, the compactification radius Rc is excluded for Rc-1<477  GeV

  • 238.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for First Generation Leptoquark Pair Production in the Electron + Missing Energy + Jets Final State2011Inngår i: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 84, nr 7, s. 071104-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a search for the pair production of first generation scalar leptoquarks (LQ) in data corresponding to an integrated luminosity of 5.4 fb(-1) collected with the D0 detector at the Fermilab Tevatron Collider in p (p) over bar collisions at root s = 1.96 TeV. In the channel LQLQ -> eqv(e)q', where q, q' are u or d quarks, no significant excess of data over background is observed, and we set a 95% C. L. lower limit of 326 GeV on the LQ mass, assuming equal probabilities of LQ decays to eq and v(e)q'.

  • 239.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Flavor Changing Neutral Currents in Decays of Top Quarks2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 701, nr 3, s. 313-320Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a search for flavor changing neutral currents in decays of top quarks. The analysis is based on a search for (,=e,μ) final states using 4.1 fb−1 of integrated luminosity of collisions at . We extract limits on the branching ratio B(tZq) (q=u,c quarks), assuming anomalous tuZ or tcZ couplings. We do not observe any sign of such anomalous coupling and set a limit of B<3.2% at 95% C.L.

  • 240.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for flavor changing neutral currents via quark–gluon couplings in single top quark production using 2.3 fb−1 of collisions2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 693, nr 2, s. 81-87Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present a search for flavor changing neutral currents via quark–gluon couplings in a sample of single top quark final states corresponding to 2.3 fb−1 of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider. We select events containing a single top quark candidates with an additional jet, and obtain separation between signal and background using Bayesian neural networks. We find consistency between background expectation and observed data, and set limits on flavor changing neutral current gluon couplings of the top quark to up quarks (tgu) and charm quarks (tgc). The cross section limits at the 95% C.L. are σtgu<0.20 pb and σtgc<0.27 pb. These correspond to limits on the top quark decay branching fractions of B(tgu)<2.0×10−4 and B(tgc)<3.9×10−3.

  • 241.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Higgs Boson Production in Dilepton and Missing Energy Final States with 5.4 fb$^{-1}$ of $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, nr 6, s. 061804-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A search for the standard model Higgs boson is presented using events with two charged leptons and large missing transverse energy selected from 5.4  fb-1 of integrated luminosity in pp̅ collisions at √s=1.96  TeV collected with the D0 detector at the Fermilab Tevatron collider. No significant excess of events above background predictions is found, and observed (expected) upper limits at 95% confidence level on the rate of Higgs boson production are derived that are a factor of 1.55 (1.36) above the predicted standard model cross section at mH=165  GeV.

  • 242.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Neutral Higgs Bosons in the Multi-b-jet Topology in 5.2fb$^{-1}$ of $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2011Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 698, nr 2, s. 97-104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    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−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.

  • 243.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Neutral Minimal Supersymmetric Standard Model Higgs Bosons Decaying to Tau Pairs Produced in Association with b Quarks in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2011Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 107, nr 12, s. 121801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report results from a search for neutral Higgs bosons produced in association with b quarks using data recorded by the D0 experiment at the Fermilab Tevatron Collider and corresponding to an integrated luminosity of 7.3 fb(-1). This production mode can be enhanced in several extensions of the standard model (SM) such as in its minimal supersymmetric extension (MSSM) at high tan beta. We search for Higgs bosons decaying to tau pairs with one tau decaying to a muon and neutrinos and the other to hadrons. The data are found to be consistent with SM expectations, and we set upper limits on the cross section times branching ratio in the Higgs boson mass range from 90 to 320 GeV/c(2). We interpret our result in the MSSM parameter space, excluding tan beta values down to 25 for Higgs boson masses below 170 GeV/c(2).

  • 244.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for New Fermions ('Quirks') at the Fermilab Tevatron Collider2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 105, s. 211803-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report results of a search for particles with anomalously high ionization in events with a high transverse energy jet and large missing transverse energy in 2.4  fb-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron pp̅ collider. Production of such particles (quirks) is expected in scenarios with extra QCD-like SU(N) sectors, and this study is the first dedicated search for such signatures. We find no evidence of a signal and set a lower mass limit of 107, 119, and 133 GeV for the mass of a charged quirk with strong dynamics scale Λ in the range from 10 keV to 1 MeV and N=2, 3, and 5, respectively.

  • 245.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Next-to-Minimal Supersymmetric Higgs Bosons in the $h\to aa\to\mu\mu \mu\mu$, $\mu\mu \tau\tau$ Channels Using $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, s. 061801-Artikkel i tidsskrift (Fagfellevurdert)
  • 246.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Pair Production of First-Generation Leptoquarks in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV}2009Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 681, s. 224-232Artikkel i tidsskrift (Fagfellevurdert)
  • 247.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Randall-Sundrum Gravitons in the Dielectron and Diphoton Final States with 5.4 fb-1 of Data from $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2010Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, s. 241802-Artikkel i tidsskrift (Fagfellevurdert)
  • 248.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Resonant Pair Production to Neutral Long-Lived Particles Decaying to $b\bar{b}$ in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2009Inngår i: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, s. 071801-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     

     

     

  • 249.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Scalar Bottom Quarks and Third-Generation Leptoquarks in $p\bar{p}$ Collisions at $\sqrt{s}=1.96$ TeV2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 693, nr 2, s. 95-101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We report the results of a search for pair production of scalar bottom quarks () and scalar third-generation leptoquarks (LQ3) in 5.2 fb−1 of collisions at the D0 experiment of the Fermilab Tevatron Collider. Scalar bottom quarks are assumed to decay to a neutralino () and a b quark, and we set 95% C.L. lower limits on their production in the (, ) mass plane such as for and for . The leptoquarks are assumed to decay to a tau neutrino and a b quark, and we set a 95% C.L. lower limit of 247 GeV on the mass of a charge-1/3 third-generation scalar leptoquark.

  • 250.
    Åsman, Barbro
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Search for Single Top Quarks in the Tau+Jets Channel Using 4.8 fb-1 of $p\bar{p}$ Collision Data2010Inngår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 690, s. 5-14Artikkel i tidsskrift (Fagfellevurdert)
2345678 201 - 250 of 449
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