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  • 2951. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Observation of Single Top-Quark Production2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 9, p. 092001-Article in journal (Refereed)
    Abstract [en]

    We report observation of the electroweak production of single top quarks in pp collisions at s=1.96 TeV based on 2.3 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider. Using events containing an isolated electron or muon and missing transverse energy, together with jets originating from the fragmentation of b quarks, we measure a cross section of sigma(pp -> tb+X,tqb+X)=3.94 +/- 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5x10(-7), corresponding to a 5.0 standard deviation significance for the observation.

  • 2952. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for a Resonance Decaying into WZ Boson Pairs in p(p)over-bar Collisions2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 6, p. 061801-Article in journal (Refereed)
    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 p (p) over bar collider. The WZ pairs are reconstructed through their decays into three charged leptons (l = e, mu). A total of 9 data events is observed in good agreement with the background prediction. We set 95% C.L. limits on the W'WZ 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.

  • 2953. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for associated production of charginos and neutralinos in the trilepton final state using 2.3 fb(-1) of data2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 680, no 1, p. 34-43Article in journal (Refereed)
    Abstract [en]

    We report the results of a search for associated production of charginos and neutralinos using a data set corresponding to an integrated luminosity of 2.3 fb(-1) collected with the Demptyset experiment during Run II of the Tevatron proton-antiproton collider. Final states containing three charged leptons and missing transverse energy are probed for a signal from supersymmetry with four dedicated trilepton event selections. No evidence for a signal is observed, and we set limits on the product of production cross section and leptonic branching fraction. Within minimal supergravity, these limits translate into bounds on m(0) and m(1/2) that are well beyond existing limits.

  • 2954. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for charged Higgs bosons in decays of top quarks2009In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 80, no 5, p. 051107-Article in journal (Refereed)
    Abstract [en]

    We present a search for charged Higgs bosons in decays of top quarks, in the mass range 80 < m(H+) < 155 GeV, assuming the subsequent decay H(+) -> tau(+)nu(tau) (and its charge conjugate). Using 0.9 fb(-1) of lepton + jets data collected with the D0 detector at the Fermilab Tevatron p (p) over bar collider, operating at a center of mass energy root s = 1.96 TeV, we find no evidence for a H(+/-) signal. Hence we exclude branching ratios B(t -> H(+)b) > 0.24 for m(H+) 80 GeV and B(t -> H(+)b) > 0.19 for m(H+) = 155 GeV at the 95% C.L.

  • 2955. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for charged Higgs bosons in top quark decays2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 682, no 3, p. 278-286Article in journal (Refereed)
    Abstract [en]

    We present a search for charged Higgs bosons in top quark decays. We analyze the e + jets, mu + jets, ee, e mu, mu mu, tau e and tau mu final states from top quark pair production events, using data from about 1 fb (1) of integrated luminosity recorded by the DO 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 tau lepton and a tau neutrino and a third one where both decays appear. We extract limits on the branching ratio B(t -> H(+)b) for all these models. We use two methods, one where the t (t) over bar production cross section is fixed, and one where the cross section is fitted simultaneously with B(t -> H(+)b). Based on the extracted limits, we exclude regions in the charged Higgs boson mass and tan beta parameter space for different scenarios of the minimal supersymmetric standard model.

  • 2956. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for CP violation in B(s)(0) -> mu(+) D(s)(-) X decays in p(p)over-bar collisions at root s=1.96 TeV2010In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 82, no 1, p. 012003-Article in journal (Refereed)
    Abstract [en]

    We have performed a search for CP violation in a sample of B(s)(0) -> mu(+)D(s)(-)X decays corresponding to 5 fb(-1) of proton-antiproton collisions collected by the D0 detector in Run II at the Fermilab Tevatron Collider. New physics in B(s)(0) mixing could contribute a significant CP violating weak phase, which would be observed as a difference in the decay-time distribution for B(s)(0) -> (B) over bar (0)(s) oscillated states versus that for (B) over bar (0)(s) -> B(s)(0). A fit to the decay-time distributions of the B(s)(0)/(B) over bar (0)(s) candidates yields the flavor-specific asymmetry as a(fs)(s) = [-1.7 +/- 9.1(stat)(-1.5)(+1.4)(syst) x 10(-3), which excludes CP violation due to new physics within the experimental sensitivity.

  • 2957. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Zverev, E. G.
    et al.,
    Search for Dark Photons from Supersymmetric Hidden Valleys2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 8, p. 081802-Article in journal (Refereed)
    Abstract [en]

    We search for a new light gauge boson, a dark photon, with the D0 experiment. In the model we consider, supersymmetric partners are pair produced and cascade to the lightest neutralinos that can decay into the hidden sector state plus either a photon or a dark photon. The dark photon decays through its mixing with a photon into fermion pairs. We therefore investigate a previously unexplored final state that contains a photon, two spatially close leptons, and large missing transverse energy. We do not observe any evidence for dark photons and set a limit on their production.

  • 2958. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    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 TeV2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 6, p. 061804-Article in journal (Refereed)
    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 p ($) over bar collisions at root 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 m(H) = 165 GeV.

  • 2959. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Zverev, E. G.
    et al.,
    Search for Next-to-Minimal Supersymmetric Higgs Bosons in the h -> aa ->mu mu mu mu, mu mu tau tau Channels Using pp Collisions at s=1.96 TeV2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 6, p. 061801-Article in journal (Refereed)
    Abstract [en]

    We report on a first search for production of the lightest neutral CP-even Higgs boson (h) in the next-to-minimal supersymmetric standard model, where h decays to a pair of neutral pseudoscalar Higgs bosons (a), using 4.2 fb(-1) of data recorded with the D0 detector at Fermilab. The a bosons are required to either both decay to mu(+)mu(-) or one to mu(+)mu(-) and the other to tau(+)tau(-). No significant signal is observed, and we set limits on its production as functions of M(a) and M(h).

  • 2960. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for pair production of first-generation leptoquarks in p(p)over-bar collisions at root s=1.96 TeV2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 681, no 3, p. 224-232Article in journal (Refereed)
    Abstract [en]

    A search for pair production of first-generation leptoquarks (LQ) is performed with data collected by the DO experiment in p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron Collider. In a sample of data corresponding to similar to 1 fb(-1) the search has been performed on the final states with two electrons and two jets or one electron, two jets and missing transverse energy. We find our data consistent with standard model expectations. The results are combined with those found in a previous analysis of events with two jets and missing transverse energy to obtain scalar LQ mass limits. We set 95% C.L. lower limits on a scalar LQ mass of 299 GeV. 284 GeV and 216 GeV for beta = 1, beta = 0.5 and beta = 0.02 respectively, where beta is the LQ branching ratio in the eq channel. This improves the results obtained with a lower luminosity sample from Run II of the Tevatron. Lower limits on vector LQ masses with different couplings from 357 GeV to 464 GeV for beta = 0.5 are also set using this analysis.

  • 2961. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for Resonant Diphoton Production with the D0 Detector2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 23, p. 231801-Article in journal (Refereed)
    Abstract [en]

    We present a search for a narrow resonance in the inclusive diphoton final state using similar to 2.7 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron p (p) over bar Collider. We observe good agreement between the data and the background prediction, and set the first 95% C. L. upper limits on the production cross section times the branching ratio for decay into a pair of photons for resonance masses between 100 and 150 GeV. This search is also interpreted in the context of several models of electroweak symmetry breaking with a Higgs boson decaying into two photons.

  • 2962. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for Resonant Pair Production of Neutral Long-Lived Particles Decaying to b(b)over-bar in p(p)over-bar Collisions at root s=1.96 TeV2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 103, no 7, p. 071801-Article in journal (Refereed)
    Abstract [en]

    We report on a first search for resonant pair production of neutral long-lived particles (NLLP) which each decay to a b (b) over bar pair, using 3.6 fb(-1) of data recorded with the D0 detector at the Fermilab Tevatron collider. We search for pairs of displaced vertices in the tracking detector at radii in the range 1.6-20 cm from the beam axis. No significant excess is observed above background, and upper limits are set on the production rate in a hidden-valley benchmark model for a range of Higgs boson masses and NLLP masses and lifetimes.

  • 2963. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for single top quarks in the tau plus jets channel using 4.8 fb(-1) of p(p)over-bar collision data2010In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 690, no 1, p. 5-14Article in journal (Refereed)
    Abstract [en]

    We present the first direct search for single top quark production using reconstructed tau leptons in the final state. The search is based on 4.8 fb(-1) of integrated luminosity collected in p (p) over bar collisions at root s= 1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. We select events with a final state including an isolated tau lepton. missing transverse energy, two or three jets, one or two of them being identified as b quark jet. We use a multivariate technique to discriminate signal from background. The number of events observed in data in this final state is consistent with the signal plus background expectation. We set in the tau + jets channel an upper limit on the single top quark cross section of 7.3 pb at the 95% C.L. This measurement allows a gain of 4% in expected sensitivity for the observation of single top production when combining it with electron + jets and muon + jets channels already published by the DO Collaboration with 2.3 fb(-1) of data. We measure a combined cross section of 3.84(-0.83)(+0.89) pb, which is the most precise measurement to date.

  • 2964. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for squark production in events with jets, hadronically decaying tau leptons and missing transverse energy at root s=1.96 TeV2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 680, no 1, p. 24-33Article in journal (Refereed)
    Abstract [en]

    A search for supersymmetric partners of quarks is performed in the topology of multijet events accompanied by at least one tau lepton decaying hadronically and large missing transverse energy. Approximately 1 fb(-1) of p (p) over bar collision data from the Fermilab Tevatron Collider at a center of mass energy of 1.96 TeV recorded by the D detector is analyzed. Results are combined with the previously published DO inclusive search for squarks and gluinos. No evidence of physics beyond the Standard Model is found and lower limits on the squark mass up to 410 GeV are derived in the framework of minimal supergravity with tan beta = 15, A(0) = -2m(0) and mu < 0, in the region where decays to tau leptons dominate. Gaugino masses m(1/2) are excluded up to 172 GeV.

  • 2965. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for the Associated Production of a b Quark and a Neutral Supersymmetric Higgs Boson that Decays into tau Pairs2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 15, p. 151801-Article in journal (Refereed)
    Abstract [en]

    We report results from a search for production of a neutral Higgs boson in association with a b quark. We search for Higgs decays to tau pairs with one tau subsequently decaying to a muon and the other to hadrons. The data correspond to 2: 7 fb(-1) of p (p) over bar collisions recorded by the D0 detector at.. root s = 1.96 TeV. The data are found to be consistent with background predictions. The result allows us to exclude a significant region of parameter space of the minimal supersymmetric model.

  • 2966. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for the Standard Model Higgs Boson in Tau Final States2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 25, p. 251801-Article in journal (Refereed)
    Abstract [en]

    We present a search for the standard model Higgs boson using hadronically decaying tau leptons, in 1 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron pp collider. We select two final states: tau(+/-) plus missing transverse energy and b jets, and tau(+)tau(-) plus jets. These final states are sensitive to a combination of associated W/Z boson plus Higgs boson, vector boson fusion, and gluon-gluon fusion production processes. The observed ratio of the combined limit on the Higgs production cross section at the 95% C.L. to the standard model expectation is 29 for a Higgs boson mass of 115 GeV.

  • 2967. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for the Standard Model Higgs Boson in the ZH -> v(v)over-barb(b)over-bar Channel in 5.2 fb(-1) of p(p)over-bar Collisions at root s=1.96 TeV2010In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 7, p. 071801-Article in journal (Refereed)
    Abstract [en]

    A search is performed for the standard model Higgs boson in 5.2 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV, collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered is a pair of b jets and large missing transverse energy, as expected from p (p) over bar -> ZH -> v (v) over barb (b) over bar production. The search is also sensitive to the WH -> lvb (b) over bar channel when the charged lepton is not identified. For a Higgs boson mass of 115 GeV, a limit is set at the 95% C.L. on the cross section multiplied by branching fraction for [p (p) over bar -> (Z/W)H](H -> b (b) over bar) that is a factor of 3.7 larger than the standard model value, consistent with the factor of 4.6 expected.

  • 2968. Abazov, V. M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Evidence of WW and WZ Production with lepton plus jets Final States in pp Collisions at root s=1.96 TeV2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 16, p. 161801-Article in journal (Refereed)
    Abstract [en]

    We present first evidence for WW+WZ production in lepton+jets final states at a hadron collider. The data correspond to 1.07 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron in pp collisions at root s=1.96 TeV. The observed cross section for WW+WZ production is 20.2 +/- 4.5 pb, consistent with the standard model and more precise than previous measurements in fully leptonic final states. The probability that background fluctuations alone produce this excess is < 5.4x10(-6), which corresponds to a significance of 4.4 standard deviations.

  • 2969. Abazov, V. M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Measurement of gamma + b + X and gamma + c + X Production Cross Sections in pp > Collisions at s=1.96 TeV2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 19, p. 192002-Article in journal (Refereed)
    Abstract [en]

    First measurements of the differential cross sections d(3)sigma/(dp(T)(gamma)dy(gamma)dy(jet)) for the inclusive production of a photon in association with a heavy quark (b, c) jet are presented, covering photon transverse momenta 30 < p(T)(gamma)< 150 GeV, photon rapidities |y(gamma)|< 1.0, jet rapidities |y(jet)|< 0.8, and jet transverse momenta p(T)(jet)> 15 GeV. The results are based on an integrated luminosity of 1 fb(-1) in pp collisions at s=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider. The results are compared with next-to-leading order perturbative QCD predictions.

  • 2970. Abazov, V. M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et. al.,
    Measurement of the Z gamma -> nu(nu)over-bar gamma Production Cross Section and Limits on Anomalous ZZ gamma and Z gamma gamma Couplings in p(p)over-bar Collisions at root s=1.96 TeV2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 20, p. 201802-Article in journal (Refereed)
    Abstract [en]

    We present the first observation of the Z gamma -> nu(nu) over bar gamma process at the Fermilab Tevatron at 5.1 standard deviations significance, based on 3.6 fb(-1) of integrated luminosity collected with the D0 detector at the Fermilab Tevatron p (p) over bar Collider at root s = 1.96 TeV. The measured Z gamma production cross section multiplied by the branching fraction of Z -> nu(nu) over bar is 32 +/- 9(stat + syst) +/- 2(lumi) fb for the photon E(T) > 90 GeV. It is in agreement with the standard model prediction of 39 +/- 4 fb. We set limits on anomalous trilinear Z gamma gamma and ZZ gamma gauge boson couplings, most of which are the most restrictive to date.

  • 2971. Abazov, V. M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for admixture of scalar top quarks in the t(t)over-bar lepton + jets final state at root s=1.96 TeV2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 674, no 1, p. 4-10Article in journal (Refereed)
    Abstract [en]

    A search for pair production of the lightest supersymmetric partner of the top quark, (t) over tilde (1), is performed in the lepton + jets channel using 0.9 fb(-1) of data collected by the D circle divide experiment. Kinematic differences between (t) over tilde (1)(t) over tilde (1) and the dominant top quark pair production background are used to separate the two processes. First limits from Run II of the Fermilab Tevatron Collider for the scalar top quark decaying to a chargino and a b quark ((t) over tilde1 -> (chi) over tilde (+)(1)b) are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.

  • 2972. Abazov, V. M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for Anomalous Top-Quark Couplings with the D0 Detector2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 9, p. 092002-Article in journal (Refereed)
    Abstract [en]

    Anomalous Wtb couplings modify the angular correlations of the top-quark decay products and change the single top-quark production cross section. We present limits on anomalous top-quark couplings by combining information from W boson helicity measurements in top-quark decays and anomalous coupling searches in the single top-quark final state. We set limits on right-handed vector couplings as well as left-handed and right-handed tensor couplings based on about 1 fb(-1) of data collected by the D0 experiment.

  • 2973. Abazov, V. M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for Long-Lived Charged Massive Particles with the D0 Detector2009In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 102, no 16, p. 161802-Article in journal (Refereed)
    Abstract [en]

    We search for long-lived charged massive particles using 1.1 fb(-1) of data collected by the D0 detector at the Fermilab Tevatron pp Collider. Time-of-flight information is used to search for pair produced long-lived tau sleptons, gauginolike charginos, and Higgsino-like charginos. We find no evidence of a signal and set 95% C.L. cross section upper limits for staus, which vary from 0.31 to 0.04 pb for stau masses between 60 and 300 GeV. We also set lower mass limits of 206 GeV (171 GeV) for pair produced charged gauginos (Higgsinos).

  • 2974. Abazov, V. M.
    et al.
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et. al.,
    Search for the lightest scalar top quark in events with two leptons in p(p)over-bar collisions at root s=1.96 TeV2009In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 675, no 3-4, p. 289-296Article in journal (Refereed)
    Abstract [en]

    We report results of a search for the pair production of the lightest supersymmetric partner of the top quark, (t) over bar (1), using a data set corresponding to an integrated luminosity of 1 fb(-1) collected by the D circle divide detector at a p (p) over bar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron collider. Both scalar top quarks are assumed to decay into a b quark, a charged lepton and a scalar neutrino. The search is performed in the electron Plus muon and dielectron final states. The signal topology consists of two isolated leptons, missing transverse energy, and jets. We find no evidence for this process and exclude regions of parameter space in the framework of the minimal supersymmetric standard model.

  • 2975. Abazov, V. M.
    et al.
    Åsman, B.
    Uppsala University.
    Bélanger-Champagne, Camille
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, High Energy Physics.
    Clément, C.
    Uppsala University.
    Gollub, N.
    Uppsala University.
    Hansson, P.
    Uppsala University.
    Strandberg, S.
    Uppsala University.
    Zverev, E. G.
    Measurement of the top quark mass in the lepton+jets channel using the ideogram method2007In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 75, no 9, p. 092001-Article in journal (Refereed)
    Abstract [en]

    A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from p (p) over bar collisions at root s=1.96 TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between t (t) over bar signal and background from other physics processes and to improve the assignment of the observed jets to the quarks in the t (1) over bar hypothesis. We extract a multiplicative jet energy scale (JES) factor in situ, greatly reducing the systematic effect related to the jet energy measurement. In a data sample with an integrated luminosity of 425 pb(-1), we observe 230 candidate events, with an estimated background of 123 events, and measure m(t)=173.7 +/- 4.4(stat+JES)(-2.0)(+2.1)(syst) GeV. This result represents the first application of the ideogram technique to the measurement of the top quark mass in lepton+jets events.

  • 2976. Abazov, V. M.
    et al.
    Åsman, B.
    Uppsala University.
    Clément, C.
    Uppsala University.
    Gollub, N.
    Uppsala University.
    Hansson, P.
    Uppsala University.
    Strandberg, S.
    Uppsala University.
    Zverev, E. G.
    Measurement of the W boson helicity in top quark decays at D02007In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 75, no 3, p. 031102-Article in journal (Refereed)
    Abstract [en]

    We present a measurement of the fraction f(+) of right-handed W bosons produced in top quark decays, based on a candidate sample of tt events in the l + jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb(-1) collected by the D0 detector at the Fermilab Tevatron pp Collider at root s = 1.96 TeV. We reconstruct the decay angle theta* for each lepton. By comparing the cos theta* distribution from the data with that for the expected background and signal for various values of f(+) (where we assume that the fraction of longitudinally-polarized W bosons has the standard model value of 0.70), we find f(+) = 0.056 +/- 0.080 (stat) +/- 0.057 (syst) (f(+) < 0.23 at 95% C. L.), consistent with the standard model prediction of f(+) = 3.6 X 10(-4).

  • 2977. Abazov, V. M.
    et al.
    Åsman, B.
    Uppsala University.
    Clément, C.
    Uppsala University.
    Gollub, N.
    Uppsala University.
    Lager, S.
    Uppsala University.
    Strandberg, J.
    Uppsala University.
    Zverev, E. G.
    Multivariate searches for single top quark production with the D0 detector2007In: Physical Review D. Particles and fields, ISSN 0556-2821, E-ISSN 1089-4918, Vol. 75, no 9, p. 092007-Article in journal (Refereed)
    Abstract [en]

    We present a search for electroweak production of single top quarks in the s-channel (p (p) over bar -> t (b) over bar +X) and t-channel (p (p) over bar -> tq (b) over bar +X) modes. We have analyzed 230 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy of root s=1.96 TeV. No evidence for a single top quark signal is found. We set 95% confidence level upper limits on the production cross sections, based on binned likelihoods formed from a neural network output. The observed (expected) limits are 6.4 pb (4.5 pb) in the s-channel and 5.0 pb (5.8 pb) in the t-channel.

  • 2978. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Combined D0 measurements constraining the CP-violating phase and width difference in the B-s(0) system2007In: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 76, no 5, p. 057101-1-057101-7Article in journal (Refereed)
    Abstract [en]

    We combine the D0 measurement of the width difference between the light and heavy B-s(0) mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the B-s(0)-> J/psi phi decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific B-s(0) lifetime, we obtain Delta Gamma(s)equivalent to(Gamma(L)-Gamma(H))=0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=0.70(-0.47)(+0.39) or Delta Gamma(s)=-0.13 +/- 0.09 ps(-1) and vertical bar phi(s)vertical bar=2.44(-0.39)(+0.47). The data sample corresponds to an integrated luminosity of 1.1 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron Collider.

  • 2979. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Direct observation of the strange b baryon Xi(-)(b)2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 5, p. 052001-1-052001-8Article in journal (Refereed)
    Abstract [en]

    We report the first direct observation of the strange b baryon Xi(-)(b)(Xi) over bar (+)(b)). We reconstruct the decay Xi(-)(b)-->J/psi Xi(-), with J/psi-->mu(+)mu(-), and Xi(-)-->Lambda pi(-)-->p pi(-)pi(-) in p (p) over bar collisions at root s = 1.96 TeV. Using 1.3 fb(-1) of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat)(-0.4)(+1.9)(syst) Xi(-)(b) candidates at a mass of 5.774 +/- 0.011(stat) +/- 0.015(syst) GeV. The significance of the observed signal is 5.5 sigma, equivalent to a probability of 3.3 x 10(-8) of it arising from a background fluctuation. Normalizing to the decay Lambda(b)-->J/psi Lambda, we measure the relative rate sigma(Xi(-)(b))xB(Xi(-)(b)-->J/psi Xi)/ sigma(Lambda(b))xB(Lambda(b)-->J/psi Lambda) = 0.28 +/- 0.09(stat)(-0.08)(+0.09)(syst).

  • 2980. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Evidence for production of single top quarks and first direct measurement of vertical bar V-tb vertical bar2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 18, p. 181802-1-181802-8Article in journal (Refereed)
    Abstract [en]

    The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron < p(p)over bar > collider. Using a 0.9 fb(-1) dataset, we apply a multivariate analysis to separate signal from background and measure sigma(< p(p)over bar >-> tb+X,tqb+X)=4.9 +/- 1.4 pb. The probability to measure a cross section at this value or higher in the absence of a signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa matrix element that describes the Wtb coupling and find 0.68 <vertical bar V-tb vertical bar <= 1 at 95% C.L. within the standard model.

  • 2981. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Lifetime difference and CP-violating phase in the B-s(0) system2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 12, p. 121801-1-121801-7Article in journal (Refereed)
    Abstract [en]

    From an analysis of the decay B-s(0)-> J/psi phi, we obtain the width difference between the light and heavy mass eigenstates Delta Gamma equivalent to(Gamma(L)-Gamma(H))=0.17 +/- 0.09(stat)+/- 0.02(syst) ps(-1) and the CP-violating phase phi(s)=-0.79 +/- 0.56(stat)(-0.01)(+0.14)(syst). Under the hypothesis of no CP violation (phi(s)equivalent to 0), we obtain 1/Gamma=tau/(B-s(0))=1.52 +/- 0.08(stat)(-0.03)(+0.01)(syst) ps and Delta Gamma=0.12(-0.10)(+0.08)(stat)+/- 0.02(syst) ps(-1). The data sample corresponds to an integrated luminosity of about 1.1 fb(-1) accumulated with the D0 detector at the Fermilab Tevatron collider. This is the first direct measurement of the CP-violating mixing phase in the B-s(0) system.

  • 2982. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the charge asymmetry in semileptonic B-s(0) decays2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 15, p. 151801-1-151801-7Article in journal (Refereed)
    Abstract [en]

    We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic B-s(0) decays A(SL)(s,unt) by comparing the decay rate of B-s(0) -> mu(+) D-s(-) nu X, where D-s(-) -> phi pi(-) and phi -> K+K-, with the charge-conjugate (B) over bar (0)(s) decay rate. This sample was selected from 1: 3 fb(-1) of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain A(SL)(s,unt) = [1.23 +/- 0.97(stat) +/- 0.17(syst)] x 10(-2). Assuming that Delta m(s)/(Gamma) over bar (s) >> 1, this result can be translated into a measurement of the CP-violating phase in B-s(0) mixing: Delta Gamma(s)/Delta m(s) tan phi(s) = [2.45 +/- 1.93(stat) +/- 0.35(syst)] x 10(-2).

  • 2983. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the Lambda(0)(b) lifetime using semileptonic decays2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 18, p. 182001-1-182001-7Article in journal (Refereed)
    Abstract [en]

    We report a measurement of the Lambda(0)(b) lifetime using a sample corresponding to 1.3 fb(-1) of data collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron collider. The Lambda(0)(b) baryon is reconstructed via the decay Lambda(0)(b)->mu(nu) over bar Lambda X-+(c). Using 4437 +/- 329 signal candidates, we measure the Lambda(0)(b) lifetime to be tau(Lambda(0)(b))=1.290(-0.110)(+0.119)(stat)(-0.091)(+0.087)(syst) ps, which is among the most precise measurements in semileptonic Lambda(0)(b) decays. This result is in good agreement with the world average value.

  • 2984. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the Lambda(b) lifetime in the exclusive decay Lambda(b)-> J/psi Lambda2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 14, p. 142001-1-142001-7Article in journal (Refereed)
    Abstract [en]

    We have measured the Lambda(b) lifetime using the exclusive decay Lambda(b)-> J/psi Lambda, based on 1.2 fb(-1) of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda(b) decays, where the J/psi and Lambda are identified via the decays J/psi ->mu(+)mu(-) and Lambda -> p pi, we measured the Lambda(b) lifetime to be tau(Lambda(b))=1.218(-0.115)(+0.130)(stat)+/- 0.042(syst) ps. We also measured the B-0 lifetime in the decay B-0 -> J/psi(mu(+)mu(-))K-S(0)(pi(+)pi(-)) to be tau(B-0)=1.501(-0.074)(+0.078)(stat)+/- 0.050(syst) ps, yielding a lifetime ratio of tau(Lambda(b))/tau(B-0)=0.811(-0.087)(+0.096)(stat)+/- 0.034(syst).

  • 2985. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the p(p)over-bar -> t(t)over-bar + X production cross section at root s=1.96 TeV in the fully hadronic decay channel2007In: Physical Review D - Particles, Fields, Gravitation and Cosmology, ISSN 1550-7998, Vol. 76, no 7, p. 072007-1-072007-11Article in journal (Refereed)
    Abstract [en]

    A measurement of the top quark pair production cross section in proton antiproton collisions at an interaction energy of root s=1.96 TeV is presented. This analysis uses 405 +/- 25 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider. Fully hadronic t (t) over bar decays with final states of six or more jets are separated from the multijet background using secondary vertex tagging and a neural network. The t (t) over bar cross section is measured as sigma(t (t) over bar)=4.5(-1.9)(+2.0)(stat)(-1.1)(+1.4)(syst)+/- 0.3(lumi) pb for a top quark mass of m(t)=175 GeV/c(2).

  • 2986. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the shape of the boson rapidity distribution for p(p)over-bar -> Z/gamma(*)-> e(+)e(-)+X events produced at root s of 1.96 TeV2007In: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 76, no 1, p. 012003-1-012003-10Article in journal (Refereed)
    Abstract [en]

    We present a measurement of the shape of the boson rapidity distribution for p (p) over bar -> Z/gamma(*)-> e(+)e(-)+X events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71 < M-ee < 111 GeV and uses 0.4 fb(-1) of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of next-to-next-to-leading order (NNLO) QCD are found to agree well with the data over the full rapidity range.

  • 2987. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the top quark mass in the lepton plus jets channel using the ideogram method2007In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 75, no 9, p. 092001-1-092001-21Article in journal (Refereed)
    Abstract [en]

    A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from p (p) over bar collisions at root s=1.96 TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between t (t) over bar signal and background from other physics processes and to improve the assignment of the observed jets to the quarks in the t (1) over bar hypothesis. We extract a multiplicative jet energy scale (JES) factor in situ, greatly reducing the systematic effect related to the jet energy measurement. In a data sample with an integrated luminosity of 425 pb(-1), we observe 230 candidate events, with an estimated background of 123 events, and measure m(t)=173.7 +/- 4.4(stat+JES)(-2.0)(+2.1)(syst) GeV. This result represents the first application of the ideogram technique to the measurement of the top quark mass in lepton+jets events.

  • 2988. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.96 TeV using kinematic characteristics of lepton plus jets events2007In: PHYSICAL REVIEW D, ISSN 1550-7998, Vol. 76, no 9, p. 092007-1-092007-22Article in journal (Refereed)
    Abstract [en]

    We present a measurement of the top quark pair production cross section in p (p) over bar collisions at root s=1.96 TeV utilizing 425 pb(-1) of data collected with the D0 detector at the Fermilab Tevatron Collider. We consider the final state of the top quark pair containing one high-p(T) electron or muon and at least four jets. We exploit specific kinematic features of t (t) over bar events to extract the cross section. For a top quark mass of 175 GeV, we measure sigma(t (t) over bar)=6.4(-1.2)(+1.3)(stat)+/- 0.7(syst)+/- 0.4(lum) pb, in good agreement with the standard model prediction.

  • 2989. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions using dilepton events2007In: Physical Review D - Particles, Fields, Gravitation and Cosmology, ISSN 1550-7998, Vol. 76, no 5, p. 052006-1-052006-28Article in journal (Refereed)
    Abstract [en]

    We present a measurement of the t (t) over bar pair production cross section in p (p) over bar collisions at root s=1.96 TeV utilizing approximately 425 pb(-1) of data collected with the D0 detector. We consider decay channels containing two high p(T) charged leptons (either e or mu) from leptonic decays of both top-daughter W bosons. These were gathered using four sets of selection criteria, three of which required that a pair of fully identified leptons (i.e., e mu, ee, or mu mu) be found. The fourth approach imposed less restrictive criteria on one of the lepton candidates and required that at least one hadronic jet in each event be tagged as containing a b quark. For a top quark mass of 175 GeV, the measured cross section is 7.4 +/- 1.4(stat)+/- 1.0(syst) pb and for the current Tevatron average top quark mass of 170.9 GeV, the resulting value of the cross section is 7.8 +/- 1.8(stat+syst) pb.

  • 2990. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Properties of l=1 B-1 and B*(2) Mesons2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 17, p. 172001-1-172001-7Article in journal (Refereed)
    Abstract [en]

    This Letter presents the first strong evidence for the resolution of the excited B mesons B-1 and B-2(*) as two separate states in fully reconstructed decays to B+(*())pi(-). The mass of B-1 is measured to be 5720.6 +/- 2.4 +/- 1.4 MeV/c(2) and the mass difference Delta M between B-2* and B-1 is 26.2 +/- 3.1 +/- 0: 9 MeV/c(2), giving the mass of the B-2* as 5746.8 +/- 2.4 +/- 1.7 MeV/c(2). The production rate for B-1 and B-2* mesons is determined to be a fraction (13.9 +/- 1.9 +/- 3.2)% of the production rate of the B+ meson.

  • 2991. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for a Higgs boson produced in association with a Z boson in p(p)over-bar collisions2007In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 655, no 5-6, p. 209-216Article in journal (Refereed)
    Abstract [en]

    We describe a search for the Standard Model Higgs boson with a mass of 105 GeV/c(2) to 145 GeV/c(2) in data corresponding to an integrated luminosity of approximately 450 pb(-1) collected with the D phi detector at the Fermilab Tevatron p (p) over bar collider at a center-of-mass energy of 1.96 TeV. The Higgs boson is required to be produced in association with a Z boson, and the Z boson is required to decay to either electrons or muons with the Higgs boson decaying to a b (b) over bar pair. The data are well described by the expected background, leading to 95% confidence level cross section upper limits sigma (p (p) over bar -> ZH) x B(H -> b (b) over bar) in the range of 3.1 pb to 4.4 pb.

  • 2992. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for production of single top quarks via tcg and tug flavor-changing-neutral-current couplings2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 19, p. 191802-1-191802-8Article in journal (Refereed)
    Abstract [en]

    We search for the production of single top quarks via flavor-changing-neutral-current couplings of a gluon to the top quark and a charm (c) or up (u) quark. We analyze 230 pb(-1) of lepton+jets data from p (p) over tilde collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters kappa(c)(g)/Lambda and kappa(u)(g)/Lambda, where kappa(g) define the strength of tcg and tug couplings, and Lambda defines the scale of new physics. The limits at 95% C.L. are kappa(c)(g)/Lambda < 0.15 TeV-1 and kappa(u)(g)/Lambda < 0.037 TeV-1.

  • 2993. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for single production of scalar leptoquarks in p(p)over-bar collisions decaying into muons and quarks with the D0 detector2007In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 647, no 2-3, p. 74-81Article in journal (Refereed)
    Abstract [en]

    We report on a search for second generation leptoquarks (LQ(2)) which decay into a muon plus quark in (p) over barp collisions at a center-of-mass energy of root s = 1.96 TeV in the DO detector using an integrated luminosity of about 300 pb(-1). No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction into a quark and a muon was determined for second generation scalar leptoquaiks as a function of the leptoquark mass. This result has been combined with a previously published DO search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark-muon-quark coupling, lambda. Assuming lambda = 1, lower limits on the mass of a second generation scalar leptoquark coupling to a u quark and a muon are m(LQ2) > 274 GeV and m(LQ2) > 226 GeV for beta = 1 and beta = 1/2, respectively.

  • 2994. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for stopped gluinos from p(p)over-bar collisions at root s=1.96 TeV2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 13, p. 131801-1-131801-8Article in journal (Refereed)
    Abstract [en]

    Long-lived, heavy particles are predicted in a number of models beyond the standard model of particle physics. We present the first direct search for such particles' decays, occurring up to 100 h after their production and not synchronized with an accelerator bunch crossing. We apply the analysis to the gluino (g), predicted in split supersymmetry, which after hadronization can become charged and lose enough momentum through ionization to come to rest in dense particle detectors. Approximately 410 pb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected with the D0 detector during Run II of the Fermilab Tevatron collider are analyzed in search of such "stopped gluinos" decaying into a gluon and a neutralino ((chi) over tilde (0)(1)). Limits are placed on the (gluino cross section) x (probability to stop) x [BR((g) over tilde -> g (chi) over tilde (0)(1))] as a function of the gluino and (chi) over tilde (0)(1) masses, for gluino lifetimes from 30 mu s-100 h.

  • 2995. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for techniparticles in e plus jets events at D02007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 98, no 22, p. 221801-1-221801-7Article in journal (Refereed)
    Abstract [en]

    We search for the technicolor process p(p) over bar ->rho(T)/omega(T)-> W pi(T) in events containing one electron and two jets, in data corresponding to an integrated luminosity of 390 pb(-1), recorded by the D0 experiment at the Fermilab Tevatron. Technicolor predicts that technipions pi(T) decay dominantly into b(b) over bar, b(c) over bar, or (b) over barc, depending on their charge. In these events b and c quarks are identified by their secondary decay vertices within jets. Two analysis methods based on topological variables are presented. Since no excess above the standard model prediction was found, the result is presented as an exclusion in the pi(T) vs rho(T) mass plane for a given set of model parameters.

  • 2996. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for the pair production of scalar top quarks in the acoplanar charm jet final state in p(p)over-bar collisions at root s=1.96 TeV2007In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 645, no 2-3, p. 119-127Article in journal (Refereed)
    Abstract [en]

    A search for the pair production of scalar top quarks, (t) over tilde, has been performed in 360 pb(-1) of data from pp collisions at a center-of-mass energy of 1.96 TeV, collected by the D phi detector at the Fermilab Tevatron collider. The (t) over tilde decay mode considered is (t) over tilde -> c (chi) over tilde (0)(1), where (chi) over tilde (0)(1) is the lightest supersymmetric particle. The topology analyzed therefore consists of a pair of acoplanar heavy-flavor jets with missing transverse energy. The data and standard model expectation are in agreement, anda 95% C.L. exclusion domain in the (m((t) over tilde), m((chi) over tilde1)(0)) plane has been determined, extending the domain excluded by previous experiments.

  • 2997. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for third-generation scalar leptoquarks in p(p)over-bar collisions at root s=1.96 TeV2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 6, p. 061801-1-061801-7Article in journal (Refereed)
    Abstract [en]

    We report on a search for charge-1/3 third-generation leptoquarks (LQ) produced in p (p) over bar collisions at root s =1.96 TeV using the D0 detector at Fermilab. Third-generation leptoquarks are assumed to be produced in pairs and to decay to a tau neutrino and a b quark with branching fraction B. We place upper limits on sigma(p (p) over bar -> LQ (LQ) over bar )B-2 as a function of the leptoquark mass M-LQ. Assuming B=1, we exclude at the 95% confidence level third-generation scalar leptoquarks with M-LQ < 229 GeV.

  • 2998. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Study of the decay B-s(0)->(DsDs(*))-D-(*)2007In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 99, no 24, p. 241801-1-241801-7Article in journal (Refereed)
    Abstract [en]

    We report a study of the decay B-s(0)->(DsDs(*))-D-(*) using a data sample corresponding to 1.3 fb(-1) of integrated luminosity collected by the D0 experiment in 2002-2006 during run II of the Fermilab Tevatron collider. One D-s((*)) meson was partially reconstructed in the decay D-s ->phi mu nu, and the other D-s((*)) meson was identified using the decay D-s ->phi pi where no attempt was made to distinguish D-s and D-s(*) states. For the branching fraction Br(B-s(0)->(DsDs(*))-D-(*)) we obtain a 90% C.L. range [0.002,0.080] and central value 0.039(-0.017)(+0.019)(stat)(-0.015)(+0.016)(syst). This was subsequently used to make the most precise estimate of the width difference Delta Gamma(CP)(s) in the B-s(0)-(B)over bar(s)(0) system: Delta Gamma(CP)(s)/Gamma(s)=0.079(-0.035)(+0.038)(stat)(-0.030)(+0.031)(syst).

  • 2999. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Z gamma production and limits on anomalous ZZ gamma and Z gamma gamma couplings in pp collisions at root s=1.96 TeV2007In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 653, no 5-6, p. 378-386Article in journal (Refereed)
    Abstract [en]

    We present a study of eey and mu mu gamma events using 1109 (1009) pb-(1) of data in the electron (muon) channel, respectively. These data were collected with the DO detector at the Fermilab Tevatron pp collider at Is = 1.96 TeV. Having observed 453 (515) candidates in the eey (jtAy) final state, we measure the Z gamma production cross section for a photon with transverse energy ET > 7 GeV, separation between the photon and leptons Delta Rey > 0.7, and invariant mass of the di-lepton pair Mee > 30 GeV/(2)(c), to be 4.96 0.30(stat. + syst.) zE 0.30(lumi.) pb, in agreement with the Standard Model prediction of 4.74 0.22 pb. This is the most precise Zy cross section measurement at a hadron collider. We set limits on anomalous trilinear Zyy and ZZy gauge boson couplings of -0.085 < h(30)(y) < 0.084, -0.0053 < h(40)(y) < 0.0054 and -0.083 < h(30)(Z) < 0.082, 30 40 30 -0.0053 < h(40)(Z) < 0.0054 at the 95% C.L. for the form-factor scale A = 1.2 TeV.

  • 3000. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Strandberg, Jonas
    Zverev, E.G.
    et al.,
    Measurement of the ratios of the Z/gamma*+ >= n jet production cross sections to the total inclusive Z/gamma* cross section in p(p)over-bar collisions at root s=1.96 TeV2008In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 658, no 4, p. 112-119Article in journal (Refereed)
    Abstract [en]

    We present a study of events with Z bosons and associated jets produced at the Fermilab Tevatron collider in p p collisions at a center of mass energy of 1.96 TeV The data sample consists of nearly 14000 Z/gamma* -> e(+)e(-) candidates corresponding to an integrated luminosity of 0.4 fb(-1) collected with the D circle divide detector. Ratios of the Z/gamma*+ >= n jet cross sections to the total inclusive Z/gamma* cross section have been measured for n = 1-4 jets, and found to be in good agreement with a next-to-leading order QCD calculation and with a tree-level QCD prediction with parton shower simulation and hadronization.

57585960616263 2951 - 3000 of 1199131
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