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  • 151. Aad, G.
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for strong gravity signatures in same-sign dimuon final states using the ATLAS detector at the LHC2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 709, nr 4-5, s. 322-340Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb(-1) of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.

  • 152. Aad, G.
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Searches for supersymmetry with the ATLAS detector using final states with two leptons and missing transverse momentum in root s=7 TeV proton-proton collisions2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 709, nr 3, s. 137-157Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results of three searches are presented for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons, e or mu. The analysis uses a data sample collected during the first half of 2011 that corresponds to a total integrated luminosity of 1 fb(-1) of root s = 7 TeV proton-proton collisions recorded with the ATLAS detector at the Large Hadron Collider. Opposite-sign and same-sign dilepton events are separately studied, with no deviations from the Standard Model expectation observed. Additionally, in opposite-sign events, a search is made for an excess of same-flavour over different-flavour lepton pairs. Effective production cross sections in excess of 9.9 fb for opposite-sign events containing supersymmetric particles with missing transverse momentum greater than 250 GeV are excluded at 95% CL For same-sign events containing supersymmetric particles with missing transverse momentum greater than 100 GeV, effective production cross sections in excess of 14.8 fb are excluded at 95% CL The latter limit is interpreted in a simplified electroweak gaugino production model excluding chargino masses up to 200 GeV, under the assumption that slepton decay is dominant.

  • 153. Aad, G.
    et al.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al.,
    Measurement of the W -> tau nu(tau) cross section in pp collisions at root s=7 TeV with the ATLAS experiment ATLAS Collaboration2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 706, nr 4/5, s. 276-294Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The cross section for the production of W bosons with subsequent decay W -> tau nu(tau) is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a proton-proton center-of-mass energy of root s = 7 TeV and corresponds to an integrated luminosity of 34 pb(-1). The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the W -> tau nu(tau) branching ratio is measured to be sigma(tot)(W -> tau nu tau) = 11.1 +/- 0.3 (stat) +/- 1.7 (syst) +/- 0.4 (lumi) nb.

  • 154. Aad, Georges
    et al.
    Jovicevic, Jelena
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Kuwertz, Emma
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Remi
    LAPP, CNRS/IN2P3 and Université de Savoie, Annecy-le-Vieux, France.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for heavy vector-like quarks coupling to light quarks in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 712, nr 1-2, s. 22-39Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This letter presents a search for singly produced vector-like quarks, Q, coupling to light quarks, q. The search is sensitive to both charged current (CC) and neutral current (NC) processes, p p --> Q q --> W q q' and p p --> Q q --> Z q q' with a leptonic decay of the vector gauge boson. In 1.04/fb of data taken in 2011 by the ATLAS experiment at a center-of-mass energy sqrt(s) = 7 TeV, no evidence of such heavy vector-like quarks is observed above the expected Standard Model background. Limits on the heavy vector-like quark production cross section times branching ratio as a function of mass m_Q are obtained. For a coupling kappa_(qQ) = v/m_Q, where v is the Higgs vacuum expectation value, 95% C.L. lower limits on the mass of a vector-like quark are set at 900 GeV and 760 GeV from CC and NC processes, respectively.

  • 155. Aad, Georges
    et al.
    Kuwertz, Emma
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Remi
    LAPP, CNRS/IN2P3 and Université de Savoie, Annecy-le-Vieux, France.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for contact interactions in dilepton events from pp collisions at sqrt(s) = 7 TeV with the ATLAS detector2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 712, nr 1-2, s. 40-58Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This Letter presents a search for contact interactions in the dielectron and dimuon channels using data from proton-proton collisions produced by the LHC at sqrt(s) = 7 TeV and recorded by the ATLAS detector. The data sample, collected in 2011, corresponds to an integrated luminosity of 1.08 and 1.21 fb^-1 in the e+ e- and mu+ mu- channels, respectively. No significant deviations from the standard model are observed. Using a Bayesian approach with a prior flat in 1/Lambda^2, the following 95% CL lower limits are placed on the energy scale of llqq contact interactions: Lambda^- > 10.1 TeV (Lambda^+ > 9.4 TeV) in the electron channel and Lambda^- > 8.0 TeV (Lambda^+ > 7.0 TeV) in the muon channel for constructive (destructive) interference in the left-left isoscalar contact interaction model. Limits are also provided for a prior flat in 1/Lambda^4.

  • 156. Aad, Georges
    et al.
    Kuwertz, Emma
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for first generation scalar leptoquarks in pp collisions at root s=7 TeV with the ATLAS detector2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 709, nr 3, s. 158-176Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report a search for first generation scalar leptoquarks using 1.03 fb(-1) of proton-proton collisions data produced by the Large Hadron Collider at root s = 7 TeV and recorded by the ATLAS experiment. Leptoquarks are sought via their decay into an electron or neutrino and a quark, producing events with two oppositely charged electrons and at least two jets, or events with an electron, missing transverse momentum and at least two jets. Control data samples are used to validate background predictions from Monte Carlo simulation. In the signal region, the observed event yields are consistent with the background expectations. We exclude at 95% confidence level the production of first generation scalar leptoquark with masses m(LQ) < 660 (607) GeV when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).

  • 157. Aad, Georges
    et al.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al.
    Measurement of the cross section for the production of a W boson in association with b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 707, nr 5, s. 418-437Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A measurement is presented of the cross section for the production of a W boson with one or two jets, of which at least one must be a b-jet, in pp collisions at root s = 7 TeV. Production via top decay is not included in the signal definition. The measurement is based on 35 pb(-1) of data collected with the ATLAS detector at the LHC. The W + b-jet cross section is defined for jets reconstructed with the anti-k(t) clustering algorithm with transverse momentum above 25 GeV and rapidity within +/-2.1. The b-jets are identified by reconstructing secondary vertices. The fiducial cross section is measured both for the electron and muon decay channel of the W boson and is found to be 10.2 +/- 1.9(stat) +/- 2.6(syst) pb for one lepton flavour. The results are compared with next-to-leading order QCD calculations, which predict a cross section smaller than, though consistent with, the measured value.

  • 158. Aad, Georges
    et al.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    A measurement of the ratio of the W and Z cross sections with exactly one associated jet in pp collisions at root s=7 TeV with ATLAS2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 708, nr 3-5, s. 221-240Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ratio of production cross sections of the W and Z bosons with exactly one associated jet is presented as a function of jet transverse momentum threshold. The measurement has been designed to maximise cancellation of experimental and theoretical uncertainties, and is reported both within a particle-level kinematic range corresponding to the detector acceptance and as a total cross-section ratio. Results are obtained with the ATLAS detector at the LHC in pp collisions at a centre-of-mass energy of 7 TeV using an integrated luminosity of 33 pb(-1). The results are compared with perturbative leading-order, leading-log, and next-to-leading-order QCD predictions, and are found to agree within experimental and theoretical uncertainties. The ratio is measured for events with a single jet with p(T) > 30 GeV to be 8.73 +/- 0.30(stat) +/- 0.40(syst) in the electron channel, and 8.49 +/- 0.23(stat) +/- 0.33(syst) in the muon channel.

  • 159. Aad, Georges
    et al.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Measurement of the pseudorapidity and transverse momentum dependence of the elliptic flow of charged particles in lead-lead collisions at root s(NN)=2.76 TeV with the ATLAS detector2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 707, nr 3-4, s. 330-348Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This Letter describes the measurement of elliptic flow of charged particles in lead-lead collisions at root s(NN) = 2.76 TeV using the ATLAS detector at the Large Hadron Collider (LHC). The results are based on an integrated luminosity of approximately 7 mu b(-1). Elliptic flow is measured over a wide region in pseudorapidity, vertical bar eta vertical bar < 2.5, and over a broad range in transverse momentum, 0.5 < p(T) < 20 GeV. The elliptic flow parameter nu(2) is obtained by correlating individual tracks with the event plane measured using energy deposited in the forward calorimeters. As a function of transverse momentum, nu(2)(p(T)) reaches a maximum at p(T) of about 3 GeV. then decreases and becomes weakly dependent on p(T) above 7-8 GeV. Over the measured pseudorapidity region, nu(2) is found to be only weakly dependent on eta, with less variation than observed at lower beam energies. The results are discussed in the context of previous measurements at lower collision energies, as well as recent results from the LHC.

  • 160. Aad, Georges
    et al.
    Lafaye, Remi
    Cern.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Measurement of the top quark pair production cross-section with ATLAS in the single lepton channel2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 711, nr 3-4, s. 244-263Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A measurement of the production cross-section for top quark pairs (t (t) over bar) in pp collisions at root s = 7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in the single lepton topology by requiring an electron or muon, large missing transverse momentum and at least three jets. With a data sample of 35 pb(-1), two different multivariate methods, one of which uses b-quark jet identification while the other does not, use kinematic variables to obtain cross-section measurements of sigma(t (t) over bar) = 187 +/- 11(stat.)(-17)(+18)(syst.) +/- 6(lumi.) pb and sigma(t (t) over bar) = 173 +/- 17(stat.)(-16)(+18)(syst.) +/- 6(lumi.) pb respectively. The two measurements are in agreement with each other and with QCD calculations. The first measurement has a better a priori sensitivity and constitutes the main result of this Letter.

  • 161. Aad, Georges
    et al.
    Lafaye, Remi
    Cern.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for diphoton events with large missing transverse momentum in 1 fb(-1) of 7 TeV proton-proton collision data with the ATLAS detector ATLAS Collaboration2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 710, nr 4-5, s. 519-537Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A search for diphoton events with large missing transverse momentum has been performed using 1.07 fb^-1 of proton-proton collision data at sqrt(s) = 7 TeV recorded with the ATLAS detector. No excess of events was observed above the Standard Model prediction and 95% Confidence Level (CL) upper limits are set on the production cross section for new physics: sigma < (22-129) fb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, sigma < (27-91) fb in the context of a minimal model of gauge-mediated supersymmetry breaking (SPS8) and (15-27) fb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 805 GeV, for bino masses above 50 GeV, is set on the GGM gluino mass. Lower limits of 145 TeV and 1.23 TeV are set on the SPS8 breaking scale Lambda and on the UED compactification scale 1/R, respectively. These limits provide the most stringent tests of these models to date.

  • 162. Aad, Georges
    et al.
    Lafaye, Remi
    Univ Savoie.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Zwalinski, L.
    et al.,
    Search for new physics in the dijet mass distribution using 1 fb(-1) of pp collision data at root s=7 TeV collected by the ATLAS detector2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 708, nr 1-2, s. 37-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Invariant mass distributions of jet pairs (dijets) produced in LHC proton-proton collisions at a centre-of-mass energy root s = 7 TeV have been studied using a data set corresponding to an integrated luminosity of 1.0 fb(-1) recorded in 2011 by ATLAS. Dijet masses up to similar to 4 TeV are observed in the data, and no evidence of resonance production over background is found. Limits are set at 95% C.L. for several new physics hypotheses: excited quarks are excluded for masses below 299 TeV, axigluons are excluded for masses below 3.32 TeV. and colour octet scalar resonances are excluded for masses below 1.92 TeV.

  • 163. Aad, Georges
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Remi
    Univ Savoie, Annecy Le Vieux, France.
    Zwalinski, L.
    et, al.
    Measurement of the top quark pair production cross section in pp collisions at sqrt(s) = 7 TeV in dilepton final states with ATLAS2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 707, nr 5, s. 459-477Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A measurement of the production cross section of top quark pairs (t (t) over bar) in proton-proton collisions at a center-of-mass energy of 7 TeV recorded with the ATLAS detector at the Large Hadron Collider is reported. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. Using a data sample corresponding to an integrated luminosity of 35 pb(-1), a t (t) over bar production cross section sigma(t (t) over bar) = 177 +/- 20(stat.) +/- 14(syst.) +/- 7(lum.) pb is measured for an assumed top quark mass of m(t) = 172.5 GeV. A second measurement requiring at least one jet identified as coming from a b quark yields a comparable result, demonstrating that the dilepton final states are consistent with being accompanied by b-quark jets. These measurements are in good agreement with Standard Model predictions.

  • 164. Aad, Georges
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Remi
    Duke Univ, Dept Phys, Durham, NC 27706 USA.
    Zwalinski, L.
    et al.,
    Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at sqrt(s) = 7 TeV with the ATLAS detector2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 707, nr 5, s. 438-458Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This Letter presents measurements of the differential cross-sections for inclusive electron and muonproduction in proton–proton collisions at a centre-of-mass energy of√s = 7 TeV, using data collectedby the ATLAS detector at the LHC. The muon cross-section is measured as a function of pT in the range4 < pT < 100 GeV and within pseudorapidity |η| < 2.5. In addition the electron and muon cross-sectionsare measured in the range 7 < pT < 26 GeV and within |η| < 2.0, excluding 1.37 < |η| < 1.52. Integratedluminosities of 1.3 pb−1and 1.4 pb−1are used for the electron and muon measurements, respectively.After subtraction of the W/Z/γ∗contribution, the differential cross-sections are found to be in goodagreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLOcalculations with NLL high-pT resummation, and to be sensitive to the effects of NLL resummation.

  • 165. Aad, Georges
    et al.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Remi
    Univ Savoie, Annecy Le Vieux, France.
    Zwalinski, L.
    et, al.
    Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 707, nr 5, s. 478-496Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results of a search for new, heavy particles that decay at a significant distance from theirproduction point into a final state containing charged hadrons in association with a high-momentummuon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV andan integrated luminosity of 33 pb−1collected in 2010 by the ATLAS detector operating at the LargeHadron Collider. Production of such particles is expected in various scenarios of physics beyond thestandard model. We observe no signal and place limits on the production cross-section of supersymmetricparticles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presentedfor different squark and neutralino masses, enabling extension of the limits to a variety of other models.

  • 166. Aad, Georges
    et al.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Remi
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al.
    Measurement of the W to tau nu Cross Section in pp Collisions at sqrt(s) = 7 TeV with the ATLAS experiment2012Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. B706, s. 276-294Artikel i tidskrift (Refereegranskat)
  • 167. Aad, Georges
    et al.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lund-Jensen, Bengt
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Lafaye, Rémi
    CNRS, IN2P3, LAPP, Annecy Le Vieux, France.
    et al.,
    Search for new phenomena with the monojet and missing transverse momentum signature using the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions2011Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 705, nr 4, s. 294-312Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A search for new phenomena in events featuring a high energy jet and large missing transverse momentum in proton-proton collisions at root s = 7 TeV is presented using a dataset corresponding to an integrated luminosity of 33 pb(-1) recorded with the ATLAS detector at the Large Hadron Collider. The number of observed events is consistent with the Standard Model prediction. This result is interpreted in terms of limits on a model of Large Extra Dimensions.

  • 168. Abazov, V. M.
    et al.
    Abbott, B.
    Abolins, M.
    Acharya, B. S.
    Adams, M.
    Adams, T.
    Aguilo, E.
    Ahsan, M.
    Alexeev, G. D.
    Alkhazov, G.
    Alton, A.
    Alverson, G.
    Alves, G. A.
    Anastasoaie, M.
    Ancu, L. S.
    Andeen, T.
    Andrieu, B.
    Anzelc, M. S.
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    Xie, Y.
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    Yu, J.
    Zeitnitz, C.
    Zelitch, S.
    Zhao, T.
    Zhou, B.
    Zhu, J.
    Zielinski, M.
    Zieminska, D.
    Zieminski, A.
    Zivkovic, L.
    Zutshi, V.
    Zverev, E. G.
    Search for pair production of second generation scalar leptoquarks2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 671, nr 2, s. 224-232Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on a search for the pair production of second generation scalar leptoquarks (LQ) in p (p) over bar collisions at the center of mass energy root s- = 1.96 TeV using a data set corresponding to an integrated luminosity of 1.0 fb(-1) collected with the D empty set experiment at the Fermilab Tevatron Collider. Topologies arising from the LQ (LQ) over bar -> mu q nu q and LQ (LQ) over bar -> mu q mu q decay modes are investigated. No excess of data over the standard model prediction is observed and upper limits on the leptoquark pair production cross section are derived at the 95% C.L. as a function of the leptoquark mass and the branching fraction beta for the decay LQ -> mu q. These are interpreted as lower limits on the leptoquark mass as a function of beta. For beta = 1 (0.5), scalar second generation leptoquarks with masses up to 316 GeV (270 GeV) are excluded.

  • 169. Abazov, V. M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Measurement of differential Z/gamma* plus jet plus X cross sections in p(p)over-bar collisions at root S=1.96 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 669, nr 5, s. 278-286Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present new measurements of differential cross sections for Z/gamma* (-> mu mu) + jet + X production in a 1 fb(-1) data sample collected with the DO detector in p (p) over bar collisions at root s = 1.96 TeV. Results include the first measurements differential in the Z/gamma* transverse momentum and rapidity, as well as new measurements differential in the leading jet transverse momentum and rapidity. Next-to-leading order perturbative QCD predictions are compared to the measurements, and reasonable agreement is observed, except in the region of low Z/gamma* transverse momentum. Predictions from two event generators based on matrix elements and parton showers, and one pure parton shower event generator are also compared to the measurements. These show significant overall normalization differences to the data and have varied success in describing the shape of the distributions.

  • 170. Abazov, V. M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Measurement of the differential cross section for the production of an isolated photon with associated jet in p(p)over-bar collisions at root s=1.96 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 666, nr 5, s. 435-445Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The process p (p) over bar -> gamma + jet + X is studied using 1.0 fb(-1) of data collected by the DO detector at the Fermilab Tevatron p (p) over bar collider at a center-of-mass energy root s = 1.96 TeV. Photons are reconstructed in the central rapidity region vertical bar y(gamma)vertical bar < 1.0 with transverse momenta in the range 30 < p(T)(gamma) < 400 GeV while jets are reconstructed in either the central vertical bar y(jet)vertical bar < 0.8 or forward 1.5 < vertical bar y(jet)vertical bar < 2.5 rapidity intervals with P(T)(jet) > 15 GeV. The differential cross section d(3 sigma)/dp(T)(gamma) dy(gamma) dy(jet) is measured as a function of p(T)(gamma) in four regions, differing by the relative orientations of the photon and the jet in rapidity. Ratios between the differential cross sections in each region are also presented. Next-to-leading order QCD predictions using different parameterizations of parton distribution functions and theoretical scale choices are compared to the data. The predictions do not simultaneously describe the measured normalization and p(T)(gamma) dependence of the cross section in the four measured regions.

  • 171. Abazov, V. M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Measurement of the ratio of the p(p)over-bar -> W + c-jet cross section to the inclusive p(p)over-bar -> W + jets cross section2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 666, nr 1, s. 23-30Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a measurement of the fraction of inclusive W +jets events produced with net charm quantum number 11, denoted W + c-jet, in p collisions at root s = 1.96 TeV using approximately 1 fb(-1) of data collected by the DO detector at the Fermilab Tevatron Collider. We identify the W +jets events via the leptonic W boson decays. Candidate W + c-jet events are selected by requiring a jet containing a muon in association with a reconstructed W boson and exploiting the charge correlation between this muon and W boson decay lepton to perform a nearly model-independent background subtraction. We measure the fraction of W + c-jet events in the inclusive W +jets sample for jet PT > 20 GeV and pseudorapidity |eta| < 2.5 to be 0.074 +/- 0.019(stat.) +/-(0.012)(0.014) (syst.), in agreement with theoretical predictions. The probability that background fluctuations could produce the observed fraction of W + c-jet events is estimated to be 2.5 x 10(-4), which corresponds to a 3.5 sigma statistical significance.

  • 172. Abazov, V. M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for scalar leptoquarks and T-odd quarks in the acoplanar jet topology using 2.5 fb(-1) of p(p)over-bar collision data at root s=1.96 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 668, nr 5, s. 357-363Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A search for new physics in the acoplanar jet topology has been performed in 2.5 fb(-1) of data from p (p) over bar collisions at root s = 1.96 TeV, recorded by the DO detector at the Fermilab Tevatron Collider. The numbers of events with exactly two acoplanar jets and missing transverse energy are in good agreement with the Standard Model expectations. The result of this search has been used to set a lower mass limit of 205 GeV at the 95% C.L. on the mass of a scalar leptoquark when this particle decays exclusively into a quark and a neutrino. In the framework of the Little Higgs model with T-parity, limits have also been obtained on the T-odd quark mass as a function of the T-odd photon mass.

  • 173. Abazov, V. M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for scalar top quarks in the acoplanar charm jets and missing transverse energy final state in p(p)over-bar collisions at root s=1.96 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 665, nr 1, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a search for the pair production of scalar top quarks, (t) over tilde, using 995 pb(-1) of data collected in p (p) over bar collisions with the Dempty set detector at the Fermilab Tevatron Collider at root s = 1.96 TeV. Both scalar top quarks are assumed to decay into a charm quark and a neutralino ((chi) over tilde (0)(1)), where (chi) over tilde (0)(1) is the lightest supersymmetric particle. This leads to a final state with two acoplanar charm jets and missing transverse energy. We find the yield of such events to be consistent with the standard model expectation, and exclude sets of (t) over tilde and (chi) over tilde (0)(1) masses at the 95% C.L. that substantially extend the domain excluded by previous searches.

  • 174. Abazov, V. M.
    et al.
    Gollub, Nils
    Strandberg, Jonas
    University of Chicago.
    Zverev, E.G.
    et al.,
    Search for t(t)over-bar resonances in the lepton plus jets final state in p(p)over-bar collisions at root s=1.96 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 668, nr 2, s. 98-104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a search for a narrow-width heavy resonance decaying into top quark pairs (X -> t (t) over bar) in p (p) over bar collisions at root s = 1.96 TeV using approximately 0.9 fb(-1) of data collected with the DO detector at the Fermilab Tevatron Collider. This analysis considers t (t) over bar candidate events in the lepton plus jets channel with at least one identified b jet and uses the t (t) over bar invariant mass distribution to search for evidence of resonant production. We find no evidence for a narrow resonance X decaying to t (t) over bar. Therefore, we set upper limits on sigma x center dot B(X -> t (t) over bar) for different hypothesized resonance masses using a Bayesian approach. For a Topcolor-assisted technicolor model, the existence of a leptophobic Z' boson with mass M(Z') < 700 GeV and width Gamma(Z') = 0.012M(Z') can be excluded at the 95% C.L.

  • 175. Abazov, V. M.
    et al.
    Strandberg, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    et, al.
    Combined measurements of anomalous charged trilinear gauge-boson couplings from diboson production in p-pbar collisions at sqrt(s)=1.96 TeV2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present measurements of the anomalous WWgamma and WWZ trilinear gauge couplings from a combination of four diboson production and decay channels using data collected by the D0 detector at the Fermilab Tevatron Collider. These results represent the first high statistics combination of limits across different diboson production processes at the Tevatron and use data corresponding to an integrated luminosity of approximately 1 fb^-1. When respecting SU(2)_L x U(1)_Y symmetry, we measure central values and 68% C.L. allowed intervals of kappa_gamma=1.07^+0.16_-0.20, lambda =0.00^+0.05_-0.04 and g_1^Z=1.05 +/- 0.06. We present the most stringent measurements to date for the W boson magnetic dipole and electromagnetic quadrupole moments of mu_W=2.02^+0.08_-0.09 (e/2M_W) and q_W=-1.00 +/- 0.09 (e/M^2_W), respectively.

  • 176. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Dependence of the t(t)over-bar production cross section on the transverse momentum of the top quark2010Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 693, nr 5, s. 515-521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a measurement of the differential cross section for t (t) over bar events produced in p (p) over bar collisions at root s = 1.96 TeV as a function of the transverse momentum (p(T)) of the top quark. The selected events contain a high-p(T) lepton (l), a large imbalance in p(T). four or more jets with at least one candidate for a b jet, and correspond to 1 fb(-1) of integrated luminosity recorded with the D0 detector. Objects in the event are associated through a constrained kinematic fit to the t (t) over bar -> WbW (b) over bar -> lvbq (q) over bar' (b) over bar process. Results from next and next-to-next-to-leading-order perturbative QCD calculations agree with the measured differential cross section. Comparisons are also provided to predictions from Monte Carlo event generators using QCD calculations at different levels of precision.

  • 177. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Measurement of the t-channel single top quark production cross section2010Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 682, nr 4-5, s. 363-369Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The DO Collaboration reports direct evidence for electroweak production of single top quarks through the t-channel exchange of a virtual W boson. This is the first analysis to isolate an individual single top quark production channel. We select events containing an isolated electron or muon, missing transverse energy, and two, three or four jets from 2.3 fb(-1) of p (p) over bar collisions at the Fermilab Tevatron Collider. One or two of the jets are identified as containing a b hadron. We combine three multivariate techniques optimized for the t-channel process to measure the t- and s-channel cross sections simultaneously. We measure cross sections of 3.14(-0.80)(+0.94) pb for the t-channel and 1.05 +/- 0.81 pb for the s-channel. The measured t-channel result is found to have a significance of 4.8 standard deviations and is consistent with the standard model prediction.

  • 178. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Measurement of the t(t)over-bar production cross section and top quark mass extraction using dilepton events in p(p)over-bar collisions2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 679, nr 3, s. 177-185Artikel i tidskrift (Refereegranskat)
    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 using approximately 1 fb(-1) collected with the DO detector. We consider decay channels containing two high p(T) charged leptons where one lepton is identified as an electron or a muon while the other lepton can be an electron, a muon or a hadronically decaying tau lepton. For a mass of the top quark of 170 GeV, the measured cross section is 7.5(-1.0)(+1.0)(stat)(-0.6)(+0.7)(syst)(-0.5)(+0.6)(lumi) pb. Using l tau events only, we measure: sigma(t (t) over bar) x B(t (t) over bar -> l tau b (b) over bar) = 0.13(-0.08)(+0.09)(stat)(-0.06)(+0.06)(syst)(-0.02)(+0.02)(lumi) pb. Comparing the measured cross section as a function of the mass of the top quark with a partial next-to-next-to leading order Quantum Chroniodynamics theoretical prediction, we extract a mass of the top quark of 171.5(-8.8)(+9-9) GeV, in agreement with direct measurements.

  • 179. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Measurement of Z/gamma* plus jet plus X angular distributions in p(p)over-bar collisions at root s=1.96 TeV2010Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 682, nr 4-5, s. 370-380Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first measurements at a hadron collider of differential cross sections for Z/gamma* + jet + X production in Delta phi(Z. jet), vertical bar Delta y(Z, jet)vertical bar and vertical bar y(boost)(Z + jet)vertical bar. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.

  • 180. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Measurements of differential cross sections of Z/gamma* plus jets plus X events in p(p)over-bar collisions at root s=1.96 TeV2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 678, nr 1, s. 45-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present cross section measurements for Z/gamma* + jets + X production, differential in the transverse momenta of the three leading jets. The data sample was collected with the DO detector at the Fermilab Tevatron p (p) over bar collider at a center-of-mass energy of 1.96 TeV and corresponds to an integrated luminosity of 1 fb(-1). Leading and next-to-leading order perturbative QCD predictions are compared with the measurements. and agreement is found within the theoretical and experimental uncertainties. We also make comparisons with the predictions of four event generators. Two parton-shower-based generators show significant shape and normalization differences with respect to the data. In contrast, two generators combining tree-level matrix elements with a parton shower give a reasonable description of the shapes observed in data. but the predicted normalizations show significant differences with respect to the data, reflecting large scale Uncertainties. For specific choices of scales, the normalizations for either generator can be made to agree with the measurements.

  • 181. 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 data2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 680, nr 1, s. 34-43Artikel i tidskrift (Refereegranskat)
    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.

  • 182. Abazov, V. M.
    et al.
    Strandberg, Jonas
    Univ Michigan, Ann Arbor.
    Zverev, E. G.
    et al.,
    Search for charged Higgs bosons in top quark decays2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 682, nr 3, s. 278-286Artikel i tidskrift (Refereegranskat)
    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.

  • 183. 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 TeV2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 681, nr 3, s. 224-232Artikel i tidskrift (Refereegranskat)
    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.

  • 184. 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 data2010Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 690, nr 1, s. 5-14Artikel i tidskrift (Refereegranskat)
    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.

  • 185. 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 TeV2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 680, nr 1, s. 24-33Artikel i tidskrift (Refereegranskat)
    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.

  • 186. 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 TeV2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 674, nr 1, s. 4-10Artikel i tidskrift (Refereegranskat)
    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.

  • 187. 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 TeV2009Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 675, nr 3-4, s. 289-296Artikel i tidskrift (Refereegranskat)
    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.

  • 188. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    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 collisions2007Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 655, nr 5-6, s. 209-216Artikel i tidskrift (Refereegranskat)
    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.

  • 189. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    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 detector2007Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 647, nr 2-3, s. 74-81Artikel i tidskrift (Refereegranskat)
    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.

  • 190. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    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 TeV2007Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 645, nr 2-3, s. 119-127Artikel i tidskrift (Refereegranskat)
    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.

  • 191. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    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 TeV2007Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 653, nr 5-6, s. 378-386Artikel i tidskrift (Refereegranskat)
    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.

  • 192. 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 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 658, nr 4, s. 112-119Artikel i tidskrift (Refereegranskat)
    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.

  • 193. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    A combined search for the standard model Higgs boson at root S=1.96 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 663, nr 1-2, s. 26-36Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present new results of the search for WH --> lvb (b) over bar production in p (p) over bar collisions at a center-of-mass energy of root S = 1.96 TeV, based on a dataset with integrated luminosity of 0.44 fb(-1). We combine these new results with previously published searches by the DO collaboration, for WH and ZH production analyzed in the E(T)b (b) over bar final state, for ZH (--> l(+)l(-)b (b) over bar) production, for WH (-->. WWW) production, and for H (--> W W) direct production. No signal-like excess is observed either in the W H analysis or in the combination of all D0 Higgs boson analyses. We set 95% C.L. (expected) upper limits on sigma(p (p) over bar --> WH) x B(H --> b (b) over bar) ranging from 1.6 (2.2) ph to 1.9 (3.3) pb for Higgs boson masses between 105 and 145 GeV, to be compared to the theoretical prediction of 0.13 pb for a Standard Model (SM) Higgs boson with mass in m(H) = 115 GeV. After combination with the other DO Higgs boson searches, we obtain for in H = 115 GeV an observed (expected) limit 8.5 (12.1) times higher than the SM predicted Higgs boson production cross section. For m(H) = 160 GeV, the corresponding observed (expected) ratio is 10.2 (9.0).

  • 194. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for squarks and gluinos in events with jets and missing transverse energy using 2.1 fb(-1) of p(p)over-bar collision data at root s=1.96 TeV - D phi Collaboration2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 660, nr 5, s. 449-457Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A data sample corresponding to an integrated luminosity of 2.1 fb(-1) collected by the D phi detector at the Fermilab Tevatron Collider was analyzed to search for squarks and gluinos produced in p (p) over bar collisions at a center-of-mass energy of 1.96 TeV. No evidence for the production of such particles was observed in topologies involving jets and missing transverse energy, and 95% C.L. lower limits of 379 GeV and 308 GeV were set on the squark and gluino masses, respectively, within the framework of minimal supergravity with tan beta = 3, A(0) = 0, and mu < 0. The corresponding previous limits are improved by 54 GeV and 67 GeV.

  • 195. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Strandberg, Sara
    Zverev, E. G.
    et al.,
    Search for supersymmetry in di-photon final states at root s=1.96 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 659, nr 5, s. 856-863Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report results of a search for supersymmetry (SUSY) with gauge-mediated symmetry breaking in di-photon events collected by the DO experiment at the Fermilab Tevatron Collider in 2002-2006. In 1.1 fb(-1) of data, we find no significant excess beyond the background expected from the standard model and set the most stringent lower limits to date for a standard benchmark model on the lightest neutralino and chargino masses of 125 GeV and 229 GeV, respectively, at 95% confidence.

  • 196. Abazov, V. M.
    et al.
    Åsman, Barbro
    Bélanger-Champagne, Camille
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Strandberg, Sara
    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 TeV2008Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 659, nr 3, s. 500-508Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Data collected by the DO detector at a p (p) over bar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider have been used to search for pair production of the lightest supersymmetric partner of the top quark decaying into bl (nu) over tilde. The search is performed in the ll' = e mu and mu mu final states. No evidence for this process has been found in data samples of approximately 400 pb(-1). The domain in the [M((t) over tilde (1)), M((nu) over tilde)] plane excluded at the 95% C.L. is substantially extended by this search.

  • 197. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Gollub, Nils
    Hansson, Per
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
    Strandberg, Jonas
    Strandberg, Sara
    Zverevak, E. G.
    et al.,
    Measurement of the top quark mass in the dilepton channel2007Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 655, nr 1-2, s. 7-14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a measurement of the top quark mass in the dilepton channel based on approximately 370 pb(-1) of data collected by the DO experiment during Run R of the Fermilab Tevatron collider. We employ two different methods to extract the top quark mass. We show that both methods yield consistent results using ensemble tests of events generated with the DO Monte Carlo simulation. We combine the results from the two methods to obtain a top quark mass m(t) = 178.1 +/- 8.2 GeV. The statistical uncertainty is 6.7 GeV and the systematic uncertainty is 4.8 GeV.

  • 198. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Gollub, Nils
    Lager, Sara
    Strandberg, Jonas
    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 in dilepton final states2005Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 626, s. 55-64Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a measurement of the top quark pair (a) production cross section in pp collisions at root s = 1.96 TeV using events with two charged leptons in the final state. This analysis utilizes an integrated luminosity of 224-243 pb(-1) collected with the DO detector at the Fermilab Tevatron Collider. We observe 13 events in the e(+)e(-), e mu and mu(+)mu(-) channels with an expected background of 3.2 +/- 0.7 events. For a top quark mass of 175 GeV, we measure a t (t) over bar production cross section of sigma(t (t) over bar) = 8.6(-2.7)(+3.2) (stat) +/- 1.1(syst) +/- 0.6(lumi) pb, consistent with the standard model prediction.

  • 199. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Gollub, Nils
    Lager, Sara
    Strandberg, Jonas
    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 events2005Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 626, s. 45-54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a measurement of the top quark pair (t (t) over bar) production cross section (sigma(t (t) over bar)) in pp collisions at a center-of-mass energy of 1.96 TeV using 230 pb(-1) of data collected by the DO detector at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), large missing transverse energy, and at least four jets, and extract the t (t) over bar content of the sample based on the kinematic characteristics of the events. For a top quark mass of 175 GeV, we measure sigma(t (t) over bar) 6.7(-1.3)(+1.4)(stat)(-1.1)(+1.6)(syst) +/- 0.4(lumi) pb, in good agreement with the standard model prediction.

  • 200. Abazov, V. M.
    et al.
    Åsman, Barbro
    Clément, Christophe
    Gollub, Nils
    Lager, Sara
    Strandberg, Jonas
    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 lepton plus jets events with lifetime b-tagging2005Ingår i: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 626, s. 35-44Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a measurement of the top quark pair (t (t) over bar) production cross section (sigma(t (t) over bar)) in pp collisions at root s = 1.96 TeV using 230 pb(-1) of data collected by the DO experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the t F purity of the selected sample. For a top quark mass of 175 GeV, we measure sigma(t (t) over bar) 8.6(-1.5)(+1.6) (stat. + syst.) +/- 0.6(lumi.) pb, in agreement with the standard model expectation.

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