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Search for charged Higgs bosons in top quark decays
DO Collaboration,Abazov, V.M.,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.,Ancu, L.S.,Anzelc, M.S.,Aoki, North-Holland Pub. Co 2009 Physics letters: B Vol.682 No.3
We present a search for charged Higgs bosons in top quark decays. We analyze the e+jets, μ+jets, ee, eμ, μμ, τe and τμ final states from top quark pair production events, using data from about 1 fb<SUP>-1</SUP> 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 τ lepton and a τ neutrino and a third one where both decays appear. We extract limits on the branching ratio B(t->H<SUP>+</SUP>b) for all these models. We use two methods, one where the tt@? production cross section is fixed, and one where the cross section is fitted simultaneously with B(t->H<SUP>+</SUP>b). Based on the extracted limits, we exclude regions in the charged Higgs boson mass and tanβ parameter space for different scenarios of the minimal supersymmetric standard model.
Search for admixture of scalar top quarks in the tt@? lepton + jets final state at s=1.96 TeV
DO Collaboration,Abazov, V.M.,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.,And North-Holland Pub. Co 2009 Physics letters: B Vol.674 No.1
A search for pair production of the lightest supersymmetric partner of the top quark, t@?<SUB>1</SUB>, is performed in the lepton+jets channel using 0.9 fb<SUP>-1</SUP> of data collected by the DO experiment. Kinematic differences between t@?<SUB>1</SUB>t@?@?<SUB>1</SUB> 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@?<SUB>1</SUB>->χ@?<SUB>1</SUB><SUP>+</SUP>b) are obtained for scalar top quark masses of 130-190 GeV and chargino masses of 90-150 GeV.
A combined search for the standard model Higgs boson at s=1.96 TeV
DO Collaboration,Abazov, V.M.,Abbott, B.,Abolins, M.,Acharya, B.S.,Adams, M.,Adams, T.,Aguilo, E.,Ahn, S.H.,Ahsan, M.,Alexeev, G.D.,Alkhazov, G.,Alton, A.,Alverson, G.,Alves, G.A.,Anastasoaie, M.,Ancu North-Holland Pub. Co 2008 Physics letters: B Vol.663 No.1
We present new results of the search for WH->@?νbb@? production in pp@? collisions at a center-of-mass energy of s=1.96 TeV, based on a dataset with integrated luminosity of 0.44 fb<SUP>-1</SUP>. We combine these new results with previously published searches by the D0 collaboration, for WH and ZH production analyzed in the E@?<SUB>T</SUB>bb@? final state, for ZH (->@?<SUP>+</SUP>@?<SUP>-</SUP>bb@?) production, for WH (->WWW) production, and for H (->WW) direct production. No signal-like excess is observed either in the WH analysis or in the combination of all D0 Higgs boson analyses. We set 95% C.L. (expected) upper limits on σ(pp@?->WH)xB(H->bb@?) ranging from 1.6 (2.2) pb 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 m<SUB>H</SUB>=115 GeV. After combination with the other D0 Higgs boson searches, we obtain for m<SUB>H</SUB>=115 GeV an observed (expected) limit 8.5 (12.1) times higher than the SM predicted Higgs boson production cross section. For m<SUB>H</SUB>=160 GeV, the corresponding observed (expected) ratio is 10.2 (9.0).
DO Collaboration,Abazov, V.M.,Abbott, B.,Abolins, M.,Acharya, B.S.,Adams, M.,Adams, T.,Aguilo, E.,Ahn, S.H.,Ahsan, M.,Alexeev, G.D.,Alkhazov, G.,Alton, A.,Alverson, G.,Alves, G.A.,Anastasoaie, M.,Ancu North-Holland Pub. Co 2008 Physics letters: B Vol.666 No.5
The process pp@?->γ+jet+X is studied using 1.0 fb<SUP>-1</SUP> of data collected by the D0 detector at the Fermilab Tevatron pp@? collider at a center-of-mass energy s=1.96 TeV. Photons are reconstructed in the central rapidity region |y<SUP>&</SUP>gamma;|<1.0 with transverse momenta in the range 30<p<SUB>T</SUB><SUP>&</SUP>gamma;<400 GeV while jets are reconstructed in either the central |y<SUP>jet</SUP>|<0.8 or forward 1.5<|y<SUP>jet</SUP>|<2.5 rapidity intervals with p<SUB>T</SUB><SUP>jet</SUP>>15 GeV. The differential cross section d<SUP>3</SUP>σ/dp<SUB>T</SUB><SUP>&</SUP>gamma;dy<SUP>&</SUP>gamma;dy<SUP>jet</SUP> is measured as a function of p<SUB>T</SUB><SUP>&</SUP>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<SUB>T</SUB><SUP>&</SUP>gamma; dependence of the cross section in the four measured regions.
Zγ production and limits on anomalous ZZγ and Zγγ couplings in pp@? collisions at s=1.96 TeV
DO Collaboration,Abazov, V.M.,Abbott, B.,Abolins, M.,Acharya, B.S.,Adams, M.,Adams, T.,Aguilo, E.,Ahn, S.H.,Ahsan, M.,Alexeev, G.D.,Alkhazov, G.,Alton, A.,Alverson, G.,Alves, G.A.,Anastasoaie, M.,Ancu North-Holland Pub. Co 2007 Physics letters: B Vol.653 No.5
We present a study of eeγ and μμγ events using 1109 (1009) pb<SUP>-1</SUP> of data in the electron (muon) channel, respectively. These data were collected with the DO detector at the Fermilab Tevatron pp@? collider at s=1.96 TeV. Having observed 453 (515) candidates in the eeγ (μμγ) final state, we measure the Zγ production cross section for a photon with transverse energy E<SUB>T</SUB>>7 GeV, separation between the photon and leptons ΔR<SUB>@</SUB>?<SUB>&</SUB>gamma;>0.7, and invariant mass of the di-lepton pair M<SUB>@</SUB>?<SUB>@</SUB>?>30 GeV/c<SUP>2</SUP>, to be 4.96+/-0.30(stat.+syst.)+/-0.30(lumi.) pb, in agreement with the Standard Model prediction of 4.74+/-0.22 pb. This is the most precise Zγ cross section measurement at a hadron collider. We set limits on anomalous trilinear Zγγ and ZZγ gauge boson couplings of -0.085<h<SUB>30</SUB><SUP>&</SUP>gamma;<0.084, -0.0053<h<SUB>40</SUB><SUP>&</SUP>gamma;<0.0054 and -0.083<h<SUB>30</SUB><SUP>Z</SUP><0.082, -0.0053<h<SUB>40</SUB><SUP>Z</SUP><0.0054 at the 95% C.L. for the form-factor scale Λ=1.2 TeV.
DO Collaboration,Abazov, V.M.,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.,And North-Holland Pub. Co 2009 Physics letters: B Vol.679 No.3
We present a measurement of the top quark pair production cross section in pp@? collisions at s=1.96 TeV using approximately 1 fb<SUP>-1</SUP> collected with the DO detector. We consider decay channels containing two high p<SUB>T</SUB> 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 τ lepton. For a mass of the top quark of 170 GeV, the measured cross section is 7.5<SUB>-1.0</SUB><SUP>+1.0</SUP>(stat)<SUB>-0.6</SUB><SUP>+0.7</SUP>(syst)<SUB>-0.5</SUB><SUP>+0.6</SUP>(lumi) pb. Using @?τ events only, we measure: σ<SUB>tt@</SUB>?xB(tt@?->@?τbb@?)=0.13<SUB>-0.08</SUB><SUP>+0.09</SUP>(stat)<SUB>-0.06</SUB><SUP>+0.06</SUP>(syst)<SUB>-0.02</SUB><SUP>+0.02</SUP>(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 Chromodynamics theoretical prediction, we extract a mass of the top quark of 171.5<SUB>-8.8</SUB><SUP>+9.9</SUP> GeV, in agreement with direct measurements.