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Search for pair production of first-generation leptoquarks in pp¯ collisions at s=1.96 TeV
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.,Andeen, T.,Anzelc, M.S.,Aoki, M.,Arn Elsevier 2009 Physics letters: B Vol.681 No.3
<P><B>Abstract</B></P><P>A search for pair production of first-generation leptoquarks (<I>LQ</I>) is performed with data collected by the DØ experiment in pp¯ collisions at s=1.96 TeV at the Fermilab Tevatron Collider. In a sample of data corresponding to ∼1<SUP> fb−1</SUP> 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 <I>LQ</I> mass limits. We set 95% C.L. lower limits on a scalar <I>LQ</I> mass of 299 GeV, 284 GeV and 216 GeV for β=1, β=0.5 and β=0.02 respectively, where <I>β</I> is the <I>LQ</I> branching ratio in the <I>eq</I> channel. This improves the results obtained with a lower luminosity sample from Run II of the Tevatron. Lower limits on vector <I>LQ</I> masses with different couplings from 357 GeV to 464 GeV for β=0.5 are also set using this analysis.</P>
Search forW′Boson Resonances Decaying to a Top Quark and a Bottom Quark
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, L. S.,Ande American Physical Society 2008 Physical Review Letters Vol.100 No.21
<P>We search for the production of a heavy W' gauge boson that decays to third generation quarks in 0.9 fb-1 of pp collisions at square root(s)=1.96 TeV, collected with the D0 detector at the Fermilab Tevatron collider. We find no significant excess in the final-state invariant mass distribution and set upper limits on the production cross section times branching fraction. For a left-handed W' boson with SM couplings, we set a lower mass limit of 731 GeV. For right-handed W' bosons, we set lower mass limits of 739 GeV if the W' boson decays to both leptons and quarks and 768 GeV if the W' boson decays only to quarks. We also set limits on the coupling of the W' boson to fermions as a function of its mass.</P>
Measurement of the Angular and Lifetime Parameters of the DecaysBd0→J/ψK*0andBs0→J/ψϕ
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.,Andeen, T.,Andr American Physical Society 2009 Physical Review Letters Vol.102 No.3
<P>We present measurements of the linear polarization amplitudes and the strong relative phases that describe the flavor-untagged decays Bd0-->J/psiK*0 and Bs0-->J/psiphi in the transversity basis. We also measure the mean lifetime taus of the Bs0 mass eigenstates and the lifetime ratio taus/taud. The analyses are based on approximately 2.8 fb(-1) of data recorded with the D0 detector. From our measurements of the angular parameters we conclude that there is no evidence for a deviation from flavor SU(3) symmetry for these decays and that the factorization assumption is not valid for the Bd0-->J/psiK*0 decay.</P>
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.,Andeen, T.,Andrieu, Elsevier 2009 Physics letters: B Vol.680 No.1
<P><B>Abstract</B></P><P>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<SUP>−1</SUP> collected with the DØ 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 <SUB>m0</SUB> and <SUB>m1/2</SUB> that are well beyond existing limits.</P>
Observation of Single Top-Quark Production
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.,Andeen, T.,Anzelc, M. S.,Aoki, American Physical Society 2009 Physical Review Letters Vol.103 No.9
<P>We report observation of the electroweak production of single top quarks in pp[over ] collisions at sqrt[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[over ]--> tb + X, tqb + X) = 3.94 + or - 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.5 x 10(-7), corresponding to a 5.0 standard deviation significance for the observation.</P>
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.,Andeen, T.,Anzelc, M. S.,Aoki, American Physical Society 2009 Physical Review Letters Vol.103 No.6
<P>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 micro;{+}micro;{-} or one to micro;{+}micro;{-} 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}.</P>
Search for AssociatedWand Higgs Boson Production inpp¯Collisions ats=1.96 TeV
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.,Andeen, T.,Andr American Physical Society 2009 Physical Review Letters Vol.102 No.5
<P>We present results of a search for WH-->lnubb[over ] production in pp[over ] collisions based on the analysis of 1.05 fb;{-1} of data collected by the D0 experiment at the Fermilab Tevatron, using a neural network for separating the signal from backgrounds. No signal-like excess is observed, and we set 95% C.L. upper limits on the WH production cross section multiplied by the branching ratio for H-->bb[over ] for Higgs boson masses between 100 and 150 GeV. For a mass of 115 GeV, we obtain an observed (expected) limit of 1.5 (1.4) pb, a factor of 11.4 (10.7) times larger than the standard model prediction.</P>
Measurement of the top quark mass in final states with two leptons
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.,Andeen, T.,Anzelc, M. S.,Aoki, American Physical Society 2009 PHYSICAL REVIEW D - Vol.80 No.9