| 11. |
- Abazov, V. M., et al.
(författare)
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Search for production of single top quarks via tcg and tug flavor-changing-neutral-current couplings
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:19, s. 191802-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
- Abazov, V. M., et al.
(författare)
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Search for single production of scalar leptoquarks in p(p)over-bar collisions decaying into muons and quarks with the D0 detector
- 2007
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 647:2-3, s. 74-81
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Tidskriftsartikel (refereegranskat)abstract
- lWe 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.
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| 13. |
- Abazov, V. M., et al.
(författare)
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Search for techniparticles in e plus jets events at D0
- 2007
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 98:22, s. 221801-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
- Abazov, V. M., et al.
(författare)
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Direct observation of the strange b baryon Xi(-)(b)
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:5, s. 052001-
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Tidskriftsartikel (refereegranskat)abstract
- 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).
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| 15. |
- Abazov, V. M., et al.
(författare)
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Measurement of the Lambda(0)(b) lifetime using semileptonic decays
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:18, s. 182001-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 16. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the Lambda(b) lifetime in the exclusive decay Lambda(b)-> J/psi Lambda
- 2007
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:14, s. 142001-
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Tidskriftsartikel (refereegranskat)abstract
- 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).
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| 17. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the p(p)over-bar -> WZ+X cross section at root s=1.96 TeV and limits on WWZ trilinear gauge couplings
- 2007
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 76:11
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the process p (P) over bar -> WZ + X -> l 'nu(l ')l (l) over bar at root s = 1:96 TeV,where l and l ' are electrons or muons. Using 1 fb(-1) of data from the D0 experiment, we observe 13 candidates with an expected background of 4.5 +/- 0.6 events and measure a cross section sigma(WZ) = 2.7(-1.3)(+1.7) pb. From the number of observed events and the Z boson transverse momentum distribution, we limit the trilinear WWZ gauge couplings to -0: 17 <= lambda(Z) <= 0.21 (Delta k(Z) <= 0.29(lambda(Z) = 0) at the 95% C.L. for a form factor scale Lambda = 2 TeV. Further, assuming that Delta g(1)(Z) = Delta k(Z), we find -0.12 <= Delta k(Z) <= 0.29(lambda(Z) = 0) at the 95% C. L. These are the most restrictive limits on the WWZ couplings available to date.
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| 18. |
- Abazov, V. M., et al.
(författare)
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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 TeV
- 2007
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Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-7998. ; 76:1, s. 012003-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 19. |
- Abazov, V. M., et al.
(författare)
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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 events
- 2007
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 76:9
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 20. |
- Abazov, V. M., et al.
(författare)
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Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions using dilepton events
- 2007
-
Ingår i: Physical Review D - Particles, Fields, Gravitation and Cosmology. - 1550-7998. ; 76:5, s. 052006-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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