1. |
- Aaltonen, T., et al.
(author)
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Combination of Tevatron Searches for the Standard Model Higgs Boson in the W+W- Decay Mode
- 2010
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:6, s. 061802-
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Journal article (peer-reviewed)abstract
- We combine searches by the CDF and D0 Collaborations for a Higgs boson decaying to W+W-. The data correspond to an integrated total luminosity of 4.8 (CDF) and 5.4 (D0) fb(-1) of p (p) over bar collisions at root s = 1.96 TeV at the Fermilab Tevatron collider. No excess is observed above background expectation, and resulting limits on Higgs boson production exclude a standard model Higgs boson in the mass range 162-166 GeV at the 95% C.L.
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2. |
- Aaltonen, T., et al.
(author)
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Combination of CDF and D0 measurements of the W boson helicity in top quark decays
- 2012
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In: Physical Review D. - 1550-7998 .- 1550-2368. ; 85:7, s. 071106-
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Journal article (peer-reviewed)abstract
- We report the combination of recent measurements of the helicity of the W boson from top quark decay by the CDF and D0 collaborations, based on data samples corresponding to integrated luminosities of 2.7-5.4 fb(-1) of p (p) over bar collisions collected during Run II of the Fermilab Tevatron collider. Combining measurements that simultaneously determine the fractions of W bosons with longitudinal (f(0)) and right-handed (f(+)) helicities, we find f(0) = 0.722 +/- 0.081[+/- 0.062(stat) +/- 0.052(syst)] and f(+) = -0.033 +/- 0.046[+/- 0.034(stat) +/- 0.031(syst)]. Combining measurements where one of the helicity fractions is fixed to the value expected in the standard model, we find f(0) = 0.682 +/- 0.057[+/- 0.035(stat) +/- 0.046(syst)] for fixed f(+) and f(+) = -0.015 +/- 0.035[+/- 0.018(stat) +/- 0.030(syst)] for fixed f(0). The results are consistent with standard model expectations.
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3. |
- Abazov, V. M., et al.
(author)
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The upgraded DO detector
- 2006
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In: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 565:2, s. 463-537
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Journal article (peer-reviewed)abstract
- The DO experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid -argon calorimeters and central muon detector, remaining from Run 1, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to DO.
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4. |
- Abazov, V. M., et al.
(author)
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Observation of ZZ Production in p(p)over-bar Collisions at root s=1.96 TeV
- 2008
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:17, s. 171803-:101, s. 171803-
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Journal article (peer-reviewed)abstract
- We present an observation for ZZ -> l(+) l(-) l'(+) l'(-) (l, l' =e or mu) production in p (p) over bar collisions at a center-of-mass energy of root s = 1.96 TeV. Using 1.7 fb(-1) of data collected by the D0 experiment at the Fermilab Tevatron Collider, we observe three candidate events with an expected background of 0.14(-0.02)(+0.03) events. The significance of this observation is 5.3 standard deviations. The combination of D0 results in this channel, as well as in ZZ -> l(+) l(-) v (v) over bar yields a significance of 5.7 standard deviations and a combined cross section of sigma(ZZ) = 1.60 +/- 0.63(stat)(-0.17)(+0.16)(syst) pb.
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5. |
- Abazov, V. M., et al.
(author)
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Direct observation of the strange b baryon Xi(-)(b)
- 2007
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:5, s. 052001-
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Journal article (peer-reviewed)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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6. |
- Abazov, V. M., et al.
(author)
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Measurement of the Angular and Lifetime Parameters of the Decays B-d(0) -> J/psi K*(0) and B-s(0) -> J/psi phi
- 2009
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:3, s. 032001-:102, s. 032001-
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Journal article (peer-reviewed)abstract
- We present measurements of the linear polarization amplitudes and the strong relative phases that describe the flavor-untagged decays B-d(0) --> J/psi K*(0) and B-s(0) --> J/psi phi in the transversity basis. We also measure the mean lifetime (tau) over bar (s) of the B-s(0) mass eigenstates and the lifetime ratio (tau) over bar (s)/tau(d). 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 B-d(0) --> J/psi K*(0) decay.
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7. |
- Abazov, V. M., et al.
(author)
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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 TeV
- 2008
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 666:5, s. 435-445
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Journal article (peer-reviewed)abstract
- 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.
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8. |
- Abazov, V. M., et al.
(author)
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A combined search for the standard model Higgs boson at root S=1.96 TeV
- 2008
-
In: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 663:1-2, s. 26-36
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Journal article (peer-reviewed)abstract
- 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).
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9. |
- Abazov, V. M., et al.
(author)
-
Evidence for production of single top quarks
- 2008
-
In: Physical Review D. - 1550-7998 .- 1550-2368. ; D:78, s. 012005-
-
Research review (peer-reviewed)abstract
- We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron p (p) over bar collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top-quark partner that is always produced from strong-coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top-quark production has been searched for in ever larger data sets. In this analysis, we select events from a 0.9 fb(-1) data set that have an electron or muon and missing transverse energy from the decay of a W boson from the top-quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a b hadron decay. The selected events are mostly backgrounds such as W + jets and t (t) over bar events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix-element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top-quark production of sigma(p (p) over bar -> tb + X, tqb + X) = 4.7 +/- 1.3 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top-quark production. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa quark mixing matrix element that describes the Wtb coupling and find vertical bar V(tb)f(1)(L)vertical bar = 1.31(-0.21)(+0.25), where f(1)(L) is a generic vector coupling. This model-independent measurement translates into 0.68 <= 1 at the 95% C.L. in the standard model.
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10. |
- Abazov, V. M., et al.
(author)
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Evidence for the Decay B-s(0)->(DsDs(*))-D-(*) and a Measurement of Delta Gamma(CP)(s)/Gamma(s)
- 2009
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:9, s. 091801-
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Journal article (peer-reviewed)abstract
- We search for the semi-inclusive process B-s(0)->(DsDs(*))-D-(*) using 2.8 fb(-1) of pp collisions at s=1.96 TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We observe 26.6 +/- 8.4 signal events with a significance above background of 3.2 standard deviations yielding a branching ratio of B(B-s(0)->(DsDs(*))-D-(*))=0.035 +/- 0.010(stat.)+/- 0.011(syst.). Under certain theoretical assumptions, these double-charm final states saturate CP-even eigenstates in the B-s(0) decays resulting in a width difference of Delta Gamma(CP)(s)/Gamma(s)=0.072 +/- 0.021(stat.)+/- 0.022(syst.).
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