| 51. |
- Abazov, V. M., et al.
(författare)
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Measurement of the semileptonic charge asymmetry in B-0 meson mixing with the D0 detector
- 2012
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Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 86:7, s. 072009-
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Tidskriftsartikel (refereegranskat)abstract
- We present a measurement of the semileptonic mixing asymmetry for B-0 mesons, a(sl)(d), using two independent decay channels: B-0 -> mu+D-X, with D- ->! K+ pi(-) pi(-); and B-0 -> mu+D*X-, with D*(-) -> (D) over bar (0) pi(-), (D) over bar (-)(0) K+ pi(-) (and charge conjugate processes). We use a data sample corresponding to 10.4 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV, collected with the D0 experiment at the Fermilab Tevatron collider. We extract the charge asymmetries in these two channels as a function of the visible proper decay length of the B-0 meson, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The final measurement combines four signal visible proper decay length regions for each channel, yielding a(sl)(d) = [0.68 +/- 0: 45(stat) +/- 0.14(syst)]%. This is the single most precise measurement of this parameter, with uncertainties smaller than the current world average of B factory measurements.
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| 52. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the W boson mass with the D0 detector
- 2014
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 89:1, s. 012005-
-
Tidskriftsartikel (refereegranskat)abstract
- We give a detailed description of the measurement of the W boson mass, M-W, performed on an integrated luminosity of 4.3 fb(-1), which is based on similar techniques as used for our previous measurement done on an independent data set of 1 fb(-1) of data. The data were collected using the D0 detector at the Fermilab Tevatron Collider. This data set yields 1.68 x 10(6) W -> ev candidate events. We measure the mass using the transverse mass, electron transverse momentum, and missing transverse energy distributions. The M-W measurements using the transverse mass and the electron transverse momentum distributions are the most precise of these three and are combined to give M-W 80.367 +/- 0.013 (stat) +/- 0.022(syst) GeV = 80: 367 +/- 0.026 GeV. When combined with our earlier measurement on 1 fb(-1) of data, we obtain M-W = 80.375 +/- 0.023 GeV.
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| 53. |
- Abazov, V. M., et al.
(författare)
-
Combined search for the Higgs boson with the D0 experiment
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:5, s. 052011-
-
Tidskriftsartikel (refereegranskat)abstract
- We perform a combination of searches for standard model Higgs boson production in p (p) over bar collisions recorded by the D0 detector at the Fermilab Tevatron Collider at a center of mass energy of root s = 1.96 TeV. The different production and decay channels have been analyzed separately, with integrated luminosities of up to 9.7 fb(-1) and for Higgs boson masses 90 <= M-H <= 200 GeV. We combine these final states to achieve optimal sensitivity to the production of the Higgs boson. We also interpret the combination in terms of models with a fourth generation of fermions, and models with suppressed Higgs boson couplings to fermions. The result excludes a standard model Higgs boson at 95% C.L. in the ranges 90 < M-H < 101 GeV and 157 < M-H < 178 GeV, with an expected exclusion of 155 < M-H < 175 GeV. In the range 120 < M-H < 145 GeV, the data exhibit an excess over the expected background of up to 2 standard deviations, consistent with the presence of a standard model Higgs boson of mass 125 GeV.
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| 54. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the combined rapidity and p(T) dependence of dijet azimuthal decorrelations in p(p)over-bar collisions at root s=1.96 TeV
- 2013
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 721:4-5, s. 212-219
-
Tidskriftsartikel (refereegranskat)abstract
- We present the first combined measurement of the rapidity and transverse momentum dependence of dijet azimuthal decorrelations, using the recently proposed quantity R-Delta phi. The variable R-Delta phi measures the fraction of the inclusive dijet events in which the azimuthal separation of the two jets with the highest transverse momenta is less than a specified value of the parameter Delta phi(max). The quantity R-Delta phi is measured in p (p) over bar collisions at root s = 1.96 TeV, as a function of the dijet rapidity interval, the total scalar transverse momentum, and Delta phi(max). The measurement uses an event sample corresponding to an integrated luminosity of 0.7 fb(-1) collected with the DO detector at the Fermilab Tevatron Collider. The results are compared to predictions of a perturbative QCD calculation at next-to-leading order in the strong coupling with corrections for non-perturbative effects. The theory predictions describe the data well, except in the kinematic region of large dijet rapidity intervals and small Delta phi(max).
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| 55. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the differential cross sections for isolated direct photon pair production in p(p)over-bar collisions at root s=1.96 TeV
- 2013
-
Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 725:1-3, s. 6-14
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of direct photon pair production cross sections using 8.5 fb(-1) of data collected with the D0 detector at the Fermilab Tevatron p (p) over bar collider. The results are presented as differential distributions of the photon pair invariant mass d sigma/dM(gamma gamma), pair transverse momentum d sigma/dp(T)(gamma gamma) azimuthal angle between the photons d sigma/d Delta(phi)(gamma gamma), and polar scattering angle in the Collins-Soper frame d sigma/d vertical bar cos theta*vertical bar. Measurements are performed for isolated photons with transverse momenta p(T)(gamma) > 18 (17) GeV for the leading (next-to-leading) photon in P-T, pseudorapidities vertical bar eta(gamma)vertical bar < 0.9, and a separation in eta-phi space Delta R-gamma gamma > 0.4. We present comparisons with the predictions from Monte Carlo event generators DIPHOX and RESBOS implementing QCD calculations at next-to-leading order, 2 gamma NNLO at next-to-next-to-leading order, and SHERPA using matrix elements with higher-order real emissions matched to parton shower.
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| 56. |
- Abazov, V. M., et al.
(författare)
-
Measurement of the ratio of differential cross sections sigma(p(p)over-bar -> Z + b jet)/sigma(p(p)over-bar -> Z + jet) in p(p)over-bar collisions at root s = 1.96 TeV
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 87:9, s. 092010-
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Tidskriftsartikel (refereegranskat)abstract
- We measure the ratio of cross sections, sigma(p (p) over bar -> Z + b jet)/sigma(p (p) over bar -> Z + jet), for associated production of a Z boson with at least one jet. The ratio is also measured as a function of the Z boson transverse momentum, jet transverse momentum, jet pseudorapidity, and the azimuthal angle between the Z boson with respect to the highest p(T) b tagged jet. These measurements use data collected by the D0 experiment in Run II of Fermilab's Tevatron p (p) over bar Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of 9.7 fb(-1). The results are compared to predictions from next-to-leading order calculations and various Monte Carlo event generators.
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| 57. |
- Abazov, V. M., et al.
(författare)
-
Muon reconstruction and identification with the Run II D0 detector
- 2014
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 737, s. 281-294
-
Tidskriftsartikel (refereegranskat)abstract
- We present an overview of the muon reconstruction and identification methods employed by the DO collaboration to analyze the Run II (2001-2011) p (p) over bar data of the Fermilab Tevatron collider at root s = 1.96 TeV. We discuss the performance of these methods, how it is measured using DO data, and how it is properly modeled by the DO simulation program. In its pseudorapidity acceptance, vertical bar eta vertical bar < 2, the muon system identifies high-p(T) muons (p(T) greater than or similar to 10 GeV) with efficiencies ranging from 72% to 89%. Muons tracks are reconstructed in the DO central tracking system with efficiencies ranging from 85% to 92% and with a typical relative momentum resolution of 10% for p(T) = 40 GeV. Isolation criteria reject multijet background with efficiencies of 87-99%.
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| 58. |
- Abazov, V. M., et al.
(författare)
-
Search for a Higgs boson in diphoton final states with the D0 detector in 9.6 fb(-1) of p(p)over-bar collisions at root s=1.96 TeV
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:5, s. 052007-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a search for a Higgs boson decaying into a pair of photons based on 9.6 fb(-1) of p (p) over bar collisions at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The search employs multivariate techniques to discriminate signal from the nonresonant background and is separately optimized for a standard model and a fermiophobic Higgs boson. No significant excess of data above the background prediction is observed and upper limits on the product of the cross section and branching fraction are derived at the 95% confidence level as a function of Higgs boson mass. For a standard model Higgs boson with mass of 125 GeV, the observed (expected) upper limits are a factor of 12.8 (8.7) above the standard model prediction. The existence of a fermiophobic Higgs boson with mass in the 100-113 GeV range is excluded at the 95% confidence level.
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| 59. |
- Abazov, V. M., et al.
(författare)
-
Search for charged massive long-lived particles at root s=1.96 TeV
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 87:5, s. 052011-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a search for charged massive long-lived particles (CMLLPs) that are pair produced in p (p) over bar collisions at root s = 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider. Our result is a combination of two searches where either one or both CMLLPs are reconstructed in the detector. We select events with muonlike particles that have both speed and ionization energy loss (dE/dx) different from muons produced in p (p) over bar collisions. In the absence of evidence for CMLLPs corresponding to 6.3 fb(-1) of integrated luminosity, we set limits on the CMLLP masses in several supersymmetric models, excluding masses below 278 GeV for long-lived gaugino-like charginos, and masses below 244 GeV for long-lived Higgsino-like charginos at the 95% C.L. We also set limits on the cross section for pair production of long-lived scalar tau leptons that range from 0.04 to 0.008 pb for scalar tau lepton masses of 100-300 GeV.
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| 60. |
- Abazov, V. M., et al.
(författare)
-
Search for Higgs boson production in oppositely charged dilepton and missing energy final states in 9.7 fb(-1) of p(p)over-bar collisions at root s=1.96 TeV
- 2013
-
Ingår i: Physical Review D. - 1550-7998 .- 1550-2368. ; 88:5, s. 052006-
-
Tidskriftsartikel (refereegranskat)abstract
- We present a search for the Higgs boson in final states with two oppositely charged leptons and large missing transverse energy as expected in H -> WW -> lvl(1)v(1)decays. The events are selected from the full Run II data sample of 9.7 fb(-1) of p (p) over bar collisions collected with the D0 detector at the Fermilab Tevatron Collider at root s = 1.96 TeV. To validate our search methodology, we measure the nonresonant WW production cross section and find sigma(WW) 11.6 +/- 0.7 pb, in agreement with the standard model prediction. In the Higgs boson search, no significant excess above the background expectation is observed. Upper limits at the 95% confidence level on the Higgs boson production cross section are therefore derived. Within the standard model, the Higgs boson mass range 159 < M-H < 176 GeV is excluded while the expected exclusion sensitivity is 156 < M-H < 172 GeV. For a mass hypothesis of M-H = 125 GeV, we exclude Higgs boson production cross sections 4.1 times larger than the standard model expectation, which is compatible with the presence of a Higgs boson at this mass. Within a theoretical framework with a fourth generation of fermions, the mass range 125 < M-H < 218 GeV is excluded. The search results are also interpreted in the context of fermiophobic Higgs boson couplings, which yields an exclusion of fermiophobic Higgs boson production cross sections 3.1 times larger than the expectation for M-H = 125 GeV.
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