2,409 research outputs found
Measurement of the t-channel single top quark production cross section
The D0 collaboration reports direct evidence for electroweak production of
single top quarks through the t-channel exchange of a virtual W boson. This is
the first analysis to isolate an individual single top quark production
channel. We select events containing an isolated electron or muon, missing
transverse energy, and two, three or four jets from 2.3 fb^-1 of ppbar
collisions at the Fermilab Tevatron Collider. One or two of the jets are
identified as containing a b hadron. We combine three multivariate techniques
optimized for the t-channel process to measure the t- and s-channel cross
sections simultaneously. We measure cross sections of 3.14 +0.94 -0.80 pb for
the t-channel and 1.05 +-0.81 pb for the s-channel. The measured t-channel
result is found to have a significance of 4.8 standard deviations and is
consistent with the standard model prediction.Comment: 7 pages, 6 figure
Evidence for an anomalous like-sign dimuon charge asymmetry
We measure the charge asymmetry A of like-sign dimuon events in 6.1 fb(-1) of p (p) over bar collisions recorded with the D0 detector at a center-of-mass energy root s = 1.96 TeV at the Fermilab Tevatron collider. From A, we extract the like-sign dimuon charge asymmetry in semileptonic b-hadron decays: A(sl)(b) = -0.00957 +/- 0.00251 (stat) +/- 0.00146 (syst). This result differs by 3.2 standard deviations from the standard model prediction A(sl)(b)(SM) = (-2.3(0.6)(+0.5)) x 10(-4) and provides first evidence of anomalous CP violation in the mixing of neutral B mesons
Precise measurement of the top quark mass in the dilepton channel at D0
We measure the top quark mass (mt) in ppbar collisions at a center of mass
energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events,
where l denotes an electron, a muon, or a tau that decays leptonically. The
data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0
detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat)
+- 2.4(syst) GeV, which is in agreement with the current world average mt =
173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the
dilepton channel.Comment: 7 pages, 4 figure
Measurement of trilinear gauge boson couplings from WW + WZ to lnu jj events in pp-bar collisions at sqrt{s}=1.96 TeV
We present a direct measurement of trilinear gauge boson couplings at gammaWW
and ZWW vertices in WW and WZ events produced in pp-bar collisions at
sqrt{s}=1.96 TeV. We consider events with one electron or muon, missing
transverse energy, and at least two jets. The data were collected using the D0
detector and correspond to 1.1/fb of integrated luminosity. Considering two
different relations between the couplings at the gammaWW and ZWW vertices, we
measure these couplings at 68% C.L. to be kappa_{gamma}=1.07^{+0.26}_{-0.29},
lambda =0.00^{+0.06}_{-0.06} and g_{1}^{Z}=1.04^{+0.09}_{-0.09} in a scenario
respecting SU(2)_L x U(1)_Y gauge symmetry and kappa =1.04^{+0.11}_{-0.11} and
lambda=0.00^{+0.06}_{-0.06} in an "equal couplings" scenario.Comment: 14 pages, 7 figures, published in Phys. Rev. D, updated to published
versio
Measurements of differential cross sections of Z/gamma*+jets+X events in proton anti-proton collisions at sqrt{s}=1.96 TeV
We present cross section measurements for Z/gamma*+jets+X production,
differential in the transverse momenta of the three leading jets. The data
sample was collected with the D0 detector at the Fermilab Tevatron proton
anti-proton collider at a center-of-mass energy of 1.96 TeV and corresponds to
an integrated luminosity of 1 fb-1. Leading and next-to-leading order
perturbative QCD predictions are compared with the measurements, and agreement
is found within the theoretical and experimental uncertainties. We also make
comparisons with the predictions of four event generators. Two
parton-shower-based generators show significant shape and normalization
differences with respect to the data. In contrast, two generators combining
tree-level matrix elements with a parton shower give a reasonable description
of the the shapes observed in data, but the predicted normalizations show
significant differences with respect to the data, reflecting large scale
uncertainties. For specific choices of scales, the normalizations for either
generator can be made to agree with the measurements.Comment: Published in PLB. 11 pages, 3 figure
Double parton interactions in photon+3 jet events in ppbar collisions sqrt{s}=1.96 TeV
We have used a sample of photon+3 jets events collected by the D0 experiment
with an integrated luminosity of about 1 fb^-1 to determine the fraction of
events with double parton scattering (f_DP) in a single ppbar collision at
sqrt{s}=1.96 TeV. The DP fraction and effective cross section (sigma_eff), a
process-independent scale parameter related to the parton density inside the
nucleon, are measured in three intervals of the second (ordered in pT) jet
transverse momentum pT_jet2 within the range 15 < pT_jet2 < 30 GeV. In this
range, f_DP varies between 0.23 < f_DP < 0.47, while sigma_eff has the average
value sigma_eff_ave = 16.4 +- 0.3(stat) +- 2.3(syst) mb.Comment: 15 pages, 13 figure
Measurement of the W boson mass
We present a measurement of the W boson mass in W -> ev decays using 1 fb^-1
of data collected with the D0 detector during Run II of the Fermilab Tevatron
collider. With a sample of 499830 W -> ev candidate events, we measure M_W =
80.401 +- 0.043 GeV. This is the most precise measurement from a single
experiment.Comment: As published in PR
Dependence of the production cross section on the transverse momentum of the top quark
We present a measurement of the differential cross section for
events produced in collisions at TeV as a function
of the transverse momentum () of the top quark. The selected events
contain a high- lepton (), four or more jets, and a large imbalance
in , and correspond to 1 fb of integrated luminosity recorded
with the D0 detector. Each event must have at least one candidate for a
jet. Objects in the event are associated through a constrained kinematic fit to
the process. Results
from next-to-leading-order perturbative QCD calculations agree with the
measured differential cross section. Comparisons are also provided to
predictions from Monte Carlo event generators using QCD calculations at
different levels of precision.Comment: 8 pages, 6 figures, 4 tables, updated to reflect the published
versio
Direct measurement of the mass difference between top and antitop quarks
We present a direct measurement of the mass difference between top and
antitop quarks (dm) in lepton+jets top-antitop final states using the "matrix
element" method. The purity of the lepton+jets sample is enhanced for
top-antitop events by identifying at least one of the jet as originating from a
b quark. The analyzed data correspond to 3.6 fb-1 of proton-antiproton
collisions at 1.96 TeV acquired by D0 in Run II of the Fermilab Tevatron
Collider. The combination of the e+jets and mu+jets channels yields dm = 0.8
+/- 1.8 (stat) +/- 0.5 (syst) GeV, which is in agreement with the standard
model expectation of no mass difference.Comment: submitted to Phys. Rev.
Measurement of the B0_s semileptonic branching ratio to an orbitally excited D_s** state, Br(B0_s -> Ds1(2536) mu nu)
In a data sample of approximately 1.3 fb-1 collected with the D0 detector
between 2002 and 2006, the orbitally excited charm state D_s1(2536) has been
observed with a measured mass of 2535.7 +/- 0.6 (stat) +/- 0.5 (syst) MeV via
the decay mode B0_s -> D_s1(2536) mu nu X. A first measurement is made of the
branching ratio product Br(b(bar) -> D_s1(2536) mu nu X).Br(D_s1(2536)->D*
K0_S). Assuming that D_s1(2536) production in semileptonic decay is entirely
from B0_s, an extraction of the semileptonic branching ratio Br(B0_s ->
D_s1(2536) mu nu X) is made.Comment: 7 pages, 2 figures, LaTeX, version with minor changes as accepted by
Phys. Rev. Let
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