427 research outputs found
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
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.
A search for charged massive long-lived particles
We report on a search for charged massive long-lived particles (CMLLPs),
based on 5.2 fb of integrated luminosity collected with the D0 detector
at the Fermilab Tevatron collider. We search for events in which one
or more particles are reconstructed as muons but have speed and ionization
energy loss inconsistent with muons produced in beam collisions.
CMLLPs are predicted in several theories of physics beyond the standard model.
We exclude pair-produced long-lived gaugino-like charginos below 267 GeV and
higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar
top quarks with mass below 285 GeV.Comment: submitted to Phys. Rev. Letter
Search for first generation leptoquark pair production in the electron + missing energy + jets final state
We present a search for the pair production of first generation scalar
leptoquarks (LQ) in data corresponding to an integrated luminosity of 5.4
fb collected with the D0 detector at the Fermilab Tevatron Collider in
ppbar collisions at TeV. In the channel , where q, q' are u or d quarks, no significant excess
of data over background is observed, and we set a 95% C.L. lower limit of 326
GeV on the leptoquark mass, assuming equal probabilities of leptoquark decays
to eq and .Comment: 7 pages, 6 figures, submitted to PRD-R
Search for the standard model and a fermiophobic Higgs boson in diphoton final states
We present a search for the standard model Higgs boson and a fermiophobic
Higgs boson in the diphoton final states based on 8.2 fb-1 of ppbar collisions
collected with the D0 detector at the Fermilab Tevatron Collider. No excess of
data above background predictions is observed and upper limits at the 95% C.L.
on the cross section multiplied by the branching fraction are set which are the
most restrictive to date. A fermiophobic Higgs boson with a mass below 112.9
GeV is excluded at the 95% C.L.Comment: 12 pages, 21 figures, submitted to PR
Zgamma production and limits on anomalous ZZgamma and Zgammagamma couplings in ppbar collisions at sqrt(s)=1.96 TeV
We present a measurement of ppbar->Zgamma->ll+gamma (l = e, mu) production
with a data sample corresponding to an integrated luminosity of 6.2 fb^{-1}
collected by the D0 detector at the Fermilab Tevatron ppbar Collider. The
results of the electron and muon channels are combined, and we measure the
total production cross section and the differential cross section
dsigma/dp_T^gamma, where p_T^gamma is the momentum of the photon in the plane
transverse to the beamline. The results obtained are consistent with the
standard model predictions from next-to-leading order calculations. We use the
transverse momentum spectrum of the photon to place limits on anomalous ZZgamma
and Zgammagamma couplings
Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production
We present measurements of lepton (l) angular distributions in ttbar -> W+ b
W- b -> l+ nu b l- nubar bbar decays produced in ppbar collisions at a
center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using
data corresponding to an integrated luminosity of 5.4fb^-1, collected with the
D0 detector at the Fermilab Collider, we find that the angular distributions of
l- relative to anti-protons and l+ relative to protons are in agreement with
each other. Combining the two distributions and correcting for detector
acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat)
+- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted)
= (4.7 +- 0.1)%. This result is further combined with the measurement based on
the analysis of the l+jets final state to obtain A^l_FB = (11.8 +- 3.2)%.
Furthermore, we present a first study of the top-quark polarization.Comment: submitted versio
Measurement of the semileptonic charge asymmetry in B0 meson mixing with the D0 detector
We present a measurement of the semileptonic mixing asymmetry for B0 mesons,
a^d_{sl}, using two independent decay channels: B0 -> mu+D-X, with D- ->
K+pi-pi-; and B0 -> mu+D*-X, with D*- -> antiD0 pi-, antiD0 -> K+pi- (and
charge conjugate processes). We use a data sample corresponding to 10.4 fb^{-1}
of ppbar collisions at sqrt(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 (VPDL) of the B0
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 VPDL regions for each
channel, yielding a^d_{sl} = [0.68 \pm 0.45 \text{(stat.)} \pm 0.14
\text{(syst.)}]%. This is the single most precise measurement of this
parameter, with uncertainties smaller than the current world average of B
factory measurements.Comment: Version includes minor textual changes following peer review by
journal, most notably the updating of Ref. [21] to reflect the most recent
publicatio
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