37 research outputs found
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
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
Search for a Narrow ttbar Resonance in ppbar Collisions at sqrt{s}=1.96 TeV
We report a search for a narrow ttbar resonance that decays into a
lepton+jets final state based on an integrated luminosity of 5.3/fb of
proton-antiproton collisions at sqrt{s}=1.96 TeV collected by the D0
Collaboration at the Fermilab Tevatron Collider. We set upper limits on the
production cross section of such a resonance multiplied by its branching
fraction to ttbar which we compare to predictions for a leptophobic topcolor Z'
boson. We exclude such a resonance at the 95% confidence level for masses below
835 GeV.Comment: 7 pages, 3 figures, submitted to Physical Review Letter
Measurements of single top quark production cross sections and |Vtb| in ppbar collisions at sqrt{s}=1.96 TeV
We present measurements of production cross sections of single top quarks in
\ppbar collisions at in a data sample corresponding
to an integrated luminosity of collected by the D0 detector
at the Fermilab Tevatron Collider. We select events with an isolated electron
or muon, an imbalance in transverse energy, and two, three, or four jets, with
one or two of them containing a bottom hadron. We obtain an inclusive cross
section of \sigma({\ppbar}{\rargap}tb+X, tqb+X) = 3.43\pm^{0.73}_{0.74}\;\rm
pb and use it to extract the CKM matrix element at
the 95% C.L. We also measure \sigma({\ppbar}{\rargap}tb+X) =
0.68\pm^{0.38}_{0.35}\;\rm pb and \sigma({\ppbar}{\rargap}tqb+X) =
2.86\pm^{0.69}_{0.63}\;\rm pb when assuming, respectively, and
production rates as predicted by the standard model.Comment: 11 pages, 8 figures, submitted to Phys. Rev.
Search for pair production of the scalar top quark in muon+tau final states
We present a search for the pair production of scalar top quarks
(), the lightest supersymmetric partners of the top quarks, in
collisions at a center-of-mass energy of 1.96 TeV, using data
corresponding to an integrated luminosity of {7.3 } collected with the
\dzero experiment at the Fermilab Tevatron Collider. Each scalar top quark is
assumed to decay into a quark, a charged lepton, and a scalar neutrino
(). We investigate final states arising from and
. With no significant excess of events observed above the
background expected from the standard model, we set exclusion limits on this
production process in the (,) plane.Comment: Submitted to Phys. Lett.
Search for Higgs bosons of the minimal supersymmetric standard model in p-pbar collisions at sqrt(s)=1.96 TeV
We report results from searches for neutral Higgs bosons produced in p-pbar
collisions recorded by the Dzero experiment at the Fermilab Tevatron Collider.
We study the production of inclusive neutral Higgs boson in the tautau final
state and in association with a b quark in the btautau and bbb final states.
These results are combined to improve the sensitivity to the production of
neutral Higgs bosons in the context of the minimal supersymmetric standard
model (MSSM). The data are found to be consistent with expectation from
background processes. Upper limits on MSSM Higgs boson production are set for
Higgs boson masses ranging from 90 to 300 GeV. We exclude tanBeta>20-30 for
Higgs boson masses below 180 GeV. These are the most stringent constraints on
MSSM Higgs boson production in p-pbar collisions.Comment: Submitted to Phys. Lett.
A measurement of the WZ and ZZ production cross sections using leptonic final states in 8.6 fb of collisions
We study the processes and \elle{\mu}^{-1} of
integrated luminosity collected by the D0 experiment at the Fermilab Tevatron
collider, we measure the production cross section to be
4.50\pmZZ \rightarrow
\ell^+\ell^-\ell^+\ell^-ZZ^{+0.35}_{-0.34}$ pb.Comment: Submitted to Phys. Rev.
Measurement of the top quark mass in \boldsymbol{\ppbar} collisions using events with two leptons
We present a measurement of the top quark mass () in
collisions at TeV using events with two leptons
(, , or ) and accompanying jets in of data
collected with the D0 detector at the Fermilab Tevatron collider. We analyze
the kinematically underconstrained dilepton events by integrating over their
neutrino rapidity distributions. We reduce the dominant systematic
uncertainties from the calibration of jet energy using a correction obtained
from events with a final state of a single lepton plus jets. We also
correct jets in simulated events to replicate the quark flavor dependence of
the jet response in data. We measure GeV and combining with our analysis in 1 fb
of preceding data we measure GeV. Taking into account statistical and systematic
correlations, a combination with the D0 matrix element result from both data
sets yields GeV.Comment: 5 pages, 1 figure, submitted to Phys. Rev. Letter
Search for universal extra dimensions in ppbar collisions
We present a search for Kaluza-Klein (KK) particles predicted by models with
universal extra dimensions (UED) using a data set corresponding to an
integrated luminosity of 7.3 fb, collected by the D0 detector at a
center of mass energy of 1.96 TeV. The decay chain of KK particles
can lead to a final state with two muons of the same charge. This signature is
used to set a lower limit on the compactification scale of GeV in
a minimal UED model.Comment: 6 pages, 6 figures, accepted for publication in Phys. Rev. Letter
Model independent search for new phenomena in pp(bar) collisions at sqrt(s) =1.96 TeV
We describe a model independent search for physics beyond the standard model
in lepton final states. We examine 117 final states using 1.1 fb of collisions data at TeV collected with the D0
detector. We conclude that all observed discrepancies between data and model
can be attributed to uncertainties in the standard model background modeling,
and hence we do not see any evidence for physics beyond the standard model.Comment: Submitted to PRD. 20 pages, 21 figure