476 research outputs found
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
Observation of ZZ production in ppbar collisions at sqrt(s) = 1.96 TeV
We present an observation for ZZ -> l+l-l'+l'- (l, l' = e or mu) production
in ppbar collisions at a center-of-mass energy of sqrt(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 +0.03
-0.02 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-nunubar,
yields a significance of 5.7 standard deviations and a combined cross section
of sigma(ZZ) = 1.60 +/- 0.63 (stat.) +0.16 -0.17 (syst.) pb.Comment: 7 pages, 1 figure, 2 tables Modified slightly following review
proces
A search for the standard model Higgs boson in the missing energy and acoplanar b-jet topology at sqrt(s) = 1.96 TeV
We report a search for the standard model Higgs boson in the missing energy
and acoplanar b-jet topology, using an integrated luminosity of 0.93 inverse
femtobarn recorded by the D0 detector at the Fermilab Tevatron Collider. The
analysis includes signal contributions from pp->ZH->nu nu b b, as well as from
WH production in which the charged lepton from the W boson decay is undetected.
Neural networks are used to separate signal from background. In the absence of
a signal, we set limits on the cross section of pp->VH times the branching
ratio of H->bb at the 95% C.L. of 2.6 - 2.3 pb, for Higgs boson masses in the
range 105 - 135 GeV, where V=W,Z. The corresponding expected limits range from
2.8 pb - 2.0 pb.Comment: Submitted to Phys. Rev. Letter
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 the electron charge asymmetry in ppbar->W+X->enu+X events at sqrt{s}=1.96 TeV
We present a measurement of the electron charge asymmetry in
ppbar->W+X->enu+X events at a center of mass energy of 1.96 TeV using 0.75 fb-1
of data collected with the D0 detector at the Fermilab Tevatron Collider. The
asymmetry is measured as a function of the electron transverse momentum and
pseudorapidity in the interval (-3.2, 3.2) and is compared with expectations
from next-to-leading order calculations in perturbative quantum chromodynamics.
These measurements will allow more accurate determinations of the proton parton
distribution functions.Comment: 7 pages, 3 figures, Fermilab-Pub-08/249-E, submitted to Phys. Rev.
Let
Measurement of sigma(ppbar -> Z + X) Br(Z -> tau+tau-) at sqrt(s)=1.96 TeV
We present a measurement of the cross section for Z boson production times
the branching fraction to tau lepton pairs sigma(ppbar -> Z + X) Br(Z -> tau+
tau-) in proton-antiproton collisions at center of mass energy 1.96 TeV. The
measurement is performed in the channel in which one tau lepton decays into a
muon and neutrinos, and the other tau lepton decays hadronically or into an
electron and neutrinos. The data sample corresponds to an integrated luminosity
of 1.0 inverse fb collected with the D0 detector at the Fermilab Tevatron
Collider. The sample contains 1511 candidate events with an estimated 20%
background from jets or muons misidentified as tau leptons. We obtain sigma Br
= 240 +/- 8 (stat) +/- 12 (sys) +/- 15 (lum) pb, which is consistent with the
standard model prediction.Comment: submitted to Phys. Lett.
Search for anomalous \boldmath{Wtb} couplings in single top quark production
In 0.9 fb of collisions, D0 has observed an excess of
events with an isolated lepton, missing transve rse momentum, and two to four
jets. This excess is consistent with single top quark production. We examine
these data to study the Lorentz structure of the coupling. The standard
model predicts a left-handed vector coupling at the vertex. The most
general lowest dimension, CP-conserving Lagrangian admits right-handed vector
and left- or right-h anded tensor couplings as well. We find that the data
prefer the left-handed vector coupling and set upper limits on the anomalous
couplings. These are the first direct constraints on a general
interaction and the first direct limits on left- and right-handed tensor
couplings.Comment: 7 pages, 4 figure
Search for new fermions ("quirks") at the Fermilab Tevatron Collider
We report results of a search for particles with anomalously high ionization
in events with a high transverse energy jet and large missing transverse energy
in fb of integrated luminosity collected by the D0 experiment at
the Fermilab Tevatron collider. Production of such particles
(quirks) is expected in scenarios with extra QCD-like {\it SU(N)} sectors, and
this study is the first dedicated search for such signatures. We find no
evidence of a signal and set a lower mass limit of 107 ~GeV for the mass of a
charged quirk with strong dynamics scale in the range from 10 keV to
1 MeV.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 scalar leptoquarks and T-odd quarks in the acoplanar jet topology using 2.5 fb-1 of ppbar collision data at sqrt(s)=1.96 TeV
A search for new physics in the acoplanar jet topology has been performed in
2.5 fb-1 of data from ppbar collisions at sqrt(s)=1.96 TeV, recorded by the D0
detector at the Fermilab Tevatron Collider. The numbers of events with exactly
two acoplanar jets and missing transverse energy are in good agreement with the
standard model expectations. The result of this search has been used to set a
lower mass limit of 205 GeV at the 95% C.L. on the mass of a scalar leptoquark
when this particle decays exclusively into a quark and a neutrino. In the
framework of the Little Higgs model with T-parity, limits have also been
obtained on the T-odd quark mass as a function of the T-odd photon mass
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