5,577 research outputs found
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We present the first measurements of the differential cross section d sigma/dp(T)(gamma) for the production of an isolated photon in association with at least two b-quark jets. The measurements consider photons with rapidities vertical bar y(gamma)vertical bar < 1.0 and transverse momenta 30 < p(T)(gamma) < 200 GeV. The b-quark jets are required to have p(T)(jet) > 15 GeVand vertical bar y(jet)vertical bar < 1.5. The ratio of differential production cross sections for gamma + 2 b-jets to gamma + b-jet as a function of p(T)(gamma) is also presented. The results are based on the proton-antiproton collision data at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The measured cross sections and their ratios are compared to the next- to- leading order perturbative QCD calculations as well as predictions based on the k(T)- factorization approach and those from the sherpa and pythia Monte Carlo event generators
Search for Zgamma events with large missing transverse energy in ppbar collisions at sqrt(s)=1.96 TeV
We present the first search for supersymmetry (SUSY) in Zgamma final states
with large missing transverse energy using data corresponding to an integrated
luminosity of 6.2 fb-1 collected with the D0 experiment in ppbar collisions at
sqrt(s)=1.96 TeV. This signature is predicted in gauge-mediated SUSY-breaking
models, where the lightest neutralino is the next-to-lightest supersymmetric
particle (NLSP) and is produced in pairs, possibly through decay from heavier
supersymmetric particles. The NLSP can decay either to a Z boson or a photon
and an associated gravitino that escapes detection. We exclude this model at
the 95% C.L. for SUSY breaking scales of Lambda < 87 TeV, corresponding to
neutralino masses of < 151 GeV.Comment: submitted to Phys. Rev. Let
Search for Decay
We have searched for the charmless hadronic decay of B0 mesons into two
neutral pions. Using 9.13fb^-1 taken at the Upsilon(4S) with the CLEO detector,
we obtain an improved upper limit for the branching fraction BR(B0-->pi0pi0) <
5.7*10^-6 at the 90% confidence level.Comment: pages postscript, also available through
http://w4.lns.cornell.edu/public/CLN
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
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 the Higgs boson in lepton, tau and jets final states
We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with two or more jets using 9.7 fb^{-1} of Run II Fermilab Tevatron Collider data collected with the D0 detector. The analysis is sensitive to Higgs boson production via gluon fusion, associated vector boson production, and vector boson fusion, followed by the Higgs boson decay to tau lepton pairs or to W boson pairs. The ratios of 95% C.L. upper limits on the cross section times branching ratio to those predicted by the standard model are obtained for orthogonal subsamples that are enriched in either H -> tau tau decays or H -> WW decays, and for the combination of these subsample limits. The observed and expected limit ratios for the combined subsamples at a Higgs boson mass of 125 GeV are 11.3 and 9.0 respectively
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
Measurement of the semileptonic charge asymmetry using Bs^0 -> D_s mu X decays
We present a measurement of the time-integrated flavor-specific semileptonic
charge asymmetry in the decays of Bs mesons that have undergone flavor mixing,
a^s_ls, using B_s^0 (barB_s^0) -> D_s^-/+ mu^+/- X decays, with D_s^-/+ -> phi
pi^-/+ and phi K^+ K^-, using 10.4 fb^-1 of proton-antiproton collisions
collected by the D0 detector during Run II at the Fermilab Tevatron Collider. A
fit to the difference between the time-integrated D_s^-$ and D_s^+ mass
distributions of the B_s^0 and barB^0_s candidates yields the flavor-specific
asymmetry a^s_ls = [-1.12 pm 0.74 (stat) +/-0.17 (syst)]% which is the most
precise measurement and in agreement with the standard model prediction.Comment: 7 pages, 3 figures (updated with changes made in journal review
process
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
Measurement of spin correlation in ttbar production using a matrix element approach
correlation, assuming that the spin of the top quark is either correlated
with the spin of the anti-top quark as predicted by the standard model or is
uncorrelated. For the first time we use a matrix-element-based approach to
study ttbar spin correlation. We use {ttbar -> W+bW-bbar ->l+nubl-nub} final
states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96
TeV, where l denotes an electron or a muon. The data correspond to an
integrated luminosity of 5.4 fb-1 and were collected with the dzero detector at
the Fermilab Tevatron collider. The result agrees with the standard model
prediction. We exclude the hypothesis that the spins of the ttbar are
uncorrelated at the 97.7% C.L.Comment: 7 pages, 3 figures, submitted to Phys. Rev. Let
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