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D0 Collaboration

Publications and source records attributed to D0 Collaboration.

At least 181 records · Page 10Linked to original sources

arXiv2010

Search for events with leptonic jets and missing transverse energy in ppbar collisions at sqrt(s)=1.96 TeV

We present the first search for pair production of isolated jets of charged leptons in association with a large imbalance in transverse energy in ppbar collisions using 5.8 fb^-1 of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider. No excess is observed above Standard Model background, and the result is used to set upper limits on the production cross section of pairs of supersymmetric chargino and neutralino particles as a function of "dark-photon" mass, where the dark photon is produced in the decay of the lightest supersymmetric particle.

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arXiv2010

Search for diphoton events with large missing transverse energy in 6.3 fb-1 of ppbar collisions at sqrt(s)=1.96 TeV

We report a search for diphoton events with large missing transverse energy produced in ppbar collisions at sqrt(s)=1.96 TeV. The data were collected with the D0 detector at the Fermilab Tevatron Collider, and correspond to 6.3 fb-1 of integrated luminosity. The observed missing transverse energy distribution is well described by the standard model prediction, and 95% C.L. limits are derived on two realizations of theories beyond the standard model. In a gauge mediated supersymmetry breaking scenario, the breaking scale Lambda is excluded for Lambda < 124 TeV. In a universal extra dimension model including gravitational decays, the compactification radius R_c is excluded for R_c-1 < 477 GeV.

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arXiv2010

Search for sneutrino production in emu final states in 5.3 fb^-1 of ppbar collisions at sqrt(s) =1.96 TeV

We report the results of a search for R parity violating (RPV) interactions leading to the production of supersymmetric sneutrinos decaying into emu final states using 5.3 fb^-1 of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron Collider. Having observed no evidence for production of emu resonances, we set direct bounds on the RPV couplings lambda^'_311 and lambda_312 as a function of sneutrino mass.

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arXiv2010

Evidence for an anomalous like-sign dimuon charge asymmetry

We measure the charge asymmetry $A\equiv(N^{++} - N^{--})/(N^{++} + N^{--})$ of like-sign dimuon events in 6.1~fb$^{-1}$ of $p\bar{p}$ collisions recorded with the D0 detector at a center-of-mass energy $\sqrt{s}=1.96$~TeV at the Fermilab Tevatron collider. From $A$ we extract the like-sign dimuon charge asymmetry in semileptonic $b$-hadron decays: $\aslb=-0.00957\pm0.00251\thinspace({\rm stat})\pm0.00146\thinspace({\rm sys})$. It differs by 3.2~standard deviations from the standard model prediction $\aslb({\rm SM})=(-2.3^{+0.5}_{-0.6})\times10^{-4}$, and provides first evidence of anomalous $CP$ violation in the mixing of neutral $B$ mesons.

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arXiv2010

Measurement of the $WZ\rightarrow \ellν\ell\ell$ cross section and limits on anomalous triple gauge couplings in $p\bar{p}$ collisions at $\sqrt{s}$ = 1.96 TeV

We present a new measurement of the $WZ\rightarrow \ellν\ell\ell$ ($\ell = e,μ$) cross section and limits on anomalous triple gauge couplings. Using 4.1 fb$^{-1}$ of integrated luminosity of $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV, we observe 34 $WZ$ candidate events with an estimated background of $6.0 \pm 0.4$ events. We measure the $WZ$ production cross section to be $3.90^{+1.06}_{-0.90}$ pb, in good agreement with the standard model prediction. We find no evidence for anomalous $WWZ$ couplings and set 95% C.L. limits on the coupling parameters, $-0.075 < λ_{Z} < 0.093$ and $-0.027 < Δκ_{Z} < 0.080$, in the HISZ parameterization for a $Λ= 2$ TeV form factor scale. These are the best limits to date obtained from the direct measurement of the $WWZ$ vertex.

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arXiv2010

Search for the Standard Model Higgs Boson in the ZH->vvbb Channel in 5.2 fb-1 of p-pbar Collisions at sqrt(s)=1.96 TeV

A search is performed for the standard model Higgs boson in 5.2 fb-1 of p-pbar collisions at sqrt(s)=1.96 TeV, collected with the D0 detector at the Fermilab Tevatron Collider. The final state considered is a pair of b jets and large missing transverse energy, as expected from p-pbar->ZH->vvbb production. The search is also sensitive to the WH->lvbb channel when the charged lepton is not identified. For a Higgs boson mass of 115 GeV, a limit is set at the 95% C.L. on the cross section multiplied by branching fraction for [p-pbar->(Z/W)H](H->b-bbar) that is a factor of 3.7 larger than the standard model value, consistent with the factor of 4.6 expected.

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arXiv2010

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.

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arXiv2009

Determination of the strong coupling constant from the inclusive jet cross section in ppbar collisions at sqrt(s)=1.96 TeV

We determine the strong coupling constant alphas and its energy dependence from the pT dependence of the inclusive jet cross section in ppbar collisions at sqrt(s)=1.96 TeV. The strong coupling constant is determined over the transverse momentum range 50 < pT < 145 GeV. Using perturbative QCD calculations to order O(alphas^3) combined with O(alphas^4) contributions from threshold corrections, we obtain alphas(MZ) = 0.1161 +0.0041 -0.0048. This is the most precise result obtained at a hadron-hadron collider.

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arXiv2009

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.

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arXiv2009

Measurement of Z/gamma*+jet+X angular distributions in ppbar collisions at sqrt{s}=1.96 TeV

We present the first measurements at a hadron collider of differential cross sections for Z+jet+X production in delta phi(Z, jet), |delta y(Z, jet)| and |y_boost(Z, jet)|. Vector boson production in association with jets is an excellent probe of QCD and constitutes the main background to many small cross section processes, such as associated Higgs production. These measurements are crucial tests of the predictions of perturbative QCD and current event generators, which have varied success in describing the data. Using these measurements as inputs in tuning event generators will increase the experimental sensitivity to rare signals.

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arXiv2009

Search for charged Higgs bosons in top quark decays

We present a search for charged Higgs bosons in top quark decays. We analyze the \eplus, \muplus, $ee$, $eμ$, $μμ$, \etau and \mutau final states from top quark pair production events, using data from about 1${\text{fb}}^{-1}$ of integrated luminosity recorded by the \dzero experiment at the Fermilab Tevatron Collider. We consider different scenarios of possible charged Higgs boson decays, one where the charged Higgs boson decays purely hadronically into a charm and a strange quark, another where it decays into a $τ$ lepton and a $τ$ neutrino and a third one where both decays appear. We extract limits on the branching ratio $B(t\to H^+ b)$ for all these models. We use two methods, one where the $t\bar{t}$ production cross section is fixed, and one where the cross section is fitted simultaneously with $B(t\to H^+b)$. Based on the extracted limits, we exclude regions in the charged Higgs boson mass and $\tan β$ parameter space for different scenarios of the minimal supersymmetric standard model.

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arXiv2009

Direct measurement of the W boson width

We present a direct measurement of the width of the W boson using the shape of the transverse mass distribution of W->enu candidates selected in 1 fb-1 of data collected with the D0 detector at the Fermilab Tevatron collider in ppbar collisions at sqrt{s}=1.96 TeV. We use the same methods and data sample that were used for our recently published W boson mass measurement, except for the modeling of the recoil, which is done with a new method based on a recoil library. Our result, 2.028 +- 0.072 GeV, is in agreement with the predictions of the standard model.

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arXiv2009

Search for the associated production of a b quark and a neutral supersymmetric Higgs boson which decays to tau pairs

We report results from a search for production of a neutral Higgs boson in association with a $b$ quark. We search for Higgs decays to $τ$ pairs with one $τ$ subsequently decaying to a muon and the other to hadrons. The data correspond to 2.7fb$^{-1}$ of $\ppbar$ collisions recorded by the D0 detector at $\sqrt{s} = 1.96$TeV. The data are found to be consistent with background predictions. The result allows us to exclude a significant region of parameter space of the minimal supersymmetric model.

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arXiv2009

Precision Electroweak Measurements and Constraints on the Standard Model

This note presents constraints on Standard Model parameters using published and preliminary precision electroweak results measured at the electron-positron colliders LEP and SLC. The results are compared with precise electroweak measurements from other experiments, notably CDF and DØat the Tevatron. Constraints on the input parameters of the Standard Model are derived from the combined set of results obtained in high-$Q^2$ interactions, and used to predict results in low-$Q^2$ experiments, such as atomic parity violation, Møller scattering, and neutrino-nucleon scattering. The main changes with respect to the experimental results presented in 2008 are new combinations of results on the W-boson mass and the mass of the top quark.

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arXiv2009

Measurement of dijet angular distributions at sqrt{s}=1.96TeV and searches for quark compositeness and extra spatial dimensions

We present the first measurement of dijet angular distributions in ppbar collisions at sqrt{s}=1.96TeV at the Fermilab Tevatron Collider. The measurement is based on a dataset corresponding to an integrated luminosity of up to 0.7fb-1 collected with the D0 detector. Dijet angular distributions have been measured over a range of dijet masses, from 0.25TeV to above 1.1TeV. The data are in good agreement with the predictions of perturbative QCD and are used to constrain new physics models including quark compositeness, large extra dimensions, and TeV-1 scale extra dimensions. For all models we set the most stringent direct limits to date.

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arXiv2009

Measurement of the WW production cross section with dilepton final states in p-pbar collisions at sqrt(s)=1.96 TeV and limits on anomalous trilinear gauge couplings

We provide the most precise measurement of the WW production cross section in p-pbar collisions to date at a center of mass energy of 1.96 TeV, and set limits on the associated trilinear gauge couplings. The WW->lvl'v (l,l'=e,mu) decay channels are analyzed in 1 fb^(-1) of data collected by the D0 detector at the Fermilab Tevatron Collider. The measured cross section is sigma(p-pbar -> WW) = 11.5 +/- 2.1 (stat + syst) +/- 0.7 (lumi) pb. One- and two-dimensional 95% C.L. limits on trilinear gauge couplings are provided.

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arXiv2009

Combination of ttbar cross section measurements and constraints on the mass of the top quark and its decays into charged Higgs bosons

We combine measurements of the top quark pair production cross section in ppbar collisions in the l+jets, ll and tau-l final states (where l is an electron or muon) at a center of mass energy of sqrt(s)=1.96 TeV in 1fb^{-1} of data collected with the D0 detector. For a top quark mass of 170 GeV, we obtain sigma_ttbar=8.18^{+0.98}_{-0.87} pb. In addition, the ratios of ttbar cross sections in different final states are used to set upper limits on the branching fractions B(t -> H^{+}b -> tau nu b) and B(t -> H^{+}b -> c sbar b) as a function of charged Higgs boson mass. Based on predictions from higher order quantum chromodynamics, we extract a mass for the top quark from the combined ttbar cross section.

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arXiv2009

Direct measurement of the mass difference between top and antitop quarks

We present a measurement of the mass difference between t and tbar quarks observed in lepton+jets final states of ttbar events in 1 fb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider in ppbar collisions at sqrt(s)=1.96 TeV. The observed mass difference of 3.8+-3.7 GeV is consistent with the equality of t and tbar masses. This is the first direct measurement of a mass difference between a quark and its antiquark partner.

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