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D0 Collaboration

Publications and source records attributed to D0 Collaboration.

At least 289 records · Page 16Linked to original sources
arXiv2007

Measurement of the shape of the boson rapidity distribution for p\bar{p}-> Z/gamma*-> e+e- +X events produced at sqrt(s) of 1.96 TeV

We present a measurement of the shape of the boson rapidity distribution for p\bar{p}-> Z/gamma*-> e+e- +X events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71< M_ee < 111 GeV and uses 0.4 fb^-1 of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of NNLO QCD are found to agree well with the data over the full rapidity range.

hep-ex↗
arXiv2007

Measurement of the top quark mass in the lepton+jets channel using the Ideogram Method

A measurement of the top quark mass using events with one charged lepton, missing transverse energy, and jets in the final state, collected by the D0 detector from p-pbar collisions at sqrt{s} = 1.96 TeV at the Fermilab Tevatron collider, is presented. A constrained fit is used to fully reconstruct the kinematics of the events. For every event a top quark mass likelihood is calculated taking into account all possible jet assignments and the probability that an event is signal or background. Lifetime-based identification of b jets is employed to enhance the separation between t-tbar signal and background from other physics processes and to improve the assignment of the observed jets to the quarks in the t-tbar hypothesis. We extract a multiplicative jet energy scale factor JES in-situ, greatly reducing the systematic effect related to the jet energy measurement. In a data sample with an integrated luminosity of 425 pb-1, we observe 230 candidate events, with an estimated background of 123 events, and measure m_t = 173.7 +-4.4 (stat + JES) +2.1/-2.0 (syst) GeV. This result represents the first application of the Ideogram technique to the measurement of the top quark mass in lepton+jets events.

hep-ex↗
arXiv2007

Measurement of the ttbar production cross section in pbarp collisions at sqrt(s) = 1.96 TeV using secondary vertex b tagging

We report a new measurement of the ttbar production cross section in pbarp collisions at a center-of-mass energy of 1.96 TeV using events with one charged lepton (electron or muon), missing transverse energy, and jets. Using 425 pb^{-1} of data collected using the D0 detector at the Fermilab Tevatron Collider, and enhancing the ttbar content of the sample by tagging b jets with a secondary vertex tagging algorithm, the ttbar production cross section is measured to be: 6.6 \pm 0.9 (stat+syst) \pm 0.4 (lum) pb. This cross section is the most precise D0 measurement to date for ttbar production and is in good agreement with standard model expectations.

hep-ex↗
arXiv2007

Search for the pair production of scalar top quarks in the acoplanar charm jet topology in p pbar collisions at sqrt(s)=1.96 TeV

A search for the pair production of scalar top quarks, or stops, has been performed in 360 pb-1 of data from p pbar collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron collider. The stop decay mode considered is stop into c chi, where chi is the lightest supersymmetric particle. The topology analyzed therefore consists of a pair of acoplanar heavy-flavor jets with missing transverse energy. The data and standard model expectation are in agreement, and a 95% C.L. exclusion domain in the stop and chi mass plane has been determined, extending the domain excluded by previous experiments.

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arXiv2007

Experimental discrimination between charge 2e/3 top quark and charge 4e/3 exotic quark production scenarios

We present the first experimental discrimination between the 2e/3 and 4e/3 top quark electric charge scenarios, using top quark pairs (ttbar) produced in ppbar collisions at sqrt{s}=1.96 TeV by the Fermilab Tevatron collider. We use 370 pb-1 of data collected by the D0 experiment and select events with at least one high transverse momentum electron or muon, high transverse energy imbalance, and four or more jets. We discriminate between b- and bbar-quark jets by using the charge and momenta of tracks within the jet cones. The data is consistent with the expected electric charge, |q|=2e/3. We exclude, at the 92% C.L., that the sample is solely due to the production of exotic quark pairs QQbar with |q|=4e/3. We place an upper limit on the fraction of QQbar pairs fq < 0.80 at the 90% C.L.

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arXiv2007

Measurement of the charge asymmetry in semileptonic Bs decays

We have performed the first direct measurement of the time integrated flavor untagged charge asymmetry in semileptonic Bs decays, Asl(unt), by comparing the decay rate of Bs --> mu+ Ds- nu X, where Ds- --> phi pi- and phi --> K+K-, with the charge-conjugate Bs-bar decay rate. This sample was selected from 1.3/fb of data collected by the D0 experiment in RunII of the Fermilab Tevatron collider. We obtain Asl(unt) = [1.23 +- 0.97(stat) +- 0.17(syst)]*10^-2. Assuming that Delta(M_s)/Gamma_s >> 1 and Delta(Gamma_s)/(2 Gamma_s) < 1, this result can be translated into a measurement on the CP-violating phase in Bs mixing: Delta(Gamma_s)/Delta(M_s)*tan(phi_s) = [2.45 +- 1.93(stat) +- 0.35(syst)]*10^-2.

hep-ex↗
arXiv2006

Search for Neutral Higgs Bosons Decaying to Tau Pairs in p-pbar Collisions at sqrt(s) = 1.96 TeV

A search for the production of neutral Higgs bosons Phi decaying into tau^+tau^- final states in p-pbar collisions at a center-of-mass energy of 1.96 TeV is presented. The data, corresponding to an integrated luminosity of up to 348 pb^-1, were collected by the D0 experiment at the Fermilab Tevatron Collider. Since no excess compared to the expectation from standard model processes is found, limits on the production cross section times branching ratio are set. The results are combined with those obtained from the D0 search for Phi b(b) to b-bbar-b(bbar) and are interpreted in the minimal supersymmetric standard model.

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arXiv2006

Measurement of the ppbar to ttbar production cross section at sqrt(s)=1.96 TeV in the fully hadronic decay channel

A measurement of the top quark pair production cross section in proton anti-proton collisions at an interaction energy of sqrt(s)=1.96 TeV is presented. This analysis uses 405 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. Fully hadronic ttbar decays with final states of six or more jets are separated from the multijet background using secondary vertex tagging and a neural network. The ttbar cross section is measured as sigma(ttbar)=4.5 -1.9 +2.0 (stat) -1.1 +1.4 (syst) +/- 0.3 (lumi) pb for a top quark mass of m(t) = 175 GeV/c^2.

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arXiv2006

Search for techniparticles in e +jets events at D0

We search for the technicolor process ppbar -> rho_T/omega_T ->W+pi_T in events containing one electron and two jets, in data corresponding to an integrated luminosity of 390 pb-1, recorded by the D0 experiment at the Fermilab Tevatron. Technicolor predicts that technipions, pi_T, decay dominantly into b-bbar, b-cbar, or bbar-c, depending on their charge. In these events b and c quarks are identified by their secondary decay vertices within jets. Two analysis methods based on topological variables are presented. Since no excess above the standard model prediction was found, the result is presented as an exclusion in the pi_T vs. rho_T mass plane for a given set of model parameters.

hep-ex↗
arXiv2006

Measurement of the $B^{0}_{s}$ Lifetime Using Semileptonic Decays

We report a measurement of the $B^0_{s}$ lifetime in the semileptonic decay channel $B^0_{s}\to D^-_s μ^{+}νX$ (and its charge conjugate), using approximately 0.4 fb$^{-1}$ of data collected with the D0 detector during 2002 -- 2004. We have reconstructed 5176 $D^-_s μ^{+}$ signal events, where the $D_s^-$ is identified via the decay $D_s^-\to ϕπ^-$, followed by $ϕ\to K^+ K^-$. Using these events, we have measured the $B^0_s$ lifetime to be $τ(B^0_{s}) = 1.398 \pm 0.044$ $({stat}) ^{+0.028}_{-0.025}$ $({syst}) {ps}$. This is the most precise measurement of the $B_s^0$ lifetime to date.

hep-ex↗
arXiv2006

Search for pair production of scalar bottom quarks in ppbar collisions at sqrt(s)=1.96 TeV

A search for direct production of scalar bottom quarks (sb) is performed with 310 pb-1 of data collected by the DO experiment in ppbar collisions at sqrt(s)=1.96 TeV at the Fermilab Tevatron Collider. The topology analyzed consists of two b jets and an imbalance in transverse momentum due to undetected neutralinos chi0_1, with chi0_1 assumed to be the lightest supersymmetric particle. We find the data consistent with standard model expectations, and set a 95% C.L. exclusion domain in the (m_sb,m_chi0_1) mass plane, improving significantly upon the results from Run I of the Tevatron.

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arXiv2006

Search for associated Higgs boson production WH->WWW*->l+-nu l'+-nu'+X in p-pbar collisions at sqrt(s)=1.96 TeV

We present a search for associated Higgs boson production in the process $p\bar{p} \to WH\to WWW^*\to l^\pmνl'^\pmν'+X$ in final states containing two like-sign isolated electrons or muons ($e^\pm e^\pm$, $e^\pm μ^\pm$, or $μ^\pm μ^\pm$). The search is based on D0 Run II data samples corresponding to integrated luminosities of 360--380 pb$^{-1}$. No excess is observed over the predicted standard model background. We set 95% C.L. upper limits on $σ(p\bar{p}\to WH)\times Br(H\to WW^*)$ between 3.2 and 2.8 pb for Higgs masses from 115 to 175 GeV.

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arXiv2006

Search for W' boson production in the W'->tb decay channel

We present a search for the production of a new heavy gauge boson W' that decays to a top quark and a bottom quark. We have analyzed 230 pb^{-1} of data collected with the Dzero detector at the Fermilab Tevatron collider at a center-of-mass energy of 1.96 TeV. No significant excess of events above the standard model expectation is found in any region of the final state invariant mass distribution. We set upper limits on the production cross section of W' bosons times branching ratio to top quarks at the 95% confidence level for several different W' boson masses. We exclude masses between 200 GeV and 610 GeV for a W' boson with standard-model-like couplings, between 200 GeV and 630 GeV for a W' boson with right-handed couplings that is allowed to decay to both leptons and quarks, and between 200 GeV and 670 GeV for a W' boson with right-handed couplings that is only allowed to decay to quarks.

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arXiv2006

Measurement of the top quark mass in the lepton+jets final state with the matrix element method

We present a measurement of the top quark mass with the Matrix Element method in the lepton+jets final state. As the energy scale for calorimeter jets represents the dominant source of systematic uncertainty, the Matrix Element likelihood is extended by an additional parameter, which is defined as a global multiplicative factor applied to the standard energy scale. The top quark mass is obtained from a fit that yields the combined statistical and systematic jet energy scale uncertainty. Using a data set of 370 pb-1 taken with the D0 experiment at Run II of the Fermilab Tevatron Collider, the mass of the top quark is measured using topological information to be: mtop(topo) = 169.2 +5.0-7.4 (stat.+JES) +1.5-1.4 (syst.) GeV, and when information about identified $b$ jets is included: mtop(b-tag) = 170.3 +4.1-4.5 (stat.+JES) +1.2-1.8 (syst.) GeV. The measurements yield a jet energy scale consistent with the reference scale.

hep-ex↗
arXiv2006

Measurement of the W boson helicity in top quark decay at D0

We present a measurement of the fraction f_+ of right-handed W bosons produced in top quark decays, based on a candidate sample of ttbar events in the l+jets and dilepton decay channels corresponding to an integrated luminosity of 370 pb^-1 collected by the DO detector at the Fermilab Tevatron ppbar Collider at sqrt{s}=1.96 TeV. We reconstruct the decay angle theta^* for each lepton. By comparing the \cosθ^* distribution from the data with those for the expected background and signal for various values of f_+, we find $f_+=0.056 +- 0.080 (stat) +- 0.057 (syst)}. (f_+ < 0.23 at 95% C.L.), consistent with the standard model prediction of f_+=3.6 x10^-4.

hep-ex↗
arXiv2006

Measurement of Bd mixing using opposite-side flavor tagging

We report on a measurement of the $B^0_d$ mixing frequency and the calibration of an opposite-side flavor tagger in the DØexperiment. Various properties associated with the $b$ quark on the opposite side of the reconstructed $B$ meson were combined using a likelihood-ratio method into a single variable with enhanced tagging power. Its performance was tested with data, using a large sample of reconstructed semileptonic $B \to μ\dzero X$ and $B \to μ\dst X$ decays, corresponding to an integrated luminosity of approximately 1 fb$^{-1}$. The events were divided into groups depending on the value of the combined tagging variable, and an independent analysis was performed in each group. Combining the results of these analyses, the overall effective tagging power was found to be eD^2 = (2.48 \pm 0.21 (stat.) ^{+0.08}_{-0.06} (syst.))%. The measured $B^0_d$ mixing frequency dmd = 0.506 \pm 0.020 {\rm (stat) \pm 0.016 (syst) ps}^{-1} is in good agreement with the world average value.

hep-ex↗
arXiv2006

Search for scalar leptoquarks in the acoplanar jet topology in ppbar collisions at sqrt(s)=1.96 TeV

A search for leptoquarks has been performed in 310 pb-1 of data from ppbar collisions at a center-of-mass energy of 1.96 TeV, collected by the D0 detector at the Fermilab Tevatron Collider. The topology analyzed consists of acoplanar jets with missing transverse energy. The data show good agreement with standard model expectations, and a lower mass limit of 136 GeV has been set at the 95% C.L. for a scalar leptoquark decaying exclusively into a quark and a neutrino.

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