arXiv subjects

D0 Collaboration

Publications and source records attributed to D0 Collaboration.

At least 325 records · Page 18Linked to original sources

arXiv2005

Search for single top quark production in ppbar collisions at sqrt(s)=1.96 TeV

We present a search for electroweak production of single top quarks in the s-channel and t-channel using neural networks for signal-background separation. We have analyzed 230 pb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy of 1.96 TeV and find no evidence for a single top quark signal. The resulting 95% confidence level upper limits on the single top quark production cross sections are 6.4 pb in the s-channel and 5.0 pb in the t-channel.

hep-ex↗

arXiv2005

Search for the Higgs boson in H->WW(*) decays in p anti-p collisions at S**(1/2) = 1.96-TEV

We present a search for the standard model Higgs boson in H->WW(*), decays with ee, emu and mumu final states in p anti-p collisions at a center-of-mass energy of S**(1/2) = 1.96-TEV. The data, collected from April 2002 to June 2004 with the D0 detector, correspond to an integrated luminosity of 300 - 325 pb**(-1), depending on the final state. The number of events observed is consistent with the expectation from backgrounds. Limits from the combination of all three channels on the Higgs production cross section times branching ratio sigma*BR(H->WW(*) are presented.

hep-ex↗

arXiv2005

Search for right-handed W bosons in top quark decay

We present a measurement of the fraction f+ of right-handed W bosons produced in top quark decays, based on a candidate sample of $t\bar{t}$ events in the lepton+jets decay mode. These data correspond to an integrated luminosity of 230pb^-1, collected by the DO detector at the Fermilab Tevatron $p\bar{p}$ Collider at sqrt(s)=1.96 TeV. We use a constrained fit to reconstruct the kinematics of the $t\bar{t}$ and decay products, which allows for the measurement of the leptonic decay angle $θ^*$ for each event. By comparing the $\cosθ^*$ distribution from the data with those for the expected background and signal for various values of f+, we find f+=0.00+-0.13(stat)+-0.07(syst). This measurement is consistent with the standard model prediction of f+=3.6x10^-4.

hep-ex↗

arXiv2005

The Upgraded D0 Detector

The D0 experiment enjoyed a very successful data-collection run at the Fermilab Tevatron collider between 1992 and 1996. Since then, the detector has been upgraded to take advantage of improvements to the Tevatron and to enhance its physics capabilities. We describe the new elements of the detector, including the silicon microstrip tracker, central fiber tracker, solenoidal magnet, preshower detectors, forward muon detector, and forward proton detector. The uranium/liquid-argon calorimeters and central muon detector, remaining from Run I, are discussed briefly. We also present the associated electronics, triggering, and data acquisition systems, along with the design and implementation of software specific to D0.

physics.ins-det↗

arXiv2005

Measurement of the Lifetime Difference in the B_s^0 System

We present a study of the decay B_s^0 -> J/psi phi We obtain the CP-odd fraction in the final state at time zero, R_perp = 0.16 +/- 0.10 (stat) +/- 0.02 (syst), the average lifetime of the (B_s, B_sbar) system, tau (B_s^0) =1.39^{+0.13}_{-0.16} (stat) ^{+0.01}_{-0.02} (syst) ps, and the relative width difference between the heavy and light mass eigenstates, Delta Gamma/Gamma = (Gamma_L - Gamma_H)/Gamma =0.24^{+0.28}_{-0.38} (stat) ^{+0.03}_{-0.04} (syst). With the additional constraint from the world average of the B_s^0$lifetime measurements using semileptonic decays, we find tau (B_s^0)= 1.39 +/- 0.06 ~ps and Delta Gamma/Γ= 0.25^{+0.14}_{-0.15}. For the ratio of the B_s^0 and B^0 lifetimes we obtain tau(B_s^0)/tau(B^0)} = 0.91 +/- 0.09 (stat) +/- 0.003 (syst).

hep-ex↗

arXiv2005

Measurement of Semileptonic Branching Fractions of B Mesons to Narrow D** States

Using the data accumulated in 2002-2004 with the DO detector in proton-antiproton collisions at the Fermilab Tevatron collider with centre-of-mass energy 1.96 TeV, the branching fractions of the decays B -> \bar{D}_1^0(2420) μ^+ ν_μX and B -> \bar{D}_2^{*0}(2460) μ^+ ν_μX and their ratio have been measured: BR(\bar{b}->B) \cdot BR(B-> \bar{D}_1^0 μ^+ ν_μX) \cdot BR(\bar{D}_1^0 -> D*- pi+) = (0.087+-0.007(stat)+-0.014(syst))%; BR(\bar{b}->B)\cdot BR(B->D_2^{*0} μ^+ ν_μX) \cdot BR(\bar{D}_2^{*0} -> D*- π^+) = (0.035+-0.007(stat)+-0.008(syst))%; and (BR(B -> \bar{D}_2^{*0} μ^+ ν_μX)BR(D2*0->D*- pi+)) / (BR(B -> \bar{D}_1^{0} μ^+ ν_μX)\cdot BR(\bar{D}_1^{0}->D*- π^+)) = 0.39+-0.09(stat)+-0.12(syst), where the charge conjugated states are always implied.

hep-ex↗

arXiv2005

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV in Dilepton Final States

We present a measurement of the top quark pair (ttbar) production cross section in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb-1 of data collected by the DO detector at the Fermilab Tevatron Collider. We select events in the dilepton final states ee, emu and mumu based on kinematical properties consistent with ttbar events. For a top quark mass of 175 GeV, we measure a top pair production cross section sigma(ttbar) = 8.6 +3.2-2.7 (stat) +/-1.1 (syst) +/-0.6 (lumi) pb, in good agreement with the standard model prediction.

hep-ex↗

arXiv2005

Measurement of $\bm{σ(p \bar p \to Z) \cdot}$Br$\bm{(Z \to ττ)}$ at $\bm{\sqrt{s}=}$1.96 TeV

We present a measurement of the cross section for $Z$ production times the branching fraction to $τ$ leptons, $σ\cdot$Br$(Z\to τ^+ τ^-)$, in $p \bar p$ collisions at $\sqrt{s}=$1.96 TeV in the channel in which one $τ$ decays into $μν_μ ν_τ$, and the other into $\rm {hadrons} + ν_τ$ or $e ν_e ν_τ$. The data sample corresponds to an integrated luminosity of 226 pb$^{-1}$ collected with the DØdetector at the Fermilab Tevatron collider. The final sample contains 2008 candidate events with an estimated background of 55%. From this we obtain $σ\cdot$Br$(Z \to τ^+ τ^-)=237 \pm 15$(stat)$\pm 18$(sys)$ \pm 15$(lum) pb, in agreement with the standard model prediction.

hep-ex↗

arXiv2005

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging

We present a measurement of the top quark pair ($t\bar{t}$) production cross section ($σ_{t\bar{t}}$) in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using 230 pb$^{-1}$ of data collected by the D0 experiment at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), missing transverse energy, and jets in the final state. We employ lifetime-based b-jet identification techniques to further enhance the $t\bar{t}$ purity of the selected sample. For a top quark mass of 175 GeV, we measure $σ_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreement with the standard model expectation.

hep-ex↗

arXiv2005

Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events

We present a measurement of the top quark pair ttbar production cross section in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1} of data collected by the DO detector at the Fermilab Tevatron Collider. We select events with one charged lepton (electron or muon), large missing transverse energy, and at least four jets, and extract the ttbar content of the sample based on the kinematic characteristics of the events. For a top quark mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1} (syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.

hep-ex↗

arXiv2005

Search for Supersymmetry via Associated Production of Charginos and Neutralinos in Final States with Three Leptons

A search for associated production of charginos and neutralinos is performed using data recorded with the D0 detector at a ppbar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider. This analysis considers final states with missing transverse energy and three leptons, of which at least two are electrons or muons. No evidence for supersymmetry is found in a dataset corresponding to an integrated luminosity of 320 pb-1. Limits on the product of the production cross section and leptonic branching fraction are set. For the minimal supergravity model, a chargino lower mass limit of 117 GeV at the 95% C.L. is derived in regions of parameter space with enhanced leptonic branching fractions.

hep-ex↗

arXiv2005

Production of WZ Events in p-barp Collisions at sqrt(s)=1.96 TeV and Limits on Anomalous WWZ Couplings

We present results from a search for WZ production with subsequent decay to l nu l'-bar l' (l and l'=electron or muon) using 0.30 fb^(-1) of data collected by the DO experiment between 2002 and 2004 at the Tevatron. Three events with WZ decay characteristics are observed. With an estimated background of 0.71+-0.08 events, we measure the WZ production cross section to be 4.5 (+3.8 -2.6) pb, with a 95% C.L. upper limit of 13.3 pb. The 95% C.L. limits for anomalous WWZ couplings are found to be -2.0 < Delta kappa_Z < 2.4 for form factor scale Lambda = 1 TeV, and -0.48 < lambda_Z < 0.48 and -0.49 < Delta g_1^Z < 0.66 for Lambda = 1.5 TeV.

hep-ex↗

arXiv2005

Search for neutral supersymmetric Higgs bosons in multijet events at sqrt(s)=1.96 TeV

We have performed a search for neutral Higgs bosons produced in association with bottom quarks in $p\bar{p}$ collisions, using 260 $pb^{-1}$ of data collected with the D0 detector in Run II of the Fermilab Tevatron Collider. The cross sections for these processes are enhanced in many extensions of the standard model (SM), such as in its minimal supersymmetric extension at large tan$β$. The results of our analysis agree with expectations from the SM, and we use our measurements to set upper limits on the production of neutral Higgs bosons in the mass range of 90 to 150 GeV.

hep-ex↗

arXiv2005

Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits

The WWgamma triple gauge boson coupling parameters are studied using p-pbar -> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were collected with the DO detector from an integrated luminosity of 162 pb^{-1} delivered by the Fermilab Tevatron Collider. The cross section times branching fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum) pb. The one-dimensional 95% confidence level limits on anomalous couplings are -0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.

hep-ex↗

arXiv2005

Study of $Zγ$ events and limits on anomalous $ZZγ$ and $Zγγ$ couplings in ppbar collisions at $sqrt(s) = 1.96$ TeV

We present a measurement of the Zγproduction cross section and limits on anomalous ZZγand Zγγcouplings for form-factor scales of Lambda = 750 and 1000 GeV. The measurement is based on 138 (152) candidate events in the eeγ(μμγ) final state using 320 (290) pb^{-1} of ppbar collisions at \sqrt{s} = 1.96 TeV. The 95% C.L. limits on real and imaginary parts of individual anomalous couplings are |h_{10,30}^{Z}|<0.23, |h_{20,40}^{Z}|<0.020, |h_{10,30}^γ|<0.23, and |h_{20,40}^γ|<0.019 for Lambda = 1000 GeV.

hep-ex↗

arXiv2005

Measurement of inclusive differential cross sections for Upsilon(1S) production in p-pbar collisions at sqrt(s) = 1.96 TeV

We present measurements of the inclusive production cross sections of the Upsilon(1S) bottomonium state in ppbar collisions at sqrt(s) = 1.96 TeV. Using the Upsilon(1S) to mu+mu- decay mode for a data sample of 159 +- 10 pb^-1 collected by the D0 detector at the Fermilab Tevatron collider, we determine the differential cross sections as a function of the Upsilon(1S) transverse momentum for three ranges of the Upsilon(1S) rapidity: 0 < |y| < 0.6, 0.6 < |y| < 1.2, and 1.2 < |y| < 1.8.

hep-ex↗

arXiv2004

A Search for the Flavor-Changing Neutral Current Decay B0_s -> mu^+mu^- in pp(bar) Collisions at \sqrt{s} = 1.96 TeV with the D0 Detector

We present the results of a search for the flavor-changing neutral current decay B0_s -> mu+ mu- using a data set with integrated luminosity of 240 pb^{-1} of pp(bar) collisions at sqrt{s}=1.96 TeV collected with the D0 detector in Run II of the Fermilab Tevatron collider. We find the upper limit on the branching fraction to be Br(B0_s -> mu+ mu-) \leq 5.0 x 10^{-7} at the 95% C.L. assuming no contributions from the decay B0_d -> mu+ mu- in the signal region. This limit is the most stringent upper bound on the branching fraction B0_s -> mu+ mu- to date.

hep-ex↗

arXiv2004

Measurement of the B^0_s lifetime in the exclusive decay channel B^0_s -> J/psi phi

Using the exclusive decay B^0_s -> J/psi (mu+mu-) phi(K+K-), we report the most precise single measurement of the B^0_s lifetime. The data sample corresponds to an integrated luminosity of approximately 220 pb-1 collected with the DO detector at the Fermilab Tevatron Collider in 2002-2004. We reconstruct 337 signal candidates, from which we extract the B^0_s lifetime, τ(B^0_s) = 1.444 +0.098/-0.090 stat +/- 0.020 sys ps. We also report a measurement for the lifetime of the B^0 meson using the exclusive decay B^0 -> J/psi (mu+mu-)K*0(892)(K+pi-). We reconstruct 1370 signal candidates, obtaining τ(B^0) = 1.473 +0.052/-0.050 stat +/- 0.023 sys ps, and the ratio of lifetimes, τ(B^0_s)/τ(B^0) = 0.980 +0.076/-0.071 stat +/- 0.003 sys.

hep-ex↗