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D0 Collaboration

Publications and source records attributed to D0 Collaboration.

At least 253 records · Page 14Linked to original sources
arXiv2008

Study of direct CP violation in $B^{\pm} \to J/ψK^{\pm}(π^{\pm})$ decays

We present a search for direct CP violation in $B^{\pm} \to J/ψK^{\pm}(π^{\pm})$ decays. The event sample is selected from 2.8 fb$^{-1}$ of $p\bar{p}$ collisions recorded by D0 experiment in Run II of the Fermilab Tevatron Collider. The charge asymmetry $A_{CP}(B^+ \to J/ψK^+) = +0.0075 \pm 0.0061$(stat.)$\pm 0.0027$(syst.) is obtained using a sample of approximately 40 thousand $B^{\pm} \to J/ψK^{\pm}$ decays. The achieved precision is of the same level as the expected deviation predicted by some extensions of the standard model. We also measured the charge asymmetry $A_{CP}(B^+ \to J/ψπ^+) = -0.09 \pm 0.08$(stat.)$\pm 0.03$(syst.).

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arXiv2008

Search for squarks and gluinos in events with jets and missing transverse energy using 2.1 fb-1 of ppbar collision data at sqrt(s)=1.96 TeV

A data sample corresponding to an integrated luminosity of 2.1 fb-1 collected by the D0 detector at the Fermilab Tevatron Collider was analyzed to search for squarks and gluinos produced in ppbar collisions at a center-of-mass energy of 1.96 TeV. No evidence for the production of such particles was observed in topologies involving jets and missing transverse energy, and 95% C.L. lower limits of 379 GeV and 308 GeV were set on the squark and gluino masses, respectively, within the framework of minimal supergravity with tan(beta)=3, A0=0, and mu<0. The corresponding previous limits are improved by 54 GeV and 67 GeV.

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arXiv2008

Measurement of $\boldmath {B_s^0}$ mixing parameters from the flavor-tagged decay

From an analysis of the flavor-tagged decay \bsdec we obtain the width difference between the $B_s^0$ light and heavy mass eigenstates, $ΔΓ_s \equiv Γ_L - Γ_H = 0.19 \pm 0.07 {\rm (stat)}\thinspace ^{+0.02}_{-0.01} {\rm (syst)}$ ps$^{-1}$, and the CP-violating phase, $ϕ_{s} =-0.57 ^{+0.24}_{-0.30} {\rm (stat)}\thinspace ^{+0.07}_{-0.02} {\rm (syst)}$. The allowed 90% C.L. intervals of $ΔΓ_s$ and $ϕ_s$ are $0.06 <ΔΓ_s <0.30$ ps$^{-1}$ and $-1.20 <ϕ_s < 0.06$, respectively. The data sample corresponds to an integrated luminosity of 2.8 fb$^{-1}$ accumulated with the D0 detector at the Fermilab Tevatron collider.

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arXiv2008

Search for production of single top quarks via $tcg$ and $tug$ flavor-changing neutral current couplings

We search for the production of single top quarks via flavor-changing neutral current couplings of a gluon to the top quark and a charm ($c$) or up ($u$) quark. We analyze 230 pb$^{-1}$ of lepton + jets data from $\ppbar$ collisions at a center of mass energy of 1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider. We observe no significant deviation from standard model predictions, and hence set upper limits on the anomalous coupling parameters $\kappacLambda$ and $\kappauLambda$, where $\kappag$ define the strength of $tcg$ and $tug$ couplings, and $Λ$ defines the scale of new physics. The limits at 95% C.L. are: $\kappacLambda < 0.15 \rm TeV^{-1}$ and $\kappauLambda < 0.037 \rm TeV^{-1}$.

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arXiv2008

Search for excited electrons in ppbar collisions at sqrt(s) = 1.96 TeV

We present the results of a search for the production of an excited state of the electron, e*, in proton-antiproton collisions at sqrt(s) = 1.96 TeV. The data were collected with the D0 experiment at the Fermilab Tevatron Collider and correspond to an integrated luminosity of approximately 1 fb^-1. We search for e* in the process ppbar -> e* e, with the e* subsequently decaying to an electron plus photon. No excess above the standard model background is observed. Interpreting our data in the context of a model that describes e* production by four-fermion contact interactions and e* decay via electroweak processes, we set 95% C.L. upper limits on the production cross section ranging from 8.9 fb to 27 fb, depending on the mass of the excited electron. Choosing the scale for contact interactions to be Lambda = 1 TeV, excited electron masses below 756 GeV are excluded at the 95% C.L.

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arXiv2008

Search for the lightest scalar top quark in events with two leptons in p-pbar collisions at sqrt(s) = 1.96 TeV

Data collected by the D0 detector at a p-pbar center-of-mass energy of 1.96 TeV at the Fermilab Tevatron Collider have been used to search for pair production of the lightest supersymmetric partner of the top quark decaying into $b \ell \tildeν$. The search is performed in the $\ell\ell' = eμ$ and $μμ$ final states. No evidence for this process has been found in data samples of approximately 400 pb^-1. The domain in the [$M(\tilde{t}_1),M(\tildeν)$] plane excluded at the 95% C.L. is substantially extended by this search.

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arXiv2007

Zgamma production and limits on anomalous ZZgamma and Zgammagamma couplings in ppbar collisions at sqrt(s) = 1.96 TeV

We present a study of eegamma and mumugamma events using 1109 (1009) pb-1 of data in the electron (muon) channel, respectively. These data were collected with the D0 detector at the Fermilab Tevatron ppbar Collider at sqrt(s) = 1.96 TeV. Having observed 453 (515) candidates in the eegamma (mumugamma) final state, we measure the Zgamma production cross section for a photon with transverse energy ET > 7 GeV, separation between the photon and leptons Delta R(lgamma) > 0.7, and invariant mass of the di-lepton pair M(ll) > 30 GeV/c^2, to be 4.96 +/- 0.30(stat. + syst.) +/- 0.30(lumi.) pb, in agreement with the standard model prediction of 4.74 +/- 0.22 pb. This is the most precise Zgamma cross section measurement at a hadron collider. We set limits on anomalous trilinear Zgammagamma and ZZgamma gauge boson couplings of -0.085 < h(30)^(gamma) < 0.084, -0.0053 < h(40)^(gamma) < 0.0054 and -0.083 < h(30)^(Z) < 0.082, -0.0053 < h(40)^(Z) < 0.0054 at the 95% C.L. for the form-factor scale Lambda = 1.2 TeV.

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arXiv2007

Model-independent measurement of the W boson helicity in top quark decays

We present the first model-independent measurement of the helicity of $W$ bosons produced in top quark decays, based on a 1 fb$^{-1}$ sample of candidate $t\bar{t}$ events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. We reconstruct the angle $θ^*$ between the momenta of the down-type fermion and the top quark in the $W$ boson rest frame for each top quark decay. A fit of the resulting \costheta distribution finds that the fraction of longitudinal $W$ bosons $f_0 = 0.425 \pm 0.166 \hbox{(stat.)} \pm 0.102 \hbox{(syst.)}$ and the fraction of right-handed $W$ bosons $f_+ = 0.119 \pm 0.090 \hbox{(stat.)} \pm 0.053 \hbox{(syst.)}$, which is consistent at the 30% C.L. with the standard model.

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arXiv2007

First measurement of the forward-backward charge asymmetry in top quark pair production

We present the first measurement of the integrated forward-backward charge asymmetry in top-antitop quark pair (ttbar) production in proton-antiproton collisions in the lepton plus jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming ttbar+X production and decay, a sample of 0.9fb-1 of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on ttbar+X production via a Z' resonance.

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arXiv2007

A combined search for the standard model Higgs boson at sqrt{s}=1.96 TeV

We present new results of the search for WH to lepton neutrino b b production in ppbar collisions at a center of mass energy of sqrt{s}=1.96 TeV, based on a dataset with integrated luminosity of 0.44 fb-1. We combine these new results with previously published searches by the D0 collaboration, for WH and ZH production analyzed in the MET b b final state, for ZH (to l+l- b b) production, for WH (to WWW) production, and for H (to WW) direct production. No signal-like excess is observed either in the WH analysis or in the combination of all D0 Higgs boson analyses. We set 95% C.L. (expected) upper limits on to 1.9 (3.3) pb for Higgs boson masses between 105 and 145 GeV, to be compared to the theoretical prediction of 0.13 pb for a standard model (SM) Higgs boson with mass m_H=115 GeV. After combination with the other D0 Higgs boson searches, we obtain for m_H=115 GeV an observed (expected) limit 8.5 (12.1) times higher than the SM predicted Higgs boson production cross section. For m_H=160 GeV, the corresponding observed (expected) ratio is 10.2 (9.0).

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arXiv2007

Search for ZZ and Zγ^* production in p-barp collisions at sqrt(s) = 1.96 TeV and limits on anomalous ZZZ and ZZγ^* couplings

We present a study of four muon, four electron, and two muon two electron events using 1 fb^(-1) of data collected with the D0 detector at the Fermilab Tevatron p-barp Collider at sqrt(s) = 1.96 TeV. Requiring the lepton pair masses to be greater than 30 GeV, we observe one event, consistent with the expected background of 0.13 +- 0.03 events and with the predicted standard model ZZ and Zγ^* production of 1.71 +-0.15 events. We set an upper limit on the ZZ and Zγ^* cross section of 4.4 pb at the 95% C.L. We also derive limits on anomalous neutral trilinear ZZZ and ZZγ^* gauge couplings. The one-parameter 95%$ C.L. coupling limits with a form factor scale Lambda = 1.2 TeV are -0.28 < f_(40)^Z < 0.28, -0.31 < f_(50)^Z < 0.29, -0.26 < f_(40)^γ< 0.26, and -0.30 < f_(5 0)^γ< 0.28.

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arXiv2007

Observation and properties of the orbitally excited B_{s2}* Meson

We report the direct observation of the excited L=1 state B_{s2}* in fully reconstructed decays to B+K-. The mass of the B_{s2}* meson is measured to be {5839.6 +- 1.1 (stat.) +- 0.7 (syst.) MeV/c^2, and its production rate relative to the B+ meson is measured to be [1.15 +- 0.23 (stat.) +- 0.13 (syst.)] %.

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arXiv2007

Measurement of the top quark mass in the dilepton channel

We present a measurement of the top quark mass in the dilepton channel based on approximately 370/pb of data collected by the D0 experiment during Run II of the Fermilab Tevatron collider. We employ two different methods to extract the top quark mass. We show that both methods yield consistent results using ensemble tests of events generated with the D0 Monte Carlo simulation. We combine the results from the two methods to obtain a top quark mass m_t = 178.1 +/- 8.2 GeV. The statistical uncertainty is 6.7 GeV and the systematic uncertainty is 4.8 GeV.

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arXiv2007

Search for Randall-Sundrum gravitons with 1 fb-1 of data from ppbar collisions at sqrt(s)=1.96 TeV

Using 1 fb-1 of data from ppbar collisions at sqrt(s)=1.96 TeV at the Fermilab Tevatron collider collected by the D0 detector, we search for decays of Kaluza-Klein excitations of the graviton in the Randall-Sundrum model of extra dimensions to e+e- and diphotons. We set 95% confidence level upper limits on the production cross section times branching fraction which translate into lower limits on the mass of the lightest excitation between 300 and 900 GeV for values of the coupling k/M(Planck) between 0.01 and 0.1.

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arXiv2007

Search for W' bosons decaying to an electron and a neutrino with the D0 detector

This Letter describes the search for a new heavy charged gauge boson W' decaying into an electron and a neutrino. The data were collected with the D0 detector at the Fermilab Tevatron proton-antiproton Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of about 1 inverse femtobarn. Lacking any significant excess in the data in comparison with known processes, an upper limit is set on the production cross section times branching fraction, and a W' boson with mass below 1.00 TeV can be excluded at the 95% C.L., assuming standard-model-like couplings to fermions. This result significantly improves upon previous limits, and is the most stringent to date.

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arXiv2007

Search for Scalar Top Admixture in the ttbar Lepton+Jets Channel at D0

A search has been performed for scalar top quark pair production in the lepton+jets channel in ~1 fb^(-1) of data. Kinematic differences between the exotic stop-stopbar and the dominant ttbar process are used to separate the two possible contributions. For scalar top quark masses of 145-175 GeV and chargino masses of 105-135 GeV we obtain upper cross section limits at 95% confidence level for stop-stopbar production that are a factor of ~7-12 higher than expected for the Minimal Supersymmetric Standard Model (MSSM).

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arXiv2007

Measurement of the muon charge asymmetry from W boson decays

We present a measurement of the muon charge asymmetry from W boson decays using 0.3 fb^{-1} of data collected at \sqrt{s}=1.96 GeV between 2002 and 2004 with the D0 detector at the Fermilab Tevatron ppbar Collider. We compare our findings with expectations from next-to-leading-order calculations performed using the CTEQ6.1M and MRST04 NLO parton distribution functions. Our findings can be used to constrain future parton distribution function fits.

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