arXiv subjects

D0 Collaboration

Publications and source records attributed to D0 Collaboration.

At least 271 records · Page 15Linked to original sources

arXiv2007

Measurement of the p\bar{p}\to WZ + X cross section at \sqrt{s}=1.96 TeV and limits on WWZ trilinear gauge couplings

We present measurements of the process $p\bar{p} \to WZ+X \to \ell^{\prime} ν_{\ell^{\prime}} \ell \bar{\ell}$ at $\sqrt{s}=1.96$ TeV, where $\ell$ and $\ell^{\prime}$ are electrons or muons. Using 1 fb$^{-1}$ of data from the D0 experiment, we observe 13 candidates with an expected background of $4.5\pm0.6$ events and measure a cross section $σ(WZ)=2.7^{+1.7}_{-1.3}$ pb. From the number of observed events and the $Z$ boson transverse momentum distribution, we limit the trilinear $WWZ$ gauge couplings to $-0.17 \le λ_Z \le 0.21$ $(Δκ_Z = 0)$ at the 95% C.L. for a form factor scale $Λ=2$ TeV. Further, assuming that $Δg^Z_1 = Δκ_Z$, we find $-0.12 \le Δκ_Z \le 0.29$ $(λ_Z=0)$ at the 95% C.L. These are the most restrictive limits on the $WWZ$ couplings available to date.

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arXiv2007

Direct observation of the strange b baryon Xi_b^{-}

We report the first direct observation of the strange b baryon Xi_b^{-}. We reconstruct the decay Xi_b^{-} to J/psi Xi^{-}, with J/psi to dimuons and Xi^{-} to Lambda pion, in ppbar collisions at sqrt(s) = 1.96 TeV. Using 1.3 fb^{-1} of data collected by the D0 detector, we observe 15.2 +/- 4.4(stat.)+ 1.9/-0.4(syst.) Xi_b^{-} candidates at a mass of 5.774 +/- 0.011(stat.) +/- 0.015 (syst.) GeV. The significance of the observed signal is 5.5 sigmas, equivalent to a probability of 3.3 X 10^{-8} of it arising from a background fluctuation. Normalizing to the decay Lambda_b to J/psi Lambda, we measure the relative rate to be 0.28 +/- 0.09(stat.)+ 0.09/-0.08 (syst.).

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arXiv2007

Measurement of the Lambda_b lifetime in the exclusive decay Lambda_b to J/psi Lambda

We have measured the Lambda_b lifetime using the exclusive decay Lambda_b to J/psi Lambda, based on 1.2 fb-1 of data collected with the D0 detector during 2002-2006. From 171 reconstructed Lambda_b decays, where the J/psi and Lambda are identified via the decays J/psi to mu+ mu- and Lambda to p pi, we measured the Lambda_b lifetime to be tau(Lambda_b) = 1.218(+0.130,-0.115)(stat) +/- 0.042(syst)ps. We also measured the B0 lifetime in the decay B0 to J/psi(mu+ mu-)K0_S(pi+ pi-) to be tau(B0) = 1.501(+0.078,-0.074)(stat) +/ -0.050(syst)ps, yielding a lifetime ratio of tau(Lambda_b)/tau(B0) = 0.811(+0.096,-0.087)(stat) +/ -0.034(syst). These measurements are consistent with the current world averages and support the shorter lifetime of the Lambda_b with respect to B mesons, in contrast to another recent measurement of significant precision.

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arXiv2007

Search for stopped gluinos from p-pbar collisions at sqrt(s)=1.96 TeV

Long-lived, heavy particles are predicted in a number of models beyond the standard model of particle physics. We present the first direct search for such particles' decays, occurring up to 100 hours after their production and not synchronized with an accelerator bunch crossing. We apply the analysis to the gluino (~g), predicted in split supersymmetry, which after hadronization can become charged and lose enough momentum through ionization to come to rest in dense particle detectors. Approximately 410 pb^-1 of p-pbar collisions at 1.96 TeV collected with the D0 detector during Run II of the Fermilab Tevatron collider are analyzed in search of such ``stopped gluinos'' decaying into a gluon and a neutralino (~X_0), reconstructed as a jet and missing energy. No excess is observed above background, and limits are placed on the (gluino cross section) x (probability to stop) x BR(~g -> g ~X_0) as a function of the gluino and ~X_0 masses, for gluino lifetimes from 30 $μ$s -- 100 hours.

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arXiv2007

Search for flavor-changing-neutral-current D meson decays

We study the flavor-changing-neutral-current process c to u mu+ mu- using 1.3 fb^-1 of p p bar collisions at sqrt(s) = 1.96 TeV recorded by the D0 detector operating at the Fermilab Tevatron Collider. We see clear indications of the Ds+ and D+ to phi pi+ to mu+ mu- pi+ final states with significance greater than four standard deviations above background for the D+ state. We search for the continuum decay of D+ to pi+mu+mu- in the dimuon invariant mass spectrum away from the phi resonance. We see no evidence of signal above background and set a limit of B(D+ to pi+mu+mu-) < 3.9 x 10^-6 at the 90% C.L. This limit places the most stringent constraint on new phenomena in the c to u mu+ mu- transition.

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arXiv2007

Search for Bs --> mu+ mu- at D0

We report results from a search for the decay Bs --> mu+ mu- using 1.3/fb of pbar p collisions at sqrt(s)= 1.96 TeV collected by the D0 experiment at the Fermilab Tevatron Collider. We find two candidate events, consistent with the expected background of 1.24 +/- 0.99, and set an upper limit on the branching fraction of B(Bs --> mu+ mu-) < 1.2e-7 at the 95% C.L.

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arXiv2007

Measurement of the ttbar production cross section in ppbar collisions using dilepton events

We present a measurement of the ttbar pair production cross section in ppbar collisions at sqrt(s) = 1.96 TeV utilizing approximately 425 pb-1 of data collected with the D0 detector. We consider decay channels containing two high pT charged leptons (either e or μ) from leptonic decays of both top-daughter W bosons. These were gathered using four sets of selection criteria, three of which required that a pair of fully identified leptons (i.e., eμ, ee, or μμ) be found. The fourth approach imposed less restrictive criteria on one of the lepton candidates and required that at least one hadronic jet in each event be tagged as containing a b quark. For a top quark mass of 175 GeV, the measured cross section is 7.4 +/-1.4(stat} +/- 1.0(syst) pb.

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arXiv2007

Search for particles decaying into a Z boson and a photon in p\bar{p} collisions at \sqrt{s} = 1.96 TeV

We present the results of the first search for a new particle X produced in $p\bar{p}$ collisions at \sqrt{s}=1.96 TeV and subsequently decaying to Zγ. The search uses 0.3 fb$^{-1}$ of data collected with the DØdetector at the Fermilab Tevatron Collider. We set limits on the production cross section times the branching fraction $σ(p \bar{p} \to X) \times B(X\to Zγ)$ that range from 0.4 -- 3.5 pb at the 95% C.L. for $X$ with invariant masses between 100 and 1000 GeV/$c^2$ over a wide range of $X$ decay widths.

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arXiv2007

Measurement of the Lambda_b lifetime using semileptonic decays

We report a measurement of the Lambda_b lifetime using a sample corresponding to 1.3 fb$^{-1}$ of data collected by the D0 experiment in 2002--2006 during Run II of the Fermilab Tevatron collider. The Lambda_b baryon is reconstructed via the decay Lambda_b -> mu nu Lambda_c X. Using $4437 \pm 329$ signal candidates, we measure the Lambda_b lifetime to be $τ(Lambda_b)$ = 1.290^{+0.119}_{-0.110}(stat) ^{+0.087}_{-0.091} (syst) ps, which is among the most precise measurements in semileptonic Lambda_b decays. This result is in good agreement with the world average value.

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arXiv2007

Observation and Properties of L=1 B_1 and B_2* Mesons

Excited B mesons B_1 and B_2* are observed directly for the first time as two separate states in fully reconstructed decays to B+(*) pi-. The mass of B_1 is measured to be (5720.6 +- 2.4 +- 1.4) MeV/c^2 and the mass difference DeltaM between B_2* and B_1 is (26.2 +- 3.1 +- 0.9) MeV/c^2, giving the mass of the B_2* as (5746.8 +- 2.4 +- 1.7) MeV/c^2. The production rate for B_1 and B_2* mesons is determined to be a fraction (13.9 +- 1.9 +- 3.2)% of the production rate of the B+ meson.

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arXiv2007

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 production cross section in ppbar collisions at sqrt(s)=1.96 TeV utilizing 425 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. We consider the final state of the top quark pair containing one high-pT electron or muon and at least four jets. We exploit specific kinematic features of ttbar events to extract the cross section. For a top quark mass of 175 GeV, we measure sigma_ttbar = 6.4 +1.3-1.2(stat} +/- 0.7(syst)+/- 0.4(lum) pb in good agreement with the standard model prediction.

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arXiv2007

Search for third-generation leptoquarks in ppbar collisions at sqrt(s)=1.96 TeV

We report on a search for charge-1/3 third-generation leptoquarks (LQ) produced in ppbar collisions at sqrt(s)=1.96 TeV using the D0 detector at Fermilab. Third generation leptoquarks are assumed to be produced in pairs and to decay to a tau neutrino and a b quark with branching fraction B. We place upper limits on sigma(ppbar->LQLQbar)*B^2 as a function of the leptoquark mass M_{LQ}. Assuming B=1, we exclude at the 95% confidence level third-generation scalar leptoquarks with M_{LQ} < 229 GeV.

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arXiv2007

Search for a Higgs boson produced in association with a Z boson in ppbar collisions

We describe a search for the standard model Higgs boson with a mass of 105 GeV/c^2 to 145 GeV/c^2 in data corresponding to an integrated luminosity of approximately 450 pb^{-1} collected with the D0 detector at the Fermilab Tevatron ppbar collider at a center-of-mass energy of 1.96 TeV. The Higgs boson is required to be produced in association with a Z boson, and the Z boson is required to decay to either electrons or muons with the Higgs boson decaying to a bbbar pair. The data are well described by the expected background, leading to 95% confidence level cross section upper limits sigma(\ppbar\to ZH)x B(H\to\bbbar) in the range of 3.1 pb to 4.4 pb.

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arXiv2007

Evidence for production of single top quarks and first direct measurement of |Vtb|

The D0 Collaboration presents first evidence for the production of single top quarks at the Fermilab Tevatron ppbar collider. Using a 0.9 fb^-1 dataset, we apply a multivariate analysis to separate signal from background and measure sigma(ppbar->tb+X,tqb+X) = 4.9 +- 1.4 pb. The probability to measure a cross section at this value or higher in the absence of signal is 0.035%, corresponding to a 3.4 standard deviation significance. We use the cross section measurement to directly determine the CKM matrix element that describes the Wtb coupling and find 0.68 < |Vtb| <= 1 at 95% C.L. within the standard model.

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arXiv2007

Measurement of the ratios of the Z/G* + >= n jet production cross sections to the total inclusive Z/G* cross section in ppbar collisions at sqrt(s) = 1.96 TeV

We present a study of events with Z bosons and jets produced at the Fermilab Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV. The data sample consists of nearly 14,000 Z/G* -> e+e- candidates corresponding to the integrated luminosity of 0.4 fb-1 collected using the D0 detector. Ratios of the Z/G* + >= n jet cross sections to the total inclusive Z/G* cross section have been measured for n = 1 to 4 jet events. Our measurements are found to be in good agreement with a next-to-leading order QCD calculation and with a tree-level QCD prediction with parton shower simulation and hadronization.

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arXiv2007

Search for single production of scalar leptoquarks in p\bar{p} collisions decaying into muons and quarks with the D0 detector

We report on a search for second generation leptoquarks LQ_2 which decay into a muon plus quark in p\bar{p} collisions at a center-of-mass energy of sqrt{s} = 1.96 TeV in the D0 detector using an integrated luminosity of about 300 pb-1. No evidence for a leptoquark signal is observed and an upper bound on the product of the cross section for single leptoquark production times branching fraction beta into a quark and a muon was determined for second generation scalar leptoquarks as a function of the leptoquark mass. This result has been combined with a previously published D0 search for leptoquark pair production to obtain leptoquark mass limits as a function of the leptoquark-muon-quark coupling, lambda. Assuming lambda=1, lower limits on the mass of a second generation scalar leptoquark are m{LQ_2}>274 GeV and m{LQ_2}>226 GeV for beta=1 and beta=1/2, respectively.

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arXiv2007

Measurement of the branching fraction Br(Bs -> Ds() Ds())

We report a measurement of the branching fraction Br(Bs -> Ds(*) Ds(*)) using a data sample corresponding to 1.3 fb^{-1} of integrated luminosity collected by the D0 experiment in 2002-2006 during Run II of the Fermilab Tevatron Collider. One Ds(*) meson was partially reconstructed in the decay Ds -> phi mu nu, and the other Ds(*) meson was identified using the decay Ds -> phi pi where no attempt was made to distinguish Ds and Ds* states. The resulting measurement is Br(Bs -> Ds(*) Ds(*)) = 0.039 +0.019 -0.017 (stat) +0.016 -0.015 (syst). This was subsequently used to estimate the width difference Delta Gamma^{CP}_s in the Bs-Bsbar system: Delta Gamma^{CP}_s / Gamma_s = 0.079 +0.038 -0.035 (stat) +0.031 -0.030 (syst).

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arXiv2007

Combined D0 Measurements Constraining the CP-violating Phase and Width Difference in the $B_s^0$ System

We combine the D0 measurement of the width difference between the light and heavy B_s^0 mass eigenstates and of the CP-violating mixing phase determined from the time-dependent angular distributions in the B_s -> J/psi phi decays along with the charge asymmetry in semileptonic decays also measured with the D0 detector. With the additional constraint from the world average of the flavor-specific B_s^0 lifetime, we obtain Delta Gamma_s = (Γ_L - Γ_H) = 0.13 +- 0.09 ps$^{-1}$ and phi_s = -0.70 ^{+0.47}_{-0.39}. The data sample corresponds to an integrated luminosity of 1.1 fb^{-1} accumulated with the D0 detector at the Fermilab Tevatron Collider.

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