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) \mu^+ \nu_\mu X and B -> \bar{D}_2^{*0}(2460) \mu^+ \nu_\mu X and their ratio have been measured: BR(\bar{b}->B) \cdot BR(B-> \bar{D}_1^0 \mu^+ \nu_\mu X) \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} \mu^+ \nu_\mu X) \cdot BR(\bar{D}_2^{*0} -> D*- \pi^+) = (0.035+-0.007(stat)+-0.008(syst))%; and (BR(B -> \bar{D}_2^{*0} \mu^+ \nu_\mu X)BR(D2*0->D*- pi+)) / (BR(B -> \bar{D}_1^{0} \mu^+ \nu_\mu X)\cdot BR(\bar{D}_1^{0}->D*- \pi^+)) = 0.39+-0.09(stat)+-0.12(syst), where the charge conjugated states are always implied.Comment: submitted to Phys. Rev. Let

Search for Large Extra Spatial Dimensions in Dimuon Production with the D0 Detector

We present the results of a search for the effects of large extra spatial dimensions in $p{\bar p}$ collisions at $\sqrt{s} =$ 1.96 TeV in events containing a pair of energetic muons. The data correspond to 246 \ipb of integrated luminosity collected by the \D0 experiment at the Fermilab Tevatron Collider. Good agreement with the expected background was found, yielding no evidence for large extra dimensions. We set 95% C.L. lower limits on the fundamental Planck scale between 0.85 TeV and 1.27 TeV within several formalisms. These are the most stringent limits achieved in the dimuon channel to date.Comment: 8 pages, 3 figures, 1 table. Published in Phys. Rev. Lett. Minor changes in v2 to match the published versio

Measurement of the Bs0B^{0}_{s} Lifetime Using Semileptonic Decays

We report a measurement of the $B^0_{s}$ lifetime in the semileptonic decay channel $B^0_{s}\to D^-_s \mu^{+}\nu X$ (and its charge conjugate), using approximately 0.4 fb$^{-1}$ of data collected with the D0 detector during 2002 -- 2004. We have reconstructed 5176 $D^-_s \mu^{+}$ signal events, where the $D_s^-$ is identified via the decay $D_s^-\to \phi\pi^-$, followed by $\phi\to K^+ K^-$. Using these events, we have measured the $B^0_s$ lifetime to be $\tau(B^0_{s}) = 1.398 \pm 0.044$ $({stat}) ^{+0.028}_{-0.025}$ $({syst}) {ps}$. This is the most precise measurement of the $B_s^0$ lifetime to date.Comment: To appear in Phys. Rev. Lett., 7 pages, 2 figure

Search for the Rare Decay B0_s -> phi mu^+ mu- with the D0 Detector

We present a search for the flavor-changing neutral current decay B0_s -> phi mu+ mu- using about 0.45 fb^-1 of data collected in p \bar p collisions at sqrt{s} =1.96 TeV with the D{\O}detector at the Fermilab Tevatron Collider. We find an upper limit on the branching ratio of this decay normalized to B0_s -> J/psi phi of B(B0_s -> phi mu+ mu-)/B(B0_s -> J/psi phi) < 4.4\times 10^{-3} at the 95% C.L. Using the central value of the world average branching fraction of B0_s -> J/psi phi, the limit corresponds to B(B0_s -> phi mu+ mu-) < 4.1 \times 10^{-6} at the 95% C.L., the most stringent upper bound to date.Comment: 7 pages, 2 figures, LaTeX, to be submitted to Physical Review Letter

Multivariate searches for single top quark production with the D0 detector

We present a search for electroweak production of single top quarks in the s-channel (p-pbar -> t bbar + X) and t-channel (p-pbar -> tq bbar + X) modes. 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 sqrt(s) = 1.96 TeV. Two separate analysis methods are used: neural networks and a cut-based analysis. No evidence for a single top quark signal is found. We set 95% confidence level upper limits on the production cross sections using Bayesian statistics, based on event counts and binned likelihoods formed from the neural network output. The limits from the neural network (cut-based) analysis are 6.4 pb (10.6 pb) in the s-channel and 5.0 pb (11.3 pb) in the t-channel.Comment: submitted to Phys. Rev. D, Fermilab preprint Fermilab-Pub-06/069-

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.Comment: 7 pages, 3 figures, LaTeX, to be submitted to Physical Review Letters, minor changes to text, reference adde

Search for a heavy resonance decaying into a Z+jet final state in p-pbar collisions at sqrt(s) = 1.96 TeV using the D0 detector

We have searched for a heavy resonance decaying into a Z+jet final state in p-pbar collisions at a center of mass energy of 1.96 TeV at the Fermilab Tevatron collider using the D0 detector. No indication for such a resonance was found in a data sample corresponding to an integrated luminosity of 370/pb. We set upper limits on the cross section times branching fraction for heavy resonance production at the 95% C.L. as a function of the resonance mass and width. The limits are interpreted within the framework of a specific model of excited quark production.Comment: 8 pages, 5 figures, submitted to Physical Review

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.Comment: submitted to Phys.Rev.Let

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.Comment: Submitted to Phys. Rev. D Rapid Communication

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 ($\sigma_{t\bar{t}}$) 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 $\sigma_{t\bar{t}}=8.6^{+1.6}_{-1.5}(stat.+syst.)\pm 0.6(lumi.)$ pb, in agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let