arXiv subjects

D0 Collaboration

Publications and source records attributed to D0 Collaboration.

At least 73 records · Page 4Linked to original sources

arXiv2013

Study of CP-violating charge asymmetries of single muons and like-sign dimuons in p pbar collisions

We measure the inclusive single muon charge asymmetry and the like-sign dimuon charge asymmetry in $p \bar{p}$ collisions using the full data set of 10.4 fb$^{-1}$ collected with the D0 detector at the Fermilab Tevatron. The standard model predictions of the charge asymmetries induced by CP violation are small in magnitude compared to the current experimental precision, so non-zero measurements could indicate new sources of CP violation. The measurements differ from the standard model predictions of CP violation in these asymmetries with a significance of 3.6 standard deviations. These results are interpreted in a framework of $B$ meson mixing within the CKM formalism to measure the relative width difference $\dgg$ between the mass eigenstates of the $\Bd$ meson system, and the semileptonic charge asymmetries $\asld$ and $\asls$ of $\Bd$ and $\Bs$ mesons respectively.

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arXiv2013

Combination of measurements of the top-quark pair production cross section from the Tevatron Collider

We combine six measurements of the inclusive top-quark pair (ttbar) production cross section (sigma_ttbar) from data collected with the CDF and D0 detectors at the Fermilab Tevatron with proton anti-proton collisions at sqrt{s} = 1.96 TeV. The data correspond to integrated luminosities of up to 8.8 fb^{-1}. We obtain a value of sigma_ttbar = 7.60 \pm 0.41 pb for a top-quark mass of m_t=172.5 GeV. The contributions to the uncertainty are 0.20 pb from statistical sources, 0.29 pb from systematic sources, and 0.21 pb from the uncertainty on the integrated luminosity. The result is in good agreement with the standard model expectation of 7.35^{+0.28}_{-0.33} pb at NNLO+NNLL in pertubative QCD.

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arXiv2013

Search for the X(4140) state in B+->J/psi phi K+ decays with the D0 detector

We investigate the decay B^+ -> J/psi phi K^+ in a search for the X(4140) state, a narrow threshold resonance in the J/psi phi system. The data sample corresponds to an integrated luminosity of 10.4 fb^{-1} of ppbar collisions at sqrt s =1.96 TeV collected by the D0 experiment at the Fermilab Tevatron collider. We observe a mass peak with a statistical significance of 3.1 standard deviations and measure its invariant mass to be M=4159.0 +-.3 (stat) +- 6.6 (syst) MeV and its width to be Gamma= 19.9+-12.6 (stat)}^{+1.0}_{-8.0} (syst) MeV. Identifying this mass peak as the X(4140), we measure, for M(J/psi phi) <4.59 GeV, the relative branching fraction B_rel= B(B^+ -> X(4140) K^+)/ B(B^+ ->J/psi phi K^+) to be 21+-8 (stat) +- 4 (syst)%. In addition, the data can accommodate the presence of a second enhancement at a mass of 4328.5+- 12.0 MeV.

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arXiv2013

Combined search for the Higgs boson with the D0 experiment

We perform a combination of searches for standard model Higgs boson production in $p\bar{p}$ collisions recorded by the D0 detector at the Fermilab Tevatron Collider at a center of mass energy of $\sqrt{s}=1.96$ TeV. The different production and decay channels have been analyzed separately, with integrated luminosities of up to 9.7 fb$^{-1}$ and for Higgs boson masses $90\leq M_H \leq 200$ GeV. We combine these final states to achieve optimal sensitivity to the production of the Higgs boson. We also interpret the combination in terms of models with a fourth generation of fermions, and models with suppressed Higgs boson couplings to fermions. The result excludes a standard model Higgs boson at 95% C.L. in the ranges $90 < M_H < 101$ GeV and $157 <M_H< 178$ GeV, with an expected exclusion of $155 <M_H<175$ GeV. In the range $120 < M_H < 145$ GeV, the data exhibit an excess over the expected background of up to two standard deviations, consistent with the presence of a standard model Higgs boson of mass 125 GeV.

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arXiv2013

Measurement of the muon charge asymmetry in ppbar to W + X to mu nu + X events at sqrt{s} = 1.96 TeV

We present a measurement of the muon charge asymmetry from the decay of the $W$ boson via W to mu nu using 7.3 fb^{-1} of integrated luminosity collected with the D0 detector at the Fermilab Tevatron Collider at sqrt{s} = 1.96 TeV. The muon charge asymmetry is presented in two kinematic regions in muon transverse momentum and event missing transverse energy: (p^μ_{T} > 25 GeV, \met > 25 GeV) and (p^μ_{T} > 35 GeV, \met > 35 GeV). The measured asymmetries are compared with theory predictions made using three parton distribution function sets. The predictions do not describe the data well for p^μ_{T} > 35 GeV, \met > 35 GeV, and larger values of muon pseudorapidity.

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arXiv2013

Measurement of the asymmetry in angular distributions of leptons produced in dilepton ttbar final states in ppbar collisions at sqrt(s)=1.96 TeV

We present measurements of asymmetries in angular distributions of leptons produced in ttbar events in proton-antiproton collisions at the Fermilab Tevatron Collider. We consider final states where the W bosons from top quark and antiquark decays both decay into l nu (l=e, mu) resulting in oppositely charged dilepton final states with accompanying jets. Using 9.7 fb^-1 of integrated luminosity collected with the D0 detector, we find the asymmetries in lepton pseudorapidity compatible with predictions based on the standard model.

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arXiv2013

Measurement of the differential cross section of photon plus jet production in ppbar collisions at sqrt{s}=1.96 TeV

We study the process of associated photon and jet production, p+pbar --> photon + jet + X, using 8.7 fb^-1 of integrated luminosity collected by the D0 detector at the Fermilab Tevatron Collider at a center-of-mass energy sqrt{s}=1.96 TeV. Photons are reconstructed with rapidity |y^gamma| <1.0 or 1.5<|y^{gamma}| < 2.5 and transverse momentum pT^gamma GeV. The highest-p_T jet is required to be in one of four rapidity regions up to |y^{jet}|< 3.2. For each rapidity configuration we measure the differential cross sections in pT_gamma separately for events with the same sign (y^{gamma} y^{jet}}>0) and opposite sign (y^{gamma} y^{jet}<=0) of photon and jet rapidities. We compare the measured triple differential cross sections, d^3 sigma / d pT_gamma y^{gamma} y^{jet}, to next-to-leading order (NLO) perturbative QCD calculations using different sets of parton distribution functions and to predictions from the SHERPA and PYTHIA Monte Carlo event generators. The NLO calculations are found to be in general agreement with the data, but do not describe all kinematic regions.

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arXiv2013

Measurement of direct CP violation parameters in B^+/- -> J/ψK^+/- and B^+/- ->J/psi pi^+/- decays with 10.4 fb^-1 of Tevatron data

We present a measurement of the direct CP-violating charge asymmetry in B^+/- mesons decaying to J/psi K^+/- and J/psi pi^+/- where J/psi decays to mu^+ mu^-, using the full Run II data set of 10.4 fb^-1 of proton-antiproton collisions collected using the D0 detector at the Fermilab Tevatron Collider. A difference in the yield of B^- and B^+ mesons in these decays is found by fitting to the difference between their reconstructed invariant mass distributions resulting in asymmetries of ajpk =[0.59 +/- 0.37]%, which is the most precise measurement to date, and ajppi= [-4.2 +/- 4.5]%. Both measurements are consistent with standard model predictions.

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arXiv2013

Measurement of the ratio of differential cross sections σ(ppbar -> Z + b jet)/σ(ppbar -> Z + jet) in ppbar collisions at sqrt(s)=1.96 TeV

We measure the ratio of cross sections, σ(ppbar -> Z + b jet)/σ(ppbar -> Z + jet), for associated production of a Z boson with at least one jet. The ratio is also measured as a function of the jet transverse momentum, jet pseudorapidity, Z boson transverse momentum, and the azimuthal angle between the Z boson and the closest jet for events with at least one b jet. These measurements use data collected by the D0 experiment in Run II of Fermilab's Tevatron ppbar Collider at a center-of-mass energy of 1.96 TeV, and correspond to an integrated luminosity of 9.7 fb$^{-1}$. The results are compared to predictions from next-to-leading order calculations and various Monte Carlo event generators.

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arXiv2013

Search for anomalous quartic WWγγ couplings in dielectron and missing energy final states in ppbar collisions at sqrt(s) = 1.96 TeV

We present a search for anomalous components of the quartic gauge boson coupling WWγγ in events with an electron, a positron and missing transverse energy. The analyzed data correspond to 9.7 fb^-1 of integrated luminosity collected by the D0 detector in ppbar collisions at sqrt(s) = 1.96 TeV. The presence of anomalous quartic gauge couplings would manifest itself as an excess of boosted WW events. No such excess is found in the data, and we set the most stringent limits to date on the anomalous coupling parameters a_0^W and a_C^W. When a form factor with Lambda_cutoff = 0.5 TeV is used, the observed upper limits at 95 % C.L. are |a_0^W/Lambda^2|< 0.0025 GeV^-2 and |a_C^W/Lambda^2| < 0.0092 GeV^-2.

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arXiv2013

Measurement of the ZZ production cross section and search for the standard model Higgs boson in the four lepton final state in ppbar collisions

We present a measurement of Z boson pair production in ppbar collisions at 1.96 TeV with 9.6 fb-1 to 9.8fb-1 of D0 data. We examine the final states with four electrons, two electrons plus two muons, and four muons. Based on selected data, the measured cross section in the mass region M(Z/gamma*) > 30 GeV is sigma(ppbar to Z/gamma* Z/gamma*)= 1.26 ^{+0.44}_{-0.36} (stat) ^{+0.17}_{-0.15} (syst) +/- 0.08 (lumi) pb; after correcting for the expected ratio of sigma(ppbar to Z/gamma* Z/gamma*) to sigma(ppbar to ZZ), we derive a cross section for ppbar to ZZ production of 1.05 ^{+0.37}_{-0.30} (stat) ^{+0.14}_{-0.12} (syst) +/- 0.06 (lumi) pb. This result is combined with a previous result from the ZZ to two charged leptons plus two neutrinos channel resulting in a combined ppbar to ZZ cross section measurement of 1.32 ^{+0.29}_{-0.25} (stat) +/- 0.12 (syst) +/- 0.04 (lumi)} pb. These measurements are consistent with the standard model expectation of 1.43 \pm 0.10 pb. We extend this analysis to search for the standard model (SM) Higgs boson between 115 and 200 GeV. At a Higgs boson mass of 125 GeV, we expect to set a limit of 43 times the SM expectation at 95% C.L., and set a limit of 42 times the SM expectation at 95% C.L.

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arXiv2013

Search for ZH -> l+l- bbar production in 9.7 fb-1 of ppbar collisions with the D0 detector

We present a search for the standard model (SM) Higgs boson produced in association with a Z boson in 9.7 fb-1 of ppbar collisions collected with the D0 detector at the Fermilab Tevatron Collider at sqrt{s} = 1.96 TeV. Selected events contain one reconstructed Z -> e+e- or Z -> mu+mu- candidate and at least two jets, including at least one jet likely to contain a b quark. To validate the search procedure, we also measure the cross section for ZZ production, and find that it is consistent with the SM expectation. We set upper limits at the 95% C.L. on the product of the ZH production cross section and branching ratio B(H -> bbbar) for Higgs boson masses 90 <= M_H <= 150 GeV. The observed (expected) limit for M_H = 125 GeV is a factor of 7.1 (5.1) larger than the SM prediction.

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arXiv2013

Measurement of Leptonic Asymmetries and Top Quark Polarization in ttbar Production

We present measurements of lepton (l) angular distributions in ttbar -> W+ b W- b -> l+ nu b l- nubar bbar decays produced in ppbar collisions at a center-of-mass energy of sqrt(s)=1.96TeV, where l is an electron or muon. Using data corresponding to an integrated luminosity of 5.4fb^-1, collected with the D0 detector at the Fermilab Collider, we find that the angular distributions of l- relative to anti-protons and l+ relative to protons are in agreement with each other. Combining the two distributions and correcting for detector acceptance we obtain the forward-backward asymmetry A^l_FB = (5.8 +- 5.1(stat) +- 1.3(syst))%, compared to the standard model prediction of A^l_FB (predicted) = (4.7 +- 0.1)%. This result is further combined with the measurement based on the analysis of the l+jets final state to obtain A^l_FB = (11.8 +- 3.2)%. Furthermore, we present a first study of the top-quark polarization.

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arXiv2013

Studies of W boson plus jets production in p\bar{p} collisions at sqrt(s)=1.96 TeV

We present a comprehensive analysis of inclusive W(\to eν)+n-jet (n\geq 1,2,3,4) production in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV at the Tevatron collider using a 3.7 fb^{-1} dataset collected by the D0 detector. Differential cross sections are presented as a function of the jet rapidities (y), lepton transverse momentum (p_T) and pseudorapidity (η), the scalar sum of the transverse energies of the W boson and all jets (H_T), leading dijet p_T and invariant mass, dijet rapidity separations for a variety of jet pairings for p_T-ordered and angular-ordered jets, dijet opening angle, dijet azimuthal angular separations for p_T-ordered and angular-ordered jets, and W boson transverse momentum. The mean number of jets in an event containing a W boson is measured as a function of H_T, and as a function of the rapidity separations between the two highest-p_T jets and between the most widely separated jets in rapidity. Finally, the probability for third-jet emission in events containing a W boson and at least two jets is studied by measuring the fraction of events in the inclusive W+2-jet sample that contain a third jet over a p_T threshold. The analysis employs a regularized singular value decomposition technique to accurately correct for detector effects and for the presence of backgrounds. The corrected data are compared to particle level next-to-leading order perturbative QCD predictions, predictions from all-order resummation approaches, and a variety of leading-order and matrix-element plus parton-shower event generators. Regions of the phase space where there is agreement or disagreement with the data are discussed for the different models tested.

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arXiv2013

Search for Higgs boson production in trilepton and like-charge electron-muon final states with the D0 detector

We present a search for Higgs bosons in multilepton final states in pp-bar collisions at sqrt(s)=1.96 TeV recorded with the D0 detector at the Fermilab Tevatron Collider, using the full Run II data set with integrated luminosities of up to 9.7 fb-1. The multilepton states considered are two electron plus muon, electron with two muons, muon with two hadronic tau leptons, and like-charge electron-muon pairs. These channels directly probe the HVV (V=W,Z) coupling of the Higgs boson in production and decay. The muon with two hadronic tau lepton channel is also sensitive to H to tau lepton pair decays. Upper limits at the 95% C.L on the rate of standard model Higgs boson production are derived in the mass range 100 <= M_H <= 200 GeV. The expected and observed limits are a factor of 6.3 and 8.4 above the predicted standard model cross section at M_H=125 GeV. We also interpret the data in a fermiophobic Higgs boson model.

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arXiv2013

Measurement of the differential cross sections for isolated direct photon pair production in $p \bar p$ collisions at $\sqrt{s} = 1.96$ TeV

We present measurements of direct photon pair production cross sections using 8.5 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron $p \bar p$ collider. The results are presented as differential distributions of the photon pair invariant mass $dσ/dM_{γγ}$, pair transverse momentum $d σ/dp^{γγ}_T$, azimuthal angle between the photons $dσ/dΔϕ_{γγ}$, and polar scattering angle in the Collins-Soper frame $dσ/d|\cos θ^*|$. Measurements are performed for isolated photons with transverse momenta $p^γ_T>18 ~(17)$ GeV for the leading (next-to-leading) photon in $p_T$, pseudorapidities $|η^γ|<0.9$, and a separation in $η-ϕ$ space $Δ\mathcal R_{γγ} > 0.4$. We present comparisons with the predictions from Monte Carlo event generators {\sc diphox} and {\sc resbos} implementing QCD calculations at next-to-leading order, $2γ${\sc nnlo} at next-to-next-to-leading order, and {\sc sherpa} using matrix elements with higher-order real emissions matched to parton shower.

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arXiv2013

Search for the Higgs boson in lepton, tau and jets final states

We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with two or more jets using 9.7 fb^{-1} of Run II Fermilab Tevatron Collider data collected with the D0 detector. The analysis is sensitive to Higgs boson production via gluon fusion, associated vector boson production, and vector boson fusion, followed by the Higgs boson decay to tau lepton pairs or to W boson pairs. The ratios of 95% C.L. upper limits on the cross section times branching ratio to those predicted by the standard model are obtained for orthogonal subsamples that are enriched in either H -> tau tau decays or H -> WW decays, and for the combination of these subsample limits. The observed and expected limit ratios for the combined subsamples at a Higgs boson mass of 125 GeV are 11.3 and 9.0 respectively.

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arXiv2013

Search for the standard model Higgs boson in $\bm{\ellν}$+jets final states in 9.7~fb$\bm{^{-1}}$ of $\bm{p\bar{p}}$ collisions with the D0 detector

We present, in detail, a search for the standard model Higgs boson, $H$, in final states with a charged lepton (electron or muon), missing energy, and two or more jets in data corresponding to 9.7 fb$^{-1}$ of integrated luminosity collected at a center of mass energy of $\sqrt{s}$ = 1.96 TeV with the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider. The search uses $b$-jet identification to categorize events for improved signal versus background separation and is sensitive to associated production of the $H$ with a $W$ boson, $WH\to\ellνb\bar{b}$; gluon fusion with the Higgs decaying to $W$ boson pairs, $H\to WW\to\ellνjj$; and associated production with a vector boson where the Higgs decays to $W$ boson pairs, $VH\to VWW \to \ellνjjjj$ production (where $V = W$ or $Z$). We observe good agreement between data and expected background. We test our method by measuring $WZ$ and $ZZ$ production with $Z\to b\bar{b}$ and find production rates consistent with the standard model prediction. For a Higgs boson mass of 125 GeV, we set a 95%\ C.L. upper limit on the production of a standard model Higgs boson of \obslimA$\timesσ_{\rm SM}$, where $σ_{\rm SM}$ is the standard model Higgs boson production cross section, while the expected limit is \explimA$\timesσ_{\rm SM}$. We also interpret the data considering models with fourth generation fermions, or a fermiophobic Higgs boson.

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