We measure the ttbar production cross section in ppbar collisions at sqrt{s}=1.96 TeV in the lepton+jets channel. Two complementary methods discriminate between signal and background, b-tagging and a kinematic likelihood discriminant. Based on 0.9 fb-1 of data collected by the D0 detector at the Fermilab Tevatron Collider, we measure sigma_ttbar=7.62+/-0.85 pb, assuming the current world average m_t=172.6 GeV. We compare our cross section measurement with theory predictions to determine a value for the top quark mass of 170+/-7 GeV.
The combined result for the TOP TOPBAR production cross section at top quark mass of 175 GeV.. The second DSYS error is the uncertainty on the luminosity.
The cross section for TOP TOPBAR production at the world average top quark mass of 172.6 GeV.. Errors contain both statistics and systematics.
We present a measurement of the fraction of inclusive $W$+jets events produced with net charm quantum number $\pm1$, denoted $W$+$c$-jet, in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV using approximately 1~fb$^{-1}$ of data collected by the D0 detector at the Fermilab Tevatron Collider. We identify the $W$+jets events via the leptonic $W$ boson decays. Candidate $W$+$c$-jet events are selected by requiring a jet containing a muon in association with a reconstructed $W$ boson and exploiting the charge correlation between this muon and $W$ boson decay lepton to perform a nearly model-independent background subtraction. We measure the fraction of $W$+$c$-jet events in the inclusive $W$+jets sample for jet $p_{T}>20$ GeV and pseudorapidity $|\eta|<2.5$ to be 0.074$\pm0.019$(stat.)$\pm^{0.012}_{0.014}$(syst.), in agreement with theoretical predictions. The probability that background fluctuations could produce the observed fraction of $W$+$c$-jet events is estimated to be $2.5\times 10^{-4}$, which corresponds to a 3.5 $\sigma$ statistical significance.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (E NU) channel for various jet PT ranges.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (MU NU) channel for various jet PT ranges.
Measured value of the W+ charm jet to W+ jet cross sections for W decay into the (LEPTON NU) channel for various jet PT ranges.
We present measurements of the process $p\bar{p} \to WZ+X \to \ell^{\prime} \nu_{\ell^{\prime}} \ell \bar{\ell}$ 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 $\sigma(WZ)=2.7^{+1.7}_{-1.3}$ pb. From the number of observed events and the $Z$ boson transverse momentum distribution, we limit the trilinear $WWZ$ gauge couplings to $-0.17 \le \lambda_Z \le 0.21$ $(\Delta \kappa_Z = 0)$ at the 95% C.L. for a form factor scale $\Lambda=2$ TeV. Further, assuming that $\Delta g^Z_1 = \Delta\kappa_Z$, we find $-0.12 \le \Delta\kappa_Z \le 0.29$ $(\lambda_Z=0)$ at the 95% C.L. These are the most restrictive limits on the $WWZ$ couplings available to date.
Measured WZ cross section.
We present a measurement of the shape of the boson rapidity distribution for $p\bar{p}\to Z / \gamma^* \to e^+e^- + X$ events at a center-of-mass energy of 1.96 TeV. The measurement is made for events with electron-positron mass 71 < M_ee < 111 GeV and uses 0.4 $fb^{-1}$ of data collected at the Fermilab Tevatron collider with the D0 detector. This measurement significantly reduces the uncertainties on the rapidity distribution in the forward region compared with previous measurements. Predictions of NNLO QCD are found to agree well with the data over the full rapidity range.
Normalized rapidity distribution.
Details of systematic errors.
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.
TTBAR production cross section.
The cross section for the inclusive production of isolated photons has been measured in p anti-p collisions at sqrt{s}=1.96 TeV with the D0 detector at the Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV and have pseudorapidity |eta|<0.9. The cross section is compared with the results from two next-to-leading order perturbative QCD calculations. The theoretical predictions agree with the measurement within uncertainties.
Measured differential cross section for the production of isolated photons.
A measurement of the $\bjet$ production cross section is presented for events containing a $Z$ boson produced in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV, using data corresponding to an integrated luminosity of 2 fb$^{-1}$ collected by the CDF II detector at the Tevatron. $Z$ bosons are selected in the electron and muon decay modes. Jets are considered with transverse energy $E_T>20$ GeV and pseudorapidity $|\eta|<1.5$ and are identified as $\bjets$ using a secondary vertex algorithm. The ratio of the integrated $Z+\bjet$ cross section to the inclusive $Z$ production cross section is measured to be $3.32 \pm 0.53 {\rm (stat.)} \pm 0.42 {\rm (syst.)}\times 10^{-3}$. This ratio is also measured differentially in jet $E_T$, jet $\eta$, $Z$-boson transverse momentum, number of jets, and number of $\bjets$. The predictions from leading order Monte Carlo generators and next-to-leading-order QCD calculations are found to be consistent with the measurements within experimental and theoretical uncertainties.
Ratio of integrated Z0 + bjet cross section to inclusive Z0 production.
Ratio of the Z0 + bjet to Z0 cross section as a function of the bjet ET.
Ratio of the Z0 + bjet to Z0 cross section as a function of the bjet pseudorapidity.
We have observed the reactions p+pbar --> p+X+pbar, with X being a centrally produced J/psi, psi(2S) or chi_c0, and gamma+gamma --> mu+mu-, in proton- antiproton collisions at sqrt{s} = 1.96 TeV using the Run II Collider Detector at Fermilab. The event signature requires two oppositely charged muons, each with pseudorapidity |eta| < 0.6, with M(mumu) in [3.0,4.0] GeV/c2, and either no other particles, or one additional photon, detected. The J/psi and the psi(2S) are prominent, on a continuum consistent with the QED process gamma+gamma --> mu+mu-. Events with a J/psi and an associated photon candidate are consistent with exclusive chi_c0 production through double pomeron exchange. The exclusive vector meson production is as expected for elastic photo- production, gamma+p --> J/psi(psi(2S)) + p, which is observed here for the first time in hadron-hadron collisions. The cross sections ds/dy(y=0) for p + pbar --> p + X + pbar with X = J/psi, psi(2S) orchi_c0 are 3.92+/-0.62 nb, 0.53+/-0.14 nb, and 75+/-14 nb respectively. The cross section for the continuum, with |eta(mu+/-)| < 0.6, M(mumu) in [3.0,4.0] GeV/c2, is [Integral ds/(dM.deta1.deta2)] = 2.7+/-0.5 pb, consistent with QED predictions. We put an upper limit on the cross section for odderon exchange in J/psi production: ds/dy(y=0) (J/psi_O/IP) < 2.3 nb at 95% C.L.
Prompt J/psi cross section from exclusive photoproduction at mid rapidity.
Prompt Psi(2S) cross section from exclusive photoproduction at mid rapidity.
Prompt photoproduction cross-section ratio Psi(2S)/(J/psi) at mid rapidity.
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 $\theta^*$ 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.
COS(THETA*) distribution for leptonic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for hadronic W decay in lepton+jets events.. Data are read from plots and errors are statistcial (sqrt(N)).
COS(THETA*) distribution for W decay in dilepton events.. Data are read from plots and errors are statistcial (sqrt(N)).
We present a measurement of the shape of the Z/gamma* boson transverse momentum (qT) distribution in ppbar -> Z/gamma* -> ee+X events at a center-of-mass energy of 1.96 TeV using 0.98 fb-1 of data collected with the D0 detector at the Fermilab Tevatron collider. The data are found to be consistent with the resummation prediction at low qT, but above the perturbative QCD calculation in the region of qT>30 GeV/c. Using events with qT<30 GeV/c, we extract the value of g2, one of the non-perturbative parameters for the resummation calculation. Data at large boson rapidity y are compared with the prediction of resummation and with alternative models that employ a resummed form factor with modifications in the small Bjorken x region of the proton wave function.
Normalized differential transverse momentum spectrum for Z0/GAMMA* events.
Correlation matrix for all rapidity Z bosons for the 12 bins used for PT < 30.
Normalized differential transverse momentum spectrum for Z0/GAMMA* events for the absolute rapidity region > 2 and PT < 30 GeV.
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