We report the first observation of single-top-quark production in the s channel through the combination of the CDF and D0 measurements of the cross section in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data correspond to total integrated luminosities of up to 9.7 fb-1 per experiment. The measured cross section is $\sigma_s = 1.29^{+0.26}_{-0.24}$ pb. The probability of observing a statistical fluctuation of the background to a cross section of the observed size or larger is $1.8 \times 10^{-10}$, corresponding to a significance of 6.3 standard deviations for the presence of an s-channel contribution to the production of single-top quarks.
The measured cross section of single-top-quark production in the s channel.
The global topologies of inclusive three-- and four--jet events produced in $\pp$ interactions are described. The three-- and four--jet events are selected from data recorded by the D\O\ detector at the Tevatron Collider operating at a center--of--mass energy of $\sqrt{s} = 1800$ GeV. The measured, normalized distributions of various topological variables are compared with parton--level predictions of tree--level QCD calculations. The parton--level QCD calculations are found to be in good agreement with the data. The studies also show that the topological distributions of the different subprocesses involving different numbers of quarks are very similar and reproduce the measured distributions well. The parton shower Monte Carlo generators provide a less satisfactory description of the topologies of the three-- and four--jet events.
The estimated systematic uncertainty is 6 PCT.
The estimated systematic uncertainty is 6 PCT.
The estimated systematic uncertainty is 6 PCT.
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.
TTBAR production cross section from the combined electron+jet and muon+jet channels.
Inclusive dijet production at large pseudorapidity intervals (delta_eta) between the two jets has been suggested as a regime for observing BFKL dynamics. We have measured the dijet cross section for large delta_eta in ppbar collisions at sqrt{s}=1800 and 630 GeV using the DO detector. The partonic cross section increases strongly with the size of delta_eta. The observed growth is even stronger than expected on the basis of BFKL resummation in the leading logarithmic approximation. The growth of the partonic cross section can be accommodated with an effective BFKL intercept of a_{BFKL}(20GeV)=1.65+/-0.07.
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
Z(P=3) and Z(P=4) are longitudinal momentum fractions of the proton and antiproton, carried by the two interacting partons: Z(P=3,4) = 2*ET(P=3,4)/SQRT(S)*EXP(+-ETARAP)*COSH(DELTA(ETARAP)/2), where ETARAP = (ETARAP(P=3)+ETARAP(P=4))/2,DELTA(ETARAP) = ABS(ETARAP(P=3)-ETARAP(P=4)).
This report describes the first search for top squark pair production in the channel stop_1 stopbar_1 -> b bbar chargino_1 chargino_1 -> ee+jets+MEt using 74.9 +- 8.9 pb~-1 of data collected using the D0 detector. A 95% confidence level upper limit on sigma*B is presented. The limit is above the theoretical expectation for sigma*B for this process, but does show the sensitivity of the current D0 data set to a particular topology for new physics.
Data are extracted from the figure. Sigma*Br.
We present the first measurement of the electron angular distribution parameter alpha_2 in W to e nu events produced in proton-antiproton collisions as a function of the W boson transverse momentum. Our analysis is based on data collected using the D0 detector during the 1994--1995 Fermilab Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of (1 +/- alpha_1 cos theta* + alpha_2 cos^2 theta*), where theta* is the polar angle of the electron in the Collins-Soper frame. In the presence of QCD corrections, the parameters alpha_1 and alpha_2 become functions of p_T^W, the W boson transverse momentum. This measurement provides a test of next-to-leading order QCD corrections which are a non-negligible contribution to the W boson mass measurement.
Angular distributions of the emitted charged lepton is fitted to the formula d(sig)/d(pt**2)/dy/d(cos(theta*)) = const*(1 +- alpha_1*cos(theta*) + alpha_2*(cos(theta*))**2). The angle theta* is measured in the Collins-Soper frame. alpha_1 velues are calculated based on the measured PT(W) of each event. Possible variations of alpha_1 are treated as a source of systematic uncertainty.
We have searched for central production of a pair of photons with high transverse energies in $p\bar p$ collisions at $\sqrt{s} = 1.8$ TeV using $70 pb^{-1}$ of data collected with the D\O detector at the Fermilab Tevatron in 1994--1996. If they exist, virtual heavy pointlike Dirac monopoles could rescatter pairs of nearly real photons into this final state via a box diagram. We observe no excess of events above background, and set lower 95% C.L. limits of $610, 870, or 1580 GeV/c^2$ on the mass of a spin 0, 1/2, or 1 Dirac monopole.
No description provided.
We have studied tbar-t production using multijet final states in pbar-p collisions at a center-of-mass energy of 1.8 TeV, with an integrated luminosity of 110.3 pb(-1). Each of the top quarks with these final states decays exclusively to a bottom quark and a W boson, with the W bosons decaying into quark-antiquark pairs. The analysis has been optimized using neural networks to achieve the smallest expected fractional uncertainty on the tbar-t production cross section, and yields a cross section of 7.1 +/- 2.8(stat.) +/- 1.5(syst.) pb, assuming a top quark mass of 172.1 GeV/c^(2). Combining this result with previous D0 measurements, where one or both of the W bosons decay leptonically, gives a tbar t production cross section of 5.9 +/- 1.2(stat) +/- 1.1(syst) pb.
The second value is the combination of the data reported here combined withthe previous result of D0 reported in PRL 79(1997)1203.
We determine the top quark mass m_t using t-tbar pairs produced in the D0 detector by \sqrt{s} = 1.8 TeV p-pbar collisions in a 125 pb^-1 exposure at the Fermilab Tevatron. We make a two constraint fit to m_t in t-tbar -> b W^+bbar W^- final states with one W boson decaying to q-qbar and the other to e-nu or mu-nu. Likelihood fits to the data yield m_t(l+jets) = 173.3 +- 5.6 (stat) +- 5.5 (syst) GeV/c^2. When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain m_t = 172.1 +- 5.2 (stat) +- 4.9 (syst) GeV/c^2. An alternate analysis, using three constraint fits to fixed top quark masses, gives m_t(l+jets) = 176.0 +- 7.9 (stat) +- 4.8 (syst) GeV/C^2, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented.
No description provided.
The shape of the transverse momentum distribution of W bosons (p_T(W)) produced in pbarp collisions at sqrt(s)= 1.8 TeV is measured with the DO detector at Fermilab. The result is compared to QCD perturbative and resummation calculations over the p_T(W) range from 0-200 GeV/c. The shape of the distribution is consistent with the theoretical prediction.
The first error is statistical, the first systematic (DSYS) error is the uncertainty in the background and efficiencies, the second is the systematic errorin the detector modelling.
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