The D0 collaboration has performed a study of spin correlation in tt-bar production for the process tt-bar to bb-bar W^+W^-, where the W bosons decay to e-nu or mu-nu. A sample of six events was collected during an exposure of the D0 detector to an integrated luminosity of approximately 125 pb^-1 of sqrt{s}=1.8 TeV pp-bar collisions. The standard model (SM) predicts that the short lifetime of the top quark ensures the transmission of any spin information at production to the tt-bar decay products. The degree of spin correlation is characterized by a correlation coefficient k. We find that k>-0.25 at the 68% confidence level, in agreement with the SM prediction of k=0.88.
No description provided.
We have searched for second generation leptoquark (LQ) pairs in the \mu\mu+jets channel using 94+-5 pb^{-1} of pbar-p collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the \mu\nu+jets and \nu\nu+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and $beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c^2 for \beta=1(1/2) are set at the 95% C.L. on the mass of scalar LQ. Mass limits are also set on vector leptoquarks as a function of \beta.
No description provided.
This Letter describes a measurement of the muon cross section originating from b quark decay in the forward rapidity range 2.4 < y(mu) < 3.2 in pbarp collisions at sqrt(s) = 1.8 TeV. The data used in this analysis were collected by the D0 experiment at the Fermilab Tevatron. We find that NLO QCD calculations underestimate b quark production by a factor of four in the forward rapidity region. A cross section measurement using muon+jet data has been included in this version of the paper.
The forward muon cross section (per unit rapidity).
The cross section for muons originating from b-quark decay.
Integrated cross sections for muons originating from b-quark decay. The statistical and systematic errors are added in quadrature.
We present measurements of the b-bbar production cross section and angular correlations using the D0 detector at the Fermilab Tevatron p-pbar Collider operating at sqrt(s) = 1.8 TeV. The b quark production cross section for |y(b)|<1.0 and p_T(b)>6 GeV/c is extracted from single muon and dimuon data samples. The results agree in shape with the next-to-leading order QCD calculation of heavy flavor production but are greater than the central values of these predictions. The angular correlations between b and bbar quarks, measured from the azimuthal opening angle between their decay muons, also agree in shape with the next-to-leading order QCD prediction.
No description provided.
The errors are combinations of statistical and systematic uncertainties.
The distribution of MU+ MU- azimuthal angle difference.
DO has measured the inclusive production cross section of W and Z bosons in a sample of 13 pb$^{-1}$ of data collected at the Fermilab Tevatron. The cross sections, multiplied by their leptonic branching fractions, for production in pbar-p collisions at sqrt{s}=1.8 TeV are sigma_W*B(W->e nu) = 2.36+-0.02+-0.08+-0.13 nb, sigma_W*B(W->mu nu) = 2.09+-0.06+-0.22+-0.11 nb, sigma_Z*B(Z->e+ e-) = 0.218+-0.008+-0.008+-0.012 nb, and sigma_Z*B(Z->mu+ mu-) = 0.178+-0.022+-0.021+-0.009 nb, where the first uncertainty is statistical and the second systematic; the third reflects the uncertainty in the integrated luminosity. For the combined electron and muon analyses, we find sigma_W*B(W->l mu)/sigma_Z*B(Z->l+ l-) = 10.90+-0.52. Assuming standard model couplings, we use this result to determine the width of the W boson, and obtain Gamma(W) = 2.044+-0.097 GeV.
No description provided.
Combined electron and muon analysis.
This paper presents the first measurement of the inclusive J/Psi production cross section in the forward pseudorapidity region 2.5<|eta|<3.7 in ppbar collisions at sqrt(s)=1.8TeV. The results are based on 9.8 pb-1 of data collected using the D0 detector at the Fermilab Tevatron Collider. The inclusive J/Psi cross section for transverse momenta between 1 and 16 GeV/c is compared with theoretical models of charmonium production.
Only statistical errors are shown. Cross section tines branching ratio.
The gauge boson pair production processes Wg, WW, WZ, and Zg were studied using pbarp collisions corresponding to an integrated luminosity of ~14 pb-1 at a center-of-mass energy of sqrt(s) = 1.8 TeV. Analysis of Wg prod with subsequent W boson decay to lv (l=e,mu) is reported, including a fit to the pT spectrum of the photons which leads to limits on anomalous WWg couplings. A search for WW prod with subsequent decay to l-lbar-v-vbar (l=e,mu) is presented leading to an upper limit on the WW prod cross section and limits on anomalous WWg and WWZ couplings. A search for high pT W bosons in WW and WZ prod is described, where one W boson decays to an ev and the second W boson or the Z boson decays to two jets. A maximum likelihood fit to the pT spectrum of W bosons resulted in limits on anomalous WWg and WWZ couplings. A combined fit to the three data sets which provided the tightest limits on anomalous WWg and WWZ couplings is also described. Limits on anomalous ZZg and Zgg couplings are presented from an analysis of the photon ET spectrum in Zg events in the decay channels (ee, mu-mu, and v-vbar) of the Z boson.
CONST(NAME=SCALE) is the model parameter, used in the modification of the couplings as follows: h = hi0/(1 + M(gamma Z)**2/CONT(NAME=SCALE)**2)**n. See article for details.
We have measured the ZZ-gamma and Z-gamma-gamma couplings by studying p-bar p -> (missing ET) gamma + X events at sqrt(s)=1.8 TeV with the D0 detector at the Fermilab Tevatron Collider. This first study of hadronic Z-gamma production in the neutrino decay channel gives the most stringent limits on anomalous couplings available. A fit to the transverse energy spectrum of the photon in the candidate event sample, based on a data set corresponding to an integrated luminosity of 13.1 pb~(-1), yields 95% CL limits on the anomalous CP-conserving ZZ-gamma couplings of |h~Z_(30)|<0.9, |h~Z_(40)|<0.21, for a form-factor scale Lambda = 500 GeV. Combining these results with our previous measurement using Z -> ee and mu-mu yields the limits:|h~Z_(30)|<0.8, |h~Z_(40)|<0.19 (Lambda = 500 GeV) and |h~Z_(30)|<0.4, |h~Z_(40)|<0.06 (Lambda = 750 GeV).
CONST(NAME=SCALE) is the model parameter, used in the modification of the couplings as follows: h = hi0/(1 + M(gamma Z)**2/CONT(NAME=SCALE)**2)**n. See article for details.. The data with Z --> lepton+ lepton- is taken from S.Abachi, PRL 75, 1028.
We have studied J ψ production in p p collisions at s = 1.8 TeV with the DØ detector at Fermilab using μ + μ − data. We have measured the inclusive J ψ production cross section as a function of J ψ transverse momentum, p T . For the kinematic range p T > 8 GeV/ c and |η| < 0.6 we obtain σ(p p → J ψ + X) · Br ( J ψ → μ + μ − ) = 2.08 ± 0.17( stat) ± 0.46(syst) nb. Using the muon impact parameter we have estimated the fraction of J ψ mesons coming from B meson decays to be f b = 0.35 ± 0.09(stat)±0.10(syst) and inferred the inclusive b production cross section. From the information on the event topology the fraction of nonisolated J ψ events has been measured to be f nonisol = 0.64 ± 0.08(stat)±0.06(syst). We have also obtained the fraction of J ψ events resulting from radiative decays of χ c states, f χ = 0.32 ± 0.07(stat)±0.07(syst). We discuss the implications of our measurements for charmonium production processes.
No description provided.
No description provided.
Integrated b-quark production cross section.
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Cross section times the branching ratio for decay into dimuons.
Forum