Small Angle Muon and Bottom Quark Production in pbarp Collisions at sqrt(s) = 1.8 TeV

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.Comment: 12 pages, 5 figures, submitted to PR

Search for narrow t(t)over-bar resonances in p(p)over-bar collisions at root s=1.8 TeV

A search for narrow resonances that decay into t (t) over bar pairs has been performed using 130 pb(-1) of data in the lepton + jets channel collected by the DO detector in p (p) over bar collisions at roots=1.8 TeV. There is no significant deviation observed from the standard-model predictions at a top-quark mass of 175 GeV/c(2). We therefore present upper limits at the 95% confidence level on the product of the production cross section and branching fraction to t (t) over bar for narrow resonances as a function of the resonance mass M-X. These limits are used to exclude the existence of a leptophobic top-color particle with mass M-X<560 GeV/c(2), using a theoretical cross section for a width Gamma(X)=0.012M(X)

Measurement of the top quark pair production cross section in pp̄ collisions using multijet final states

We have studied tt̄ production using multijet final states in pp̄ 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 tt̄ 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/c2. Combining this result with previous DØ measurements, where one or both of the W bosons decay leptonically, gives a tt̄ production cross section of 5.9±1.2 (stat)±1.1 (syst) pb. ©1999 The American Physical Society

Measurement of W and Z boson production cross sections in pp̄ collisions at √s=1.8 TeV

DØ 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 pp̄ collisions at √s=1.8 TeV are σWB(W→eν)=2.36±0.02±0.08±0.13 nb, σWB(W →μν)=2.09±0.06±0.22±0.11 nb, σZB(Z→e+e -)=0.218±0.008±0.008±0.012 nb, and σZB(Z →μ+μ -)=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 σWB(W→lν)/σZB(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 Γ(W)=2.044±0.097 GeV. ©1999 The American Physical Society

Measurement of the top quark mass in the dilepton channel

We report a measurement of the top quark mass using six candidate events for the process pp̄→tt̄+X →l+vbl-v̄b̄+X, observed in the D0 experiment at the Fermilab pp̄ collider. Using maximum likelihood fits to the dynamics of the decays, we measure a mass for the top quark of mt=168.4±12.3(stat) ±3.6(syst) Gev. We combine this result with our previous measurement in the tt̄→l+jets channel to obtain mt=172.1 ± 7.1 GeV as the best value of the mass of the top quark measured by D0. ©1999 The American Physical Society

Limits on anomalous WWγ and WWZ couplings from WW/WZ→e vjj production

Limits on anomalous WWγ and WWZ couplings are presented from a study of WW/WZ→e vjj events produced in pp̄ collisions at √s=1.8 TeV. Results from the analysis of data collected using the DØ detector during the 1993-1995 Tevatron collider run at Fermilab are combined with those of an earlier study from the 1992-1993 run. A fit to the transverse momentum spectrum of the W boson yields direct limits on anomalous WWγ and WWZ couplings. With the assumption that the WWγ and WWZ couplings are equal, we obtain -0.34&lt;λ&lt;0.36 (with Δκ=0) and -0.43&lt;Δκ&lt;0.59 (with λ=0) at the 95% confidence level for a form-factor scale Λ=2.0 TeV. ©2000 The American Physical Society

Search for new physics in aμX data at DØ using SLEUTH: A quasi-model-independent search strategy for new physics

We present a quasi-model-independent search for the physics responsible for electroweak symmetry breaking. We define final states to be studied, and construct a rule that identifies a set of relevant variables for any particular final state. A new algorithm ("SLEUTH") searches for regions of excess in those variables and quantifies the significance of any detected excess. After demonstrating the sensitivity of the method, we apply it to the semi-inclusive channel eμX collected in 108 pb-1 of pp̄ collisions at √s=1.8 TeV at the DØ experiment during 1992-1996 at the Fermilab Tevatron. We find no evidence of new high pT physics in this sample. ©2000 The American Physical Society

Limits on quark compositeness from high energy jets in p̄p collisions at 1.8 TeV

Events in p̄p collisions at √s= 1.8 TeV with total transverse energy exceeding 500 GeV are used to set limits on quark substructure. The data are consistent with next-to-leading order QCD calculations. We set a lower limit of 2.0 TeV at 95% confidence on the energy scale ΛLL for compositeness in quarks, assuming a model with a left-left isoscalar contact interaction term. The limits on ΛLL are found to be insensitive to the sign of the interference term in the Lagrangian. ©2000 The American Physical Society