We report on a measurement of the mass dependence of the forward-backward charge asymmetry, A_FB, and production cross section dsigma/dM for e+e- pairs with mass M_ee>40 GeV/c2. The data sample consists of 108 pb-1 of p-pbar collisions at sqrt(s)=1.8 TeV taken by the Collider Detector at Fermilab during 1992-1995. The measured asymmetry and dsigma/dM are compared with the predictions of the Standard Model and a model with an extra Z' gauge boson.
The E+ E- production cross section and the forward-backward asymmetry. The errors contain the statistical and systematic uncertainties combined in quadrature, but not the additional uncertainty of the luminosity.
The forward, backward and total production cross sections for dielectron production for the mass regions above 105 GeV. The errors contain the statistical and systematic uncertainties combined in quadrature, but not the additional uncertainty of the luminosity.
The production cross section for di-muons for the mass region above 105 GeV. The errors contain the statistical and systematic uncertainties combined in quadrature, but not the additional uncertainty of the luminosity.
We present a search for electroweak production of single top quarks in $\approx 90$ $pb^{-1}$ of data collected with the DZero detector at the Fermilab Tevatron collider. Using arrays of neural networks to separate signals from backgrounds, we set upper limits on the cross sections of 17 pb for the s-channel process $p\bar{p} \to tb + X$, and 22 pb for the t-channel process $p\bar{p} \to tqb + X$, both at the 95% confidence level.
No description provided.
An investigation of the polar angle distribution of charged hadrons is presented using data taken by the JADE experiment at the PETRA e^+e^- collider at centre-of-mass energies of 35 and 44 GeV. From fits to the polar angle distribution the longitudinal, sigma_L, and transverse, sigma_T, cross-section relative to the total hadronic are determined at an average energy scale of 36.6 GeV. The results are sigma_L/sigma_tot = 0.067 +/- 0.013, sigma_T/sigma_tot = 0.933 -/+ 0.013 where total errors are given and the results are exactly anti-correlated. Using the next-to-leading order QCD prediction for the longitudinal cross-section, the value alpha_S(36.6 GeV) = 0.150 +/- 0.025 of the strong coupling constant is obtained in agreement with the world average value of alpha_S evolved to an energy scale of 36.6 GeV.
The distribution oF Q*COS(THETA) where Q is the charge of the individual hadron and THETA is the polar angle between the direction of the incoming E- beam and the outgoing hadron. The data are corrected for detector effects.
Value of the longitudinal cross section relative to the total cross section.
Value of the strong coupling constant ALPHAS deduced from the measurements. The second DSYS error is the uncertainty on the renormalisation scale.
The inclusive cross section for production of isolated photons has been measured in \pbarp collisions at $\sqrt{s} = 630$ GeV with the \D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy ($E_T$) range from 7-49 GeV and have pseudorapidity $|\eta| < 2.5$. This measurement is combined with to previous \D0 result at $\sqrt{s} = 1800$ GeV to form a ratio of the cross sections. Comparison of next-to-leading order QCD with the measured cross section at 630 GeV and ratio of cross sections show satisfactory agreement in most of the $E_T$ range.
No description provided.
No description provided.
No description provided.
The magnitude of the CKM matrix element Vub is determined by measuring the inclusive charmless semileptonic branching fraction of beauty hadrons at OPAL based on b -> Xu l nu event topology and kinematics. This analysis uses OPAL data collected between 1991 and 1995, which correspond to about four million hadronic Z decays. We measure Br(b -> Xu l) to be (1.63 +/- 0.53 +0.55/-0.62) x 10^(-3). The first uncertainty is the statistical error and the second is the systematic error. From this analysis, Vub is determined to be: |Vub| = (4.00 +/- 0.65(stat) +0.67/-0.76(sys) +/- 0.19(HQE)) x 10^(-3). The last error represents the theoretical uncertainties related to the extraction of |Vub| from Br(b -> Xu l) using the Heavy Quark Expansion.
CKM is Cabibbo-Kobayashi-Maskawa (CKM) matrix element. The last DSYS error comes from the theoretical uncertainty.
Three-jet production is studied for the first time in deep-inelastic positron-proton scattering. The measurement carried out with the H1 detector at HERA covers a large range of four-momentum transfer squared 5 < Q^2 < 5000 GeV^2 and invariant three-jet masses 25 < M_(3jet) < 140 GeV. Jets are defined by the inclusive k_T algorithm in the Breit frame. The size of the three-jet cross section and the ratio of the three-jet to the dijet cross section R_(3/2) are described over the whole phase space by the predictions of perturbative QCD in next-to-leading order. The shapes of angular jet distributions deviate significantly from a uniform population of the available phase space but are well described by the QCD calculation.
The inclusive 3-Jet cross section as a function of Q**2.
The ratio of 3 jets to 2 jets as a function of Q**2.
The inclusive 3-JET cross section as a function of Bjorken scaling variableX for the Q**2 range 5 to 100 GeV**2.
The minimum bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons (h-) in Au+Au interactions at sqrt(s_nn) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dNh-/deta|_{eta = 0} = 280 +- 1(stat)+- 20(syst), an increase per participant of 38% relative to ppbar collisions at the same energy. The mean transverse momentum is 0.508 +- 0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h- yield per participant is a strong function of pt. The pseudorapidity distribution is almost constant within |eta|<1.
Normalized multiplicity distribution of $h^{−}$ with $p_{T} > 100$ MeV/$c$ at $|\eta| < 0.5$ in Au+Au collisions at $\sqrt{s_{NN}} = 130$ GeV. Systematic error on the vertical scale is estimated to be $10\%$. The systematic error on the horizontal scale is $6\%$ for the entire range of multiplicity. The shaded area is $5\%$ most central collisions, selected by ZDC coincidence. The solid curve is the prediction from the HIJING model.
$h^{−}$ $p_{T}$-spectra for the $5\%$ most central Au+Au collisions at midrapidity ($|\eta| < 0.1$) for several systems. The correlated systematical error is estimated to be below $6\%$. The curves are power-law fits to the data.
ratio of STAR and scaled UA1 $p_{T}$-distributions. The errors given are the errors of the STAR data only and do not include the systematic errors from the scaling of the UA1 data to $130$ GeV (i.e., the shaded region in Fig.2 lower panel). The STAR data is for the $5\%$ most central collisions.
We report on a measurement of the ratio of the differential cross sections for W and Z boson production as a function of transverse momentum in proton-antiproton collisions at sqrt(s) = 1.8 TeV. This measurement uses data recorded by the D0 detector at the Fermilab Tevatron in 1994-1995. It represents the first investigation of a proposal that ratios between W and Z observables can be calculated reliably using perturbative QCD, even when the individual observables are not. Using the ratio of differential cross sections reduces both experimental and theoretical uncertainties, and can therefore provide smaller overall uncertainties in the measured mass and width of the W boson than current methods used at hadron colliders.
The measured W and Z0 cross sections used to compute the ratio.
The measured ratios of W+-/Z0 cross sections, corrected for the branching ratios BR(W-->e-nue)=0.1073+-0.0025 and BR(Z0-->E+E-)=0.033632+-0.000059 (PDG 2000). The error given is the total error, but note that the 4.3pct error in the luminosity cancels completely in the ratio.
We report results from a study of Λ0 polarization in the exclusive reaction pp→pf(Λ0K+) at 800−GeV/c. We observe a dependence of the polarization on the Λ0K+ invariant mass with large (+71%) positive polarization at small mass (1.63−GeV/c2) and large (−43%) negative polarization at large mass (2.75−GeV/c2). This observation confirms the result of the CERN ISR R608 experiment and extends the range over which the effect is observed. The strong dependence of the polarization on the Λ0K+ invariant mass suggests that the origin of the polarization is closely related to the production dynamics of the diffractively produced Λ0K+ system.
The measured LAMBDA polarisation as a function of the (LAMBDA K+) invariantmass.
The measured LAMBDA polarisation as functions of the LAMBDA transverse momentum and Feynman X.
We report on a measurement of the mean charged-particle multiplicity of jets in dijet events with dijet masses in the range 80–630GeV/c2, produced at the Tevatron in pp¯ collisions with s=1.8TeV and recorded by the Collider Detector at Fermilab. The data are fit to perturbative-QCD calculations carried out in the framework of the modified leading log approximation and the hypothesis of local parton-hadron duality. The fit yields values for two parameters in that framework: the ratio of parton multiplicities in gluon and quark jets, $r≡N_{partons}^{g−jet} / N_{partons}^{q−jet} = 1.7 \pm 0.3$, and the ratio of the number of charged hadrons to the number of partons in a jet, $K_{LPHD}^{charged} ≡ N_{hadrons}^{charged} / N_{partons} = 0.57 \pm 0.11$.
Measured values of inclusive charged particle multiplicity per jet for jets falling in restricted cones with opening angles 0.17, 0.28 and 0.47 radians. Note that the systematic errors are strongly correlated.
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