arXiv subjects

D0 Collaboration

Publications and source records attributed to D0 Collaboration.

At least 361 records · Page 20Linked to original sources

arXiv2001

A Search forthe Scalar Top Quark in $p \bar{p}$ Collisions at $\sqrt{s}=$ 1.8 TeV

We have performed a search for scalar top quark (stop) pair production in the inclusive electron-muon-missing transverse energy final state, using a sample of $p \bar{p}$ events corresponding to 108.3 pb$^{-1}$ of data collected with the DØdetector at Fermilab. The search is done in the framework of the minimal supersymmetric standard model assuming that the sneutrino is the lightest supersymmetric particle. For the dominant decays of the lightest stop, $\bc$ and $\bls$, no evidence for signal is found. We derive cross-section limits as a function of stop (\stt), chargino (\ca), and sneutrino (\snu) masses.

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arXiv2001

Search for First-Generation Scalar and Vector Leptoquarks

We describe a search for the pair production of first-generation scalar and vector leptoquarks in the eejj and enujj channels by the D0 Collaboration. The data are from the 1992--1996 ppbar run at sqrt{s} = 1.8 TeV at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the eejj and enujj channels are combined with those from a previous D0 analysis of the nunujj channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross section as a function of mass and of beta, the branching fraction to a charged lepton. These limits are compared to next-to-leading-order theory to set 95% C.L. lower limits on the mass of a first-generation scalar leptoquark of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345, 337, and 206 GeV/c^2 are set on the mass for beta=1, 1/2, and 0, respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings.

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arXiv2001

Search for New Physics Using Quaero: A General Interface to D0 Event Data

We describe Quaero, a method that i) enables the automatic optimization of searches for physics beyond the standard model, and ii) provides a mechanism for making high energy collider data generally available. We apply Quaero to searches for standard model WW, ZZ, and ttbar production, and to searches for these objects produced through a new heavy resonance. Through this interface, we make three data sets collected by the D0 experiment at sqrt(s)=1.8 TeV publicly available.

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arXiv2001

The Inclusive Jet Cross Section in ppbar Collisions at sqrt{s}=1.8 TeV using the kT Algorithm

We present a preliminary measurement of the central inclusive jet cross section using a successive combination algorithm based on relative transverse momenta (kT) for jet reconstruction. We analyze a 87.3 pb-1 data sample collected by the D0 detector at the Fermilab Tevatron ppbar Collider during 1994-1995. The cross section, reported as a function of transverse momentum (pT > 60 GeV) in the central region of pseudo-rapidity (|eta| < 0.5), is in reasonable agreement with next-to-leading order QCD predictions. This is the first jet production measurement in a hadron collider using a successive combination type of jet algorithm.

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arXiv2001

Measurement of the ratio of the differential cross sections for W and Z boson production as a function of transverse momentum in pbarp collisions at sqrt(s)=1.8TeV

We report on a preliminary 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. It has been shown that the ratio between W and Z observables can be reliably calculated using perturbative QCD, even when the individual observables are not. We present the first comparison between the measurement of a W and Z observable ratio and a purely perturbative calculation. The use of the ratio reduces both experimental and theoretical uncertainites and might result in smaller overall uncertainties on the measured W mass and width, compared to currently used methods at hadron colliders.

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arXiv2001

Search for heavy particles decaying into electron-positron pairs in p-pbar collisions

We present results of searches for technirho, techniomega, and Z' particles, using the decay channels technirho, techniomega, Z' -> e+e-. The search is based on 124.8 pb-1 of data collected by the D0 detector at the Fermilab Tevatron during 1992-1996. In the absence of a signal, we set 95% C.L. upper limits on the cross sections for the processes p pbar -> technirho, techniomega, Z' -> e+e- as a function of the mass of the decaying particle. For certain model parameters, we exclude the existence of degenerate technirho and techniomega states with masses below about 200 GeV. We exclude a Z' with mass below 670 GeV, assuming that it has the same couplings to fermions as the Z boson.

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arXiv2001

Inclusive Jet Production in pbar p Collisions

We report a new measurement of the pseudorapidity (eta) and transverse-energy (Et) dependence of the inclusive jet production cross section in pbar b collisions at sqrt(s) = 1.8 TeV using 95 pb**-1 of data collected with the DZero detector at the Fermilab Tevatron. The differential cross section d^2sigma/dEt deta is presented up to |eta| = 3, significantly extending previous measurements. The results are in good overall agreement with next-to-leading order predictions from QCD and indicate a preference for certain parton distribution functions.

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arXiv2001

The Ratio of Jet Cross Sections at s**(1/2)=630 GeV and 1800 GeV

The DO Collaboration has measured the inclusive jet cross section in proton-antiproton collisions at s**2 = 630 GeV. The results for pseudorapidities -0.5 to 0.5 are combined with our previous results at s**2 = 1800 GeV to form a ratio of cross sections with smaller uncertainties than either individual measurement. Next-to-leading-order QCD predictions show excellent agreement with the measurement at 630 GeV; agreement is also satisfactory for the ratio. Specifically, despite a 10% to 15% difference in the absolute normalization, the dependence of the ratio on jet transverse momentum is very similar for data and theory.

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arXiv2000

Search for Large Extra Dimensions in Dielectron and Diphoton Production

We report a search for effects of large extra spatial dimensions in ppbar collisions at a center-of-mass energy of 1.8 TeV with the DZero detector, using events containing a pair of electrons or photons. The data are in good agreement with the expected background and do not exhibit evidence for large extra dimensions. We set the most restrictive lower limits to date, at the 95% confidence level, on the effective Planck scale between 1.0 TeV and 1.4 TeV for several formalisms and numbers of extra dimensions.

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arXiv2000

Search for New Physics in e mu X Data at D0 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 e mu X collected in 108 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV at the D0 experiment during 1992-1996 at the Fermilab Tevatron. We find no evidence of new high p_T physics in this sample.

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arXiv2000

Probing BFKL Dynamics in the Dijet Cross Section at Large Rapidity Intervals in ppbar Collisions at sqrt{s}=1800 and 630 GeV

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.

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arXiv2000

The b-bbar Production Cross Section and Angular Correlations in p-pbar Collisions at sqrt(s) = 1.8 TeV

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.

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arXiv2000

Spin Correlation in tt-bar Production from pp-bar Collisions at sqrt(s)=1.8 TeV

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.

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arXiv2000

A Measurement of the W to tau+nu Production Cross Section in p-pbar Collisions at sqrt(s) = 1.8 TeV

We report on a measurement of sigma(p-pbar to W+X) times B(W to tau+nu) in p-pbar collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron. The measurement is based on an integrated luminosity of 18 pb^-1 of data collected with the D0 detector during 1994-1995. We find that sigma(p-pbar to W+X) times B(W to tau+nu) = 2.22 +- 0.09 (stat) +- 0.10 (syst) +- 0.10 (lum) nb. Lepton universality predicts that the ratio of the tau and electron electroweak charged current couplings to the W boson, g_tau^W / g_e^W, be unity. We find g_tau^W / g_e^W = 0.980 +- 0.031, in agreement with lepton universality.

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arXiv2000

A Search for Dilepton Signatures from Minimal Low-Energy Supergravity in $p\bar{p}$ Collisions at $\sqrt{s}=1.8$ TeV

We report on a search for supersymmetry using the DØdetector. The 1994-1996 data sample of $\sqrt{s}=1.8$ TeV $p\bar{p}$ collisions was analyzed for events containing two leptons ($e$ or $μ$), two or more jets, and missing transverse energy. Assuming the minimal supergravity model, with $A_0=0$ and $μ<0$, various thresholds were employed to optimize the search. No events were found beyond expectation from background. We set a lower limit at the 95% C.L. of 255 GeV/$c^2$ for equal mass squarks and gluinos for $\tanβ=2$, and present exclusion contours in the $(m_0,m_{1/2})$ plane for $\tanβ=2$--6.

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arXiv1999

The Isolated Photon Cross Section in p pbar Collisions at sqrt(s) = 1.8 TeV

We report a new measurement of the cross section for the production of isolated photons, with transverse energies (ET) above 10 GeV and pseudorapidities |eta| < 2.5, in p pbar collisions at sqrt{s} = 1.8 TeV. The results are based on a data sample of 107.6 pb-1 recorded during 1992--1995 with the D0 detector at the Fermilab Tevatron collider. The background, predominantly from jets which fragment to neutral mesons, was estimated using the longitudinal shower shape of photon candidates in the calorimeter. The measured cross section is in good agreement with the next-to-leading order (NLO) QCD calculation for ET > 36 GeV.

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arXiv1999

Differential Production Cross Section of Z Bosons as a Function of Transverse Momentum at sqrt{s}=1.8 TeV

We present a measurement of the transverse momentum distribution of Z bosons produced in ppbar collisions at sqrt{s}=1.8 TeV using data collected by the D0 experiment at the Fermilab Tevatron Collider during 1994--1996. We find good agreement between our data and a current resummation calculation. We also use our data to extract values of the non-perturbative parameters for a particular version of the resummation formalism, obtaining significantly more precise values than previous determinations.

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arXiv1999

Evidence of Color Coherence Effects in W+jets Events from ppbar Collisions at sqrt(s) = 1.8 TeV

We report the results of a study of color coherence effects in ppbar collisions based on data collected by the D0 detector during the 1994-1995 run of the Fermilab Tevatron Collider, at a center of mass energy sqrt(s) = 1.8 TeV. Initial-to-final state color interference effects are studied by examining particle distribution patterns in events with a W boson and at least one jet. The data are compared to Monte Carlo simulations with different color coherence implementations and to an analytic modified-leading-logarithm perturbative calculation based on the local parton-hadron duality hypothesis.

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