Showing papers by "M. Abolins published in 1999"

Search for charged Higgs bosons in decays of top quark pairs

Abstract: We present a search for charged Higgs bosons in decays of pair-produced top quarks using 109.2{plus_minus}5.8 pb{sup {minus}1} of data recorded from p{ovr p} collisions at {radical}(s)=1.8 TeV by the D0 detector during 1992{endash}1996 at the Fermilab Tevatron. No evidence is found for charged Higgs production, and most parts of the [M{sub H{sup +}} {beta}] parameter space where the decay t{r_arrow}H{sup +}b has a branching fraction close to or larger than that for t{r_arrow}W{sup +}b are excluded at 95{percent} confidence level. Assuming m{sub t}=175 GeV and {sigma}(p{ovr p}{r_arrow} t{ovr t})=5.5 pb , for M{sub H{sup +}}=60 GeV , we exclude tan{number_sign}{beta}{lt}0.97 and tan{number_sign}{beta}{gt}40.9 . {copyright} {ital 1999} {ital The American Physical Society}

Determination of the absolute jet energy scale in the DØ calorimeters

Abstract: The DO detector is used to study p p collisions at the 1800 and 630 GeV center-of-mass energies available at the Fermilab Tevatron. To measure jets, the detector uses a sampling calorimeter composed of uranium and liquid argon as the passive and active media, respectively. Understanding the jet energy calibration is not only crucial for precision tests of QCD, but also for the measurement of particle masses and the determination of physics backgrounds associated with new phenomena. This paper describes the energy calibration of jets observed with the DO detector at the two p p center-of-mass energies in the transverse energy and pseudorapidity range ET>8 GeV and |η|

Measurement of the high-mass Drell-Yan cross section and limits on quark-electron compositeness scales

Abstract: We present a measurement of the Drell-Yan cross section at high dielectron invariant mass using $120\mathrm{pb}{}^{\ensuremath{-}1}$ of data collected in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ by the D0 Collaboration during 1992--1996. No deviation from standard model expectations is observed. We use the data to set limits on the quark-electron compositeness scale. The $95%$ confidence level lower limits on the compositeness scale vary between 3.3 and 6.1 TeV depending on the assumed form of the effective contact interaction.

Search for squarks and gluinos in events containing jets and a large imbalance in transverse energy

Abstract: Using data corresponding to an integrated luminosity of $79{\mathrm{pb}}^{\ensuremath{-}1}$, D0 has searched for events containing multiple jets and large missing transverse energy in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}18\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$ at the Fermilab Tevatron collider Observing no significant excess beyond what is expected from the standard model, we set limits on the masses of squarks and gluinos and on the model parameters ${m}_{0}$ and ${m}_{1/2}$, in the framework of the minimal low-energy supergravity models of supersymmetry For $\mathrm{tan}\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$ and ${A}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$, with $\ensuremath{\mu}l0$, we exclude all models with ${m}_{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{q}}l250\phantom{\rule{0ex}{0ex}}\mathrm{GeV}{/c}^{2}$ For models with equal squark and gluino masses, we exclude $ml260\phantom{\rule{0ex}{0ex}}\mathrm{GeV}{/c}^{2}$

The Dijet Mass Spectrum and a Search for Quark Compositeness in bar{p}p Collisions at sqrt{s} = 1.8 TeV

Abstract: Using the DZero detector at the 1.8 TeV pbarp Fermilab Tevatron collider, we have measured the inclusive dijet mass spectrum in the central pseudorapidity region |eta_jet| < 1.0 for dijet masses greater than 200 Gev/c^2. We have also measured the ratio of spectra sigma(|eta_jet| < 0.5)/sigma(0.5 < |eta_jet| < 1.0). The order alpha_s^3 QCD predictions are in good agreement with the data and we rule out models of quark compositeness with a contact interaction scale < 2.4 TeV at the 95% confidence level.

Small angle J/ψ production in pp¯ collisions at √s=1.8TeV

Abstract: 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.

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

Abstract: D\O{} has measured the inclusive production cross section of W and Z bosons in a sample of 13 ${\mathrm{pb}}^{\ensuremath{-}1}$ of data collected at the Fermilab Tevatron The cross sections, multiplied by their leptonic branching fractions, for production in $p\overline{p}$ collisions at $\sqrt{s}=18$ TeV are ${\ensuremath{\sigma}}_{W}\mathrm{B}(\stackrel{\ensuremath{\rightarrow}}{W}e\ensuremath{ u})=236\ifmmode\pm\else\textpm\fi{}002\ifmmode\pm\else\textpm\fi{}008\ifmmode\pm\else\textpm\fi{}013\mathrm{}\mathrm{nb},$ ${\ensuremath{\sigma}}_{W}\mathrm{B}(\stackrel{\ensuremath{\rightarrow}}{W}\ensuremath{\mu}\ensuremath{ u})=209\ifmmode\pm\else\textpm\fi{}006\ifmmode\pm\else\textpm\fi{}022\ifmmode\pm\else\textpm\fi{}011\mathrm{}\mathrm{nb},$ ${\ensuremath{\sigma}}_{Z}\mathrm{B}(\stackrel{\ensuremath{\rightarrow}}{Z}{e}^{+}{e}^{\ensuremath{-}})=0218\ifmmode\pm\else\textpm\fi{}0008\ifmmode\pm\else\textpm\fi{}0008\ifmmode\pm\else\textpm\fi{}0012\mathrm{}\mathrm{nb}$, and ${\ensuremath{\sigma}}_{Z}\mathrm{B}(\stackrel{\ensuremath{\rightarrow}}{Z}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})=0178\ifmmode\pm\else\textpm\fi{}0022\ifmmode\pm\else\textpm\fi{}0021\ifmmode\pm\else\textpm\fi{}0009\mathrm{}\mathrm{nb}$, 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 ${\ensuremath{\sigma}}_{W}\mathrm{B}(\stackrel{\ensuremath{\rightarrow}}{W}l\ensuremath{ u})/{\ensuremath{\sigma}}_{Z}\mathrm{B}(\stackrel{\ensuremath{\rightarrow}}{Z}{l}^{+}{l}^{\ensuremath{-}})=1090\ifmmode\pm\else\textpm\fi{}052$ Assuming standard model couplings, we use this result to determine the width of the W boson, and obtain $\ensuremath{\Gamma}(W)=2044\ifmmode\pm\else\textpm\fi{}0097 \mathrm{GeV}$

Measurement of the Λb0 lifetime using semileptonic decays

Abstract: We report a measurement of the Bs(0) lifetime in the semileptonic decay channel Bs(0) --> Ds- mu+ nuX (and its charge conjugate), using approximately 0.4 fb(-1) of data collected with the D0 detector during 2002-2004. Using 5176 reconstructed Ds- mu+ signal events, we have measured the Bs(0) lifetime to be tau(Bs(0))=1.398+/-0.044(stat)(-0.025)(+0.028)(syst) ps. This is the most precise measurement of the Bs(0) lifetime to date.

Spin correlation in tt̄ production from pp̄ collisions at √s = 1.8 TeV

Abstract: 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.

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

Abstract: This if the publisher's version, also available electronically from http://journals.aps.org/prd/abstract/10.1103/PhysRevD.60.012001.

Measurement of the top quark pair production cross-section in the all jets decay channel

Abstract: We present a measurement of $t\overline{t}$ production in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ from $110{\mathrm{pb}}^{\ensuremath{-}1}$ of data collected in the all-jets decay channel with the D0 detector at Fermilab. A neural network analysis yields a cross section of $7.1\ifmmode\pm\else\textpm\fi{}2.8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.5(\mathrm{syst})\mathrm{pb}$ at a top quark mass $({m}_{t})$ of $172.1\mathrm{GeV}{/c}^{2}$. Using previous D0 measurements from dilepton and single lepton channels, the combined D0 result for the $t\overline{t}$ production cross section is $5.9\ifmmode\pm\else\textpm\fi{}1.2(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}1.1(\mathrm{syst})\mathrm{pb}$ for ${m}_{t}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}172.1\phantom{\rule{0ex}{0ex}}\mathrm{GeV}{/c}^{2}$.

Search for second-generation leptoquark pairs in $\bar{p}p$ collisions at $\sqrt s$ = 1.8 TeV

Abstract: 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 u+jets and u u+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.

Search for R-parity violating supersymmetry in the dielectron channel

Abstract: We report on a search for R-parity violating supersymmetry in p-pbar collisions at sqrt(s) = 1.8 TeV using the D0 detector at Fermilab. Events with at least two electrons and four or more jets were studied. We observe 2 events in 99 +- 4.4 pb-1 of data, consistent with the expected background of 1.8 +- 0.4 events. This result is interpreted within the framework of minimal low-energy supergravity supersymmetry models. Squarks with mass below 243 GeV/c^2 and gluinos with mass below 227 GeV/c^2 are excluded at the 95% confidence level (C. L.) for A_0=0, mu < 0$, tan beta=2 and a finite value for R-parity violating Yukawa coupling lambda'_1jk (j=1, 2 and k=1, 2, 3). For equal squark and gluino masses, the corresponding mass limit is 277 GeV/c^2.

Studies of WW and WZ production and limits on anomalous WWγ and WWZ couplings

Abstract: Evidence of anomalous WW and WZ production was sought in pbar{p} collisions at a center-of-mass energy of sqrt(s) = 1.8 TeV. The final states $WW (WZ) to mu-nu-jet-jet + X, WZ to mu-nu-e-e + X and WZ to e-nu-e-e + X were studied using a data sample corresponding to an integrated luminosity of approximately 90 pb-1. No evidence of anomalous diboson production was found. Limits were set on anomalous WWgamma and WWZ couplings and were combined with our previous results. The combined 95% confidence level anomalous coupling limits for Lambda=2 TeV are -0.25 LE Delta-kappa LE 0.39 (lambda=0) and -0.18 LE lambda LE 0.19 (Delta \kappa = 0), assuming the WWgamma couplings are equal to the WWZ couplings.

Search for bottom squarks in pp̄ collisions at √s=1.8 TeV

Abstract: We report on a search for bottom squarks produced in pbarp collisions at sqrt(s) = 1.8 TeV using the D0 detector at Fermilab. Bottom squarks are assumed to be produced in pairs and to decay to the lightest supersymmetric particle (LSP) and a b quark with branching fraction of 100%. The LSP is assumed to be the lightest neutralino and stable. We set limits on the production cross section as a function of bottom squark mass and LSP mass.

Search for squarks and gluinos in single-photon events with jets and large missing transverse energy in p¯p collisions at √ s = 1.8 TeV

Abstract: We search for new physics using events with one high transverse energy photon, two or more jets, and an apparent imbalance in transverse energy, in p{ovr p} collisions at the Fermilab Tevatron at {radical} (s) =1.8 TeV . Such events are predicted for production of supersymmetric particles in some models. No excess is observed beyond expected background. For the parameter space of the minimal supersymmetric standard model with branching fraction B({tilde {chi}}{sup 0}{sub 2}{r_arrow}{gamma}thinsp{tilde {chi}}{sup 0}{sub 1})=1 and m{sub {tilde {chi}}{sup 0}{sub 2 }}{minus}m{sub {tilde {chi}}{sup 0}{sub 1}}{gt}20 GeV , we obtain a 95{percent} confidence level lower mass limit of 310thinspthinspGeV for equal mass squarks and gluinos. The results are also interpreted in models with low energy gauge mediated supersymmetry breaking. {copyright} {ital 1998} {ital The American Physical Society }

Search for second generation leptoquark pairs decaying to μv + jets in pp collisons at √ s = 1.8 Tev

Abstract: We report on a search for second generation leptoquarks (LQ) produced in p (p) over bar collisions at root s = 1.8 TeV using the DO detector at Fermilab. Second generation leptoquarks are assumed to be produced in pairs and to decay to either mu. or nu and either a strange or a charm quark (q). Limits an placed on sigma(p (p) over bar --> LQ --> mu nu + jets) as a function of the mass of the leptoquark. For equal branching ratios to mu q and nu q, second generation scalar leptoquarks with a mass below 160 GeV/c(2), vector leptoquarks with anomalous minimal vector couplings with a mass below 240 GeV/c(2), and vector leptoquarks with Yang-Mills couplings with a mass below 290 GeV/c(2), are excluded at the 95% confidence level.

The ATLAS high level trigger ATM testbed

Abstract: This paper describes an implementation of the high level trigger for the ATLAS experiment on a large testbed based on a 32 node switch attached to data sources, event processing units, supervisor modules and interface to the level-1 trigger. We describe the functionality of each component and investigate its performance. We show the operation of the complete system and outline future activities.