1,721,012 research outputs found
Measurement of W±Z production in proton-proton collisions at √s=7 TeV with the ATLAS detector
Get PDFA study of W ± Z production in proton-proton collisions at √s=7 TeV is presented using data corresponding to an integrated luminosity of 4.6 fb−1 collected with the ATLAS detector at the Large Hadron Collider in 2011. In total, 317 candidates, with a background expectation of 68±10 events, are observed in double-leptonic decay final states with electrons, muons and missing transverse momentum. The total cross-section is determined to be σtotWZ=19.0+1.4−1.3(stat.)±0.9(syst.)±0.4(lumi.) pb , consistent with the Standard Model expectation of 17.6+1.1−1.0 pb . Limits on anomalous triple gauge boson couplings are derived using the transverse momentum spectrum of Z bosons in the selected events. The cross-section is also presented as a function of Z boson transverse momentum and diboson invariant mass
Electroweak measurements in electron–positron collisions at W-boson-pair energies at LEP
No full textMeasurement of the Top Quark Mass at D0 Run II with the Matrix Element Method in the Lepton+Jets Final State
Get PDFThe mass of the top quark is a fundamental parameter of the Standard Model. Its precise knowledge yields valuable insights into unresolved phenomena in and beyond the Standard Model. A measurement of the top quark mass with the matrix element method in the lepton+jets final state in D0 Run II is presented. Events are selected requiring an isolated energetic charged lepton (electron or muon), significant missing transverse energy, and exactly four calorimeter jets. For each event, the probabilities to originate from the signal and background processes are calculated based on the measured kinematics, the object resolutions and the respective matrix elements. The jet energy scale is known to be the dominant source of systematic uncertainty. The reference scale for the mass measurement is derived from Monte Carlo events. The matrix element likelihood is defined as a function of both, mtop
and jet energy scale JES, where the latter represents a scale factor with respect to the reference scale. The top mass is obtained from a two-dimensional correlated fit, and the likelihood yields both the statistical and jet energy scale uncertainty. Using a dataset of 320 pb-1 of D0 Run II data, the mass of the top quark is measured to be
mtop (ljets) = 169.5 +/- 4.4(stat.+JES) +1.7-1.6(syst.) GeV
mtop (ejets) = 168.8 +/- 6.0(stat.+JES) +1.9-1.9(syst.) GeV
mtop (mujets)= 172.3 +/- 9.6(stat.+JES) +3.4-3.3(syst.) GeV
The jet energy scale measurement in the lepton+jets sample yields JES=1.034 +/- 0.034, suggesting good consistency of the data with the simulation. The measurement forecasts significant improvements to the total top mass uncertainty during Run II before the startup of the LHC, as the data sample will grow by a factor of ten and D0's tracking capabilities will be employed in jet energy reconstruction and flavor identification.Die Masse des Top-Quarks ist ein fundamentaler Parameter des
Standard-Modells. Ihre genaue Kenntnis liefert wertvolle Aufschlüsse bezüglich unverstandener Phänomene im Standard-Model und darüber hinaus. Die Messung der Top-Quark-Masse mit der Matrixelement-Methode im
Lepton+Jets Zerfallskanal in Run II des D0 Experiments wird präsentiert. Ereignisse werden selektiert, wenn sie ein isoliertes Lepton (Elektron oder Myon), signifikante fehlende transversale Energie und genau vier Kalorimeter-Jets aufweisen. Für jedes Ereignis werden die Wahrscheinlichkeiten berechnet, dass das Ereignis durch den Signal- bzw. Untergrund-Prozess produziert worden ist, basierend auf der gemessenen Kinematik, den Auflösungen
der rekonstrierten Objekte und der prozess-spezifischen
Matrixelemente. Die Kenntnis der Jet Energie Skala ist die dominierende Quelle systematischer Unsicherheit dieser Messung. Die Referenz-Skala wird in Monte Carlo Ereignissen bestimmt. Die Matrixelement-Likelihood wird definiert als Funktion beider Variablen, mtop und JES, wobei letzterer einen Skalierungs-Faktor bezüglich der Referenzskala beschreibt. Die Topmasse wird mittels eines zweidimensionalen korrelierten Fits bestimmt, wobei der Likelihood sowohl den statistischen Fehler als auch den Fehler durch Jet Energie Skala liefert. Die Methode wird auf einen D0 Run II Datensatz angewandt, der einer integrierten Luminosität von 320 pb-1 entspricht, und die Messung ergibt
mtop (ljets) = 169.5 +/- 4.4(stat.+JES) +1.7-1.6(syst.) GeV
mtop (ejets) = 168.8 +/- 6.0(stat.+JES) +1.9-1.9(syst.) GeV
mtop (mujets)= 172.3 +/- 9.6(stat.+JES) +3.4-3.3(syst.) GeV
Die Messung der Jet Energie Skala im lepton+jets Datensatz ergibt JES=1.034 +/- 0.034, was auf gute Übereinstimmung der Daten mit der Simulation hinweist. Die vorliegende Messung verspricht signifikante Verbesserungen des Gesamtfehlers der Topmasse in Run II noch vor dem Start des LHC, wenn der Datensatz sich verzehnfachen und D0's Spurvermessung in die
Rekonstruktion von Jet Energien und die Identifikation von b-Jets einbezogen werden
Constraints on Standard Model Parameters from Combined Preliminary Data of the LEP Experiments
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Updated Parameters of the Z Resonance from Combined Preliminary Data of the LEP Experiments
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Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP
No full textAbstract: Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be: m(w) = 80.376 +/- 0.033 GeV Gamma(w) = 2.195 +/- 0.083 GeV B(W -> had) = 67.41 +/- 0.27% g(1)(Z) = 0.984(-0.020)(+0.018) K-gamma - 0.982 +/- 0.042 lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved
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