Search for $W'\to T B $ in Events with Large Missing Transverse Energy and Jets with the CDF Detector at the Fermilab Tevatron Collider PDF Download
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In the scope of the strong ongoing data analysis efforts of the CDF col- laboration at Fermilab, we present a search for the production of mas sive W1 bosons decaying to a top and a bottom quark in p$\bar{p}$ collisions at √s = 1.96 TeV. To perform this search, we select events with large Missing Transverse Energy plus two or three jets, in which the W generated from top decays leptonically, and either the e or μ is lost or the [tau] is reconstructed as a jet. A complete study of the selected sample is discussed, including the creation and subsequent optimization of a Neural Network-based multivariate tool to reject the QCD multijet background from the signal region. Finally, we perform a likelihood-based multichannel Bayesian fit procedure on the invariant transverse mass of the Missing Transverse Energy and jets to extract 95% CL limits on [sigma](p$\bar{p}$ . → W') × B(W' → tb) for MW' = 200 GeV/c2.
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Languages : en
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In the scope of the strong ongoing data analysis efforts of the CDF col- laboration at Fermilab, we present a search for the production of mas sive W1 bosons decaying to a top and a bottom quark in p$\bar{p}$ collisions at √s = 1.96 TeV. To perform this search, we select events with large Missing Transverse Energy plus two or three jets, in which the W generated from top decays leptonically, and either the e or μ is lost or the [tau] is reconstructed as a jet. A complete study of the selected sample is discussed, including the creation and subsequent optimization of a Neural Network-based multivariate tool to reject the QCD multijet background from the signal region. Finally, we perform a likelihood-based multichannel Bayesian fit procedure on the invariant transverse mass of the Missing Transverse Energy and jets to extract 95% CL limits on [sigma](p$\bar{p}$ . → W') × B(W' → tb) for MW' = 200 GeV/c2.
Author: Mark Stephen Cooke
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Languages : en
Pages : 290
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Languages : en
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We present a search for a new particle T decaying to a top quark via T = t + X, where X goes undetected. We use a data sample corresponding to 5.7 fb-1 of integrated luminosity of pp collisions with √s = 1.96 TeV, collected at Fermilab Tevatron by the CDF II detector. Our search for pair production of T' is focused on the hadronic decay channel, pp = TT= tt+XX=bqqbqq + XX. We interpret our results in terms of a model where T is an exotic fourth generation quark and X is a dark matter particle. The data are consistent with standard model expectations. We set a limit on the generic production of TT = tt =+ XX, excluding the fourth generation exotic quarks T at 95% confidence level up to mT = 400 GeV/c2 for mX ≤ 70 GeV/c2.
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Languages : en
Pages : 162
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This thesis is focused on an inclusive search of the t{bar t} --> E{sub T} + jets decay channel by means of neural network tools in proton antiproton collisions at (square root)s = 1.96 TeV recorded by the Collider Detector at Fermilab (CDF). At the Tevatron p{bar p} collider top quarks are mainly produced in pairs through quark-antiquark annihilation and gluon-gluon fusion processes; in the Standard Model description, the top quark then decays to a W boson and a b quark almost 100% of the times, so that its decay signatures are classified according to the W decay modes. When only one W decays leptonically, the t{bar t} event typically contains a charged lepton, missing transverse energy due to the presence of a neutrino escaping from the detector, and four high transverse momentum jets, two of which originate from b quarks. In this thesis we describe a t{bar t} production cross section measurement which uses data collected by a 'multijet' trigger, and selects this kind of top decays by requiring a high-P{sub T} neutrino signature and by using an optimized neural network to discriminate top quark pair production from backgrounds. In Chapter 1, a brief review of the Standard Model of particle physics will be discussed, focusing on top quark properties and experimental signatures. In Chapter 2 will be presented an overview of the Tevatron accelerator chain that provides p{bar p} collisions at the center-of-mass energy of (square root)s = 1.96 TeV, and proton and antiproton beams production procedure will be discussed. The CDF detector and its components and subsystems used for the study of p{bar p} collisions provided by the Tevatron will be described in Chapter 3. Chapter 4 will detail the reconstruction procedures used in CDF to detect physical objects exploiting the features of the different detector subsystems. Chapter 5 will provide an overview of the main concepts regarding Artificial Neural Networks, one of the most important tools we will use in the analysis. Chapter 6 will be devoted to the description of the main characteristics of the t{bar t} --> E{sub T} + jets decay channel used to train our neural network to discriminate the top pair production from background processes. We will discuss the event selection method and the technique used for background prediction, that will rely on b-jets identification rate parameterization. Finally, Chapter 7 will provide a description of the final data sample and a detailed discussion of the systematic uncertainties before determining the cross section measurement by means of a likelihood maximization.
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Author: Andrea Messina
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Languages : en
Pages : 170
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Languages : en
Pages : 7
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We present new limits on resonant tb production in ppbar collisions at sqrt(s) = 1.96 TeV, using 1.9 fb−1 of data recorded with the CDF II detector at the Fermilab Tevatron. We reconstruct a putative tb mass in events with a lepton, neutrino candidate, and two or three jets, and search for anomalous tb production as modeled by W′ → tb. We set a new limit on a right-handed W′ with standard model-like coupling, excluding any mass below 800 GeV at 95% C.L. For any narrow W′-like state with mass above 800 GeV, the cross-section is found to be less than 0.28 pb at 95% C.L. We also present an exclusion of the W′ coupling strength versus W′ mass.
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Languages : en
Pages : 8
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The production properties of jets in W events have been measured using (square root)s = 1.8 TeV pp collisions at the Fermilab Tevatron Collider. Experimental results from several CDF and D0 analyses are compared to leading-order and next-to-leading-order QCD predictions.
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Languages : en
Pages : 3
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Observing WZ/ZZ production at the Tevatron in a final state with a lepton, missing transverse energy and jets is extremely difficult because of the low signal rate and the huge background. In an attempt to increase the acceptance we study the sample where three high-energy jets are reconstructed, where about 1/3 of the diboson signal events are expected to end. Rather than choosing the two E{sub T}-leading jets to detect a Z signal, we make use of the information carried by all jets. To qualify the potential of our method, we estimate the probability of observing an inclusive diboson signal at the three standard deviations level (P{sub 3{sigma}}) to be about four times larger than when using the two leading jets only. Aiming at applying the method to the search for the exclusive WZ/ZZ → l?q{bar q} channel in the three jets sample, we analyzed separately the sample with at least one b-tagged jet and the sample with no tags. In WZ/ZZ → l?b{bar b} search, we observe a modest improvement in sensitivity over the option of building the Z-mass from the two leading jets in E{sub T}. Studies for improving the method further are on-going.
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Languages : en
Pages : 7
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The authors report the results from a search for t{anti t} production in p{anti p} collisions at √s = 1.8 TeV with the D0 detector at Fermilab in the final states consisting of one isolated high p{sub T} lepton (e or?), multiple jets and a substantial missing transverse energy (E{sub T}), excluding the events that have?-tagged jets. Two independent analysis approaches lead them to similar estimates for the cross-section. They see no conclusive evidence for top production in the 13.5 pb−1 of data taken during the 1992--1993 run of the Tevatron.
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Languages : en
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In this paper we report a measurement of the t{anti t} production cross section in p{anti p} collisions at √{ovr s} = 1.96 TeV using data corresponding to an integrated luminosity of 2.2 fb−1 collected with the CDF II detector at the Tevatron accelerator. We select events with significant missing transverse energy and high jet multiplicity. This measurement vetoes the presence of explicitly identified electrons and muons, thus enhancing the tau contribution of t{anti t} decays. Signal events are discriminated from the background using a neural network and heavy flavor jets are identified by a secondary-vertex tagging algorithm. We measure a t{anti t} production cross section of 7.99 ± 0.55 (stat) ± 0.76 (syst) ± 0.46 (lumi) pb, assuming a top mass m{sub top} = 172.5 GeV/c2, in agreement with previous measurements and standard model predictions.
