Download or read book Measurement of Single Top Quark Production at D0 Using a Matrix Element Method written by Jovan Mitrevski and published by . This book was released on 2007 with total page 524 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measurement of Single Top Quark Production at D0 Using a Matrix Element Method written by and published by . This book was released on 2007 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: Until now, the top quark has only been observed produced in pairs, by the strong force. According to the standard model, it can also be produced singly, via an electroweak interaction. Top quarks produced this way provide powerful ways to test the charged-current electroweak interactions of the top quark, to measure.

Download or read book Measurement of the Top Quark Mass in the Dilepton Final State Using the Matrix Element Method written by Alexander Grohsjean and published by Springer Science & Business Media. This book was released on 2010-10-01 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main pacemakers of scienti?c research are curiosity, ingenuity, and a pinch of persistence. Equipped with these characteristics a young researcher will be s- cessful in pushing scienti?c discoveries. And there is still a lot to discover and to understand. In the course of understanding the origin and structure of matter it is now known that all matter is made up of six types of quarks. Each of these carry a different mass. But neither are the particular mass values understood nor is it known why elementary particles carry mass at all. One could perhaps accept some small generic mass value for every quark, but nature has decided differently. Two quarks are extremely light, three more have a somewhat typical mass value, but one quark is extremely massive. It is the top quark, the heaviest quark and even the heaviest elementary particle that we know, carrying a mass as large as the mass of three iron nuclei. Even though there exists no explanation of why different particle types carry certain masses, the internal consistency of the currently best theory—the standard model of particle physics—yields a relation between the masses of the top quark, the so-called W boson, and the yet unobserved Higgs particle. Therefore, when one assumes validity of the model, it is even possible to take precise measurements of the top quark mass to predict the mass of the Higgs (and potentially other yet unobserved) particles.

Download or read book Single Top Quark Production at written by and published by . This book was released on 2008 with total page 8 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present first evidence for the production of single top quarks at the Fermilab Tevatron p{bar p} collider. Using a 0.9 fb−1 dataset, we apply a multivariate analysis to separate signal from background and measure cross section for single top quark production. We use the cross section measurement to directly determine the CKM matrix element that describes the Wtb coupling. We also present results of W0 and charged Higgs searches with the same final states as standard model single top quark production.

Download or read book Measurement of the Top Quark Mass in the Dilepton Final State Using the Matrix Element Method written by and published by . This book was released on 2008 with total page 153 pages. Available in PDF, EPUB and Kindle. Book excerpt: The top quark, discovered in 1995 by the CDF and D0 experiments at the Fermilab Tevatron Collider, is the heaviest known fundamental particle. The precise knowledge of its mass yields important constraints on the mass of the yet-unobserved Higgs boson and allows to probe for physics beyond the Standard Model. The first measurement of the top quark mass in the dilepton channel with the Matrix Element method at the D0 experiment is presented. After a short description of the experimental environment and the reconstruction chain from hits in the detector to physical objects, a detailed review of the Matrix Element method is given. The Matrix Element method is based on the likelihood to observe a given event under the assumption of the quantity to be measured, e.g. the mass of the top quark. The method has undergone significant modifications and improvements compared to previous measurements in the lepton+jets channel: the two undetected neutrinos require a new reconstruction scheme for the four-momenta of the final state particles, the small event sample demands the modeling of additional jets in the signal likelihood, and a new likelihood is designed to account for the main source of background containing tauonic Z decay. The Matrix Element method is validated on Monte Carlo simulated events at the generator level. For the measurement, calibration curves are derived from events that are run through the full D0 detector simulation. The analysis makes use of the Run II data set recorded between April 2002 and May 2008 corresponding to an integrated luminosity of 2.8 fb−1. A total of 107 t{bar t} candidate events with one electron and one muon in the final state are selected. Applying the Matrix Element method to this data set, the top quark mass is measured to be m{sub top}{sup Run IIa} = 170.6 ± 6.1(stat.){sub -1.5}{sup +2.1}(syst.)GeV; m{sub top}{sup Run IIb} = 174.1 ± 4.4(stat.){sub -1.8}{sup +2.5}(syst.)GeV; m{sub top}{sup comb} = 172.9 ± 3.6(stat.) ± 2.3(syst.)GeV. Systematic uncertainties are discussed, and the results are interpreted within the Standard Model of particle physics. As the main systematic uncertainty on the top quark mass comes from the knowledge of the absolute jet energy scale, studies for a simultaneous measurement of the top quark mass and the b jet energy scale are presented. The prospects that such a simultaneous determination offer for future measurements of the top quark mass are outlined.

Download or read book Measurement of the Electroweak Top Quark Production Cross Section and the CKM Matrix Element Vtb with the D0 Experiment written by and published by . This book was released on 2009 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt: At particle accelerators the Standard Model has been tested and will be tested further to a great precision. The data analyzed in this thesis have been collected at the world's highest energetic-collider, the Tevatron, located at the Fermi National Accelerator Laboratory (FNAL) in the vicinity of Chicago, IL, USA. There, protons and antiprotons are collided at a center-of-mass energy of √s = 1.96 TeV. The discovery of the top quark was one of the remarkable results not only for the CDF and D0 experiments at the Tevatron collider, but also for the Standard Model, which had predicted the existence of the top quark because of symmetry arguments long before already. Still, the Tevatron is the only facility able to produce top quarks. The predominant production mechanism of top quarks is the production of a top-antitop quark pair via the strong force. However, the Standard Model also allows the production of single top quarks via the electroweak interaction. This process features the unique opportunity to measure the.

Download or read book Measurement of the Top Quark Mass with the Matrix Element Method in the Semileptonic Decay Channel at written by and published by . This book was released on 2008 with total page 194 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Measurement of Single Top Quark Production in the Tau jets Channel Using Boosted Decision Trees at D0 written by Zhiyi Liu and published by . This book was released on 2009 with total page 424 pages. Available in PDF, EPUB and Kindle. Book excerpt: The top quark is the heaviest known matter particle and plays an important role in the Standard Model of particle physics. At hadron colliders, it is possible to produce single top quarks via the weak interaction. This allows a direct measurement of the CKM matrix element Vtb and serves as a window to new physics. The first direct measurement of single top quark production with a tau lepton in the final state (the tau+jets channel) is presented in this thesis. The measurement uses 4.8 fb1 of Tevatron Run II data in p\bar{p} collisions at \sqrt{s}=1.96 TeV acquired by the D0 experiment. After selecting a data sample and building a background model, the data and background model are in good agreement. A multivariate technique, boosted decision trees, is employed in discriminating the small single top quark signal from a large background. The expected sensitivity of the tau+jets channel in the Standard Model is 1.8 standard deviations. Using a Bayesian statistical approach, an upper limit on the cross section of single top quark production in the tau+jets channel is measured as 7.3 pb at 95% confidence level, and the cross section is measured as 3.4+2.0−1.8 pb. The result of the single top quark production in the tau+jets channel is also combined with those in the electron+jets and muon+jets channels. The expected sensitivity of the electron, muon and tau combined analysis is 4.7 standard deviations, to be compared to 4.5 standard deviations in electron and muon alone. The measured cross section in the three combined final states is sigma(p\bar{p}->tb+X,tqb+X) = 3.84+0.89−0.83 pb. A lower limit on Vth is also measured in the three combined final states to be alrger than 0.85 at 95% confidence level. These results are consistent with Standard Model expectations.

Download or read book A Measurement of the Top Quark Mass with a Matrix Element Method written by Adam Paul Gibson and published by . This book was released on 2006 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Properties of the Top Quark written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Recent measurements of top-quark properties at the LHC and the Tevatron are presented. Most recent measurements of the top quark mass have been carried out by CMS using $19.7/$fb of $\sqrt{s} = 8$ TeV data including the study of the dependence on event kinematics. ATLAS uses the full Run I data at $\sqrt{s} = 7$ TeV for a "3D" measurement that significantly reduces systematic uncertainties. D0 employs the full Run II data using the matrix element method to measure the top quark mass with significantly reduced systematic uncertainties. Many different measurements of the top quark exist to date and the most precise ones per decay channel per experiment have been combined into the first world combination with a relative precision of 0.44%. Latest updates of measurements of production asymmetries include the measurement of the \ttbar production asymmetry by D0 employing the full Run II data set, by CMS and ATLAS (including the polarization of the top quark) employing both the full data set at $\sqrt{s} = 7$ TeV. CMS uses the full $\sqrt{s} = 8$ TeV data to measure the top quark polarization in single top production, the ratio ${\cal R}$ of the branching fractions ${\cal B}(t \rightarrow Wb) / {\cal B}(t \rightarrow Wq)$ and to search for flavor changing neutral currents. The results from all these measurements agree well with their respective Standard Model expectation.

Download or read book Measurement of the Single Top Quark Production Cross Section at sqrt s written by and published by . This book was released on 2011 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: Within the standard model top quarks are predicted to be most often produced in pairs via the strong interaction. However they can also be produced singly through the weak interation. This is a rarer process with many experimental challenges. It is interesting because it provides a new window to search for evidence of physics beyond the standard model picture, such as a fourth generation of quarks or to search for insight into the Higgs Mechanism. Single top production also provides a direct way to calculate the CKM matrix element Vtb. This thesis presents new measurements for single top quark production in the s+t, s and t channels using 5.4 fb-1 of data collected at the DØ detector at Fermilab in Batavia, IL. The analysis was performed using Boosted decision trees to separate signal from background and Bayesian statistcs to calculate all the cross sections.

Download or read book Measurement of Single Top Quark Production in the Tau jets Channnel Using Boosted Decision Trees at written by and published by . This book was released on 2009 with total page 235 pages. Available in PDF, EPUB and Kindle. Book excerpt: The top quark is the heaviest known matter particle and plays an important role in the Standard Model of particle physics. At hadron colliders, it is possible to produce single top quarks via the weak interaction. This allows a direct measurement of the CKM matrix element V{sub tb} and serves as a window to new physics. The first direct measurement of single top quark production with a tau lepton in the final state (the tau+jets channel) is presented in this thesis. The measurement uses 4.8 fb−1 of Tevatron Run II data in p{bar p} collisions at √s = 1.96 TeV acquired by the D0 experiment. After selecting a data sample and building a background model, the data and background model are in good agreement. A multivariate technique, boosted decision trees, is employed in discriminating the small single top quark signal from a large background. The expected sensitivity of the tau+jets channel in the Standard Model is 1.8 standard deviations. Using a Bayesian statistical approach, an upper limit on the cross section of single top quark production in the tau+jets channel is measured as 7.3 pb at 95% confidence level, and the cross section is measured as 3.4{sub -1.8}{sup +2.0} pb. The result of the single top quark production in the tau+jets channel is also combined with those in the electron+jets and muon+jets channels. The expected sensitivity of the electron, muon and tau combined analysis is 4.7 standard deviations, to be compared to 4.5 standard deviations in electron and muon alone. The measured cross section in the three combined final states is [sigma](p{bar p} → tb + X,tqb + X) = 3.84{sub -0.83}{sup +0.89} pb. A lower limit on.

Download or read book Measurement of the Electroweak Single Top Quark Production Cross Section and the CKM Matrix Element written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The establishment of the electroweak single top quark production at CDF is experimentally challenging. The small single top signal hidden under large uncertain background processes makes it necessary an excellent understanding of the detector and a detailed study of the processes involved. Moreover, simple counting experiments are not sufficient to extract enough information from the candidate event sample and multivariate analysis techniques are crucial to distinguish signal from background. This thesis presents the world's most sensitive individual search, together with CDF's Neural Network analysis, for the combined s- and t-channel single top production. This analysis uses a dataset that corresponds to an integrated luminosity of 3.2fb-1, and is based on a Boosted Decision Tree method that combines information from several input variables to construct a final powerful discriminant, reaching a sensitivity to the combined single top quark production equivalent to 5.2[sigma]. The measured combined single top quark production cross section is 2.1+0.7 -0.6 pb assuming a top quark mass of 175 GeV/c2. The probability that this result comes from a background-only fluctuation (p-value) is 0.0002, which corresponds to 3.5[sigma].

Download or read book Observation of Single Top Quark Production with the D0 Detector written by and published by . This book was released on 2009 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report on the observation of single top quark production by the D0 collaboration using a dataset of 2.3 fb−1 collected at the Fermilab Tevatron p{bar p} collider. Several multivariate techniques are combined to separate the single top signal from backgrounds. The measured single top cross section is [sigma]{sub tb+tqb} = 3.94 ± 0.88 pb. The probability to measure a cross section at this value or higher in the absence of signal is 2.9 x 10−7, corresponding to a 5.0 standard deviation significance for the presence of signal. The lower limit at the 95% C.L. on the CKM matrix element V{sub tb} is.

Download or read book Measurement of the Top Quark Mass at D0 Run II with the Matrix Element Method in the Lepton Jets Final State written by Philipp Schieferdecker and published by . This book was released on 2005 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: The 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, m{sub top} 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{sup -1} of D0 Run II data, the mass of the top quark is measured to be: m{sub top}{sup {ell}+jets} = 169.5 {+-} 4.4(stat. + JES){sub -1.6}{sup +1.7}(syst.) GeV; m{sub top}{sup e+jets} = 168.8 {+-} 6.0(stat. + JES){sub -1.9}{sup +1.9}(syst.) GeV; m{sub top}{sup {mu}+jets} = 172.3 {+-} 9.6(stat.+JES){sub -3.3}{sup +3.4}(syst.) GeV. The jet energy scale measurement in the {ell}+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.

Download or read book Discovery of Single Top Quark Production written by Dag Gillberg and published by Springer Science & Business Media. This book was released on 2011-01-22 with total page 149 pages. Available in PDF, EPUB and Kindle. Book excerpt: The top quark is by far the heaviest known fundamental particle with a mass nearing that of a gold atom. Because of this strikingly high mass, the top quark has several unique properties and might play an important role in electroweak symmetry breaking—the mechanism that gives all elementary particles mass. Creating top quarks requires access to very high energy collisions, and at present only the Tevatron collider at Fermilab is capable of reaching these energies. Until now, top quarks have only been observed produced in pairs via the strong interaction. At hadron colliders, it should also be possible to produce single top quarks via the electroweak interaction. Studies of single top quark production provide opportunities to measure the top quark spin, how top quarks mix with other quarks, and to look for new physics beyond the standard model. Because of these interesting properties, scientists have been looking for single top quarks for more than 15 years. This thesis presents the first discovery of single top quark production. It documents one of the flagship measurements of the D0 experiment, a collaboration of more than 600 physicists from around the world. It describes first observation of a physical process known as “single top quark production”, which had been sought for more than 10 years before its eventual discovery in 2009. Further, his thesis describes, in detail, the innovative approach Dr. Gillberg took to this analysis. Through the use of Boosted Decision Trees, a machine-learning technique, he observed the tiny single top signal within an otherwise overwhelming background. This Doctoral Thesis has been accepted by Simon Fraser University, Burnaby, BC, Canada.

Download or read book Higher Order QCD Corrections to Single Top Quark Production written by Mohammad Assadsolimani and published by disserta Verlag. This book was released on 2014-08 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is known that the LHC has a considerable discovery potential because of its large centre-of-mass energy (vs =14 TeV) and the high design luminosity. In addition, the two experiments ATLAS and CMS perform precision measurements for numerous models in physics. The increasing experimental precision demands an even higher level of accuracy on the theoretical side. For a more precise prediction of outcomes, one has to consider the corrections obtained typically from Quantum Chromodynamics (QCD). The calculation of these corrections in the high energy regime is described by perturbation theory. In the present study, multi-loop calculations in QCD, including in particular two-loop corrections for single top quark production, are considered. There are several phenomenological motivations to study single top quark production: Firstly, the process is sensitive to the electroweak Wtb-vertex; moreover, non-standard couplings can hint at physics beyond the Standard Model. Secondly, the t-channel cross section measurement provides information on the b-quark Parton Distribution Functions (PDF). Finally, single top quark production enables us to directly measure the Cabibbo-Kobayashi-Maskawa(CKM) matrix element Vtb. The next-to-next-to-leading-order (NNLO) calculation of the single top quark production has many building blocks. In this study, two blocks will be presented: one-loop corrections squared and two-loop corrections interfered with Born. Initially, the one-loop squared contribution at NNLO for single top quark production will be calculated. Before we begin with the calculation of the two-loop corrections to single top quark production, we calculate the QCD form factors of heavy quarks at NNLO, along with the axial vector coupling as a first independent check. A comparison with the relevant literature suggests that this approach is in line with generally accepted procedure. This consistency check provides a proof of the validity of our setup. In the next step, the two-loop corrections to single top quark production will be calculated. After reducing all occurring tensor integrals to scalar integrals, we apply the integration by parts method (IBP) to find the master integrals. This step is a major challenge compared to all similar calculations because of the number of variables in the problem (two Mandelstam variables s and t, the dimension d and the mass of the top quark mt as well as the mass of the W boson mw). Finally, the calculation of the three kinds of topologies – vertex corrections, double boxes and non-planar double boxes – in the two-loop contribution at NNLO calculation will be presented.