Download or read book Off shell Effects for Single Top quark Production Processes at Hadron Colliders written by Paul Mellor and published by . This book was released on 2011 with total page 167 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: We present a calculation of s- and t-channel single top-quark production and decay at next-to-leading order in QCD for the Tevatron and for the LHC. The calculation includes the off-shell effects of the intermediate top-quark and the non-factorisable corrections arising from interferences between the production and decay subprocesses, extending the results beyond the narrow-width approximation. A general method for including such effects is outlined. The method comprises a simultaneous expansion in the coupling constants, as in a standard perturbative approach, along with an expansion in the virtuality of the intermediate heavy-particle. This expansion makes it possible to identify the contributions relevant to the calculation, up to a desired accuracy, before computation of the amplitudes, allowing significant simplifications to be made to the final calculation. Results obtained using this method are presented, along with results obtained using both the standard and improved narrow-width approximations. This enables us to investigate the impact of both off-shell and spin-correlation effects on the cross section and various kinematic distributions. In general, both effects are found to be small except close to kinematic boundaries or for specific distributions, such as the top-quark invariant-mass, where their effects can become sizeable.

Download or read book Off shell Effects for Top Quark Production at Hadron Colliders written by Andrew Sofronis Papanastasiou and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A good description of processes involving the production and decay of top quarks is crucial to phenomenology at the Tevatron and LHC. In this thesis, a general method constructed using ideas from Effective Theories is presented, allowing predictions to be made for differential observables that importantly include the effects of non-zero top quark virtuality. Calculations using this method can be significantly simpler than those in standard perturbation theory and its use enables the identification of potentially important structures in the amplitudes. The method is applied to the example of top-pair production for a realistic experimental setup at the Tevatron. A number of observables are studied and an evaluation of off-shell effects is given. The latter tend to be small in general but do become enhanced in regions near kinematical boundaries for distributions that are sensitive to the invariant mass of top quarks.

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 Physics of Single top Quark Production at Hadron Colliders written by Doulgas Olaf Carlson and published by . This book was released on 1995 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Finite width Effects in Top Quark Production at Hadron Colliders written by Nikolas Kauer and published by . This book was released on 2001 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics at the Large Hadron Collider written by Amitava Datta and published by Springer Science & Business Media. This book was released on 2010-05-30 with total page 260 pages. Available in PDF, EPUB and Kindle. Book excerpt: In an epoch when particle physics is awaiting a major step forward, the Large Hydron Collider (LHC) at CERN, Geneva will soon be operational. It will collide a beam of high energy protons with another similar beam circulation in the same 27 km tunnel but in the opposite direction, resulting in the production of many elementary particles some never created in the laboratory before. It is widely expected that the LHC will discover the Higgs boson, the particle which supposedly lends masses to all other fundamental particles. In addition, the question as to whether there is some new law of physics at such high energy is likely to be answered through this experiment. The present volume contains a collection of articles written by international experts, both theoreticians and experimentalists, from India and abroad, which aims to acquaint a non-specialist with some basic issues related to the LHC. At the same time, it is expected to be a useful, rudimentary companion of introductory exposition and technical expertise alike, and it is hoped to become unique in its kind. The fact that there is substantial Indian involvement in the entire LHC endeavour, at all levels including fabrication, physics analysis procedures as well as theoretical studies, is also amply brought out in the collection.

Download or read book Searches for Lorentz Violation in Top Quark Production and Decay at Hadron Colliders written by and published by . This book was released on 2012 with total page 224 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present a first-of-its-kind confirmation that the most massive known elementary particle obeys the special theory of relativity. Lorentz symmetry is a fundamental aspect of special relativity which posits that the laws of physics are invariant regardless of the orientation and velocity of the reference frame in which they are measured. Because this symmetry is a fundamental tenet of physics, it is important to test its validity in all processes. We quantify violation of this symmetry using the Standard-Model Extension framework, which predicts the effects that Lorentz violation would have on elementary particles and their interactions. The top quark is the most massive known elementary particle and has remained inaccessible to tests of Lorentz invariance until now. This model predicts a dependence of the production cross section for top and antitop quark pairs on sidereal time as the orientation of the experiment in which these events are produced changes with the rotation of the Earth. Using data collected with the DØ detector at the Fermilab Tevatron Collider, we search for violation of Lorentz invariance in events involving the production of a $t\bar{t}$ pair. Within the experimental precision, we find no evidence for such a violation and set upper limits on parameters describing its possible strength within the Standard-Model Extension. We also investigate the prospects for extending this analysis using the ATLAS detector at the Large Hadron Collider which, because of the higher rate of $t\bar{t}$ events at that experiment, has the potential to improve the limits presented here.

Download or read book Discovery of Single Top Quark Production written by and published by . This book was released on 2009 with total page 199 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. An analysis is performed using 2.3 fb−1 of data recorded by the D0 detector at the Fermilab Tevatron Collider at centre-of-mass energy √s = 1.96 TeV. Boosted decision trees are used to isolate the single top signal from background, and the single top cross section is measured to be [sigma](p{bar p} → tb + X, tqb + X) = 3.74{sub -0.74}{sup +0.95} pb. Using the same analysis, a measurement of the amplitude of the CKM matrix element V{sub tb}, governing how top and b quarks mix, is also performed. The measurement yields:

Download or read book Studies of Top Quark Production at written by and published by . This book was released on 2011 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: I present recent results on top quark production in pp collisions at a center of mass energy of 1.96 TeV. The studies were performed by the D0 collaboration using approximately 5 fb−1 of data taken during Run II at the Fermilab Tevatron accelerator. The top quark is the heaviest known elementary particle and completes the quark sector of the three-generation structure of the standard model (SM). It differs from the other quarks not only by its much larger mass, but also by its lifetime which is too short to build hadronic bound states. The SM predicts that top quarks are created via two independent production mechanisms at hadron colliders. The primary mode, in which a t{bar t} pair is produced from a gtt vertex via the strong interaction, was used by the D0 and CDF collaborations to establish the existence of the top quark in 1995. The second production mode of top quarks at hadron colliders is the electroweak production of a single top quark from a Wtb vertex. The predicted cross section for single top quark production is about half that of t{bar t} pairs but the signal-to-background ratio is much worse; observation of single top quark production has therefore until recently been impeded by its low rate and difficult background environment compared to the top pair production. In the following sections I will present results for the measurement of the t{bar t} pair and the single top quark production cross section using respectively 5.3 fb−1 and 5.4 fb−1 of data taken by the D0 experiment.

Download or read book Single Top Quark Production and Decay in Hadron Collision at Next to leading Order written by Qinghong Cao and published by . This book was released on 2005 with total page 466 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Quark Structure of Matter written by Maurice Jacob and published by World Scientific. This book was released on 1992-11-01 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding the quark structure of matter has been one of the most important advances in contemporary physics. It has unravelled a new and deeper level of structure in matter, and physics at that level reveals a unity and aesthetic simplicity never before attained. All forces emerge from a unique invariance principle and each of the basic interactions results from a specific symmetry property. Quarks interact among themselves through their ?colour?, as now accurately described by quantum chromodynamics.This volume brings together eight major review articles by Maurice Jacob, a physicist at the forefront of research on the quark structure of matter. He has, in particular, been involved with two research topics in this field. The first is the study of hadronic jets, which one actually sees instead of quarks, because of the opacity of the vacuum to colour. The second is the search for quark matter, a new form of matter believed to exist at high temperatures, when the vacuum should become transparent to colour.The papers in this volume provide a comprehensive review of these phenomenological studies on the quark structure of matter, and also a fasinating insight into the pace of recent progress in these areas. The book comes complete with an original introduction by the author, and also contains a pedagogical review on what is a most engrossing and rewarding field of research in physics.

Download or read book Heavy Quark Associated Production with One Hard Photon at Hadron Colliders written by and published by . This book was released on 2013 with total page 119 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present the calculation of heavy-quark associated production with a hard photon at hadron colliders, namely $pp(par p) → Qar Q +X$? (for $Q=t,b$), at Next-to-Leading Order (NLO) in Quantum Chromodynamics (QCD). We study the impact of NLO QCD corrections on the total cross section and several differential distributions at both the Tevatron and the Large Hadron Collider (LHC). For $tar t$? production we observe a sizeable reduction of the renormalization and factorization scale dependence when the NLO QCD corrections are included, while for $bar b$? production a considerable scale dependence still persists at NLO in QCD. This is consistent with what emerges in similar processes involving $b$ quarks and vector bosons and we explain its origin in detail. For $bar b$? production we study both the case in which at least one $b$ jet and the case in which at least two $b$ jets are observed. We perform the $bar b$? calculation using the Four Flavor Number Scheme (4FNS) and compare the case where at least one $b$ jet is observed with the corresponding results from the Five Flavor Number Scheme (5FNS) calculation. Finally we compare our results for $par p →+b+X$? with the Tevatron data.

Download or read book Physics at the Terascale written by Ian Brock and published by John Wiley & Sons. This book was released on 2011-05-04 with total page 437 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written by authors working at the forefront of research, this accessible treatment presents the current status of the field of collider-based particle physics at the highest energies available, as well as recent results and experimental techniques. It is clearly divided into three sections; The first covers the physics -- discussing the various aspects of the Standard Model as well as its extensions, explaining important experimental results and highlighting the expectations from the Large Hadron Collider (LHC). The second is dedicated to the involved technologies and detector concepts, and the third covers the important - but often neglected - topics of the organisation and financing of high-energy physics research. A useful resource for students and researchers from high-energy physics.

Download or read book Search for Electroweak Top Quark Production in the Electron Jets Channel in the D0 Experiment at the Tevatron written by Emmanuel Busato and published by . This book was released on 2005 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Top Quark Physics at Hadron Colliders written by Arnulf Quadt and published by Springer Science & Business Media. This book was released on 2007-08-16 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: This will be a required acquisition text for academic libraries. More than ten years after its discovery, still relatively little is known about the top quark, the heaviest known elementary particle. This extensive survey summarizes and reviews top-quark physics based on the precision measurements at the Fermilab Tevatron Collider, as well as examining in detail the sensitivity of these experiments to new physics. Finally, the author provides an overview of top quark physics at the Large Hadron Collider.

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 Theoretical Aspects of Top Quark Production at Hadron Collider written by and published by . This book was released on 1996 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: We summarize our calculation of the total cross section for top quark production at hadron colliders within the context of perturbative quantum chromodynamics, including resummation of the effects of initial-state soft gluon radiation to all orders in the strong coupling strength.