Before any kind of new physics discovery could be made at the LHC, a precise understanding and measurement of the Standard Model of particle physics' processes was necessary. The book provides an introduction to top quark production in the context of the Standard Model and presents two such precise measurements of the production of top quark pairs in proton-proton collisions at a center-of-mass energy of 7 TeV that were observed with the ATLAS Experiment at the LHC. The presented measurements focus on events with one charged lepton, missing transverse energy and jets. Using novel and advanced analysis techniques as well as a good understanding of the detector, they constitute the most precise measurements of the quantity at that time.
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.
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.
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.
High Energy Physics 99 contains the 18 invited plenary presentations and 250 contributions to parallel sessions presented at the International Europhysics Conference on High Energy Physics. The book provides a comprehensive survey of the latest developments in high energy physics. Topics discussed include hard high energy, structure functions, soft interactions, heavy flavor, the standard model, hadron spectroscopy, neutrino masses, particle astrophysics, field theory, and detector development.
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.
From the first attempts to split the atom to the discovery of the top quark, the 20th century has witnessed a revolution in basic physics. Probing successively smaller constituents of matter has also revealed the conditions present at the time of the Big Bang. In a series of essays by scientists who have been closely involved in this exciting research, The Particle Century describes the unprecedented advances in our understanding of the universe. The book covers major historical developments as well as current advances, including early accelerator physics, the rise of the Standard Model, new comprehension of the big bang theory, and the cutting edge of today's investigations. These essays add novel insight into the continuing efforts to unravel the deepest secrets of nature.
These proceedings are devoted to a wide variety of both theoretical and experimental areas in particle physics. The topics include physics at accelerators and studies of Standard Model and Beyond, neutrino and astroparticle physics, cosmology, CP Violation and rare decays, hadron physics, and new developments in quantum field theory. The papers of the volume reveal the present status and new development in the above mentioned items. In particular, the first results on measurement of LHC pp collision events are also reported.
The XIX Physics in Collision conference reviewed experimental results in electroweak, quantum chromodynamics, neutrino, bottom and rare kaon physics, and updated recent developments in the area of gamma ray bursts as well as the issue of the cosmological constant and dark matter.The conference opened with reports on electroweak physics. A decade of precision experiments in laboratories around the world failed to uncover any significant deviations from standard model predictions. Precise W boson and top quark mass measurements suggest a low mass Higgs boson in the standard model, possibly within the reach of the LEP II and the upgraded Tevatron colliders. These presentations were followed by a summary of the latest results on searches for Higgs and supersymmetry.There were three reports on neutrino physics: atmospheric, solar and reactor/accelerator based neutrino experiments and results. Impressive Super-K results strongly suggest ????? oscillation, a scenario confirmed by less precise Soudan2 and MACRO data.The latest results on strange and heavy quark physics were summarized. High statistics from CLEO, LEP I and Tevatron have enabled experimenters to study many rare charm and bottom quark decays for the first time. Among many other interesting results presented, the first measurements of sin 2? by CDF and î?/î by KTeV provide a preview of expected developments in the near future.
The XIX Physics in Collision conference reviewed experimental results in electroweak, quantum chromodynamics, neutrino, bottom and rare kaon physics, and updated recent developments in the area of gamma ray bursts as well as the issue of the cosmological constant and dark matter.The conference opened with reports on electroweak physics. A decade of precision experiments in laboratories around the world failed to uncover any significant deviations from standard model predictions. Precise W boson and top quark mass measurements suggest a low mass Higgs boson in the standard model, possibly within the reach of the LEP II and the upgraded Tevatron colliders. These presentations were followed by a summary of the latest results on searches for Higgs and supersymmetry.There were three reports on neutrino physics: atmospheric, solar and reactor/accelerator based neutrino experiments and results. Impressive Super-K results strongly suggest νμ→νς oscillation, a scenario confirmed by less precise Soudan2 and MACRO data.The latest results on strange and heavy quark physics were summarized. High statistics from CLEO, LEP I and Tevatron have enabled experimenters to study many rare charm and bottom quark decays for the first time. Among many other interesting results presented, the first measurements of sin 2β by CDF and ε′/ε by KTeV provide a preview of expected developments in the near future.
