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This thesis presents the first experimental calibration of the top-quark Monte-Carlo mass. It also provides the top-quark mass-independent and most precise top-quark pair production cross-section measurement to date. The most precise measurements of the top-quark mass obtain the top-quark mass parameter (Monte-Carlo mass) used in simulations, which are partially based on heuristic models. Its interpretation in terms of mass parameters used in theoretical calculations, e.g. a running or a pole mass, has been a long-standing open problem with far-reaching implications beyond particle physics, even affecting conclusions on the stability of the vacuum state of our universe. In this thesis, this problem is solved experimentally in three steps using data obtained with the compact muon solenoid (CMS) detector. The most precise top-quark pair production cross-section measurements to date are performed. The Monte-Carlo mass is determined and a new method for extracting the top-quark mass from theoretical calculations is presented. Lastly, the top-quark production cross-sections are obtained – for the first time – without residual dependence on the top-quark mass, are interpreted using theoretical calculations to determine the top-quark running- and pole mass with unprecedented precision, and are fully consistently compared with the simultaneously obtained top-quark Monte-Carlo mass.
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.
Articles focus on the planned European proton-proton collider, and concentrate on physics issues, rather than the more technical concerns addressed in the three previous workshops. The use of energies much higher than those of the American Superconducting Super Collider is featured. Topics include reviews of current projects, hadron collisions, lep
The fourth course of the International School on Physics with Low Energy Antiprotons was held in Erice, Sicily, at the Ettore Majorana Centre for Scientific Culture from 25 to 31 January, 1990. The previous courses covered topics related to fundamental symmetries, light and heavy quark spectroscopy, and antiproton-nucleus interactions. The purpose of this school is to review theoretical and experimental aspects of low energy antiproton physics concerning the quark-gluon structure of hadrons and the dynamics of the. antiproton-nucleon interaction. Another important objective is the discussion of future directions of research with low-and medium-energy antiprotons in the context of future medium energy facilities at CERN and elsewhere. These proceedings contain both the tutorial lectures and the various contributions presented during the school by the participants. The proceedings have been organised in three sections. The first section is devoted to the theoretical lectures and contributions. The selection of the various subjects wants to emphasize the correlation between antiproton-nucleon physics and the underlying description in terms of quarks and gluons. The second section contains an overview about 35 years of experiments with antiprotons. It gives an introduction to the particle physics aspects of the field by outlining the historical development of experiment and theory, and by describing the motivation and the results of three recent LEAR experiments in more detail. The third section contains most of the contributions of the participants describing in more detail certain aspects of current or planned experiments at LEAR.
This volume reviews the physics studied at the CERN proton-antiproton collider during its first phase of operation, from the first physics run in 1981 to the last one at the end of 1985.The volume consists of a series of review articles written by physicists who are actively involved with the collider research program. The first article describes the proton-antiproton collider facility itself, including the antiproton source and its principle of operation based on stochastic cooling.The subsequent six articles deal with the various physics subjects studied at the collider. Each article describes in detail the experimental results on a particular subject, and also provides the theoretical framework necessary for their interpretation. Finally the last two articles discuss the physics expectations from the improved collider (the so-called ACOL program, which has just started operation), and also from the next generation of ?supercolliders? which are being considered both in Europe and in the United States America.
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In recent years the Standard Model of electroweak interactions has successfully passed a number of crucial tests, most notably in neutral current reactions and through the observation of W- and Z-bosons in proton-antiproton collisions. How ever, experiments are only beginning to verify one of the most basic consequences of its theoretical formulation as a local quantum field theory: quantum corrections as calculated in perturbation theory. Measurements that will be carried out at electron positron colliders at Stanford and CERN in the very near future will improve the accuracy by more than an order of magnitude. Thus either these crucial elements of the present theoretical framework will be confirmed or the road to physics beyond the Standard Model will be opened. A huge amount of theoretical work has been invested during the past few years to match the envisaged experimental precision. QED corrections, in particular from initial state radiation, will playa dominant role in the interpretation of measurements and have to be understood at a hitherto unrivalled level of accuracy. Analytical cal culations - either to a fixed order in a or by summing large logarithms to arbitrary order - are complementary to recent developments of Monte Carlo techniques in the simulation of events with multiple photon emission. Measurements with hadronic final states evidently require the understanding of hadronic corrections to high accu racy. Even purely leptonic reactions are influenced by hadronic interactions through vacuum polarization.
Inclusive pion, kaon, proton, and antiproton production from proton-proton collisions is studied at a variety of proton energies. Various available parameterizations of Lorentz-invariant differential cross sections as a function of transverse momentum and rapidity are compared with experimental data. The Badhwar and Alper parameterizations are moderately satisfactory for charged pion production. The Badhwar parameterization provides the best fit for charged kaon production. For proton production, the Alper parameterization is best, and for antiproton production the Carey parameterization works best. However, no parameterization is able to fully account for all the data. Norbury, John W. and Blattnig, Steve R. Langley Research Center ANTIPROTONS; KAONS; PROTON ENERGY; SCATTERING CROSS SECTIONS; PIONS; PARAMETERIZATION; TRANSVERSE MOMENTUM
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.