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Jets comprise a rich class of emergent phenomena stemming the underlying theory of the strong nuclear force, Quantum Chromodynamics. As jets are produced in copious quantities in hadron colliders, understanding their internal structure and evolution is of the utmost importance for modern particle physics. In this thesis, we study various aspects of a special class of jets---that is, jets containing heavy quarks, such as charm, bottom and top---which can all be understood from a statistical point of view. In the first part, we consider situations in which the observation of back-to-back heavy-quark dijet pairs shed light on key physics governing the final and initial states of high-energy particle collisions---from the modification of dijet mass spectra by the quark-gluon plasma created in the collisions of heavy ions to the probing of the Sivers spin asymmetry in deep inelastic scattering. In the second part, we analyze the internal landscapes of jets initiated by heavy quarks and demonstrate how the so-called ``dead-cone'' effect manifests in the cumulants of jet substructure distributions. In the third and final part, we adapt concepts from the machine learning community to tag top jets from a background of jets initiated by light quarks and gluons as well develop a novel data type that is particularly well-suited to exposing the characteristic angular structure of top decay products.
The Mark II detector in the ee− storage ring PEP at the Stanford Liner Accelerator Center (SLAC) is used to measure selected properties of hadronic events corresponding to produced bottom or charm quarks. Heavy flavor enrichment is accomplished by tagging events with prompt electrons or muons. Differences between bottom, charm and average jets are observed for momentum, transverse momentum, rapidity and jet mass distributions. A detailed study of the charged multiplicity of b- and c-enriched events finds the mean multiplicity of bottom and charm events to be 16.2 +- 0.5 +- 1.0 and 13.2 +- 0.5 +- 0.9, respectively, where the first error is statistical and the second is systematic. The corresponding 'non-leading' multiplicities of charged particles accompanying the pair of heavy hadrons are 5.2 +- 0.5 +- 0.9 for bottom, and 8.0 +- 0.5 +- 0.9 for charm. We find from these non-leading multiplicities that bottom and charm hadrons fragment with mean energy fractions of z/sub b/ = 0.79/sub -0.05//sup +0.10/ and z/sub c/ = 0.60/sub -0.11//sup +0.09/. These results confirm the expected hard fragmentation of heavy quarks and agree with previous measurements based on leptonic inclusive spectra and D* fragmentation. 48 refs., 29 figs.
This thesis contains new research in both experimental and theoretical particle physics, making important contributions in each. Two analyses of collision data from the ATLAS experiment at the LHC are presented, as well as two phenomenological studies of heavy coloured resonances that could be produced at the LHC. The first data analysis was the measurement of top quark-antiquark production with a veto on additional jet activity. As the first detector-corrected measurement of jet activity in top-antitop events it played an important role in constraining the theoretical modelling, and ultimately reduced these uncertainties for ATLAS's other top-quark measurements by a factor of two. The second data analysis was the measurement of Z+2jet production and the observation of the electroweak vector boson fusion (VBF) component. As the first observation of VBF at a hadron collider, this measurement demonstrated new techniques to reliably extract VBF processes and paved the way for future VBF Higgs measurements. The first phenomenological study developed a new technique for identifying the colour of heavy resonances produced in proton-proton collisions. As a by-product of this study an unexpected and previously unnoticed correlation was discovered between the probability of correctly identifying a high-energy top and the colour structure of the event it was produced in. The second phenomenological study explored this relationship in more detail, and could have important consequences for the identification of new particles that decay to top quarks.
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.
This concise primer reviews the latest developments in the field of jets. Jets are collinear sprays of hadrons produced in very high-energy collisions, e.g. at the LHC or at a future hadron collider. They are essential to and ubiquitous in experimental analyses, making their study crucial. At present LHC energies and beyond, massive particles around the electroweak scale are frequently produced with transverse momenta that are much larger than their mass, i.e., boosted. The decay products of such boosted massive objects tend to occupy only a relatively small and confined area of the detector and are observed as a single jet. Jets hence arise from many different sources and it is important to be able to distinguish the rare events with boosted resonances from the large backgrounds originating from Quantum Chromodynamics (QCD). This requires familiarity with the internal properties of jets, such as their different radiation patterns, a field broadly known as jet substructure. This set of notes begins by providing a phenomenological motivation, explaining why the study of jets and their substructure is of particular importance for the current and future program of the LHC, followed by a brief but insightful introduction to QCD and to hadron-collider phenomenology. The next section introduces jets as complex objects constructed from a sequential recombination algorithm. In this context some experimental aspects are also reviewed. Since jet substructure calculations are multi-scale problems that call for all-order treatments (resummations), the bases of such calculations are discussed for simple jet quantities. With these QCD and jet physics ingredients in hand, readers can then dig into jet substructure itself. Accordingly, these notes first highlight the main concepts behind substructure techniques and introduce a list of the main jet substructure tools that have been used over the past decade. Analytic calculations are then provided for several families of tools, the goal being to identify their key characteristics. In closing, the book provides an overview of LHC searches and measurements where jet substructure techniques are used, reviews the main take-home messages, and outlines future perspectives.
This book describes the memorable theoretical work that motivated the construction of the electron-positron accelerators at CERN and SLAC, and the monumental experimental effort that led to a verification of the main theoretical expectations at these laboratories and at Fermilab.The aim is to provide a description of the theoretical work, as well as a synthesis of the experimental effort, which makes interesting reading for both theorists and experimentalists. In particular, the experimental measurements, discussed in the second part of the book, are systematically related to the theoretical quantities discussed in the first. The topics still to be investigated, unsolved problems, and the perspectives at future giant accelerators conclude this fascinating text.
Heavy quark physics serves as a probe to understand QCD, measure standard model parameters, and look for signs of new physics. We study several aspects of heavy quark systems in an effective field theory framework, including both phenomenological and formal applications. Phenomenological applications include the leading calculation of penguin amplitudes in charmless non-leptonic B-decays to light mesons, including power suppressed effects that are numerically enhanced by the chiral condensate. We compare our determination of the penguin amplitudes with the experimental results. Also, we calculate the heavy quark jet function at two loops, which is an important ingredient for the next-to-next-to-leading-log invariant-mass distribution of jets induced by tt pair production at a future linear collider. Formal applications include: a definition of top mass relevant for measurements that use top induced jets, a new renormalization group equation in an infrared scale intrinsic to heavy quark masses and its generalization for QCD matrix elements, a threshold mass definition which smoothly connects to the MS mass, and a new method to analyze renormalons in the operator product expansion.
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.