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Jets are collimated, high energy streams of particles that are ubiquitous at hadron colliders such as the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland. It has been recognized that jets are a feature of the strong force, quantum chromodynamics (QCD). QCD predicts an approximate scaling behavior at high energies. Due to the very high energies made available by the LHC, the decay products of heavy, unstable particles can also be collimated into a narrow cone and these are observed as jets by the LHC experiments. Recently, there has been significant interest in studying the substructure of jets with the goal of discriminating QCD jets from jets initiated by heavy particle decay. In this thesis, I will describe the modeling of jets in QCD as well as the pattern of radiation from heavy particles, such as the top quark. This will lead to a discussion of a correlation function on the constituents of a jet that is useful in understanding jet substructure. This correlation function encodes angular scaling properties of jets and its behavior in QCD will be studied.
Particle physics seeks to understand the interactions and properties of the fundamental particles. To gain understanding, there is an interplay between theory and experiment. Models are proposed to explain how particles behave and interact. These models make precise predictions that can be tested. Experiments are built and executed to measure the properties of these particles, providing necessary tests for the theories that attempt to explain the realm of fundamental particles. However, there is also another level of interaction between theory and experiment; the development of new experiments demands the study of how particles will behave with respect to the measured observables toward the goal of understanding the details and idiosyncrasies of the measurements very well. Only once these are well-modeled and understood can one be con dent that the data that are measured is trustworthy. The modeling and interpretation of the physics of a proton collider, such as the LHC, is the main topic of this thesis.
High energy jets are observed both in hadronic machines like the Tevatron and electron machines like LEP. These jets have an extended structure in phase space which can be measured. This distribution is usually called the jet shape. There is an intrinsic relation between jet variables, like energy and direction, the jet algorithm used, and the jet shape. Jet shape differences can be used to separate quark and gluon jets.
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.
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.
Hadronic jets feature in many final states of interest in modern collider experiments. They form a significant Standard Model background for many proposed new physics processes and also probe QCD interactions at several different scales. At high energies incoming protons produce beam jets. Correctly accounting for the beam and central jets is critical to precise understanding of hadronic final states at the Large Hadron Collider. We study jet cross sections as a function of the shape of both beam and central jets. This work focuses on measuring jet mass but our methods can be applied to other jet shape variables as well. Measuring jet mass introduces additional scales to the collision process and these scales produce large logarithms that need to be resummed. Factorizing the cross section into hard, jet, beam, and soft functions enables such resummation. We begin by studying jet production at e + e- collisions in order to focus on the effects of jet algorithms. These results can be carried over to the more complicated case of hadron collisions. We use the Sterman-Weinberg algorithm as a specific example and derive an expression for the quark jet function. Turning to hadron colliders, we show how the N-jettiness event shape divides phase space into N +2 regions, each containing one central or beam jet. Thus, N-jettiness works as a jet algorithm. Using a geometric measure gives central jets with circular boundaries. We then give a factorization theorem for the cross section fully differential in the mass of each jet, and compute the corresponding soft function at next-to-leading order (NLO). We use a method of hemisphere decomposition, which can also be applied to calculate N-jet soft functions defined with other jet algorithms. Our calculation of the N-jettiness soft function provides the final missing ingredient to extend NLO cross sections to resunmmed predictions at next-to-next-to-leading logarithmic order. We study the production of an exclusive jet together with a Standard Model Higgs boson. Based on theoretical reasons and agreement between our calculation and data from the ATLAS collaboration, we argue that our results for the jet mass spectrum are a good approximation also for inclusive jet production and other hard processes.
I Opening Review on Hadron-Collider Physics.- Hadron Colliders, the Standard Model, and Beyond.- 1 What is the Standard Model?.- 2 Hadron Colliders and the Standard Model.- 2.1 Precision electroweak.- 2.2 CKM.- 2.3 Top quark.- 2.4 Higgs boson.- 2.5 QCD.- 3 Beyond the Standard Model.- 3.1 Direct evidence.- 3.2 Indirect evidence.- References.- II Status of the Accelerators and Detectors.- Tevatron Collider Run II Status.- 1 Introduction.- 2 Overview.- 3 Run II Milestones.- 4 Parameters.- 5 Performance to Date.- 6 Accomplishments.- 6.1 Accomplishments: Helix Adjustments.- 6.2 Accomplishments: Antiproton Emittance.- 6.3 Accomplishments: Tevatron Injection Closure.- 7 Outstanding Issues.- 8 Future Prospects.- 9 Reliability.- 10 Summary.- 11 Acknowledgements.- Status of CDF II and Prospects for Run II.- 1 Introduction.- 2 The CDF II Detector and Trigger Upgrades.- 3 Physics Results and Prospects.- 4 Conclusions.- References.- Status of the D Detector.- 1 Introduction.- 2 Overview.- 3 Silicon Vertex Detector.- 4 Central Fiber Tracker.- 5 Calorimeters.- 6 Muon Detectors.- 7 Forward Proton Detectors.- 8 Trigger and Data Acquisition.- 9 Conclusions.- References.- III Standard Model Processes: Parton Luminosities, QCD Evolution.- The Proton Structure as Measured at HERA.- 1 Introduction.- 2 NC Cross Sections in the Complete Kinematic Plane.- 3 High-Q2 Measurements.- 4 Charged Current Measurements.- 5 Summary and Outlook.- References.- Global Fits of Parton Distributions.- 1 Introduction.- 2 Parton Uncertainties.- 2.1 Hessian (Error Matrix) approach.- 2.2 Offset method.- 2.3 Statistical approach.- 2.4 Lagrange multiplier method.- 2.5 Results.- 3 Theoretical Errors.- 3.1 Problems in the fit.- 3.2 Types of Theoretical Error, NNLO.- 3.3 Empirical approach.- 4 Conclusions.- References.- Low x Physics at HERA.- 1 Introduction.- 2 Formalism and Theory.- 3 Results.- 3.1 Inclusive measurements.- 3.2 Exclusive results.- 4 Summary.- References.- Saturation Effects in Hadronic Cross Sections.- 1 Introduction.- 2 The Loop-Loop Correlation Model.- 3 Saturation in Proton-Proton Scattering.- 4 Gluon Saturation.- 5 Conclusion.- References.- IV Standard Model Processes: QCD at High pt.- Progress in NNLO Calculations for Scattering Processes.- 1 Why NNLO Calculations are Important.- 1.1 Renormalisation scale uncertainty.- 1.2 Factorisation scale dependence.- 1.3 Jet algorithms.- 1.4 Transverse momentum of the incoming partons.- 1.5 Power corrections.- 1.6 The shape of the prediction.- 1.7 Parton densities at NNLO.- 2 Recent Progress in the Field.- 3 What Remains to be Done.- References.- Heavy Flavour Production at D .- 1 Introduction.- 2 b-production Cross-section.- 2.1 Muon and Jet Cross-section.- 2.2 b-tagging.- 3 J/? Cross-section.- 4 Other Measurements.- References.- Heavy Quark Production at CDF.- 1 Introduction.- 2 Beauty Production at CDF.- 2.1 CDF Run I results.- 2.2 Preliminary results from CDF Run II.- 3 Quarkonia Production at CDF.- 4 Charm Production at CDF.- 4.1 Run I results.- 4.2 Run II charm production cross-sections.- 5 Conclusion.- References.- Heavy Quark Production at HERA.- 1 Introduction.- 2 Open Charm Production.- 3 Charmonium.- 4 Beauty Production.- 5 Summary.- References.- Theoretical Developments on Hard QCD Processes at Colliders.- 1 Introduction.- 2 Heavy Quarks.- 2.1 Total Cross Sections.- 2.2 Transverse Momentum Distributions.- 2.3 Top Quark Spin Correlations.- 3 Jets.- 3.1 Jet Definitions.- 3.2 Precision Jet Physics.- 3.3 Multiparton Processes.- 4 Photons and Massive Gauge Bosons.- 4.1 Isolated Photons.- 4.2 Photon Pairs.- 4.3 Vector Boson and Higgs Production.- 4.4 Transverse Momentum Distributions.- 5 Conclusions and Outlook.- References.- Jet Production at CDF.- 1 Introduction.- 2 Inclusive Jet Production.- 3 Three-jet Production.- 4 Study of Jet Shapes in Run 2.- 5 Study of the Underlying Event.- 6 Study of W+Njet Production.- References.- Jet Algorithms at D .- 1 Introduction.- 2 The Measurement of Jets.- 3 Run I Co
Recent results from the study of hadronic jets in hadron-hadron collisions at order a{sub s}3 in perturbation theory are presented. The numerical results are in good agreement with data and this agreement is illustrated where possible.
Recent results from the study of hadronic jets in hadron-hadron collisions at order a{sub s}3 in perturbation theory are presented. The numerical results are in good agreement with data and this agreement is illustrated where possible.
Recent results from the study of hadronic jets in hadron-hadron collisions at order a{sub s}3 in perturbation theory are presented. The numerical results are in good agreement with data and this agreement is illustrated where possible.