Looking Inside Jets
Looking Inside Jets

Author: Simone Marzani

Publisher: Springer

Published: 2019-05-11

Total Pages: 205

ISBN-13: 3030157091

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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.

Advances in Jet Substructure at the LHC
Advances in Jet Substructure at the LHC

Author: Roman Kogler

Publisher: Springer Nature

Published: 2021-05-10

Total Pages: 287

ISBN-13: 3030728587

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This book introduces the reader to the field of jet substructure, starting from the basic considerations for capturing decays of boosted particles in individual jets, to explaining state-of-the-art techniques. Jet substructure methods have become ubiquitous in data analyses at the LHC, with diverse applications stemming from the abundance of jets in proton-proton collisions, the presence of pileup and multiple interactions, and the need to reconstruct and identify decays of highly-Lorentz boosted particles. The last decade has seen a vast increase in our knowledge of all aspects of the field, with a proliferation of new jet substructure algorithms, calculations and measurements which are presented in this book. Recent developments and algorithms are described and put into the larger experimental context. Their usefulness and application are shown in many demonstrative examples and the phenomenological and experimental effects influencing their performance are discussed. A comprehensive overview is given of measurements and searches for new phenomena performed by the ATLAS and CMS Collaborations. This book shows the impressive versatility of jet substructure methods at the LHC.

Measuring Jet Substructure in Topologies Containing W, Top and Light Jets with the ATLAS Detector
Measuring Jet Substructure in Topologies Containing W, Top and Light Jets with the ATLAS Detector

Author: Amal Vaidya

Publisher:

Published: 2020

Total Pages: 0

ISBN-13:

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The use of substructure information has become ubiquitous in the study of hadronic jets, primarily for jet classification. Recent developments in jet grooming techniques have facilitated analytical calculations of jet substructure variables which, coupled with their frequent use, motivate a set of precision measurements of these variables. This thesis presents work undertaken on the ATLAS detector with a focus on jet substructure using data collected during 2016 in the second run of the Large Hadron Collider. Firstly, the development of a substructure based jet classifier is presented. A large dataset obtained from simulation is used to define a substructure based classifier in order to separate jets from the hadronic decays of W bosons and top quarks from light quark and gluon jets. Its performance is also discussed in the context of ATLAS physics analyses. Secondly a measurement of a large number of jet substructure variables is presented. The measurement uses data collected in 2016 and is done in three distinct regions of phase space, one selecting light jets from inclusive multijet events and the other two selecting top quark and W boson jets from tt ̄ events. A single jet trigger is used to select events with two central jets and no leptons in for the inclusive jet selection. Semi-leptonic tt ̄ events are selected where the leptonic top is tagged and the recoiling hadronic system is probed. Top quark and W boson jets are separated primarily based on the angular separation of the jet from the closes b-tagged jet, with additional requirements on the jet mass. A novel method of bottom-up calorimeter cluster based uncertainties was used and the relevant substructure distributions are presented after being corrected for detector effects.

Measuring the Standard Model and Searching for New Physics with Jet Substructure Using the ATLAS Detector
Measuring the Standard Model and Searching for New Physics with Jet Substructure Using the ATLAS Detector

Author: Maximilian Swiatlowski

Publisher:

Published: 2015

Total Pages:

ISBN-13:

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Collisions at the Large Hadron Collider have offered an unprecedented window into some of the highest energy scales ever observed in experiments. Understanding these collisions, especially those that produce particles charged under quantum chromodynamics (QCD), requires a deep understanding of jets: the collimated sprays of particles produced by the parton shower and hadronization processes which emerge from the asymptotic freedom of QCD. Recent theoretical advances and the unprecedented capabilities of the ATLAS detector have enabled a new class of jet physics measurements based on the internal structure of jets, referred to as jet substructure. Three new types of measurements relying on jet substructure are presented. The first is a set of measurements sensitive which can discriminate between jets initiated by quarks and gluons. Separation is possible by studying variables sensitive to the magnitude of the color charge. Several such variables are measured, and a data-driven technique is used to construct a tagger, the first of its kind at a hadron collider, which can improve the sensitivity of searches for new physics in hadronic final states. A second measurement studies the color connections of jets in top-antitop events using an observable called the jet pull angle: sensitivity to the color representation of particles decaying to dijet pairs at a hadron collider is demonstrated for the first time. A final analysis searches for R-parity violating supersymmetry (SUSY) in all hadronic final states. These classes of models remove the characteristic missing energy signature which existing SUSY searches rely on, and require new discrimination techniques. Jet substructure provides a powerful handle to analyze these very high multiplicity states using a variable called the total jet mass. No signal is observed over the Standard Model (SM) prediction, and new limits are set on these previously unexplored models. The techniques of jet substructure lie at the hearts of all of these analyses, enabling both new measurements of SM phenomena and entirely new searches for physics beyond the SM.

Exploring Electroweak Symmetry Breaking with Jet Substructure at the ATLAS Experiment
Exploring Electroweak Symmetry Breaking with Jet Substructure at the ATLAS Experiment

Author: A. R. Davison

Publisher:

Published: 2011

Total Pages:

ISBN-13:

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An important unsolved problem in physics is the nature of electroweak symmetry breaking in the Standard Model. The ATLAS experiment aims to gain insight by studying proton-proton collisions at ps = 14 TeV. In order to dierentiate between dierent theoretical models it is important to measure processes where hadrons are produced, such as the hadronic decay of aW, Z or a Higgs boson. However, these decays produce extremely complex signals in the detector which must be analysed carefully. Jet substructure techniques are presented as a novel approach to analysing hadronic signatures relevant to electroweak symmetry breaking. The potential performance of these techniques is evaluated in detail using simulated ATLAS data. Additionally material related to the use of visualisation software to explore ATLAS data is presented.