Jet Calibration, Cross Section Measurements and New Physics Searches with the ATLAS Experiment Within the Run 2 Data
Jet Calibration, Cross Section Measurements and New Physics Searches with the ATLAS Experiment Within the Run 2 Data

Author: Robert Hankache

Publisher:

Published: 2019

Total Pages: 0

ISBN-13:

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The Standard Model is the current theory used to describe the elementary particles and their fundamental interactions (except the gravity). My PhD within the ATLAS experiment put this model under test using objects called jets, to study final state particles that interact through the strong force. First, I contributed to a method of jet calibration aiming at calibrating the energy scale of jets in the forward region of the detector with respect to central region. I improved the calibration by making it faster and more precise. Next, I worked on a search analysis of new physics using events with two jets. The Standard Model predicts a smooth distribution of the invariant mass of di-jets, hence we search for a bump which could come from a new particle. Since no significant bump is found, we put limits on signals as predicted by Beyond Standard Model theories and on model-independent signals. Last, I developed a new physics analysis measuring the leading (highest in transverse momentum) jet differential cross-section as a function of transverse momentum and rapidity. The challenge was to factorize the detector effects (resolution and acceptance) from the observable, which I did using a new unfolding technique. I also worked on the theoretical predictions calculation which was very challenging to perform and needed the implementation of special regularizations. The measurement and the predictions are then compared and tensions are observed due to the difficulties of theoretical predictions calculation.

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.

Jet Substructure Without Trees
Jet Substructure Without Trees

Author:

Publisher:

Published: 2011

Total Pages: 22

ISBN-13:

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We present an alternative approach to identifying and characterizing jet substructure. An angular correlation function is introduced that can be used to extract angular and mass scales within a jet without reference to a clustering algorithm. This procedure gives rise to a number of useful jet observables. As an application, we construct a top quark tagging algorithm that is competitive with existing methods. In preparation for the LHC, the past several years have seen extensive work on various aspects of collider searches. With the excellent resolution of the ATLAS and CMS detectors as a catalyst, one area that has undergone significant development is jet substructure physics. The use of jet substructure techniques, which probe the fine-grained details of how energy is distributed in jets, has two broad goals. First, measuring more than just the bulk properties of jets allows for additional probes of QCD. For example, jet substructure measurements can be compared against precision perturbative QCD calculations or used to tune Monte Carlo event generators. Second, jet substructure allows for additional handles in event discrimination. These handles could play an important role at the LHC in discriminating between signal and background events in a wide variety of particle searches. For example, Monte Carlo studies indicate that jet substructure techniques allow for efficient reconstruction of boosted heavy objects such as the W{sup {+-}} and Z° gauge bosons, the top quark, and the Higgs boson.

Energy Frontier Research With ATLAS
Energy Frontier Research With ATLAS

Author:

Publisher:

Published: 2016

Total Pages:

ISBN-13:

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The Boston University (BU) group is playing key roles across the ATLAS experiment: in detector operations, the online trigger, the upgrade, computing, and physics analysis. Our team has been critical to the maintenance and operations of the muon system since its installation. During Run 1 we led the muon trigger group and that responsibility continues into Run 2. BU maintains and operates the ATLAS Northeast Tier 2 computing center. We are actively engaged in the analysis of ATLAS data from Run 1 and Run 2. Physics analyses we have contributed to include Standard Model measurements (W and Z cross sections, t\bar{t} differential cross sections, WWW^* production), evidence for the Higgs decaying to \tau^+\tau^-, and searches for new phenomena (technicolor, Z' and W', vector-like quarks, dark matter).

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.

Particle Physics Reference Library
Particle Physics Reference Library

Author: Christian W. Fabjan

Publisher: Springer Nature

Published: 2020

Total Pages: 1083

ISBN-13: 3030353184

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This second open access volume of the handbook series deals with detectors, large experimental facilities and data handling, both for accelerator and non-accelerator based experiments. It also covers applications in medicine and life sciences. A joint CERN-Springer initiative, the "Particle Physics Reference Library" provides revised and updated contributions based on previously published material in the well-known Landolt-Boernstein series on particle physics, accelerators and detectors (volumes 21A, B1,B2,C), which took stock of the field approximately one decade ago. Central to this new initiative is publication under full open access