Study Of The Electroweak Symmetry Breaking Sector For The Lhc

In this dissertation, we revisit the prospects of a strongly interacting theory for the Electroweak Symmetry Breaking Sector of the Standard Model, after the discovery of a Higgs-like boson at 125GeV. As the LHC constrains new phenomena near the Higgs mass, it is natural to assume that the new scale is of order 1TeV. This mass gap might indicate strongly interacting new physics. This work is of quite general validity and model independence. With only a few parameters at the Lagrangian level, multiple channels (possibly with new physics resonances) are describable, and many BSM theories can be treated. It will be of interest to postgraduate students and researchers, and is accessible to newcomers in the field. Many calculations are given in full detail and there are ample graphical illustrations.

Fundamental interactions are mediated by bosonic fields, quanta of which are realized as particles. The properties of these fields typically obey certain symmetry rules. In this book we discuss the symmetry between two types of interactions — electromagnetic, which are familiar to anyone who turned on the electric lights, and weak, which govern the nuclear reactions that fuel the Sun. While there is a symmetry between these two types of interactions, it is broken. The unified theory of electroweak interactions was developed over 50 years ago. The Higgs scalar field named after one of the theorists that proposed it, is believed to be responsible for the breaking of the electroweak symmetry. Yet, it is only now after the discovery of the Higgs boson in 2012 by the LHC experiments, that we can study the mechanism of the electroweak symmetry breaking. This book discusses the theoretical developments that led to the construction of this theory, the discovery and the experimental observations that need to come to fully establish the validity of the model.

This is an expanded version of the report by the Electroweak Symmetry Breaking and Beyond the Standard Model Working Group which was contributed to Particle Physics — Perspectives and Opportunities, a report of the Division of Particles and Fields Committee for Long Term Planning. One of the Working Group's primary goals was to study the phenomenology of electroweak symmetry breaking and attempt to quantify the “physics reach” of present and future colliders. Their investigations encompassed the Standard Model — with one doublet of Higgs scalars — and approaches to physics beyond the Standard Model. These include models of low-energy supersymmetry, dynamical electroweak symmetry breaking, and a variety of extensions of the Standard Model with new particles and interactions. The Working Group also considered signals of new physics in precision measurements arising from virtual processes and examined experimental issues associated with the study of electroweak symmetry breaking and the search for new physics at present and future hadron and lepton colliders.This volume represents an important contribution to the efforts being made to advance the frontiers of particle physics.

The author summarizes an update on the study for a strongly interacting electroweak symmetry breaking sector via longitudinal vector boson scattering at the 14 TeV Large Hadron Collider. In the update, the decay mode ZZ → ll−?{bar {nu}} and a new vector-resonance signal via q{bar q} → V → W+W−/W{sup {+-}}Z are also included.

In this thesis we study possible deviations from the electroweak symmetry breaking mechanism as predicted by the Standard Model (SM), and we introduce a new framework to analyze hadronic final states at colliders. In the first part, we begin by considering supersymmetric extensions of the SM and by studying the connection between electroweak symmetry breaking and supersymmetry breaking. Contrary to the common lore, we show that a visible dynamics in the Higgs sector can contribute to supersymmetry breaking, as long as soft masses receive contributions also from one or more hidden sectors. A striking feature is the presence of a light pseudo-goldstino in the spectrum. We study potential collider signatures of visible supersymmetry breaking in Higgs and neutralino decays. Then, we move to a study of the Higgs data collected at the Large Hadron Collider (LHC). By using both measurements of the Higgs boson couplings, and limits on Higgs-like states at higher masses, we investigate whether the data support the possibility that the SM Higgs is mixed with another scalar. We consider fits to simplified models and we find that mixing angles with sin 2 6 > 0.2 are disfavored at 95% CL over a scalar mass range 200 - 1000 GeV. In the second part, we propose a new way to define inclusive jet (and subject) based observables at colliders. We introduce a new class of event shapes that characterize the jet-like structure of the event by using only information in the neighborhood of each particle. We show that conventional jet-based observables such as jet multiplicity, summed scalar transverse momentum, and missing transverse momentum can be recovered within this approach. We show that in this framework trimming can be recast as a particle weight assignment, without explicit jet identification. Finally, we comment on potential applications of the method both at trigger and analysis level.

During more than 10 years, from 1989 until 2000, the LEP accelerator and the four LEP experiments, ALEPH, DELPHI, L3 and OPAL, have taken data for a large amount of measurements at the frontier of particle physics. The main outcome is a thorough and successful test of the Standard Model of electroweak interactions. Mass and width of the Z and W bosons were measured precisely, as well as the Z and photon couplings to fermions and the couplings among gauge bosons. The rst part of this work will describe the most important physics results of the LEP experiments. Emphasis is put on the properties of the W boson, which was my main research eld at LEP. Especially the precise determination of its mass and its couplings to the other gauge bosons will be described. Details on physics effects like Colour Reconnection and Bose-Einstein Correlations in W-pair events shall be discussed as well. A conclusive summary of the current electroweak measurements, including low-energy results, as the pillars of possible future ndings will be given. The important contributions from Tevatron, like the measurement of the top quark and W mass, will round up the present day picture of electroweak particle physics. This is an open access book.

Exploring the phenomenology of the Large Hadron Collider (LHC) at CERN, LHC Physics focuses on the first years of data collected at the LHC as well as the experimental and theoretical tools involved. It discusses a broad spectrum of experimental and theoretical activity in particle physics, from the searches for the Higgs boson and physics beyond the Standard Model to studies of quantum chromodynamics, the B-physics sector, and the properties of dense hadronic matter in heavy-ion collisions. Covering the topics in a pedagogical manner, the book introduces the theoretical and phenomenological framework of hadron collisions and presents the current theoretical models of frontier physics. It offers overviews of the main detector components, the initial calibration procedures, and search strategies. The authors also provide explicit examples of physics analyses drawn from the recently shut down Tevatron. In the coming years, or perhaps even sooner, the LHC experiments may reveal the Higgs boson and offer insight beyond the Standard Model. Written by some of the most prominent and active researchers in particle physics, this volume equips new physicists with the theory and tools needed to understand the various LHC experiments and prepares them to make future contributions to the field.

Fine tuning in the Standard Model (SM) is the basis for a widespread expectation that the minimal model for electroweak symmetry breaking, with a single Higgs boson, is not realised in nature and that new physics, in addition to (or instead of) the Higgs, will be discovered at the Large Hadron Collider (LHC). However constraints on new physics indicate that many models which go beyond the SM (BSM) may also be fine tuned (although to a much lesser extent). To test this a reliable, quantitative measure of tuning is required. We review the measures of tuning used in the literature and propose an alternative measure. We apply this measure to several toy models and a constrained version of the Minimal Supersymmetric Standard Model. The Exceptional Supersymmetric Standard Model (E6SSM) is another BSM motivated by naturalness. As a supersymmetric theory it solves the SM hierarchy problem and by breaking a new gauged U(1) symmetry it also solves the Âμ-problem of the MSSM. We investigate the Renormalisation Group Evolution of the model and test for radiative electroweak symmetry breaking in two versions of the model with different high scale constraints. First we briefly look at scenarios with non-universal Higgs masses at the GUT scale and present a particle spectrum that could be observed at the LHC. Secondly we study the constrained E6SSM (CE6SSM), with universal scalar (m0), trilinear (A0) and gaugino (M) masses. We reveal a large volume of CE6SSM parameter space where the correct breakdown of the gauge symmetry can be achieved and all experimental constraints can be satisfied. We present benchmark points corresponding to different patterns of the particle spectrum. A general feature of the benchmark spectra is a light sector of SUSY particles consisting of a light gluino, two light neutralinos and a light chargino. Although the squarks, sleptons and Z boson are typically much heavier, the exotic color triplet charge 1/3 fermions as well as the lightest stop can be also relatively light leading to spectacular new physics signals at the LHC.

The Standard Model (SM) is the backbone of elementary particle physics-not only does it provide a consistent framework for studying the interactions of quark and leptons, but it also gives predictions which have been extensively tested experimentally. In these notes, I review the electroweak sector of the Standard Model, discuss the calculation of electroweak radiative corrections to observables, and summarize the status of SM Higgs boson searches. Despite the impressive experimental successes, however, the electroweak theory is not completely satisfactory and the mechanism of electroweak symmetry breaking is untested. I will discuss the logic behind the oft-repeated statement: 'There must be new physics at the TeV scale'. These lectures reflect my strongly held belief that upcoming results from the LHC will fundamentally change our understanding of electroweak symmetry breaking. In these lectures, I review the status of the electroweak sector of the Standard Model, with an emphasis on the importance of radiative corrections and searches for the Standard Model Higgs boson. A discussion of the special role of the TeV energy scale in electroweak physics is included.