A Search for New Physics in Events with a Leptonically Decaying Z Boson and a Large Transverse Momentum Imbalance with the CMS Detector at the LHC PDF Download

Author: Nicholas Charles Smith
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

View

Book Description
A search for new physics in events with a leptonically decaying Z boson and a large transverse momentum imbalance in proton-proton collisions collected at sqrt(s) = 13 TeV in 2016 with the Compact Muon Solenoid detector at the Large Hadron Collider is presented. The results of this search are interpreted in terms of a simplified model of dark matter production via spin-0 or spin-1 mediators, a scenario with a standard-model-like Higgs boson produced in association with the Z boson and decaying invisibly, a model of unparticle production, and a model with large extra spatial dimensions. No significant deviations from the background expectations are found, and limits are set on relevant model parameters, significantly extending the results previously achieved in this channel.

Author: Lesya Horyn
Publisher: Springer Nature
ISBN: 3030916723
Category : Science
Languages : en
Pages : 146

View

Book Description
This thesis presents a search for long-lived particles decaying into displaced electrons and/or muons with large impact parameters. This signature provides unique sensitivity to the production of theoretical lepton-partners, sleptons. These particles are a feature of supersymmetric theories, which seek to address unanswered questions in nature. The signature searched for in this thesis is difficult to identify, and in fact, this is the first time it has been probed at the Large Hadron Collider (LHC). It covers a long-standing gap in coverage of possible new physics signatures. This thesis describes the special reconstruction and identification algorithms used to select leptons with large impact parameters and the details of the background estimation. The results are consistent with background, so limits on slepton masses and lifetimes in this model are calculated at 95% CL, drastically improving on the previous best limits from the Large Electron Positron Collider (LEP).

Author: Joseph A. Gartner
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
ABSTRACT: This dissertation describes the full details of 2 studies of Z0 bosons performed using the Compact Muon Solenoid detector at the Large Hadron Collider of proton on proton collisions with center of mass energy of 7TeV. The first study searches for physics beyond the Standard Model by looking for an excess in production of Z0 bosons by examining the Z0pT spectrum. As no excess is found, limits on new physics models are presented as a function of mass and other free parameters. The second study focuses on a precision measurement of the Z0pT distribution, and is compared to theoretical calculations for the purposes of testing high order QCD calculations in addition to probing the predictions of various tunes of the underlying event.

Author: Cecilia Tosciri
Publisher: Springer Nature
ISBN: 3030879380
Category : Science
Languages : en
Pages : 171

View

Book Description
The discovery in 2012 of the Higgs boson at the Large Hadron Collider (LHC) represents a milestone for the Standard Model (SM) of particle physics. Most of the SM Higgs production and decay rates have been measured at the LHC with increased precision. However, despite its experimental success, the SM is known to be only an effective manifestation of a more fundamental description of nature. The scientific research at the LHC is strongly focused on extending the SM by searching, directly or indirectly, for indications of New Physics. The extensive physics program requires increasingly advanced computational and algorithmic techniques. In the last decades, Machine Learning (ML) methods have made a prominent appearance in the field of particle physics, and promise to address many challenges faced by the LHC. This thesis presents the analysis that led to the observation of the SM Higgs boson decay into pairs of bottom quarks. The analysis exploits the production of a Higgs boson associated with a vector boson whose signatures enable efficient triggering and powerful background reduction. The main strategy to maximise the signal sensitivity is based on a multivariate approach. The analysis is performed on a dataset corresponding to a luminosity of 79.8/fb collected by the ATLAS experiment during Run-2 at a centre-of-mass energy of 13 TeV. An excess of events over the expected background is found with an observed (expected) significance of 4.9 (4.3) standard deviation. A combination with results from other \Hbb searches provides an observed (expected) significance of 5.4 (5.5). The corresponding ratio between the signal yield and the SM expectation is 1.01 +- 0.12 (stat.)+ 0.16-0.15(syst.). The 'observation' analysis was further extended to provide a finer interpretation of the V H(H → bb) signal measurement. The cross sections for the VH production times the H → bb branching ratio have been measured in exclusive regions of phase space. These measurements are used to search for possible deviations from the SM with an effective field theory approach, based on anomalous couplings of the Higgs boson. The results of the cross-section measurements, as well as the constraining of the operators that affect the couplings of the Higgs boson to the vector boson and the bottom quarks, have been documented and discussed in this thesis. This thesis also describes a novel technique for the fast simulation of the forward calorimeter response, based on similarity search methods. Such techniques constitute a branch of ML and include clustering and indexing methods that enable quick and efficient searches for vectors similar to each other. The new simulation approach provides optimal results in terms of detector resolution response and reduces the computational requirements of a standard particles simulation.

Author: Tilman Plehn
Publisher: Springer
ISBN: 3319059424
Category : Science
Languages : en
Pages : 340

View

Book Description
With the discovery of the Higgs boson, the LHC experiments have closed the most important gap in our understanding of fundamental interactions, confirming that such interactions between elementary particles can be described by quantum field theory, more specifically by a renormalizable gauge theory. This theory is a priori valid for arbitrarily high energy scales and does not require an ultraviolet completion. Yet, when trying to apply the concrete knowledge of quantum field theory to actual LHC physics - in particular to the Higgs sector and certain regimes of QCD - one inevitably encounters an intricate maze of phenomenological know-how, common lore and other, often historically developed intuitions about what works and what doesn’t. These lectures cover three aspects to help understand LHC results in the Higgs sector and in searches for physics beyond the Standard Model: they discuss the many facets of Higgs physics, which is at the core of this significantly expanded second edition; then QCD, to the degree relevant for LHC measurements; as well as further standard phenomenological background knowledge. They are intended to serve as a brief but sufficiently detailed primer on LHC physics to enable graduate students and all newcomers to the field to find their way through the more advanced literature, and to help those starting to work in this very timely and exciting field of research. Advanced readers will benefit from this course-based text for their own lectures and seminars. .

Author: Howard Baer
Publisher: Cambridge University Press
ISBN: 1009289845
Category : Science
Languages : en
Pages : 557

View

Book Description
This OA text develops the basic concepts of supersymmetry for experimental and phenomenological particle physicists and graduate students.

Author: Fred Jegerlehner
Publisher: Springer Science & Business Media
ISBN: 3540726330
Category : Science
Languages : en
Pages : 433

View

Book Description
This book reviews the present state of knowledge of the anomalous magnetic moment a=(g-2)/2 of the muon. The muon anomalous magnetic moment is one of the most precisely measured quantities in elementary particle physics and provides one of the most stringent tests of relativistic quantum field theory as a fundamental theoretical framework. It allows for an extremely precise check of the standard model of elementary particles and of its limitations.

Author: Manuel Drees
Publisher: World Scientific
ISBN: 9814495344
Category : Science
Languages : en
Pages : 582

View

Book Description
Supersymmetry or SUSY, one of the most beautiful recent ideas of physics, predicts sparticles existing as superpartners of particles. This book gives a theoretical and phenomenological account of sparticles. Starting from a basic level, it provides a comprehensive, pedagogical and user-friendly treatment of the subject of four-dimensional N=1 supersymmetry as well as its observational aspects in high energy physics and cosmology. Part One of the book introduces the requisite formal theory, preceded by a discussion of the naturalness problem. Part Two describes the supersymmetrization of the Standard Model of particle interactions as well as the origin of soft supersymmetry breaking and how it can be mediated from higher energies. Search strategies for sparticles, supersymmetric Higgs bosons, nonminimal scenarios and cosmological implications are some of the other topics covered. Novel features of the book include a dictionary between two-component and four-component spinor notation, a step-by-step derivation of the nonrenormalization theorem, an extended discussion of supersymmetric renormalization group evolution, detailed analyses of minimal and nonminimal models with gravity (including anomaly) mediated and gauge mediated supersymmetry breaking as well as elaborate self-contained presentations of collider signals of sparticles plus supersymmetric Higgs bosons and of supersymmetric cosmology. Appendices list all Feynman rules for the vertices of the Minimal Supersymmetric Standard Model.

Author: Md. Naimuddin
Publisher: Springer
ISBN: 3319731718
Category : Science
Languages : en
Pages : 879

View

Book Description
These proceedings gather invited and contributed talks presented at the XXII DAE-BRNS High Energy Physics (HEP) Symposium, which was held at the University of Delhi, India, on 12–16 December 2016. The contributions cover a variety of topics in particle physics, astroparticle physics, cosmology and related areas from both experimental and theoretical perspectives, namely (1) Neutrino Physics, (2) Standard Model Physics (including Electroweak, Flavour Physics), (3) Beyond Standard Model Physics, (4) Heavy Ion Physics & QCD (Quantum Chromodynamics), (5) Particle Astrophysics & Cosmology, (6) Future Experiments and Detector Development, (7) Formal Theory, and (8) Societal Applications: Medical Physics, Imaging, etc. The DAE-BRNS High Energy Physics Symposium, widely considered to be one of the leading symposiums in the field of Elementary Particle Physics, is held every other year in India and supported by the Board of Research in Nuclear Sciences (BRNS), Department of Atomic Energy (DAE), India. As many as 400 physicists and researchers attended the 22nd Symposium to discuss the latest advances in the field. A poster session was also organized to highlight the work and findings of young researchers. Bringing together the essential content, the book offers a valuable resource for both beginning and advanced researchers in the field.

Author: D. T. Pignotti
Publisher:
ISBN:
Category :
Languages : en
Pages : 85

View

Book Description
The ATLAS detector at the Large Hadron Collider is used to search for the lepton flavor violating process Z -> eμ in pp collisions using 20.3 fb^(-1) of data collected at sqrt(s)= 8 TeV. An enhancement in the eμ invariant mass spectrum is searched for at the Z boson mass. The number of Z bosons produced in the data sample is estimated using events of similar topology, Z -> ee and μμ, significantly reducing the systematic uncertainty in the measurement. There is no evidence of an enhancement at the Z boson mass, resulting in an upper limit on the branching fraction, B(Z -> eμ)