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Title: Search for the Higgs boson in the ZH to ℓ +-b$$\bar{b}$$ channel at CDF Run II

Abstract

The Standard Model of particle physics is in excellent agreement with the observed phenomena of particle physics. Within the Standard Model, the weak and electromagnetic forces are successfully combined. However, this combination is only valid if the masses of the force carriers of the weak force, the Z and W bosons, are massless. In fact, these two particles are the second and third most massive observed elementary particles. Within the minimal Standard Model, the Higgs mechanism is introduced to reconcile this contradiction. Conclusive proof of this theory would come with the discovery of the Higgs boson.

Authors:
 [1]
  1. The Ohio State Univ., Columbus, OH (United States)
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
917090
Report Number(s):
FERMILAB-THESIS-2007-20
TRN: US0804442
DOE Contract Number:
AC02-07CH11359
Resource Type:
Thesis/Dissertation
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ELEMENTARY PARTICLES; FERMILAB COLLIDER DETECTOR; HIGGS BOSONS; INTERMEDIATE BOSONS; PHYSICS; STANDARD MODEL; Experiment-HEP

Citation Formats

Efron, Jonathan Zvi. Search for the Higgs boson in the ZH to ℓ+ℓ-b$\bar{b}$ channel at CDF Run II. United States: N. p., 2007. Web. doi:10.2172/917090.
Efron, Jonathan Zvi. Search for the Higgs boson in the ZH to ℓ+ℓ-b$\bar{b}$ channel at CDF Run II. United States. doi:10.2172/917090.
Efron, Jonathan Zvi. Mon . "Search for the Higgs boson in the ZH to ℓ+ℓ-b$\bar{b}$ channel at CDF Run II". United States. doi:10.2172/917090. https://www.osti.gov/servlets/purl/917090.
@article{osti_917090,
title = {Search for the Higgs boson in the ZH to ℓ+ℓ-b$\bar{b}$ channel at CDF Run II},
author = {Efron, Jonathan Zvi},
abstractNote = {The Standard Model of particle physics is in excellent agreement with the observed phenomena of particle physics. Within the Standard Model, the weak and electromagnetic forces are successfully combined. However, this combination is only valid if the masses of the force carriers of the weak force, the Z and W bosons, are massless. In fact, these two particles are the second and third most massive observed elementary particles. Within the minimal Standard Model, the Higgs mechanism is introduced to reconcile this contradiction. Conclusive proof of this theory would come with the discovery of the Higgs boson.},
doi = {10.2172/917090},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Thesis/Dissertation:
Other availability
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  • The standard model of particle physics provides a detailed description of a universe in which all matter is composed of a small number of fundamental particles, which interact through the exchange of force - carrying gauge bosons (the photon, W ±, Z and gluons). The organization of the matter and energy in this universe is determined by the effects of three forces; the strong, weak, and electromagnetic. The weak and electromagnetic forces are the low energy manifestations of a single electro-weak force, while the strong force binds quarks into protons and neutrons. The standard model does not include gravity, as the effect of this force on fundamental particles is negligible. Four decades of experimental tests, spanning energies from a few electron-volts (eV) up to nearly two TeV, confirm that the universe described by the standard model is a reasonable approximation of our world. For example, experiments have confirmed the existence of the top quark, the W ± and the Z bosons, as predicted by the standard model. The latest experimental averages for the masses of the top quark, W ± and Z are respectively 173.1 ± 0.6(stat.) ± 1.1(syst.), 80.399 ± 0.023 and 91.1876 ± 0.0021 GeV/c 2. The SM is a gauge field theory of zero mass particles. However, the SM is able to accommodate particles with non-zero mass through the introduction of a theoretical Higgs field which permeates all of space. Fermions gain mass through interactions with this field, while the longitudinal components of the massive W ± and Z are the physical manifestations of the field itself. Introduction of the Higgs field, directly leads to the predicted existence of an additional particle, the Higgs boson. The Higgs boson is the only particle of the standard model that has not been observed, and is the only unconfirmed prediction of the theory. The standard model describes the properties of the Higgs boson in terms of its mass, which is a free parameter in the theory. Experimental evidence suggests that the Higgs mass has a value between 114.4 and 186 GeV/c 2. Particles with a mass in this range can be produced in collisions of less massive particles accelerated to near the speed of light. Currently, one of only a few machines capable of achieving collision energies large enough to potentially produce a standard model Higgs boson is the Tevatron proton-antiproton collider located at Fermi National Accelerator Laboratory in Batavia, Illinois. This dissertation describes the effort to observe the standard model Higgs in Tevatron collisions recorded by the Collider Detector at Fermilab (CDF) II experiment in the ZH →ℓ +-bmore » $$\bar{b}$$ production and decay channel. In this process, the Higgs is produced along with a Z boson which decays to a pair of electrons or muons (Z →ℓ +-), while the Higgs decays to a bottom anti-bottom quark pair (H → b$$\bar{b}$$). A brief overview of the standard model and Higgs theory is presented in Chapter 2. Chapter 3 explores previous searches for the standard model Higgs at the Tevatron and elsewhere. The search presented in this dissertation expands upon the techniques and methods developed in previous searches. The fourth chapter contains a description of the Tevatron collider and the CDF II detector. The scope of the discussion in Chapter 4 is limited to the experimental components relevant to the current ZH →ℓ +-b$$\bar{b}$$ search. Chapter 5 presents the details of object reconstruction; the methods used to convert detector signals into potential electrons, muons or quarks. Chapter six describes the data sample studied for the presence of a ZH →ℓ +-b$$\bar{b}$$ signal and details the techniques used to model the data. The model accounts for both signal and non-signal processes (backgrounds) which are expected to contribute to the observed event sample. Chapters 7 and 8 summarize the event selection applied to isolate ZH →ℓ +-b$$\bar{b}$$} candidate events from the data sample, and the advanced techniques employed to maximize the separation of the signal from background processes. Chapters 9 and 10 present the systematic uncertainties affecting our modeling of the data sample and the results of the search. Chapter 11 presents a discussion of ZH →ℓ +-b$$\bar{b}$$ in the context of the overall Tevatron efforts to observe a standard model Higgs signal.« less
  • This analysis focuses on a low mass Higgs boson search with 1.7 fb -1 of data. The focus is on Higgs events in which it is produced in association with a W or Z boson. Such events are expected to leave a distinct signature of large missing transverse energy for either a Z → vv decay or a leptonic W decay in which the lepton goes undetected, as well as jets with taggable secondary vertices from the H → bmore » $$\bar{b}$$ decay. Utilizing a new track based technique for removing QCD multi-jet processes as well as a neural network discriminant, an expected limit of 8.3 times the Standard Model prediction at the 95% CL for a Higgs boson mass of 115 GeV/c 2 is calculated, with an observed limit of 8.0*SM.« less
  • We present a search for the Standard Model Higgs Boson using the processmore » $$ZH\to\mu^+\mu^- b\bar{b}$$. We use a dataset corresponding to 9.2 fb$$^{-1}$$ of integrated luminosity from proton-antiproton collisions with center-of-mass energy 1.96 TeV at the Fermilab Tevatron, collected with the CDF II detector. This analysis benefits from several new multivariate techniques that have not been used in previous analyses at CDF. We use a multivariate function to select muon candidates, increasing signal acceptance while simultaneously keeping fake rates small. We employ an inclusive trigger selection to further increase acceptance. To enhance signal discrimination, we utilize a multi-layer approach consisting of expert discriminants. This multi-layer discriminant method helps isolate the two main classes of background events, $$t\bar{t}$$ and $Z$+jets production. It also includes a flavor separator, to distinguish light flavor jets from jets consistent with the decay of a $B$-hadron. Wit h this novel multi-layer approach, we proceed to set limits on the $ZH$ production cross section times branching ratio. For a Higgs boson with mass 115 GeV/$c^2$, we observe (expect) a limit of 8.0 (4.9) times the Standard Model prediction.« less
  • The organization of this thesis consists of three main ideas: the first presents the theoretical framework and experimental, as well as objects used in the analysis and the second relates to the various work tasks of service that I performed on the calorimeter, and the third is the search for the Higgs boson in the channel ZH → e +e -bmore » $$\bar{b}$$. Thus, this thesis has the following structure: Chapter 1 is an introduction to the standard model of particle physics and the Higgs mechanism; Chapter 2 is an overview of the complex and the acceleration of the Tevatron at Fermilab DØ detector; Chapter 3 is an introduction to physical objects used in this thesis; Chapter 4 presents the study made on correcting the energy measured in the calorimeter; Chapter 5 describes the study of certification of electrons in the calorimeter; Chapter 6 describes the study of certification of electrons in the intercryostat region of calorimeter; Chapter 7 Detailed analysis on the search for Higgs production in the channel ZH → e +e -b$$\bar{b}$$; and Chapter 8 presents the final results of the calculations of upper limits to the production cross section of the Higgs boson on a range of low masses.« less
  • A search for the standard model Higgs boson is performed in 5.2 fb -1 of pmore » $$\bar{p}$$ collisions at p √s = 1.96 TeV, collected with the DØ detector at the Fermilab Tevatron. The final state considered is a pair of b jets with large missing transverse energy, as expected from p$$\bar{p}$$→ ZH → v$$\bar{v}$$b$$\bar{b}$$ production. The search is also sensitive to the WH → ℓvb$$\bar{b}$$ channel, where the charged lepton is not identified. Boosted decision trees are used to discriminate signal from background. Good agreement is observed between data and expected backgrounds, and, for a Higgs-boson mass of 115 GeV, a limit is set at 95% C.L. on the cross section multiplied by branching fraction of (p$$\bar{p}$$ → (Z/W)H) × (H → b$$\bar{b}$$) that is a factor 4.57 expected and 3.73 observed larger than the value expected from the standard model.« less