Search for the Standard Model Higgs Boson in Proton-antiproton Interactions with the Decay Mode H Going to W+W- Going to Muon+ Neutrino Muon- Neutrino at the D0 Experiment PDF Download

Author: Dale Morgan Johnston
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ISBN: 9781109714548
Category : Higgs bosons
Languages : en
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Languages : en
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Search for the standard model Higgs boson in the Z boson-H boson decaying to positive muon-negative muon and bottom-anti-bottom quark channel in proton-antiproton collisions at the center of mass energy = 1.96 TeV.

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Languages : en
Pages : 196

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The question of the nature and principles of the universe and our place in it is the driving force of science since Mesopotamian astronomers glanced for the first time at the starry sky and Greek atomism has been formulated. During the last hundred years modern science was able to extend its knowledge tremendously, answering many questions, opening entirely new fields but as well raising many new questions. Particularly Astronomy, Astroparticle Physics and Particle Physics lead the race to answer these fundamental and ancient questions experimentally. Today it is known that matter consists of fermions, the quarks and leptons. Four fundamental forces are acting between these particles, the electromagnetic, the strong, the weak and the gravitational force. These forces are mediated by particles called bosons. Our confirmed knowledge of particle physics is based on these particles and the theory describing their dynamics, the Standard Model of Particles. Many experimental measurements show an excellent agreement between observation and theory but the origin of the particle masses and therefore the electroweak symmetry breaking remains unexplained. The mechanism proposed to solve this issue involves the introduction of a complex doublet of scalar fields which generates the masses of elementary particles via their mutual interactions. This Higgs mechanism also gives rise to a single neutral scalar boson with an unpredicted mass, the Higgs boson. During the last twenty years several experiments have searched for the Higgs boson but so far it escaped direct observation. Nevertheless these studies allow to further constrain its mass range. The last experimental limits on the Higgs mass have been set in 2001 at the LEP collider, an electron positron machine close to Geneva, Switzerland. The lower limit set on the Higgs boson mass is m{sub H}> 114.4 GeV/c2 and remained for many years the last experimental constraint on the Standard Model Higgs Boson due to the shutdown of the LEP collider and the experimental challenges at hadron machines as the Tevatron. This thesis was performed using data from the D0 detector located at the Fermi National Accelerator Laboratory in Batavia, IL. Final states containing two electrons or a muon and a tau in combination with missing transverse energy were studied to search for the Standard Model Higgs boson, utilizing up to 4.2 fb−1 of integrated luminosity. In 2008 the CDF and D0 experiments in a combined effort were able to reach for the first time at a hadron collider the sensitivity to further constrain the possible Standard Model Higgs boson mass range. The research conducted for this thesis played a pivotal role in this effort. Improved methods for lepton identification, background separation, assessment of systematic uncertainties and new decay channels have been studied, developed and utilized. Along with similar efforts at the CDF experiment these improvements led finally the important result of excluding the presence of a Standard Model Higgs boson in a mass range of m{sub H} = 160-170 GeV/c2 at 95% Confidence Level. Many of the challenges and methods found in the present analysis will probably in a similar way be ingredients of a Higgs boson evidence or discovery in the near future, either at the Tevatron or more likely at the soon starting Large Hadron Collider (LHC). Continuing to pursue the Higgs boson we are looking forward to many exciting results at the Tevatron and soon at the LHC. In Chapter 2 an introduction to the Standard Model of particle physics and the Higgs mechanism is given, followed by a brief outline of existing theoretical and experimental constraints on the Higgs boson mass before summarizing the Higgs boson production modes. Chapter 3 gives an overview of the experimental setup. This is followed by a description of the reconstruction of the objects produced in proton-antiproton collisions in Chapter 4 and the necessary calorimeter calibrations in Chapter 5. Chapter 6 follows with an explanation of the phenomenology of the proton-antiproton collisions and the data samples used. In Chapter 7 the search for the Standard Model Higgs boson using a di-electron final state is discussed, followed by the analysis of the final states using muons and hadronic decaying taus in Chapter 8. Finally a short outlook for the prospects of Higgs boson searches is given in Chapter 9.

Author:
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Category : Power resources
Languages : en
Pages : 1470

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Author: Amy Lynn Connolly
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Category :
Languages : en
Pages : 498

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Languages : en
Pages : 176

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A search for the standard model Higgs boson in p{bar p} collisions resulting in two muons and large missing transverse energy is presented. The analysis uses 4.2 fb−1 of integrated luminosity at a center-of-mass energy of √s = 1.96 TeV collected between April 2002 and December 2008 with the D0 detector at the Fermilab Tevatron collider. No significant excess above the background estimation is observed and limits are derived on Higgs boson production.

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Languages : en
Pages : 149

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A search for the Standard Model Higgs boson was carried out in WH 2!l[nu]b{bar b} process in p{bar p} collisions at a center of mass energy of 1.96 TeV, where W, H, l, [nu], b and p denote either a W or W− boson, Higgs boson, lepton (electron or muon), neutrino, bottom quark and proton, respectively. The data were collected with the Collider Detector at Fermilab from February 2002 to August 2004. The corresponding integrated luminosity is 319 pb−1. We select events containing a single high-p{sub T} electron or muon, a large imbalance of the total transverse energy from a neutrino and two b quark jets. The main backgrounds are the W + light flavor/gluon jets and W + heavy flavor jets processes. Requiring the secondary vertex b-tagging enables us to reject the W + light flavor/gluon jets events effectively. After all event selections, they observe 187 events which is in agreement with the Standard Model background expectation of 175.2 ± 26.3 events, and there is no significant excess originating from the Higgs boson in the reconstructed dijet invariant mass distribution. They thus set a 95% confidence level upper limit on the production cross section times branching ratio decaying into bb, [sigma](p{bar p} 2!W H) x Br(H 2!b{bar b}). The detection efficiency for the W H events, which is necessary for calculating the upper limit, is determined by the Monte Carlo except for the lepton identification efficiency, the lepton trigger efficiency and the b-tagging efficiency which are estimated from the CDF real data. The resultant 95% confidence level upper limits are 10.0 pb to 2.8 pb using at least one b-tagging method and 9.7 pb to 6.6 pb using double b-tagging method for the Higgs boson mass region 110 GeV/c2 to 150 GeV/c2, where the Standard Model prediction is approximately one or two order of magnitude lower than the results.

Author: Valentina Dutta
Publisher:
ISBN:
Category :
Languages : en
Pages : 185

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In this thesis, I describe the search for a Higgs boson through its decay to a pair of tan leptons with the tau-pair subsequently decaying to ail electron, a muon, and neutrinos. The search is performed using data collected from proton-proton collisions by the Compact Muon Solenoid experiment at the Large Hadron Collider, corresponding to 5.0 fb-1 of integrated luminosity recorded at a center-of-mass energy of 7 TeV and 19.7 fb-1 at 8 TeV. The expected significance for a Standard Model Higgs boson signal with a mass of 125 GeV is at the level of 1.2 standard deviations for the electron muon tau-pair decay mode. A mild excess of events is seen above the SM background expectation in this decay mode, consistent with a SM Higgs boson of mass 125 GeV. In combination with results using other tau-pair decay modes, an excess of events above the background expectation is seen at the level of 3.4 standard deviations. This constitutes the first evidence for a Higgs boson to decay to leptons. This thesis also describes an analysis of the data in the context of physics beyond the Standard Model, particularly in the framework of its Minimal Supersymnnetric extension.

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Languages : en
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We present a search for the standard model Higgs boson (H) in ppbar collisions at sqrt{s}=1.96 TeV in events containing a charged lepton (ell), missing transverse energy, and at least two jets, using 5.4 fb-̂1 of integrated luminosity recorded with the D0 detector at the Fermilab Tevatron Collider. This analysis is sensitive primarily to Higgs bosons produced through the fusion of two gluons or two electroweak bosons, with subsequent decay H->WW->ell+nu+q'qbar, where ell is an electron or muon. The search is also sensitive to contributions from other production channels, such as WH->ell+nu+bbbar In the absence of signal, we set limits at the 95% C.L. on the cross section for H production sigma(ppbar->H+X) in these final states. For a mass of MH=160 GeV, the limit is a factor of 3.9 larger than the cross section in the standard model, and consistent with expectation.

Author: Luciano Maiani
Publisher: World Scientific Publishing Company
ISBN: 9814733512
Category : Science
Languages : en
Pages : 483

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The book gives a quite complete and up-to-date picture of the Standard Theory with an historical perspective, with a collection of articles written by some of the protagonists of present particle physics. The theoretical developments are described together with the most up-to-date experimental tests, including the discovery of the Higgs Boson and the measurement of its mass as well as the most precise measurements of the top mass, giving the reader a complete description of our present understanding of particle physics.