Search For The Standard Model Higgs Boson In P Bar P Interactions With The Decay Mode H U2192 W W U2192 V V At The D Experiment
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Search For The Standard Model Higgs Boson In P Bar P Interactions With The Decay Mode H U2192 W W U2192 V V At The D Experiment
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Author :
language : en
Publisher:
Release Date : 2010
Search For The Standard Model Higgs Boson In P Bar P Interactions With The Decay Mode H U2192 W W U2192 V V At The D Experiment written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
A search for the standard model Higgs boson in p$ar{p}$ 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.
Search For The Standard Model Higgs Boson In The Decay Mode H U2192 W W U2192 L Vl V
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Author :
language : en
Publisher:
Release Date : 2009
Search For The Standard Model Higgs Boson In The Decay Mode H U2192 W W U2192 L Vl V written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
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 mH > 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 mH = 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 calorim...
First Search For The Standard Model Higgs Boson Using The Semileptonic Decay Channel
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Author :
language : en
Publisher:
Release Date : 2010
First Search For The Standard Model Higgs Boson Using The Semileptonic Decay Channel written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
This dissertation presents the first search for the standard model Higgs boson (H) in decay topologies containing a muon, an imbalance in transverse momentum (ET) and jets, using p$ar{p}$ collisions at √s = 1.96 TeV with an integrated luminosity of 4.3 fb-1 recorded with the D0 detector at the Fermilab Tevatron Collider. This analysis is sensitive primary to contributions from Higgs bosons produced through gluon fusion, with subsequent decay H → WW → ??jj where W represents a real or virtual W boson. In the absence of signal, limits are set at 95% confidence on the production and decay of the standard model Higgs boson for MH in the range of 115-200 GeV. For MH = 165 GeV, the observed and expected limits are factors of 11.2 larger than the standard model value. Combining this channel with e?jj final states and including earlier data to increase the integrated luminosity to 5.4 fb-1 produces observed(expected) limits of 5.5(3.8) times the standard model value.
Search For The Standard Model Higgs Boson In P Anti P Interactions With The Decay Mode H W W Mu Nu Mu Anti Nu At The D0 Experiment
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Author :
language : en
Publisher:
Release Date : 2010
Search For The Standard Model Higgs Boson In P Anti P Interactions With The Decay Mode H W W Mu Nu Mu Anti Nu At The D0 Experiment written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
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.
A Search For The Standard Model Higgs Boson In The Process Zh U2192 L L B Bar B In 4 1 Fb 1 Of Cdf Ii Data
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Author :
language : en
Publisher:
Release Date : 2010
A Search For The Standard Model Higgs Boson In The Process Zh U2192 L L B Bar B In 4 1 Fb 1 Of Cdf Ii Data written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
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/c2. 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/c2. 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+l-b$ar{b}$ 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+l-), while the Higgs decays to a bottom anti-bottom quark pair (H → b$ar{b}$). 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+l-b$ar{b}$ 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+l-b$ar{b}$ 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 selectio...
Search For The Standard Model Higgs Boson In Zh U2192 V Bar V B Bar B Channel In P Bar P Collisions At U221a S
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Author :
language : en
Publisher:
Release Date : 2011
Search For The Standard Model Higgs Boson In Zh U2192 V Bar V B Bar B Channel In P Bar P Collisions At U221a S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
A search for the standard model Higgs boson is performed in 5.2 fb-1 of p$ar{p}$ 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$ar{p}$→ ZH → v$ar{v}$b$ar{b}$ production. The search is also sensitive to the WH → lvb$ar{b}$ 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$ar{p}$ → (Z/W)H) × (H → b$ar{b}$) that is a factor 4.57 expected and 3.73 observed larger than the value expected from the standard model.
Search For The Standard Model Higgs Boson In The Decay Mode H Ww Lnulnu
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Author :
language : en
Publisher:
Release Date : 2009
Search For The Standard Model Higgs Boson In The Decay Mode H Ww Lnulnu written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
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.
Search For The Standard Model Higgs Boson In The Wh U2192 V B Bar B Channel With The D0 Detector
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Author :
language : en
Publisher:
Release Date : 2009
Search For The Standard Model Higgs Boson In The Wh U2192 V B Bar B Channel With The D0 Detector written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2009 with categories.
A search for the Standard Model Higgs boson is performed in 4.0 fb-1 of p$ar{p}$ collisions at √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 and one hadronic tau decay as expected from the reaction p$ar{p}$ → WH → ? v b$ar{b}$. Boosted decision trees are used to discriminate the signal from the background. Good agreement is observed between data and expected backgrounds. For a Higgs boson mass of 115 GeV, a limit is set at 95% C.L. on the cross-section times branching fraction of (p$ar{p}$→ (Z/W)H)×(H → b$ar{b}$) which is 14 times larger than the Standard Model value.
Measurement Of P Bar P U2192 Z Br Z U2192 And Search For Higgs Bosons Decaying To At U221a S
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Author :
language : en
Publisher:
Release Date : 2008
Measurement Of P Bar P U2192 Z Br Z U2192 And Search For Higgs Bosons Decaying To At U221a S written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2008 with categories.
The resonant production of tau-lepton pairs is as interesting for the study of Standard Model (SM) physics as the production of lighter leptons pairs. For new phenomena, such as Higgs boson production or in case new particles beyond the SM would arise, the detection of (resonant) pairs of tau leptons becomes much more interesting. This is due to the fact that tau leptons are much heavier than the other leptons, which increases the chance that these new phenomena would be observed first in this channel. Unfortunately their clean detection is far more difficult than that of muons or electrons. The cross section times branching ratio ?. Br for the process p$ar{p}$ → Z → ?+?- was measured at √s = 1.96 GeV using 1.0 fb-1 of data collected by the D0 experiment. This measurement was performed in the channel in which one of the tau leptons decays to a muon and neutrinos, while the other decays either hadronically or to an electron and neutrinos. A set of 1511 events, of which about 20% estimated background, passed all selection criteria. The trigger and muon reconstruction efficiencies, as well as the efficiency for track reconstruction were obtained from data using the 'tag and probe' method on Z → ?+?- events. The multijet background was estimated from the sample of events which passed all selection criteria but in which the muon and the tau candidate had the same charge. The W → ?v + jets background was modeled by Monte Carlo simulations, but normalized to data. All the other backgrounds, as well as the efficiency for Z → ?+?- events were estimated using simulated events normalized to the theoretical calculations of cross sections at next-to-leading order or next-to-next-to-leading order. The energy of the tau candidates was corrected for the estimated response of the charged pions in the calorimeter, which is of the order 50-80%. Since the charged pion response in data was not well reproduced by the default simulation of hadronic interactions (Geisha), a different simulation (gCALOR) was used to obtain an estimated charged pion response consistent with the one measured in data. This tau energy correction method makes use of the superior resolution of the track momentum measurement compared to the resolution of the tau candidate energy as measured by the calorimeter, which leads to a better data--simulation agreement and a decrease of 10% in the resolution of the visible mass peak. The result of this measurement is ?(p$ar{p}$ → Z) • Br(Z → ?+?-) = 240 ± 8(stat) ± 12(syst) ± 15(lumi) pb, in good agreement with the theoretical predictions of 241.6$+3.6top{3.2}$ pb [79] or 251.9$+5.1top{-12}$ pb [93-95], as well as with other measurements performed by the D0 and CDF experiments in all channels in which the Z boson decays leptonically [96-100]. This is the most precise Z boson cross section measurement to date performed in the tau lepton channel at hadron colliders. The analysis demonstrates the ability of the D0 experiment to identify tau leptons decaying hadronically with good efficiency and high purity, a challenging task in p{bar p} collisions where the number of jets resembling tau leptons is very high. This achievement forms a solid basis for other analyses using hadronic tau lepton decays, such as the search for the Higgs boson decaying into tau-lepton pairs, which was performed for the last part of this thesis.
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
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Author : Dale Morgan Johnston
language : en
Publisher:
Release Date : 2010
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 written by Dale Morgan Johnston and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with Higgs bosons categories.