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Author: Publisher: ISBN: Category : Languages : en Pages : 274
Book Description
I present a search for the standard model Higgs boson, H, produced in association with a W boson in data events containing a charged lepton (electron or muon), missing energy, and two or three jets. The data analysed correspond to 9.7 fb-1 of integrated luminosity collected at a center-of-momentum energy of √s = 1.96 TeV with the D0 detector at the Fermilab Tevatron p$ar{p}$ collider. This search uses algorithms to identify the signature of bottom quark production and multivariate techniques to improve the purity of H → b$ar{b}$ production. We validate our methodology by measuring WZ and ZZ production with Z → b$ar{b}$ and find production rates consistent with the standard model prediction. For a Higgs boson mass of 125 GeV, we determine a 95% C.L. upper limit on the production of a standard model Higgs boson of 4.8 times the standard model Higgs boson production cross section, while the expected limit is 4.7 times the standard model production cross section. I also present a novel method for improving the energy resolution for charged particles within hadronic signatures. This is achieved by replacing the calorimeter energy measurement for charged particles within a hadronic signature with the tracking momentum measurement. This technique leads to a ̃20% improvement in the jet energy resolution, which yields a ̃7% improvement in the reconstructed dijet mass width for H → b$ar{b}$ events. The improved energy calculation leads to a ̃5% improvement in our expected 95% C.L. upper limit on the Higgs boson production cross section.
Author: Publisher: ISBN: Category : Languages : en Pages : 274
Book Description
I present a search for the standard model Higgs boson, H, produced in association with a W boson in data events containing a charged lepton (electron or muon), missing energy, and two or three jets. The data analysed correspond to 9.7 fb-1 of integrated luminosity collected at a center-of-momentum energy of √s = 1.96 TeV with the D0 detector at the Fermilab Tevatron p$ar{p}$ collider. This search uses algorithms to identify the signature of bottom quark production and multivariate techniques to improve the purity of H → b$ar{b}$ production. We validate our methodology by measuring WZ and ZZ production with Z → b$ar{b}$ and find production rates consistent with the standard model prediction. For a Higgs boson mass of 125 GeV, we determine a 95% C.L. upper limit on the production of a standard model Higgs boson of 4.8 times the standard model Higgs boson production cross section, while the expected limit is 4.7 times the standard model production cross section. I also present a novel method for improving the energy resolution for charged particles within hadronic signatures. This is achieved by replacing the calorimeter energy measurement for charged particles within a hadronic signature with the tracking momentum measurement. This technique leads to a ̃20% improvement in the jet energy resolution, which yields a ̃7% improvement in the reconstructed dijet mass width for H → b$ar{b}$ events. The improved energy calculation leads to a ̃5% improvement in our expected 95% C.L. upper limit on the Higgs boson production cross section.
Author: Savanna Marie Shaw Publisher: ISBN: 9781303570667 Category : Electronic dissertations Languages : en Pages : 242
Book Description
I present a search for the standard model Higgs boson, H, produced in association with a W boson in data events containing a charged lepton (electron or muon), missing energy, and two or three jets. The data analysed correspond to 9.7 fb-1 of integrated luminosity collected at a center-of-momentum energy of √s = 1.96 TeV with the D0 detector at the Fermilab Tevatron p$\bar{p}$ collider. This search uses algorithms to identify the signature of bottom quark production and multivariate techniques to improve the purity of H → b$\bar{b}$ production. We validate our methodology by measuring WZ and ZZ production with Z → b$\bar{b}$ and find production rates consistent with the standard model prediction. For a Higgs boson mass of 125 GeV, we determine a 95% C.L. upper limit on the production of a standard model Higgs boson of 4.8 times the standard model Higgs boson production cross section, while the expected limit is 4.7 times the standard model production cross section. I also present a novel method for improving the energy resolution for charged particles within hadronic signatures. This is achieved by replacing the calorimeter energy measurement for charged particles within a hadronic signature with the tracking momentum measurement. This technique leads to a ~ 20% improvement in the jet energy resolution, which yields a ~ 7% improvement in the reconstructed dijet mass width for H → b$\bar{b}$ events. The improved energy calculation leads to a ~ 5% improvement in our expected 95% C.L. upper limit on the Higgs boson production cross section.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
We present a search for the standard model Higgs boson production in association with a $W$ boson in proton-antiproton collisions ($p\bar{p}\rightarrow W\̂pm H \rightarrow \ell\nu b\bar{b}$) at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector which correspond to an integrated luminosity of approximately 2.7 fb${̂-1}$. We recorded this data with two kinds of triggers. The first kind required high-p$_T$ charged leptons and the second required both missing transverse energy and jets. The search selects events consistent with a signature of a single lepton ($e\̂pm/\mu\̂pm$), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method and a jet probability tagging method. Kinematic information is fed in an artificial neural network to improve discrimination between signal and background. The search finds that both the observed number of events and the neural network output distributions are consistent with the standard model background expectations, and sets 95% confidence level upper limits on the production cross section times branching ratio. The limits are expressed as a ratio to the standard model production rate. The limits range from 3.6 (4.3 expected) to 61.1 (43.2 expected) for Higgs masses from 100 to 150 GeV/$c{̂2}$, respectively.
Author: Martin J. Frank Publisher: ISBN: Category : Languages : en Pages :
Book Description
We present a search for a standard model Higgs boson produced in association with a W boson using data collected with the CDF II detector from proton/antiproton collisions at a center of mass energy of 1.96 TeV. The search is performed in the WH channel where the W boson decays leptonically and the Higgs boson decays to a bottom/antibottom quark pair. The two quarks usually fragment into two jets, but sometimes a third jet can be produced via gluon radiation, so we have increased the standard two-jet sample by including events that contain three jets. We reconstruct the Higgs boson using two or three jets depending on the kinematics of the event. We find an improvement in our search sensitivity using the larger sample together with this multijet reconstruction technique. Our data show no evidence of a Higgs boson, so we set 95% confidence level upper limits on the WH production rate. We set limits between 3.36 and 28.7 times the standard model prediction for Higgs boson masses ranging from 100 to 150 GeV/c^2.
Author: Publisher: ISBN: Category : Languages : en Pages : 177
Book Description
We present a search for a standard model Higgs boson produced in association with a W boson using data collected with the CDF II detector from p$ar{p}$ collisions at √s = 1.96 TeV. The search is performed in the WH → lvb$ar{b}$ channel. The two quarks usually fragment into two jets, but sometimes a third jet can be produced via gluon radiation, so we have increased the standard two-jet sample by including events that contain three jets. We reconstruct the Higgs boson using two or three jets depending on the kinematics of the event. We find an improvement in our search sensitivity using the larger sample together with this multijet reconstruction technique. Our data show no evidence of a Higgs boson, so we set 95% confidence level upper limits on the WH production rate. We set limits between 3.36 and 28.7 times the standard model prediction for Higgs boson masses ranging from 100 to 150 GeV/c2.
Author: Publisher: ISBN: Category : Languages : en Pages : 195
Book Description
In this thesis a direct search for the Standard Model Higgs boson production in association with a W boson at the CDF detector in the Tevatron is presented. This search contributes predominantly in the region of low mass Higgs region, when the mass of Higgs boson is less than about 135 GeV. The search is performed in a final state where the Higgs boson decays into two b quarks, and the W boson decays leptonically, to a charged lepton (it can be an electron or a muon) and a neutrino. This work is organized as follows. Chapter 2 gives an overview of the Standard Model theory of particle physics and presents the SM Higgs boson search results at LEP, and the Tevatron colliders, as well as the prospects for the SM Higgs boson searches at the LHC. The dataset used in this analysis corresponds to 4.8 fb−1 of integrated luminosity of p{bar p} collisions at a center of mass energy of 1.96 TeV. That is the luminosity acquired between the beginning of the CDF Run II experiment, February 2002, and May 2009. The relevant aspects, for this analysis, of the Tevatron accelerator and the CDF detector are shown in Chapter 3. In Chapter 4 the particles and observables that make up the WH final state, electrons, muons, E{sub T}, and jets are presented. The CDF standard b-tagging algorithms to identify b jets, and the neural network flavor separator to distinguish them from other flavor jets are also described in Chapter 4. The main background contributions are those coming from heavy flavor production processes, such as those coming from Wbb, Wcc or Wc and tt. The signal and background signatures are discussed in Chapter 5 together with the Monte CArlo generators that have been used to simulate almost all the events used in this thesis. WH candidate events have a high-p{sub T} lepton (electron or muon), high missing transverse energy, and two or more than two jets in the final state. Chapter 6 describes the event selection applied in this analysis and the method used to estimate the background contribution. The Matrix Element method, that was successfully used in the single t0p discovery analysis and many other analyses within the CDF collaboration, is the multivariate technique used in this thesis to discriminate signal from background events. With this technique is possible to calculate a probability for an event to be classified as signal or background. These probabilities are then combined into a discriminant function called the Event Probability Discriminant, EPD, which increases the sensitivity of the WH process. This method is described in detail in Chapter 7. As no evidence for the signal has been found, the results obtained with this work are presented in Chapter 8 in terms of exclusion regions as a function of the mass of the Higgs boso, taking into account the full systematics. The conclusions of this work to obtain the PhD are presnted in Chapter 9.
Author: Adrian Buzatu Publisher: ISBN: Category : Languages : en Pages :
Book Description
The Higgs boson is the only elementary particle predicted by the Standard Model (SM) that has not yet been observed experimentally. If it exists, it explains the spontaneous electroweak symmetry breaking and the origin of mass for gauge bosons and fermions. We test the validity of the SM by performing a search for the associated production of a Higgs boson and a W boson in the channel where the Higgs boson decays to a bottom-antibottom quark pair and the W boson decays to a charged lepton and a neutrino (the WH channel). We study a dataset of proton-antiproton collisions at a centre-of-mass energy of 1.96 TeV provided by the Tevatron accelerator, corresponding to an integrated luminosity of 5.7 inverse femtobarns, and recorded using the Collider Detector at Fermilab (CDF). We select events consistent with the signature of exactly one charged lepton (electron or muon), missing transverse energy due to the undetected neutrino (MET) and two collimated streams ...
Author: Giulia Di Gregorio Publisher: Springer Nature ISBN: 3031200136 Category : Science Languages : en Pages : 229
Book Description
The analysis described in this thesis is the search for the Higgs boson, decaying into bb pair, in the associated production with a vector boson, in the extreme Higgs boson transverse momentum region where the Higgs boson is reconstructed using the large-R jet technique. The use of the large-R jets allows to add a part of the phase space unexplored so far, which is particularly sensitive to possible new physics. The analysed data have been collected at LHC by the ATLAS detector between 2015 and 2018 at a centre-of-mass energy of √s = 13 TeV. The same dataset has been used to perform the differential pp → ZH and pp → WH cross-section measurements used to extract the information on the Higgs couplings and to put limits on Beyond the Standard Model effects. Furthermore the analysis has been re-used to perform a cross-section measurement of the diboson ZZ and WZ processes because the diboson and the Higgs processes have a similar topology. For the first time the ZZ(bb) and WZ(bb) cross-sections are measured at √s = 13 TeV and the observed cross-section measurements are consistent with the Standard Model predictions.
Author: Publisher: ISBN: Category : Languages : en Pages :
Book Description
We present a search for standard model Higgs boson production in association with a W boson in proton-antiproton collisions (p{bar p} → W{sup {+-}}H → l[nu]b{bar b}) at a center of mass energy of 1.96 TeV. The search employs data collected with the CDF II detector that correspond to an integrated luminosity of approximately 1.9 fb−1. We select events consistent with a signature of a single charged lepton (e{sup {+-}}/[mu]{sup {+-}}), missing transverse energy, and two jets. Jets corresponding to bottom quarks are identified with a secondary vertex tagging method, a jet probability tagging method, and a neural network filter. We use kinematic information in an artificial neural network to improve discrimination between signal and background compared to previous analyses. The observed number of events and the neural network output distributions are consistent with the standard model background expectations, and we set 95% confidence level upper limits on the production cross section times branching fraction ranging from 1.2 to 1.1 pb or 7.5 to 102 times the standard model expectation for Higgs boson masses from 110 to 150 GeV/c2, respectively.
Author: Francesco Pandolfi Publisher: Springer Science & Business Media ISBN: 3319009036 Category : Science Languages : en Pages : 137
Book Description
The theoretical foundations of the Standard Model of elementary particles relies on the existence of the Higgs boson, a particle which has been revealed for the first time by the experiments run at the Large Hadron Collider (LHC) in 2012. As the Higgs boson is an unstable particle, its search strategies were based on its decay products. In this thesis, Francesco Pandolfi conducted a search for the Higgs boson in the H → ZZ → l + l - qq Decay Channel with 4.6 fb -1 of 7 TeV proton-proton collision data collected by the Compact Muon Solenoid (CMS) experiment. The presence of jets in the final state poses a series of challenges to the experimenter: both from a technical point of view, as jets are complex objects and necessitate of ad-hoc reconstruction techniques, and from an analytical one, as backgrounds with jets are copious at hadron colliders, therefore analyses must obtain high degrees of background rejection in order to achieve competitive sensitivity. This is accomplished by following two directives: the use of an angular likelihood discriminant, capable of discriminating events likely to originate from the decay of a scalar boson from non-resonant backgrounds, and by using jet parton flavor tagging, selecting jets compatible with quark hadronization and discarding jets more likely to be initiated by gluons. The events passing the selection requirements in 4.6 fb -1 of data collected by the CMS detector are examined, in the search of a possible signal compatible with the decay of a heavy Higgs boson. The thesis describes the statistical tools and the results of this analysis. This work is a paradigm for studies of the Higgs boson with final states with jets. The non-expert physicists will enjoy a complete and eminently readable description of a proton-proton collider analysis. At the same time, the expert reader will learn the details of the searches done with jets at CMS.
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Author: Savanna Marie Shaw
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Author: Martin J. Frank
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Author: Adrian Buzatu
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Author: Francesco Pandolfi