We present a search for associated production of the standard model (SM) Higgs boson and a Z boson where the Z boson decays to two leptons and the Higgs decays to a pair of b quarks in p{bar p} collisions at the Fermilab Tevatron. We use event probabilities based on SM matrix elements to construct a likelihood function of the Higgs content of the data sample. In a CDF data sample corresponding to an integrated luminosity of 2.7 fb−1 we see no evidence of a Higgs boson with a mass between 100 GeV/c2 and 150 GeV/c2. We set 95% confidence level (C.L.) upper limits on the cross-section for ZH production as a function of the Higgs boson mass m{sub H}; the limit is 8.2 times the SM prediction at m{sub H} = 115 GeV/c2.

The authors present a search for the Higgs boson in the process q{bar q} → ZN → l+l− b{bar b}. The analysis uses an integrated luminosity of 1 fb−1 of p{bar p} collisions produced at √s = 1.96 TeV and accumulated by the upgraded Collider Detector at Fermilab (CDF II). They employ artificial neural networks both to correct jets mismeasured in the calorimeter, and to distinguish the signal kinematic distributions from those of the background. They see no evidence for Higgs boson production, and set 95% CL upper limits on [sigma]{sub ZH} · [Beta](H → b{bar b}), ranging from 1.5 pb to 1.2 pb for a Higgs mass (m{sub H}) of 110 to 150 GeV/c2.

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.

This paper presents a search for standard model Higgs boson production in association with a W boson using events recorded by the CDF experiment in a dataset corresponding to an integrated luminosity of 5.6 fb−1. The search is performed using a matrix element technique in which the signal and background hypotheses are used to create a powerful discriminator. The discriminant output distributions for signal and background are fit to the observed events using a binned likelihood approach to search for the Higgs boson signal. We find no evidence for a Higgs boson, and 95% confidence level (C.L.) upper limits are set on?(p{bar p} → WH) x?(H → b{bar b}). The observed limits range from 3.5 to 37.6 relative to the standard model expectation for Higgs boson masses between m{sub H} = 100 GeV/c2 and m{sub H} = 150 GeV/c2. The 95% C.L. expected limit is estimated from the median of an ensemble of simulated experiments and varies between 2.9 and 32.7 relative to the production rate predicted by the standard model over the Higgs boson mass range studied.

This dissertation describes a search for the Standard Model Higgs boson produced in association with the Z boson via Higgs-strahlung at the CDF II detector at the Tevatron. At a Higgs boson mass between 100 GeV/c2 and 135 GeV/c2, the primary Higgs decay mode is to a pair of b quarks. The associated Z boson can decay to a pair of electrons or muons, allowing detection of a final event signature of two visible leptons and two b quarks. This final state allows reduction of large QCD backgrounds compared to a hadronic Z boson decay, leading to a more sensitive search. To increase sensitivity, standard model matrix element probabilities for ZH signal and the dominant backgrounds are used as components to a likelihood fit in signal fraction. In 2.7 fb−1 of CDF II data, we see no evidence of production of a Higgs boson with a mass between 100 GeV c2 and 150 GeV/c2. Using the Feldman-Cousins technique to set a limit, at 95% coverage and a Higgs boson mass of 115 GeV/c2, the median expected limit was 12.1 x [sigma]{sub SM} and a limit of 8.2 x [sigma]{sub SM} was observed, where [sigma]{sub SM} is the NNLO theoretical cross section of p{bar p} →ZH → l +l -b{bar b} at √s=1.96 TeV . Cross section limits are computed at a range of Higgs boson mass values between 100 GeV/c 2 and 150 GeV/c2.

The discovery in 2012 of the last elementary particle predicted by the Standard Model, the Higgs boson, has opened a new era in particle physics. One of the objectives now is to probe the coupling of the Higgs boson to other particles in order to confirm the validity of the model. The work of this thesis focused initially on the identification of jets coming from b quark at trigger level. The goal is to allow for the selection of one thousand events among the forty million produced every second at the LHC, by identifiying objects present in the final states of interesting physics processes such as the associated production of a Higgs boson decaying in a pair of b quark with a Z boson decaying into undetected neutrinos. The work then moved to the study of the coupling of the Higgs boson to the quark top, most massive particle in the Standard Model. After a study of one of the important background of the associated production of the Higgs boson and a top quark pair, a new method called matrix element method has been used to improve the discrimination between signal and background. This analysis has led to the first experimental evidence of coupling between the Higgs boson and the top quark.