In 2001, the D0 experiment entered a new era. Run II of the Tevatron at the Fermi National Accelerator Laboratory began, and the collider became the highest energy particle accelerator in the world. Accordingly, the D0 detector had already undergone a series of upgrades in order to fully exploit the physics now within reach. These included improvements to the tracking, calorimetry, muon detection and triggering capabilities. In the Standard Model, the Higgs boson is the last piece of the puzzle that remains to be discovered. The Higgs mechanism and consequently the Higgs boson is thought to be the fundamental ingredient by which particles acquire mass, and its existence (or lack of existence) is one of the most pressing issues in particle physics today. As such, one of the main goals of the Run II physics programme at D0 is to search for it. Armed with new accelerator capabilities, D0 will be able to impose tighter constraints on the mass of the Higgs, and perhaps even detect this elusive particle. If the Higgs does exist, it will be extremely difficult to find. One of the main challenges at a hadron-hadron collider is to reduce the large QCD background that masks the …

The D0 experiment is based at the Tevatron, which is currently the world's highest-energy accelerator. The detector comprises three major subsystems: the tracking system, the calorimeter and the muon detector. Jets, seen in the calorimeter, are the most common product of the proton-proton interactions at 2TeV. This thesis is divided into two parts. The first part focuses on jets and describes the derivation of a jet energy scale using p{bar p} {yields} (Z + jets) events as a cross-check of the official D0 jet energy scale (Versions 4.2 and 5.1) which is derived using p{bar p} {yields} {gamma} + jets events. Closure tests were also carried out on the jet energy calibration as a further verification. Jets from b-quarks are commonly produced at D0, readily identified and are a useful physics tool. These require a special correction in the case where the b-jet decays via a muon and a neutrino. Thus a semileptonic correction was also derived as an addition to the standard energy correction for jets. The search for the Higgs boson is one of the largest physics programs at D0. The second part of this thesis describes a search for the Standard Model Higgs boson in the ZH …

The authors searched for decays of the type B{sub (s)}{sup 0} {yields} h{sup +}h{prime}{sup -} (where h, h{prime} = K or {pi}) in a sample corresponding to 180 pb{sup -1} of p{bar p} collisions at {radical}s = 1.96 TeV, collected by the upgraded Collider Detector at the Fermilab Tevatron. A total signal of approximately 900 events was reconstructed, and the relative branching fractions ({Beta}) of each decay mode were determined with a likelihood fit.

In this thesis we present a new technique to analyze events containing two highly energetic leptons, as a probe of the Standard Model. The philosophy is to consider the data in a more global way, as opposed to the more traditional process dependent approach of extracting a given signal over the expected backgrounds by using various kinematical requirements. We use our global technique to simultaneously measure the cross sections of the main Standard Model processes; the t{bar t}, WW and Z {yields} {tau}{tau} production from p{bar p} collisions at {radical}s = 1.96 TeV in the CDF detector at Fermilab. We select events by requiring they contain two highly energetic leptons (e{mu}, ee, or {mu}{mu}), and make no other kinematic requirements, except for the ee and {mu}{mu} channels. We then use a likelihood fit of the data in the two-dimensional phase space defined by the missing transverse energy (E{sub T}) and the number of jets in the event (N{sub jet}), to the expected Standard Model distributions, to simultaneously extract the production cross-sections of the main process contributing to our dilepton sample.

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In this thesis the author has described the first measurement performed at a hadron collider of the branching fraction of the Cabibbo-suppressed mode B{sup +} {yields} {bar D}{sup 0} K{sup +}. The analysis has been performed with 360 pb{sup -1} of data collected by the CDF II detector.

In this dissertation, they present a study of the untagged decay of B{sub s}{sup 0} {yields} J/{psi}{phi}, the final state of which is a superposition of the CP-even and CP-odd states. Within the framework of the standard model (SM), to a good approximation, the two CP eigenstates of the (B{sub s}{sup 0}, {bar B}{sub s}{sup 0}) system are equivalent to mass eigenstates. The data collected by the D0 detector between June 2002 to August 2004 (an integrated luminosity of approximately 450 pb{sup -1}) has been used for the analysis presented in this thesis. From a simultaneous fit to the B{sub s}{sup 0} candidate mass, lifetime, and the angular distribution of the decay products, they obtain the CP-odd fraction in the final state at production time to be 0.16 {+-} 0.10(stat) {+-} 0.02(syst). The average lifetime of the (B{sub s}{sup 0}, {bar B}{sub s}{sup 0}) system is measured to be 1.39{sub -0.16}{sup +0.13}(stat){sub -0.02}{sup +0.01}(syst) ps, with the relative width difference between the heavy and light mass eigenstates, {Delta}{Gamma}/{bar {Gamma}} = ({Gamma}{sup L}/{Gamma}{sup H})/{bar {Gamma}} = 0.24{sub -0.38}{sup +0.28}(stat){sub -0.04}{sup +0.03}(syst). With the additional constraint from the world average of the B{sub s}{sup 0} lifetime measurements using semileptonic decays, they find …

This thesis presents a search for physics beyond the standard model of elementary particles in events containing three or more charged leptons in the final state. The search is based on an R-parity violating supersymmetric model that assumes supersymmetric particles are pair produced at hadron colliders and the R-parity violating coupling is small enough so that these particles ''cascade'' decay into the lightest supersymmetric particle. The lightest supersymmetric particle may only decay into two charged leptons (electrons or muons) plus a neutrino through a lepton number violating interaction. Proton-antiproton collision events produced with {radical} s= 1.96 TeV are collected between March 2002 and August 2004 with an integrated luminosity of 346 pb{sup -1}. R-parity violating supersymmetry is sought for in two data samples, one with exactly three leptons and one with four or more leptons. The trilepton sample has a modest background primarily from Drell-Yan events where an additional lepton is a result of photon conversions or jet misidentification while the four or more lepton sample has an extremely low background. In the three lepton samples 6 events are observed while in the four or more lepton sample zero events are observed. These results are consistent with the standard model …

This analysis describes a search for a standard model Higgs boson produced in association with a Z boson through the decay mode ZH {yields} e{sup +}e{sup -}b{bar b} in p{bar p} collisions at {radical}s = 1.96 TeV at the Fermilab Tevatron Collider. The data sample used in this analysis corresponds to 452 pb{sup -1} of integrated luminosity accumulated with the D{null} detector. Agreement between data and standard model predictions is observed. A 95% confidence level upper exclusion limit for the {sigma}(p{bar p} {yields} ZH) x BR(H {yields} b{bar b}) channel is set between 3.2-8.2 pb for Higgs masses of 105 to 145 GeV.

Results obtained from a search for the trilepton signature {mu}{mu}{ell} (with {ell} = e, or {mu}) are combined with two complementary searches for the trilepton signatures ee{ell} and eer and interpreted in the framework of R-parity violating Supersymmetry. Pairwise, R-parity conserving production of the supersymmetric particles is assumed, followed by R-parity violating decays via an LL{bar E}-operator with one dominant coupling {lambda}{sub 122}. An LL{bar E}-operator couples two weak isospin doublet and one singlet (s)lepton fields and thus violates lepton number conservation. The data, collected with the D0 detector at the Fermilab proton-antiproton collider Tevatron, corresponds to an integrated luminosity of {integral} L dt = 360 {+-} 23 pb{sup -1}. No evident is observed, while 0.41 {+-} 0.11(stat) {+-} 0.07(sys) events are expected from Standard Model processes. The resulting 95% confidence level cross section limits on new physics producing a {mu}{mu}{ell} signature in the detector are of the order of 0.020 to 0.136 pb. They are interpreted in two different supersymmetry scenarios: the mSUGRA and the MSSM model. The corresponding lower limits on the masses of the lightest neutralino ({tilde {chi}}{sub 1}{sup 0}) and the lightest chargino ({tilde {chi}}{sub 1}{sup {+-}}) in case of the mSUGRA model are found to …