Run IIa of the D0 experiment at the Tevatron took place between Spring 2002 and Spring 2006, collecting approximately 1.2 fb{sup -1} of data. A fundamental principal of the D0 computing model is the utilization of globally distributed computing resources as part of a grid. In particular use is made of the 'SAMGrid'. The first part of this thesis describes the work undertaken at Imperial College on several D0 distributed computing projects. These included the deployment and development of parts of the SAMGrid software suite, and participation in the Winter 2003/2004 data reprocessing effort. One of the major goals of the D0 experiment is the observation of mixing in the B{sub s}{sup 0}-meson system. The measurement of the mixing frequency is important as it can be used to constrain the CKM matrix, which describes CP violation in the Standard Model. The second part of this thesis describes the development of an opposite side flavour tagging algorithm and its calibration using B{sup +} and B{sub d}{sup 0} meson decays. The application of this algorithm to an analysis of the B{sub s}{sup 0} meson system is then described, which lead to the world's first two-sided limit on the B{sub s}{sup 0} meson …

A first study of single diffractive central high-p{sub T} dijet events in p{bar p} collisions at center-of-mass energy {radical}s = 1.96 TeV is presented, using data recorded by the D0 detector at the Tevatron during RunIIa in 2002-2004. The total integrated luminosity corresponding to the data sample is 398 pb{sup -1}. A diffractive sample is selected using a rapidity gap approach. A precise definition of the rapidity gap constitutes the first part of the thesis. The rapidity gap is defined by means of two parts of the D0 detector--luminosity detectors and calorimeter. Luminosity detectors serve as a basic indicators of diffractive candidates and the calorimeter is used to confirm the low energy activity in the forward region (a rapidity gap). Presented studies of energy deposited in forward part of calorimeter by various types of events yield two rapidity gap definitions. Both of them use a fixed rapidity interval in calorimeter |{eta}| {element_of} [2.6,5.2] and introduce an upper limit on the energy deposited in this region. First definition, which corresponds to the lowest systematical errors, uses a limit of 10 GeV, an energy limit in the second definition is set to 3 GeV. This alternative definition corresponds to the lowest contamination …

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This dissertation describes the development andimplementation of a visible/near infrared pump/mid-infrared probeapparatus. Chapter 1 describes the background and motivation ofinvestigating optically induced structural dynamics, paying specificattention to solvation and the excitation selection rules of highlysymmetric molecules such as carotenoids. Chapter 2 describes thedevelopment and construction of the experimental apparatus usedthroughout the remainder of this dissertation. Chapter 3 will discuss theinvestigation of DCM, a laser dye with a fluorescence signal resultingfrom a charge transfer state. By studying the dynamics of DCM and of itsmethyl deuterated isotopomer (an otherwise identical molecule), we areable to investigate the origins of the charge transfer state and provideevidence that it is of the controversial twisted intramolecular (TICT)type. Chapter 4 introduces the use of two-photon excitation to the S1state, combined with one-photon excitation to the S2 state of thecarotenoid beta-apo-8'-carotenal. These 2 investigations show evidencefor the formation of solitons, previously unobserved in molecular systemsand found only in conducting polymers Chapter 5 presents an investigationof the excited state dynamics of peridinin, the carotenoid responsiblefor the light harvesting of dinoflagellates. This investigation allowsfor a more detailed understanding of the importance of structuraldynamics of carotenoids in light harvesting.

W{sup {+-}} + b{bar b} events contain the associated production of a W{sup {+-}} boson, a pair of bottom quarks (b{bar b}), and any number of additional partons. This process is of much importance at hadron collider experiments due to its role as a background source in searches for Standard Model Higgs boson and single top-quark production. In this thesis the results are presented for a measurement of the b-jet cross-section in W{sup {+-}} + b{bar b} events containing 1 or 2 jets in 695 pb{sup -1} of {radical}s =1.96 TeV p{bar p} collisions at the CDF experiment. This is the first measurement of the cross-section of W{sup {+-}} b{bar b} performed in any experiment. The cross-section is defined to be proportional to the number of b-jets from W{sup {+-}} b{bar b} events with one or two jets, and a leptonically decaying W{sup {+-}} with decay products passing kinematics cuts (p{sub T}({ell}{sup {+-}}) {ge} 20.0 GeV, |{eta}({ell}{sup {+-}})| {le} 1.1, p{sub T}({nu}) {ge} 25.0 GeV). The invariant mass distribution of jets identified as containing a long-lived hadron is fit with components for bottom, charm, and light-flavor to find the fraction due to true b-decays. Background b-jet sources are subtracted to …

The search for and study of flavor oscillations in the neutral B{sub s}B{sub s} meson system is an experimentally challenging task. It constitutes a flagship analysis of the Tevatron physics program. In this dissertation, they develop an analysis of the time-dependent B{sub s} flavor oscillations using data collected with the CDF detector. The data samples are formed of both fully and partially reconstructed B meson decays: B{sub s} {yields} D{sub s}{pi}({pi}{pi}) and B{sub s} {yields} D{sub s}lv. A likelihood fitting framework is implemented and appropriate models and techniques developed for describing the mass, proper decay time, and flavor tagging characteristics of the data samples. The analysis is extended to samples of B{sup +} and B{sup 0} mesons, which are further used for algorithm calibration and method validation. The B mesons lifetimes are extracted. The measurement of the B{sup 0} oscillation frequency yields {Delta}m{sub d} = 0.522 {+-} 0.017 ps{sup -1}. The search for B{sub s} oscillations is performed using an amplitude method based on a frequency scanning procedure. Applying a combination of lepton and jet charge flavor tagging algorithms, with a total tagging power {epsilon}'D{sup 2} of 1.6%, to a data sample of 355 pb{sup -1}, a sensitivity of 13.0 …

The authors observed a new neutral kaon decay mode, K{sub L} {yields} {pi}{sup {+-}}e{sup {-+}}{bar {nu}}e{sup +}e{sup -} for the first time. Based on the 20225 events including 1018 {+-} 25 background events, they determined the branching ratio, B(K{sub L} {yields} {pi}{sup {+-}}e{sup {-+}}{bar {nu}}e{sup +}e{sup -}; M{sub e{sup +}e{sup -}} > 5 MeV/c{sup 2}, E*{sub e{sup +}e{sup -}} > 30 MeV) = (1.281 {+-} 0.041) x 10{sup -5}. This branching ratio agrees with a theoretical prediction based on the chiral perturbation theory ({chi}PT) calculation at {Omicron}(p{sup 4}). Most of the kinematical distributions agree with the {chi}PT {Omicron}(p{sup 4}) calculation. They also measured one of the low energy coupling constants for the {chi}PT {Omicron}(p{sup 4}), L{sub 9}{sup r} = (8.0 {+-} 1.6) x 10{sup -3}. The M{sub e{sup +}e{sup -}} distribution below 100 MeV showed a 3 {sigma} deviation from the {chi}PT {Omicron}(p{sup 4}) calculation. This requires further studies in theory and experiments.

In this thesis, we report the study on one such particle called the B{sub s}{sup 0} meson made up of a bottom and a strange quark. B{sub s}{sup 0} mesons are currently produced in a great numbers only at the Tevatron and we report a study done to measure the mixing parameter {Delta}m{sub s} between the B{sub s}{sup 0} meson and its anti-particle {bar B}{sub s}{sup 0}. Mixing is the ability of a very few neutral mesons to change from their particle to their antiparticle and vice versa. Until recently there existed only a lower limit on this measurement, here we report an upper bound and a most probable value for the mixing parameter. In the following chapter, we discuss the theoretical motivation behind this study. The measurement technique and the different factors that effect the measurement are also given. In Chapter 3, we provide an overview of the experimental setup needed to perform the study. In Chapter 4, we present a new initial state flavor tagging algorithm using electrons and measurement of the B{sub d}{sup 0} mixing parameter {Delta}m{sub d} with the new technique. Details of the combined initial state tagging used in the B{sub s}{sup 0} mixing study …

The advance of High Energy Physics research using circulating accelerators strongly depends on increasing the magnetic bending field which accelerator magnets provide. To achieve high fields, the most powerful present-day accelerator magnets employ NbTi superconducting technology; however, with the start up of Large Hadron Collider (LHC) in 2007, NbTi magnets will have reached the maximum field allowed by the intrinsic properties of this superconductor. A further increase of the field strength necessarily requires a change in superconductor material; the best candidate is Nb{sub 3}Sn. Several laboratories in the US and Europe are currently working on developing Nb{sub 3}Sn accelerator magnets, and although these magnets have great potential, it is suspected that their performance may be fundamentally limited by conductor thermo-magnetic instabilities: an idea first proposed by the Fermilab High Field Magnet group early in 2003. This thesis presents a study of thermo-magnetic instability in high field Nb{sub 3}Sn accelerator magnets. In this chapter the following topics are described: the role of superconducting magnets in High Energy Physics; the main characteristics of superconductors for accelerator magnets; typical measurements of current capability in superconducting strands; the properties of Nb{sub 3}Sn; a description of the manufacturing process of Nb{sub 3}Sn strands; superconducting cables; …