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 ps{sup -1} is achieved. They develop a preliminary same side kaon tagging algorithm, which is found to provide a superior tagging power of about 4.0% for the B{sub s} meson species. A study of the dilution systematic uncertainties is not reported. From its application as is to the B{sub s} samples the sensitivity is significantly increased to about 18 ps{sup -1} and a hint of a signal is seen at about 175. ps{sup -1}. They demonstrate that the extension of the analysis to the increasing data samples with the inclusion of the same side tagging algorithm is capable of providing an observation of B{sub s} mixing beyond the standard model expectation. They show also that the improved knowledge of {Delta}m{sub s} has a considerable impact on constraining the CKM matrix elements.

(Cont.) In a preliminary study, we develop a same side kaon tagging algorithm, which is found to provide a superior tagging power, of about 4.0% for the B, meson species. An evaluation of the dilution systematic uncertainties is not reported but after including the algorithm as is in the analysis the sensistivity is significantly increased to about 18 ps-'. An indication of a B, oscillation signal is seen at a frequency of about 17.5 ps-1. We show that the extension of the analysis to the increasing data samples with the inclusion of the same side tagging algorithm is capable of providing an observation of B, mixing beyond the standard model expectation. We show also that the improved knowledge of Am, has a considerable impact on constraining the CKM matrix elements.

The search for flavor oscillations in the neutral Bs - B meson system constitutes a flagship analysis of the Tevatron proton-anti-proton collider physics program and an important probe for effects due to new physics beyond the Standard Model of particles and interactions. In particular, the precise measurement of a process such as Boscillations sets a strong constraint on the parameters of quark-flavor mixing in the Standard Model. This dissertation reports the analysis which, for the first time, observed B- Bs oscillations, using data collected with the CDF detector. The sub-percent precision of the measurement is also noteworthy. The data sample used for this analysis includes fully and partially reconstructed Bdecays: ... The focus of this thesis is the algorithm of same-side-kaon tagging which provides _-0 a large fraction of the flavor-tagging power available to this analysis of B- B8 oscillations. Flavor tagging consists in assessing whether a B, meson is creates as a B_--0 or a B, state, and constitutes an important ingredient in the analysis presented in this document. The algorithm which is here described combines particle identification information and kinematic characteristics of the Bevent in an artificial neural network to provide improved tagging power E'2 of about 4.0 - 4.8%, depending on the data sample to which the algorithm is applied. The search for B1 oscillations is performed using an amplitude method based on a frequency scanning procedure. Applying a neural network-based combination of lepton, kaon and jet charge opposite-side tagging algorithms, with a total tagging power of ED2 = 1.8%, and the same-side-kaon tagging algorithm to a data sample of 1 fb-1, a signal of B- B_ oscillations with a significance greater than 5 standard deviations is found ...

I report the results of the first search for B{sub s} flavor oscillations performed at CDF II. We analyze a dataset of approximately 355 pb{sup -1} from proton-antiproton collisions at {radical}s = 1.96 TeV collected in 2002-2004 with the CDF II Detector at the Tevatron Collider. Samples of both fully reconstructed, B{sub s} {yields} D{sub s}{pi}, and partially reconstructed, B{sub s} {yields} D{sub s}/{nu}, decays are employed. A combination of tagging algorithms is used to determine the flavor of the B{sub s} mesons at production time. We fit the data using an unbinned likelihood technique which combines mass, proper decay time, and flavor tagging information of the B{sub s} candidates. Information about the oscillation frequency of the system {Delta}m{sub s} is obtained by performing an amplitude scan of the data, from which an exclusion limit: {Delta}m{sub s}> 7.9 ps{sup -1} (95% C.L.) is achieved, with a measured sensitivity of 8.4 ps{sup -1} Improvements currently under development, together with the increasing data samples, are expected to enhance the sensitivity beyond the Standard Model favored region before the end of Run II. Since the time the conference took place, part of the here mentioned improvements to the analysis have been incorporated, which result in the following updates: combined exclusion limit of {Delta}m{sub s}> 8.6 ps{sup -1}, with a measured sensitivity of 13.0 ps{sup -1}; combination with previously available measurements increases the world exclusion limit from 14.5 ps{sup -1} to 16.6 ps{sup -1} (95% C.L.).

Over the past decades the current theoretical description, the Standard Model of elementary particle physics, was solidified by many measurements as the basic theory describing fundamental particles and their interactions. It is extremely successful in explaining the high-precision data collected by experiments so far. The Standard Model includes several intrinsic parameters which have to be measured in experiments. Independent analyses of different physical processes can constrain those parameters. By combining those measurements physicists might be sensitive to physics beyond the Standard Model. If they are inconsistent it allows to get a hint on the theory that might supersede the Standard Model. The goal of the analysis presented in this thesis is to measure some of these parameters in the B{sub s} meson system. The B{sub s} meson, consisting of an anti-b and s quark, is not a pure mass eigenstate, thus allowing a B{sub s} meson to oscillate into its antiparticle via weak interacting processes. This is a general feature of any neutral meson. The history of meson mixing measurements is more then 50 years old. It was first observed in the kaon system. The oscillation in the B{sub d} system was measured very precisely by the B factories, whereas the oscillation frequency of the Bs was measured with more than 5[sigma] significance last year by CDF and first evidence for mixing in the D0 system was presented only this year.

This thesis reports a time dependent measurement of the B°{sub s}-{bar B}°{sub s} oscillation frequency [Delta]m{sub s} using semileptonic decays B°{sub s} → D−{sub s}l+X. We use a data sample of 1 fb−1 of p{bar p} collisions at √s = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron Collider to reconstruct ≈ 61, 500 semileptonic B°{sub s} decays. This analysis of B°{sub s}-{bar B}°{sub s} mixing has a sensitivity of 19.4 ps−1 and shows an evidence of B°{sub s} oscillations at [Delta]m{sub s} ≈17.75 ps−1 with an amplitude significance of ≈2. In combination with the analyses of ≈ 8,700 hadronic B°{sub s} decays at CDF, we have made the first direct observation of time-dependent B°{sub s}-{bar B}°{sub s} flavor oscillations measuring [Delta]m{sub s} = 17.77 {sup +0.09}{sub -0.10} (stat) ± 0.07 (syst) ps−1. The obtained value of [Delta]m{sub s} agrees with the Standard Model expectation. When combined with the world average values for [Delta]m{sub d}, m{sub {bar B}0} and m{sub {bar B}0s}, along with other theoretical input, this result yields the ratio of CKM matrix elements.