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Title: Measurement of the strong-phase difference between D⁰ and D⁻⁰ decays to K⁰sK⁺K⁻ at CLEO-c and a determination of observables related to CP violation in B±→DK± decays at LHCb
Author: Thomas, Christopher M.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2011
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A central goal of flavour physics is a precise determination of the elements of the CKM matrix, which quantifies the strength of charged-current weak interactions between quarks. Of particular interest is the angle γ in the 'b-d' unitarity triangle parameterisation of the CKM matrix. One of the most promising methods to determine γ directly is to measure CP violation in interfering B±->DK± decays, where D indicates a coherent superposition of D0 and D0bar, both of which decay to the same final state. When using this method it is essential to determine the hadronic decay parameters of the D precisely in order to reduce the systematic uncertainties on the measurement of γ. One such parameter is the strong-phase difference between D0 and D0bar decays, which must be accurately known across the entire kinematic phase space. In this thesis we present measurements related to the determination of γ at both the CLEO-c experiment at Cornell University and the LHCb experiment at CERN. Firstly, we describe a model-independent determination of the D->KsKK strong-phase difference using 818pb-1 of quantum-correlated D0-D0bar data collected by CLEO-c at the ψ(3770) resonance. We reconstruct D->KsKK decays tagged with a variety of final states. By studying these decays we determine the weighted cosine and sine of the strong-phase difference in bins across the Dalitz plane. We run simulations to estimate the impact of these measurements on a determination of γ using B±->D(KsKK)K± decays. The resulting uncertainty on γ due to the CLEO-c inputs is between 3.2° and 3.9°, depending on how the Dalitz plane is binned. Furthermore, we present a model-independent measurement of the CP content of the decay D0->KsKK in the kinematic region of the φ->KK resonance. The fraction of CP-odd events in this region is 0.76 or higher at the 90% C.L. We also present an analysis of data recorded by LHCb in 2010, corresponding to an integrated luminosity of 36.5pb-1. We reconstruct the decays B±->D(Kπ)h± and B±->D(KK)h±, where h± indicates either K± or π±. Although there are not enough events in this dataset to measure γ, we are able to measure other observables related to CP violation in the B±->Dh± system. We measure B(DK,Fav)/B(Dπ,Fav), the ratio of the branching fraction of B±->D(Kπ)K± to that of B±->D(Kπ)π±, to be 0.066 ± 0.005 ± 0.004, and B(DK,CP)/B(Dπ,CP), the ratio of the branching fraction of B±->D(KK)K± to that of B±->D(KK)π±, to be 0.093 ± 0.019 ± 0.005. We determine several CP asymmetries: A(CP+,DK), the CP asymmetry in B±->D(KK)K± decays, is measured as 0.06 ± 0.17 ± 0.07; A(CP+,Dπ), the CP asymmetry in B±->D(KK)π± decays, is found to be 0.009 ± 0.042 ± 0.011; and A(Fav,DK), the CP asymmetry in B±->D(Kπ)K± decays, is measured as -0.109 ± 0.085 ± 0.019. Finally we calculate R(CP+), the ratio of the branching fraction of B±->D(KK)K± to that of B±->D(Kπ)K±, to be 1.41 ± 0.31 ± 0.11. These results indicate that LHCb is in a strong position to make a world-leading measurement of γ with a larger data sample.
Supervisor: Wilkinson, Guy ; Ricciardi, Stefania Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Particle physics ; Flavour physics ; charm physics ; B physics ; CP violation ; LHCb ; CLEO-c