Title:

Measurement of the strongphase difference between D⁰ and D⁻⁰ decays to K⁰sK⁺K⁻ at CLEOc and a determination of observables related to CP violation in B±→DK± decays at LHCb

A central goal of flavour physics is a precise determination of the elements of the CKM matrix, which quantifies the strength of chargedcurrent weak interactions between quarks. Of particular interest is the angle γ in the 'bd' 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 strongphase 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 CLEOc experiment at Cornell University and the LHCb experiment at CERN. Firstly, we describe a modelindependent determination of the D>KsKK strongphase difference using 818pb1 of quantumcorrelated D0D0bar data collected by CLEOc 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 strongphase 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 CLEOc inputs is between 3.2° and 3.9°, depending on how the Dalitz plane is binned. Furthermore, we present a modelindependent measurement of the CP content of the decay D0>KsKK in the kinematic region of the φ>KK resonance. The fraction of CPodd 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 36.5pb1. 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 worldleading measurement of γ with a larger data sample.
