Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

An accurate determination of the angle γ of the Unitary Triangle is one of the most important goals of the LHCb experiment. The LHCb detector is a single-arm spectrometer at the LHC, optimised for beauty and charm flavour physics. As the angle γ is the least experimentally constrained parameter of the Unitary Triangle, its precise experimental determination can be used to test the validity of the Standard Model. The Unitary Triangle phase γ can be extracted in B → DK decays at tree-level, exploiting the interference between b → c(ūs) and b → u(c̄s) transitions. This interference is sensitive to γ and can give measurable charge asymmetries. In particular, γ ≠ 0 is required to produce direct CP violation in B decays and this is the only CP-violating mechanism for the decay of charged B^± mesons. In this thesis, an analysis of CP violation in B^± → DK^± and B^± → Dπ^± decays is presented, where the D meson is reconstructed in the two-body final states: K^±π^∓, K⁺K⁻, π⁺π⁻ and π^±K^∓. The analysis uses the full 2011 LHCb dataset of 1.0 fb^-1, collected from pp collisions at √s = 7 TeV. Several CP-related quantities, e.g the ratio of B → DK and B → Dπ branching fractions and their charge asymmetries, are measured via a simultaneous fit to the invariant mass distributions of the modes considered. The suppressed B^± → DK^± mode is observed for the first time with ≈ 10σ significance. Once all measurements are combined, direct CP violation is established in B^± decays with a total significance of 5.8σ.

The CP violating phase β^J/ψφ_s is measured in decays of B⁰_s → J/ψφ. This measurement uses 5.2 fb^-1 of data collected in √s = 1.96 TeV p‾p collisions at the Fermilab Tevatron with the CDF Run-II detector. CP violation in the B⁰_s-‾B⁰_sbar system is predicted to be very small in the Standard Model. However, several theories beyond the Standard Model allow enhancements to this quantity by heavier, New Physics particles entering second order weak mixing box diagrams. Previous measurements have hinted at a deviation from the Standard Model expectation value for β^J/ψφ_s with a significance of approximately 2σ. The measurement described in this thesis uses the highest statistics sample available to date in the B⁰_s → J/ψφ decay channel, where J/ψ → μ⁺ μ^- and φ → K⁺K^-. Furthermore, it contains several improvements over previous analyses, such as enhanced signal selection, fully calibrated particle ID and flavour tagging, and the inclusion of an additional decay component in the likelihood function. The added decay component considers S-wave states of KK pairs in the B⁰_s → J/ψK⁺K^- channel. The results are presented as 2-dimensional frequentist confidence regions for β^J/ψφ<sub >s</sub> and ΔΓ (the width difference between the B⁰_s mass eigenstates), and as a confidence interval for β^J/ψφ_s of [0.02,0.52] U [1.08, 1.55] at the 68% confidence level. The measurement of the CP violating phase obtained in this thesis is complemented by the world's most precise measurement of the lifetime τ_s = 1.53 ± 0.025 (stat.) ± 0.012 (syst.) ps and decay width difference ΔΓ = 0.075 ± 0 .035 (stat.) ± 0.01 (syst.) ps⁻¹ of the B⁰_s meson, with the assumption of no CP violation.

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

This thesis presents two studies of charged charm meson decays using proton- proton collision data, corresponding to an integrated luminosity of 3 fb⁻¹, recorded by the LHCb experiment. A search for D_(s)^&plus; &rarr; &pi;^&plus;&mu;^&plus;&mu;^- decays is performed. Rare decays of charged charm mesons have not previously been observed unlike their counterpart B meson and kaon decays. Such decays are c &rarr; u quark transitions and take place via loop diagrams within the Standard Model. Measurements of their branching fractions are an indirect test of New Physics, whose virtual contributions may enhance such quantities. No signals are observed and the 90&percnt; (95&percnt;) CL limits on the branching fractions, the most stringent to date, are found to be, B(D^&plus; &rarr; &pi;^&plus;&mu;^&plus;&mu;^-) &LT; 2.9 (3.3) × 10^-8, B(D_s^&plus; &rarr; &pi;^&plus;&mu;^&plus;&mu;^-) &LT; 1.76 (1.91) × 10^-7. The charge asymmetry measurement of D+ &rarr; &pi;+&pi;0 using &pi;0 &rarr; e^&plus;e^-&gamma; decays is also described. Charge asymmetry in the Standard Model is expected to be small for charm meson decays. Any measured deviation from zero would be evidence of New Physics. This decay has not previously been observed at a hadron collider and the measurement acts as a 'proof of principle' study allowing a future analysis to examine the decay mode. No evidence of CP violation is found.

Using data equivalent to an integrated luminosity of 3 fb⁻¹ collected by the LHCb experiment during Run I (2011-2012), studies of beauty mesons decaying to a final state containing open charm are performed, concluding with a number of new results. Direct CP-violation is explored in <i>B</i>^± → <i>Dh</i>^± decays through several measurements of CP violating observables, where the charmed meson <i>D</i> is reconstructed in both 2-track and 4-track final states. A measurement of the <i>B</i>^± production asymmetry at LHCb is reported using <i>B</i>^± → <i>D</i>π^± decays, and a complementary measurement of the CP asymmetry in <i>B</i>^± → <i>J</i>/ψ<i>K</i>^± decays made. A search for the rare <i>B</i>_c− → <i>D</i>(*)π⁻ and B_c− → <i>D</i> (*)<i>K</i>⁻ decays concludes this work.

This thesis documents searches for direct CP violation in the Cabibbo-suppressed D+ to K-K+pi+ decay at the LHCb experiment. Two complementary analyses are described. Direct CP-violating asymmetries are predicted to exist in singly Cabibbo-suppressed charm decays with magnitudes of up to O(0.001) in the Standard Model, and can be enhanced to the percent level by contributions from new physics. No such asymmetry has yet been observed. The LHCb detector is a forward spectrometer with a precise vertex detector and powerful particle identification capabilities, designed to collect large, pure samples of charm and $B$ decays. Data collected at LHCb in 2010 corresponding to an integrated luminosity of 35pb^-1 are used to perform a model-independent search for direct CP violation in the D+ to K-K+pi+ decay. The Dalitz plot is divided into bins and a chi^2 test of the compatibility of the dataset with no CP violation is performed. No evidence of CP violation is found. A second search for CP violation in the region of the D+ to K-K+pi+ Dalitz plot around the phi resonance is described. The charge asymmetry in this decay is calculated and compared to that in the control channel D+ to Ks(pi+pi-)pi+. The 1.0fb^-1 of data collected at LHCb in 2011 are used. The CP-violating asymmetry is found to be (-0.04+/-0.14+/-0.14)% where the uncertainties are statistical and systematic, respectively. A new observable sensitive to CP violation that varies across the phi resonance is defined and measured, and is consistent with no CP violation at the current level of sensitivity. In addition, the CP-violating asymmetry in the decay Ds+ to Ks pi+ is determined to be (0.61+/-0.83+/-0.14)%. There is no evidence for CP violation in either channel. The prospects for new results using data collected in 2012 are very promising and a significant improvement in our understanding of these decays is anticipated.

In dieser Dissertation untersuchen wir CP verletzende Effekte von MSSM-Phasen in Produktion und Zwei-Teilchen-Zerfaellen von Neutralinos, Charginos und Sfermionen. Fuer verschiedene supersymmetrische Prozesse definieren und berechnen wir CP-ungerade Asymmetrien, welche auf Spatprodukten basieren. Wir zeigen numerische Ergebnisse fuer Elektron-Positron-Kollisionen an einem zukuenftigen Linearbeschleuniger mit einer Energie von 500 - 800 GeV, hoher Luminositaet und longitudinal polarisierten Strahlen. / In this thesis we analyze CP violating effects of MSSM phases in production and two-body decays of neutralinos, charginos and sfermions. For different supersymmetric processes we define and calculate CP-odd asymmetries, which base on triple products. We present numerical results for electron-positron collisions at a future linear collider with a center of mass energy of 500-800 GeV, high luminosity and longitudinally polarized beams.

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