CP Violation in Rare B-Meson Decays

While the Standard Model of particle physics has been highly successful in explaining a wide range of phenomena, it leaves several fundamental questions unanswered. One approach to uncovering new physics beyond the Standard Model is to search for deviations from its predictions using particle colliders like the Large Hadron Collider at CERN, Geneva. Among the most promising targets for this search are rare B-meson decays, which are heavily suppressed in the Standard Model and highly sensitive to new physics effects. This thesis explores rare B-meson decays from a phenomenological perspective, focusing on CP violation—the differences in the behaviour of matter and antimatter. We explore the effects of possible new sources of CP violation on rare B-meson decays, leading to several significant results. A central finding in this thesis concerns electron–muon universality, a principle that holds within the weak interaction of the Standard Model and is normally tested through measurements of ratios of B-meson branching fractions. We show, however, that these ratios have inherent blind spots when CP violation beyond the Standard Model is present. As such, we propose a complementary approach that addresses this issue and enables more accurate tests of electron–muon universality. In addition, we develop methods to detect and quantify the presence of CP-violating physics beyond the Standard Model. We first examine the decay of a Bs meson into two muons, a decay particularly sensitive to (pseudo-)scalar new physics effects. Here, we present a novel method with the potential to detect, for the first time, CP-violating phases in the (pseudo-)scalar sector. Next, we turn our attention to semileptonic rare B-meson decays, which have recently garnered significant attention due to discrepancies between measurements and predictions suggesting the presence of new physics. We develop methods to quantify possible CP-violating physics in these decays. The final finding addresses hadronic long-distance effects, which are notoriously difficult to calculate. While existing methods can quantify these effects using experimental data, they yield ambiguous results. We propose a novel method to resolve these ambiguities utilising the interplay between different CP asymmetries. The results presented in this thesis pave the way for a deeper experimental exploration of rare B-meson decays. They offer new methodologies to probe CP violation and its role in physics beyond the Standard Model, contributing in a small way to a deeper understanding of the fundamental forces that govern the universe.