Angular analysis of B⁰→ K*0μ⁺μ⁻ decays with the full LHCb Run 1 and 2 data sample

The Standard Model of particle physics (SM) describes the fundamental interactions between the smallest constituents of matter with great precision. Over the past decades, it has been incredibly successful in predicting the outcome of a wide range of particle physics experiments. However, there are experimental observations that the SM in its current form can not explain. This implies the existence of yet undiscovered New Physics (NP) beyond the SM, which needs to be incorporated into the SM to complete the theory. Precision measurements of observables from flavor-changing neutral currents are highly sensitive to NP effects due to their strong suppression in the SM. Previous analyses of these types of decays displayed intriguing tensions with the SM predictions. Among the most prominent results is the measurement of the angular observables of the decay B⁰→ K*0μ⁺μ⁻ performed using data collected with the experiment during the years 2011, 2012, and 2016, where the optimized angular observable P'₅ displays local tensions with the SM prediction. This thesis presents the legacy measurement of both the -symmetry and asymmetry angular observables as well as the branching fraction of the decay B⁰→ K*0μ⁺μ⁻ using the Run 1 and 2016-2018 data sets collected with the LHCb experiment. These observables are determined in bins of the squared invariant dimuon mass (q²) using a five-dimensional maximum likelihood fit. The well-known angular observable P'₅ is measured to be P'₅ = -0.481 ± 0.073\, (stat.) ± 0.006\, (syst.) in the 4.0-6.0 GeV²/c⁴ region and P'₅ = -0.587 ± 0.055 \,(stat.) ± 0.004\, (syst.) in the 6.0-8.0 GeV²/c⁴ region.This corresponds to local discrepancies at the level of 2.6\,σ and 3.1\,σ with respect to the SM predictions calculated using the Flavio theory framework. The deviation of the Wilson coefficient Re(C₉) from the SM value determined using constraints from the angular observables, and the branching fraction is found to be Δ Re(C₉) = -0.92+0.18-0.16\, , which corresponds to a global significance of the deviation from the SM of 4.1\,σ.However, the significance of this deviation depends on assumptions made on the parameterization of the non-local form factors, which is currently a topic of debate in the theory community.