CP Violation in B → Kℓ ⁺ℓ ⁻ Decays: New Opportunities in the High-Precision Era

Experimental data on rare B-meson decays indicate deviations from Standard Model predictions. In studies of these decays, new sources of CP violation are often neglected. We discuss CP violation in the rare B-meson decays B → Kℓ ⁺ℓ ⁻(ℓ = μ, e) and point to two phenomena that arise when new sources of CP violation are included. First, the Wilson coefficients C _9ℓ and C ₁₀ℓ become complex, and we show how we can extract their values from measurements of direct and mixing-induced CP asymmetries. Second, new sources of CP violation can generate nontrivial lepton flavour universality violation. Such violation is usually measured through ratios like R _K and R _K∗, but we show that measuring only these ratios leaves a large parameter space unexplored. These results bring exciting opportunities to reveal New Physics effects in the high-precision era.