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, possible 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 a 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.