New strategy to explore CP violation with Bs0→K−K

The U-spin symmetry provides a powerful tool to extract the angle γ of the Unitarity Triangle and the Bs0–B¯s0 mixing phase ϕs from CP violation in the Bs0→K−K+, Bd0→π−π+ system. LHCb has obtained first results with uncertainties at the 7° level. Due to U-spin-breaking corrections, it will be challenging to reduce the uncertainty below O(5°) at Belle II and the LHCb upgrade. We propose a new strategy, using γ as input and utilizing Bs0→K−ℓ+νℓ, Bd0→π−ℓ+νℓ decays, which allows an extraction of ϕs with a future theoretical precision of up to O(0.5°), thereby matching the experimental prospects. Since Bs0→K−K+ is dominated by penguin topologies, new sources of CP violation may be revealed.