Precision Measurement of C P Violation and Branching Fractions in B ± → K S 0 h ± ( h = π , K ) Decays and Search for the Rare Decay B c ± → K S 0 K ±

The decay B^{±}→K_{S}^{0}π^{±}, with a CP asymmetry expected to be close to zero in the standard model, is theoretically clean and sensitive to potential new physics. An analysis of the decays B^{±}→K_{S}^{0}π^{±} and B^{±}→K_{S}^{0}K^{±} is performed using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb^{-1}. The CP asymmetries are determined to be A^{CP}(B^{±}→K_{S}^{0}π^{±})=-0.028±0.009±0.009 and A^{CP}(B^{±}→K_{S}^{0}K^{±})=0.118±0.062±0.031, and the branching fraction ratio is measured to be B(B^{±}→K_{S}^{0}K^{±})/B(B^{±}→K_{S}^{0}π^{±})=0.055±0.004±0.002, where the first uncertainties are statistical and the second are systematic. These results are the most precise measurements of these quantities to date. A search for the rare decay B_{c}^{±}→K_{S}^{0}K^{±} is also performed. No significant signal is observed, and the upper limit on the product of the branching fraction ratio B(B_{c}^{±}→K_{S}^{0}K^{±})/B(B^{±}→K_{S}^{0}π^{±}) and the fragmentation-fraction ratio f_{c}/f_{u} is set to be 0.015 (0.016) at the 90% (95%) confidence level.