U-spin breaking in CP asymmetries in B decays

U-spin symmetry predicts equal CP rate asymmetries with opposite signs in pairs of ΔS=0 and ΔS=1B meson decays in which initial and final states are related by U-spin reflection. Of particular interest are six decay modes to final states with pairs of charged pions or kaons, including Bs→π+K− and Bs→K+K− for which asymmetries have been reported recently by the LHCb collaboration. After reviewing the current status of these predictions, highlighted by the precision of a relation between asymmetries in Bs→π+K− and B0→K+π−, we perform a perturbative study of U-spin breaking corrections, searching for relations among asymmetries which hold to first order. No such relation is found in these six decays, in two-body decays involving a neutral kaon, and in three-body B+ decays to charged pions and kaons.