| Summary: | Abstract The LHCb experiment measured the time-dependent CP asymmetries C KK and S KK in B s → K + K − decay. Combining with the corresponding CP asymmetries C ππ and S ππ in B → π + π − decay, we find that the size of U-spin breaking in this system is of order 20%. Moreover, the data suggest that these effects are dominated by factorizable contributions. We further study the constraints on new physics contributions to b → u u ¯ q $$ u\overline{u}q $$ (q = s, d). New physics that is minimally flavor violating (MFV) cannot be distinguished from the Standard Model (SM) in these decays. However, new physics that is not MFV can mimic large U-spin breaking. Requiring that the U-spin breaking parameters remain below the size implied by the data leads to a lower bound of 5 − 10 TeV on the scale of generic new physics. If the new physics is subject to the selection rules that follow from the Froggatt-Nielsen (FN) mechanism or from General Minimal Flavor Violation (GMFV), the bound is relaxed to 2 TeV.
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