SU(3) Breaking in Charmless B Decays

There are many charmless B decay pairs whose amplitudes are related by U spin (d <--> s) or flavor SU(3). The theoretical uncertainty in any analysis involving such pairs must take into account U-spin/SU(3) breaking. In the past, such considerations generally used theoretical input, but we show that this can be experimentally measured. We present lists of two- and three-body decay pairs from which the size of the breaking can be obtained. We detail the values of U-spin/SU(3) breaking given by the present experimental data. One pair -- Bd -> pi+ pi- and Bd -> pi- K+ -- exhibits large nonfactorizable breaking. We present other signals of SU(3) breaking in two- and three-body decays, and discuss further tests for nonfactorizable effects. Finally, we also point out that the pure-penguin decay Bs -> Kbar0 Kbar0 K0 is intriguing because it can be used to cleanly probe the Bs-Bsbar mixing phase.