Ultra-rare B decays

A good place to look for deviations from the Standard Model is in decay modes of B mesons, like purely leptonic decays B --> lnu, for which a very long Standard Model lifetime is due to an accidental suppression of the decay amplitude. For other rare decay modes involving no hadrons in the final state (e.g., B --> gammal(+)l(-), B --> gammalnu(l), and B --> nunugamma) new results on QCD factorization in exclusive processes show that all the decay rates are given in terms of a single universal form factor. Hence, trustworthy relations between different processes can be used to test the Standard Model of electroweak interactions. Sometimes, surprisingly, a large energy expansion may allow computation when a hadron is in the final state. An example is B --> pil(+)l(-) which can be used to settle the ambiguity in a from a measurement of sin2alpha from CP asymmetries.