Tree-level contributions to the rare decays B+ --> pi+ nu anti-nu, B+ --> K+ nu anti-nu, and B+ --> K*+ nu anti-nu in the Standard Model

摘要

The tree-level contributions to the rare decays B+ --> pi+ nu anti-nu, B+ -->K+ nu anti-nu, and B+ --> K*+ nu anti-nu are analyzed and compared to thoseoccurring in K+ --> pi+ nu anti-nu, D+ --> pi+ nu anti-nu, and Ds+ --> pi+ nuanti-nu. It is shown that these purely long-distance contributions, arisingfrom the exchange of a charged lepton, can be significant in B+ decays for anintermediate tau, potentially blurring the distinction between the modes usedto extract B --> tau nu and those used to probe the genuine short-distance b--> (s,d) nu anti-nu FCNC transitions. Numerically, the tree-levelcontributions are found to account for 97%, 12% and 14% of the total B+ --> pi+nu anti-nu, B+ --> K+ nu anti-nu, and B+ --> K*+ nu anti-nu rates,respectively.