Martin Heck (Karlsruhe Institute of Technology)
Leptonic decays of B mesons are well understood in the Standard Model (SM) and highly suppressed due to helicity conservation. The leptonic branching fraction measurements can provide stringent constraints on New Physics, where particles or forces outside of the SM can suppress or enhance the decay rate. Experimentally, due to the small branching fractions, it is a challenge to measure the decay rates and this requires intense B-meson beams and sophisticated analysis techniques for signal selection. We review the recent results from B factories where the clean e+e- environment and excellent detector performances allow us to study B-meson decays into a charged lepton and a neutrino, as well as their implications for New Physics searches.