Speaker
marko staric
(J. Stefan Institute, Ljubljana, Slovenia)
Description
We search for the flavor-changing neutral current decays D0 --> mu^+ mu^- and D0 --> e^+e^-, and for the lepton-flavor violating decays D0 --> e^(+-) mu^(-+) using a large data sample collected with the Belle detector at the KEKB asymmetric-energy e^{+}e^{-} collider. We find no evidence for any of these decays. We obtain significantly improved upper limits on the branching fractions: BR(D0 --> mu^{+} mu^{-})<1.4 x 10^{-7},
BR(D0 --> e^+e^-)<7.9 x 10^{-8} and BR(D0 --> e^{+} mu^{-})+BR(D0 --> mu^{+}e^{-})<2.6 x 10^{-7} at the 90% confidence level. The purely leptonic decay B^+ --> l^+ nu (l = e, mu) is highly suppressed in the Standard Model due to lepton helicity mismatch but can be strongly enhanced in New Physics scenarios. We present the results of a search for the decays B^+ --> e^+ nu and B^+ --> mu^+ nu. We also present a search for B decays into invisible final states. The nu anti-nu signal is identified by fully reconstructing the accompanying B mesons and requiring no other charged particles and no extra energy deposited in the calorimeter.
Primary author
Collaboration BELLE
(KEK)
