# Conclusions & Perspectives (2)

- ## Determine fB

##

- ## B -

  - B.R. = (fBu |Vub|)2 F(Gf,MB,M )
    S.M. ~ 5 10 -5
    L3 < 5.7 10 -4
  - Babar/CLEO : tough
  - (Vub ) / Vub ~ 30 %
    - difficult/unlikely task

##

- ## extrapolate from charm

  - fDs / fD+ fB /fD (use lattice QCD)
  - fDs = 255 20 31 MeV (from Ds )
    - fB = 178 25(exp.) ??? (th.)MeV
  - - charm (fDs /fD+ ) ~ 3 % (?)

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