Measurement of \cal{B}(D^+ --> mu^+ nu) and the Pseudoscalar Decay   Constant $f_{D^+}$
  In 60 pb-1 of data taken on the psi(3770) resonance with the CLEO-c detector, we find 8 D+ to mu+ nu event candidates that are mostly signal, containing only 1 estimated background. Using this statistically compelling sample, we measure preliminary values of B(D+ to mu+ nu) = (3.5 +- 1.4 +- 0.6)*10^{-4}, and determine f_{D+} =(201+- 41+- 17) MeV. 
D. Besson, et al, CLEO Collaboration