Direct Measurement of the Pseudoscalar Decay Constant fD+

BES Collaboration

The absolute branching fraction of $D^{+}\to {\mu }^{+}\nu$ has been directly measured by an analysis of a data sample of about 33 $\mathrm{p}{\mathrm{b}}^{-1}$ collected around $\sqrt{s}=3.773$ GeV with…