The recent observations of the purely leptonic decay $\Ds \to \mu^+ \nu_{ \mu}$ and $\tau^+\nu_{ \tau}$ at CLEO-c and $B$ factory may allow a possible contribution from a charged Higgs boson. One such measurement of the decay constant $f_{ D_s}$ differs from the most precise unquenched lattice QCD calculation by 4 $\sigma$ level. Meanwhile, the measured ratio, ${ \cal BR}(\Ds \to \mu^+ \nu_{ \mu})$ / ${ \cal BR}(\Dp \to \mu^+ \nu_{ \mu})$, is larger than the standard model prediction at 2.0$\sigma$ level. We discuss that the precise measurement of the ratio ${ \cal BR}(\Ds \to \mu^+ \nu_{ \mu})$ / ${ \cal BR}(\Dp \to \mu^+ \nu_{ \mu})$ at BES-III will shed light on the presence of new intermediate particles by comparing the theoretical predictions, especially, the predictions of high precise unquenched lattice QCD calculation.
Categories: hep-ex hep-ph