Heavy-quark symmetry violation in semileptonic decays ofDmesons

The decays of $D$ mesons to $\mathrm{Kl}\nu$ and $K^{*}l\nu$ final states exhibit significant deviations from the predictions of heavy-quark symmetry, as one might expect since the strange quark's mass is of the same order as the QCD scale. Nonetheless, in order to understand where the most significant effects might lie for heavier systems (such as $B\to \mathrm{Dl}\nu$ and $B\to D^{*}l\nu$), the pattern of these deviations is analyzed from the standpoint of perturbative QCD and $O\left(\frac{1}{m_s}\right)$ corrections. Two main effects are noted. First, the perturbative QCD corrections lead to an overall decrease of predicted rates, which can be understood in terms of production of excited kaonic states. Second, $O\left(\frac{1}{m_s}\right)$ effects tend to cancel the perturbative QCD corrections in the case of $\mathrm{Kl}\nu$ decay, while they have minimal effect in $K^{*}l\nu$ decay.