Charm physics at BESIII

Abstract: The study of mesons and baryons which contain at least one charm quark is referred to as open charm physics. It offers the possibility to study up-type quark transitions. Since the $c$ quark can not be treated in any mass limit, theoretical predictions are difficult and experimental input is crucial. BESIII collected large data samples of $e^{+}e^{-}$ collisions at several charm thresholds. The at-threshold decay topology offers special opportunities to study open charm decays. We present a selection of recent BESIII results. Branching fractions and the $D_{s}^{+}$ decay constant are measured using the leptonic decays to $\mu^{+}\nu$ and $\tau^{+}\nu$. From a data sample of $0.482 fb^{-1}$ collected at the $D_{s}^{+}D_{s}^{-}$ threshold we measure $f_{Ds}=(241 \pm 16.3(stat.) \pm 6.6(sys.)) MeV$. BESIII recently found preliminary evidence of the decay $D_{s}^{+}\rightarrow\tau^{+}\nu$ and with a significance larger than $4 \sigma$ using $2.81 fb^{-1}$ of data at the $D^0\overline{D^0}$ threshold. Using the same data sample the decay $D^0\rightarrow K^0_{S/L} \pi^0(\pi^0)$ is analysed. The branching fractions are measured and using the $CP$ eigenstates $K_{S/L}^0\pi^0$ the $D^0$ mixing parameter $y_{CP} = (0.98 \pm 2.43)\%$ is measured.