# Charm physics at BESIII

## TL;DR

This paper reports recent experimental results from BESIII on charm meson decays, including measurements of decay constants, branching fractions, and mixing parameters, providing valuable data for understanding charm quark physics.

## Contribution

It presents new measurements of charm meson decay constants, branching fractions, and mixing parameters using BESIII data, advancing experimental knowledge in open charm physics.

## Key findings

- Measured $f_{Ds} = (241 \, ext{MeV})$ with uncertainties.
- Found preliminary evidence for $D_{s}^{+} o au^{+}
u$ decay.
- Measured $y_{CP} = (0.98 \, ext{±} \, 2.43)\%$ for $D^0$ mixing.

## 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.