### Speaker

Jiangchuan Chen
(Institute of High Energy Physics, CAS)

### Description

BESIII accumulated the world largest samples of $e^+e^-$ collision at $\sqrt(s) = 3.773$ and 4.178 GeV. The purely leptonic decays $D^+_{(s)} \to l^+\nu$, and the semi-leptonic decays of $D^0 \to K(\pi)^-e^+\nu$, $K(\pi)^-\mu^+\nu$, $\rho^- e^+\nu$; $D^+ \to K^0(\pi^0)e^+\nu$, $K^0(\pi^0) \mu^+\nu$; $D_s^+ \to K^{(*)0}e^+\nu$ and $\eta^{(')}e^+\nu$ have been studied. We will report the improved measurements of the branching fractions of these decays, of the CKM matrix elements $|V_{cs(d)}|$, of the $D_{(s)}^+$ decay constants, and of the form factors of $D_{(s)}$ semi-leptonic decays. These results are important to calibrate the LQCD calculations of $D_{(s)}^+$ decay constants and form factors as well as to test the CKM unitarity.