Measurement of the branching fraction of $\textit{D}$

By analyzing $\textit{e}$ $\textit{e}$ collision data with an integrated luminosity of 7.9 fb collected with the BESIII detector at the center-of-mass energy of 3.773 GeV, the branching fraction of $\textit{D}$ $\textit{→ τ}$ $\textit{ν}$ is determined as = (9.9 $\textit{±}$ 1.1 $\textit{±}$ 0.5 ) $\textit{×}$ 10 . Using the most precise result ($\textit{D}$ $\textit{→ μ}$ $\textit{ν}$ ) = (3.981 $\textit{±}$ 0.079 $\textit{±}$ 0.040 ) $\textit{×}$ 10 [1], we determine $\textit{R}$ = Γ($\textit{D}$ → $\textit{τ}$ $\textit{ν}$ )/Γ($\textit{D}$ → $\textit{μ}$ $\textit{ν}$ ) = 2.49 ± 0.31, achieving a factor of two improvement in precision compared to the previous BESIII result. This measurement is in agreement with the standard model prediction of lepton flavor universality within one standard deviation.