Measurement of the branching fraction of $D^{+}\to {\tau }^{+}{\nu }_{\tau }$

By analyzing $e^{+}{e}^{-}$ collision data with an integrated luminosity of 7.9~fb${}^{-1}$ collected with the BESIII detector at the center-of-mass energy of 3.773~GeV, the branching fraction of $D^{+}\to {\tau }^{+}{\nu }_{\tau }$ is determined as $\mathcal{B}=(9.9\pm {1.1}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}}\pm {0.5}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}})\times {10}^{-4}$. Taking the most precise result $\mathcal{B}(D^{+}\to {\mu }^{+}{\nu }_{\mu })=(3.981\pm {0.079}_{\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t}}\pm {0.040}_{\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t}})\times {10}^{-4}$, we determine $R_{\tau \mathrm{/}\mu }=\mathrm{\Gamma }(D^{+}\to {\tau }^{+}{\nu }_{\tau })\mathrm{/}\mathrm{\Gamma }(D^{+}\to {\mu }^{+}{\nu }_{\mu })=2.49\pm 0.31$, 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.