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

Abstract

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 $\mathcal{B}=(9.9\pm 1.1_{\mathrm{stat}}\pm 0.5_{\mathrm{syst}})\times 10^{-4}$. Taking the most precise result $\mathcal{B}(D^{+}\to {\mu }^{+}{\nu }_{\mu })=(3.981\pm 0.079_{\mathrm{stat}}\pm 0.040_{\mathrm{syst}})\times 10^{-4}$, we determine $R_{\tau /\mu }=\Gamma (D^{+}\to {\tau }^{+}{\nu }_{\tau })/\Gamma (D^{+}\to {\mu }^{+}{\nu }_{\mu })=2.49\pm 0.31$, 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.

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