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

TL;DR

This paper measures the branching fraction of the decay $D^+ o au^+ u_ au$ using BESIII data, confirming lepton flavor universality with improved precision and comparing it to the muon decay channel.

Contribution

First precise measurement of $D^+ o au^+ u_ au$ branching fraction with improved accuracy, supporting lepton flavor universality.

Findings

Measured $ranching$ as $(9.9 imes 10^{-4})$ with uncertainties.

Determined ratio $R_{ au/ ext{mu}}$ as $2.49 imes$ with reduced error.

Results agree with Standard Model predictions within one standard deviation.

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 $\mathcal{B}=(9.9\pm 1.1_\mathrm{stat}\pm 0.5_\mathrm{syst})\times10^{-4}$. Taking the most precise result $\mathcal{B}(D^+\to\mu^+\nu_{\mu})=(3.981\pm 0.079_\mathrm{stat}\pm0.040_\mathrm{syst})\times10^{-4}$, we determine $R_{\tau/\mu} = \Gamma(D^+\to\tau^+\nu_{\tau})/\Gamma(D^+\to\mu^+\nu_{\mu})= 2.49\pm0.31$, 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.