Improved measurement of the absolute branching fraction of $D^{+}\to {\bar{K}}^0{\mu }^{+}{\nu }_{\mu }$

By analyzing 2.93 fb${}^{-1}$ of data collected at $\sqrt{s}=3.773$ GeV with the BESIII detector, we measure the absolute branching fraction ${\mathcal B}(D^{+}\rightarrow\bar K^0\mu^{+}\nu_{\mu})=(8.72 \pm 0.07_{\rm stat.} \pm 0.18_{\rm sys.})%$, which is consistent with previous measurements within uncertainties but with significantly improved precision. Combining the Particle Data Group values of $\mathcal{B}(D^0\to K^{-}{\mu }^{+}{\nu }_{\mu })$, ${\mathcal B}(D^{+}\rightarrow\bar K^0 e^{+}\nu_{e})$,andthelifetimesofthe$D^0$and$D^+$mesonswiththevalueof${\mathcal B}(D^{+}\rightarrow\bar K^0 \mu^{+}\nu_{\mu})$ measured in this work, we determine the following ratios of partial widths: $\Gamma(D^0\to K^-\mu^+\nu_\mu)/\Gamma(D^{+}\rightarrow\bar K^0\mu^{+}\nu_{\mu})=0.963\pm0.044$and$\Gamma(D^{+}\rightarrow\bar K^0 \mu^{+}\nu_{\mu})/\Gamma(D^{+}\rightarrow\bar K^0 e^{+}\nu_{e})=0.988\pm0.033$.