Study of the $D^0\to K^-μ^+ν_μ$ dynamics and test of lepton flavor universality with $D^0\to K^-\ell^+ν_\ell$ decays

Abstract

Using $e^+e^-$ annihilation data of $2.93~\mathrm{fb}^{-1}$ collected at center-of-mass energy $\sqrt{s}=3.773$ GeV with the BESIII detector, we measure the absolute branching fraction of $D^{0}\to K^{-}μ^{+}ν_μ$ with significantly improved precision: ${\mathcal B}_{D^{0}\to K^{-}μ^{+}ν_μ}=(3.413\pm0.019_{\rm stat.}\pm0.035_{\rm syst.})\%$. Combining with our previous measurement of ${\mathcal B}_{D^0\to K^-e^+ν_e}$, the ratio of the two branching fractions is determined to be ${\mathcal B}_{D^0\to K^-μ^+ν_μ}/{\mathcal B}_{D^0\to K^-e^+ν_e}=0.974\pm0.007_{\rm stat.}\pm0.012_{\rm syst.}$, which agrees with the theoretical expectation of lepton flavor universality within the uncertainty. A study of the ratio of the two branching fractions in different four-momentum transfer regions is also performed, and no evidence for lepton flavor universality violation is found with current statistics. Taking inputs from global fit in the standard model and lattice quantum chromodynamics separately, we determine $f_{+}^{K}(0)=0.7327\pm0.0039_{\rm stat.}\pm0.0030_{\rm syst.}$ and $|V_{cs}| = 0.955\pm0.005_{\rm stat.}\pm0.004_{\rm syst.}\pm0.024_{\rm LQCD}$.