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

Abstract

Using e+e− annihilation data of 2.93 fb−1 collected at center-of-mass energy s = 3.773 GeV with the BESIII detector, we measure the absolute branching fraction of D0→K−μ+νμ with significantly improved precision: BD0→K−μ+νμ=(3.413±0.019stat.±0.035syst.)%. Combining with our previous measurement of BD0→K−e+νe, the ratio of the two branching fractions is determined to be BD0→K−μ+νμ/BD0→K−e+νe=0.974±0.007stat.±0.012syst., 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±0.0039stat.±0.0030syst. and |Vcs|=0.955±0.005stat.±0.004syst.±0.024LQCD.