Physical Review D, vol.101, no.7, 2020 (SCI-Expanded)
© 2020 authors. Published by the American Physical Society.We report the first observation of the semimuonic decay D+→ωμ+νμ using an e+e- collision data sample corresponding to an integrated luminosity of 2.93 fb-1 collected with the BESIII detector at a center-of-mass energy of 3.773 GeV. The absolute branching fraction of the D+→ωμ+νμ decay is measured to be BD+→ωμ+νμ=(17.7±1.8stat±1.1syst)×10-4. Its ratio with the world average value of the branching fraction of the D+→ωe+νe decay probes lepton flavor universality and it is determined to be BD+→ωμ+νμ/BD+→ωe+νePDG=1.05±0.14, in agreement with the standard model expectation within one standard deviation.