First Observation of $D^{+}\to \eta {\mu }^{+}{\nu }_{\mu }$ and Measurement of its Decay Dynamics

BESIII Collaboration

By analyzing a data sample corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measu…