Observation of the semi-muonic decay $D^{+}\to \ddot{I}‰\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$

Abstract

We report the first observation of the semi-muonic decay $D^{+}\to \ddot{I}‰\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ using an $e^{+}{e}^{-}$ collision data sample corresponding to an integrated luminosity of $2.93{\mathrm{fb}}^{-1}$ collected with the BESIII detector at a center-of-mass energy of 3.773 GeV. The absolute branching fraction of the $D^{+}\to \ddot{I}‰\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ decay is measured to be ${\mathcal{B}}_{D^{+}\to \ddot{I}‰\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼}=(17.7\pm 1.8_{\mathrm{stat}}\pm 1.1_{\mathrm{syst}})\times 10^{-4}$. Its ratio with the world average value of the branching fraction of the $D^{+}\to \ddot{I}‰e^{+}\hat{I}{½}_e$ decay probes lepton flavor universality and it is determined to be ${\mathcal{B}}_{D^{+}\to \ddot{I}‰\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼}/{\mathcal{B}}_{D^{+}\to \ddot{I}‰e^{+}\hat{I}{½}_e}^{\mathrm{PDG}}=1.05\pm 0.14$, in agreement with the standard model expectation within one standard deviation.

8 pages, 2 figures