Observation of the leptonic decay $D^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„$

Abstract

We report the first observation of $D^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„$ with a significance of $5.1\ddot{I}ƒ$. We measure $\mathcal{B}(D^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„)=(1.20\pm 0.24_{\text{stat.}}\pm 0.12_{\text{syst.}})\times 10^{-3}$. Taking the world average $\mathcal{B}(D^{+}\to \hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)=(3.74\pm 0.17)\times 10^{-4}$, we obtain $R_{\ddot{I}„/\hat{I}¼}=\hat{I}“(D^{+}\to \ddot{I}{„}^{+}\hat{I}{½}_{\ddot{I}}„)/\hat{I}“(D^{+}\to \hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)=3.21\pm 0.64_{\text{stat.}}\pm 0.43_{\text{syst.}}$, which is consistent with the Standard Model expectation of lepton flavor universality. Using external inputs, our results give values for the $D^{+}$ decay constant $f_{D^{+}}$ and the CKM matrix element $|V_{cd}|$ that are consistent with, but less precise than, other determinations.

8 pages, 3 figures, as published