Precise Measurement of the $D^0$ and $D^{+}$ Lifetimes at Belle II

We report a measurement of the $D^0$ and $D^{+}$ lifetimes using $D^0\to K^{-}{\pi }^{+}$ and $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ decays reconstructed in $e^{+}{e}^{-}\to c\overline{c}$ data recorded by the Belle II experiment at the SuperKEKB asymmetric-energy $e^{+}{e}^{-}$ collider. The data, collected at center-of-mass energies at or near the $\mathrm{\Upsilon }(4S)$ resonance, correspond to an integrated luminosity of $72{\mathrm{fb}}^{-1}$. The results, $\tau (D^0)=410.5\pm 1.1(\mathrm{stat})\pm 0.8(\mathrm{syst})\mathrm{fs}$ and $\tau (D^{+})=1030.4\pm 4.7(\mathrm{stat})\pm 3.1(\mathrm{syst})\mathrm{fs}$, are the most precise to date and are consistent with previous determinations.

Figure 1

Mass distributions of (top) $D^0\to K^{-}{\pi }^{+}$ and (bottom) $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ candidates with fit projections overlaid. The vertical dashed and (for the bottom plot) dotted lines indicate the signal regions and the sideband, respectively.

Figure 2

Decay-time distributions of (top) $D^0\to K^{-}{\pi }^{+}$ and (bottom) $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ candidates in their respective signal regions with fit projections overlaid.