000002866 001__ 2866 000002866 005__ 20220220114758.0 000002866 037__ $$aBELLE2-CONF-PROC-2022-003 000002866 041__ $$aeng 000002866 100__ $$aNiharika Rout 000002866 245__ $$aFirst results of $B \to DK$ decays at Belle II 000002866 260__ $$a$$c2022-02-20 000002866 300__ $$a6 000002866 520__ $$aThis proceeding reports the first measurement of the observables related to hadronic $B$ decays containing charm mesons using 62.8 fb$^{-1}$ of dataset collected by the Belle II experiment along with the first measurement of the the CKM unitarity triangle angle $\phi_3$ from a combining Belle and Belle II datasets that correspond to integrated luminosities of 711~fb$^{-1}$ and 128~fb$^{-1}$, respectively. The measured value of $\phi_3$ is $\left(78.4 \pm 11.4 \pm 0.5 \pm 1.0 \right)^{\circ}$, where the first uncertainty is statistical, the second is the experimental systematic uncertainty and the third is from the uncertainties on external measurements of the $D$-decay strong-phase parameters. 000002866 6531_ $$aCKM, phi3 000002866 8560_ $$fniharikarout@physics.iitm.ac.in 000002866 8564_ $$uhttps://docs.belle2.org/record/2866/files/BELLE2-CONF-PROC-2022-003.pdf