First Observation Ofcpviolation and Improved Measurement of the Branching Fraction and Polarization Ofb0→d*+

We report the measurement of the branching fraction, the polarization, and the parameters of the time-dependent $CP$ violation in ${B}^{0}\ensuremath{\rightarrow}{D}^{*+}{D}^{*\ensuremath{-}}$ decays using a data sample of $772\ifmmode\times\else\texttimes\fi{}{10}^{6}B\overline{B}$ pairs, collected at the $\ensuremath{\Upsilon}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. We obtain a branching fraction of $\mathcal{B}=(7.82\ifmmode\pm\else\textpm\fi{}0.38\ifmmode\pm\else\textpm\fi{}0.63)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$, a $CP$-odd fraction of ${R}_{\ensuremath{\perp}}=0.138\ifmmode\pm\else\textpm\fi{}0.024\ifmmode\pm\else\textpm\fi{}0.006$ and, additionally, a fraction of the longitudinal component in the transversity base of ${R}_{0}=0.624\ifmmode\pm\else\textpm\fi{}0.029\ifmmode\pm\else\textpm\fi{}0.011$. The measured values of the parameters of the $CP$ violation are ${S}_{{D}^{*+}{D}^{*\ensuremath{-}}}=\ensuremath{-}0.79\ifmmode\pm\else\textpm\fi{}0.13\ifmmode\pm\else\textpm\fi{}0.03$ and ${A}_{{D}^{*+}{D}^{*\ensuremath{-}}}=0.15\ifmmode\pm\else\textpm\fi{}0.08\ifmmode\pm\else\textpm\fi{}0.04$.