Study of the decays $B^0\to D^{\left(*\right)+}{D}^{\left(*\right)-}$

The decays $B^0\to D^{*+}{D}^{*-},$ $B^0\to D^{*\pm }{D}^{\mp }$ and $B^0\to D^{+}{D}^{-}$ are studied in $9.7\times {10}^6\hspace{0.5em}{\rm Y}\left(4\mathrm{}\mathrm{S}\right)\to B\overline{B}$ decays accumulated with the CLEO detector. We determine $\mathcal{B}{(B}^0\to D^{*+}{D}^{*-}{)=(9.9\mathrm{}}_{-3.3}^{+4.2\mathrm{}}\left[\mathrm{stat}\right]\pm 1.2\left[\mathrm{syst}\right])\times {10}^{-4}$ and limit $\mathcal{B}{(B}^0\to D^{*\pm }{D}^{\mp })<\mathrm{}6.3\mathrm{}\times {10}^{-4}$ and $\mathcal{B}{(B}^0\to D^{+}{D}^{-})<\mathrm{}9.4\mathrm{}\times {10}^{-4}$ at 90% confidence level (C.L.). We also perform the first angular analysis of the $B^0\to D^{*+}{D}^{*-}$ decay and determine that the $\mathrm{CP}$-even fraction of the final state is greater than $0.11$ at 90% C.L. Future measurements of the time dependence of these decays may be useful for the investigation of $\mathrm{CP}$ violation in neutral B meson decays.