Search for the $W$-exchange decays $B^0\to D_s^{(*)-}{D}_s^{(*)+}$

We report a search for the decays $B^0\to D_s^{-}{D}_s^{+}$, $B^0\to D_s^{*-}{D}_s^{+}$, and $B^0\to D_s^{*-}{D}_s^{*+}$ in a sample of $232\times {10}^6$ ${\rm Y}(4S)$ decays to $B\overline{B}$ pairs collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ storage ring. We find no significant signal and set upper bounds for the branching fractions: $\mathcal{B}(B^0\to D_s^{-}{D}_s^{+})<1.0\times {10}^{-4}$, $\mathcal{B}(B^0\to D_s^{*-}{D}_s^{+})<1.3\times {10}^{-4}$, and $\mathcal{B}(B^0\to D_s^{*-}{D}_s^{*+})<2.4\times {10}^{-4}$ at 90% confidence level.

Figure 1

$W$-exchange decay diagram for $B^0\to D_s^{(*)-}{D}_s^{(*)+}$.

Figure 2

Distributions of events in the $\Delta E$ versus $m_{\mathrm{ES}}$plane, for (i) $B^0\to D_s^{-}{D}_s^{+}$, (ii) $B^0\to D_s^{*-}{D}_s^{+}$, and (iii) $B^0\to D_s^{*-}{D}_s^{*+}$ decays after all selection criteria are applied. The box in each plot is the signal region based on studies with MC simulation as described in the text.