Evidence for the Rare Decay $B^{+}\to D_s^{+}{\pi }^0$

We have searched for the rare decay $B^{+}\to D_s^{+}{\pi }^0$. The analysis is based on a sample of $232\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the SLAC PEP-II $e^{+}{e}^{-}$ storage ring. We find 19.6 signal events, corresponding to a significance of $4.7\sigma$. The extracted signal yield including statistical and systematic uncertainties is ${20.1}_{-6.0-1.5}^{+6.8+0.4}$, and we measure $\mathcal{B}(B^{+}\to D_s^{+}{\pi }^0)=({1.5}_{-0.4}^{+0.5}\pm 0.1\pm 0.2)\times {10}^{-5}$, where the first uncertainty is statistical, the second is systematic, and the last is due to the uncertainty on the $D_s^{+}$ decay and its daughter decay branching fractions.

Figure 1

Likelihood projections on $m_{\mathrm{ES}}$ and $\Delta E$ after a cut on the signal-to-background likelihood ratio. Points with error bars: data; black solid line: result of the full fit; gray dashed curve: signal; gray dash-dotted curve: peaking background; gray solid curve: combinatorial background.