Observation of Tree-Level $B$ Decays with $s\overline{s}$ Production from Gluon Radiation

We report on our search for decays proceeding via a tree-level $b\to c$ quark transition in which a gluon radiates into an $s\overline{s}$ pair. We present observations of the decays $B^{-}\to D_s^{(*)+}{K}^{-}{\pi }^{-}$ and ${\overline{B}}^0\to D_s^{+}{K}_S^0{\pi }^{-}$ and evidence for $B^{-}\to D_s^{+}{K}^{-}{K}^{-}$ and set upper limits on the branching fractions for ${\overline{B}}^0\to D_s^{*+}{K}_S^0{\pi }^{-}$ and $B^{-}\to D_s^{*+}{K}^{-}{K}^{-}$ using $383\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ events collected by the BABAR detector at SLAC. We present evidence that the invariant mass distributions of $D_s^{(*)+}{K}^{-}$ pairs from $B^{-}\to D_s^{(*)+}{K}^{-}{\pi }^{-}$ decays are inconsistent with the phase-space model, suggesting the presence of charm resonances lying below the $D_s^{(*)+}{K}^{-}$ threshold.

Figure 1

Feynman diagram for $B^{-}\to D_s^{(*)+}{K}^{-}{\pi }^{-}$.

Figure 2

$m_{\mathrm{ES}}$ spectra for all modes as labeled. Solid curves show the fits described in the text. Dashed lines in the signal regions correspond to the peaking and nonpeaking background components of the fit. The data are the points with error bars.

Figure 3

$D_s^{(*)+}{K}^{-}$ invariant mass spectra using data (points with error bars) and nonresonant signal MC events scaled to the number of events in data (solid curves) subjected to signal selection described in the text and $m_{\mathrm{ES}}>5.270\mathrm{GeV}/c^2$. Combinatorial background is approximated and then subtracted using events outside the signal region ($m_{\mathrm{ES}}<5.265\mathrm{GeV}/c^2$).