Search for $B$-meson decays to two-body final states with $a_0$(980) mesons

We present a search for $B$ decays to charmless final states involving charged or neutral $a_0$ mesons. The data sample corresponds to $89\times {10}^6$ $B\overline{B}$ pairs collected with the BABAR detector operating at the PEP-II asymmetric-energy $B$ Factory at Stanford Linear Accelerator Center. We find no significant signals and determine the following 90% C.L. upper limits: $\mathcal{B}(B^0\to a_0^{-}{\pi }^{+})<5.1\times {10}^{-6}$, $\mathcal{B}(B^0\to a_0^{-}{K}^{+})<2.1\times {10}^{-6}$, $\mathcal{B}(B^{-}\to a_0^{-}{\overline{K}}^0)<3.9\times {10}^{-6}$, $\mathcal{B}(B^{+}\to a_0^0{\pi }^{+})<5.8\times {10}^{-6}$, $\mathcal{B}(B^{+}\to a_0^0{K}^{+})<2.5\times {10}^{-6}$, and $\mathcal{B}(B^0\to a_0^0{K}^0)<7.8\times {10}^{-6}$, where in all cases $\mathcal{B}$ indicates the product of branching fractions for $B\to a_{0}X$ and $a_0\to \eta \pi$, where $X$ indicates $K$ or $\pi$.

Figure 1

Feynman diagrams for decays involving charged $a_0$ mesons: (a) dominant and (b) $G$-parity-suppressed tree diagrams for $B^0\to a_0^{\mp }{\pi }^{\pm }$, (c) penguin diagram for the same decay mode, and (d) penguin diagram for the decay $B^0\to a_0^{-}{K}^{+}$.

Figure 2

The likelihood ratio $\mathcal{L}(S)/[\mathcal{L}(S)+\mathcal{L}(B)]$ for $a_0^{-}({\eta }_{\gamma \gamma })h^{+}$. The points represent the on-resonance data, the solid histograms are from MC generated from background (dark shaded) and background plus signal (light shaded) PDFs.

Figure 3

Projections of the $B$ candidate $m_{\mathrm{E}\mathrm{S}}$ and $\Delta E$ for (a, b) $a_0^{-}{h}^{+}$ and (c, d) $a_0^0{h}^{+}$. Points with errors represent data, solid curves the full fit functions, dashed curves the background functions (the peaking $B\overline{B}$ background component is negligible), and the dotted curve shows the kaon portion of the signal. These plots are made with a minimum requirement on the likelihood and thus do not show all events in the data samples.

Figure 4

Projections of the $B$ candidate $m_{\mathrm{E}\mathrm{S}}$ and $\Delta E$ for (a, b) $a_0^{-}{K}_S^0$ and (c, d) $a_0^0{K}_S^0$. Points with errors represent data, solid curves the full fit functions, and dashed curves the background functions. These plots are made with a minimum requirement on the likelihood and thus do not show all events in the data samples.