Observation of $B^{+}\to b_1^{+}{K}^0$ and search for $B$-meson decays to $b_1^0{K}^0$ and $b_1{\pi }^0$

We present the results of searches for decays of $B$ mesons to final states with a $b_1$ meson and a neutral pion or kaon. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent $465\times {10}^6$ $B\overline{B}$ pairs produced in $e^{+}{e}^{-}$ annihilation. The results for the branching fractions are, in units of ${10}^{-6}$, $\mathcal{B}(B^{+}\to b_1^{+}{K}^0)=9.6\pm 1.7\pm 0.9$, $\mathcal{B}(B^0\to b_1^0{K}^0)=5.1\pm 1.8\pm 0.5$ ($<7.8$), $\mathcal{B}(B^{+}\to b_1^{+}{\pi }^0)=1.8\pm 0.9\pm 0.2$ ($<3.3$), and $\mathcal{B}(B^0\to b_1^0{\pi }^0)=0.4\pm 0.8\pm 0.2$ ($<1.9$), with the assumption that $\mathcal{B}(b_1\to \omega \pi )=1$. We also measure the charge asymmetry ${\mathcal{A}}_{\mathrm{ch}}(B^{+}\to b_1^{+}{K}^0)=-0.03\pm 0.15\pm 0.02$. The first error quoted is statistical, the second systematic, and the upper limits in parentheses indicate the 90% confidence level.

Figure 1

Distributions for signal-enhanced subsets (see text) of the data projected onto the fit observables for the decay $B^{+}\to b_1^{+}{K}^0$: (a) $m_{\mathrm{ES}}$, (b) $\Delta E$, (c) $\mathcal{F}$, (d) $m({\pi }^{+}{\pi }^{-}{\pi }^0)$ for the $\omega$ candidate, and (e) $m(\omega \pi )$ for the $b_1$ candidate. The solid lines represent the results of the fits, and the dashed and dot-dashed lines the signal and background contributions, respectively.

Figure 2

Distributions for signal-enhanced subsets (see text) of the data projected onto $m_{\mathrm{ES}}$ (a), (c), (e) and $\Delta E$ (b), (d), (f) for the decays $B^0\to b_1^0{K}^0$ (a), (b), $B^{+}\to b_1^{+}{\pi }^0$ (c), (d), and $B^0\to b_1^0{\pi }^0$ (e), (f). The solid lines represent the results of the fits, and the dashed and dot-dashed lines the signal and background contributions, respectively.