Observation of $B$ Meson Decays to $b_1\pi$ and $b_{1}K$

We present the results of searches for decays of $B$ mesons to final states with a $b_1$ meson and a charged pion or kaon. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent $382\times {10}^6$ $B\overline{B}$ pairs produced in $e^{+}{e}^{-}$ annihilation. The results for the branching fractions are, in units of ${10}^{-6}$, $\mathcal{B}(B^{+}\to b_1^0{\pi }^{+})=6.7\pm 1.7\pm 1.0$, $\mathcal{B}(B^{+}\to b_1^0{K}^{+})=9.1\pm 1.7\pm 1.0$, $\mathcal{B}(B^0\to b_1^{\mp }{\pi }^{\pm })=10.9\pm 1.2\pm 0.9$, and $\mathcal{B}(B^0\to b_1^{-}{K}^{+})=7.4\pm 1.0\pm 1.0$, with the assumption that $\mathcal{B}(b_1\to \omega \pi )=1$. We also measure charge and flavor asymmetries ${\mathcal{A}}_{\mathrm{ch}}(B^{+}\to b_1^0{\pi }^{+})=0.05\pm 0.16\pm 0.02$, ${\mathcal{A}}_{\mathrm{ch}}(B^{+}\to b_1^0{K}^{+})=-0.46\pm 0.20\pm 0.02$, ${\mathcal{A}}_{\mathrm{ch}}(B^0\to b_1^{\mp }{\pi }^{\pm })=-0.05\pm 0.10\pm 0.02$, $C(B^0\to b_1^{\mp }{\pi }^{\pm })=-0.22\pm 0.23\pm 0.05$, $\Delta C(B^0\to b_1^{\mp }{\pi }^{\pm })=-1.04\pm 0.23\pm 0.08$, and ${\mathcal{A}}_{\mathrm{ch}}(B^0\to b_1^{-}{K}^{+})=-0.07\pm 0.12\pm 0.02$. The first error quoted is statistical, and the second systematic.

Figure 1

Distributions for signal-enhanced subsets of the data projected onto the fit observables for the decays: (a–e) $B^{+}\to b_1^0{\pi }^{+}$, (f–j) $B^{+}\to b_1^0{K}^{+}$, (k–o) $B^0\to b_1^{\mp }{\pi }^{\pm }$, and (p–t) $B^0\to b_1^{-}{K}^{+}$. The solid line represents the result of the fit and the dashed line the background contribution.