Evidence for Charged $B$ Meson Decays to $a_1^{\pm }(1260){\pi }^0$ and $a_1^0(1260){\pi }^{\pm }$

We present measurements of the branching fractions for the decays $B^{\pm }\to a_1^{\pm }(1260){\pi }^0$ and $B^{\pm }\to a_1^0(1260){\pi }^{\pm }$ from a data sample of $232\times {10}^6$ $B\overline{B}$ pairs produced in $e^{+}{e}^{-}$ annihilation through the ${\rm Y}(4S)$ resonance. We measure the branching fraction $\mathcal{B}\mathbf{(}{B}^{\pm }\to a_1^{\pm }(1260){\pi }^0\mathbf{)}\times \mathcal{B}\mathbf{(}{a}_1^{\pm }(1260)\to {\pi }^{-}{\pi }^{+}{\pi }^{\pm }\mathbf{)}=(13.2\pm 2.7\pm 2.1)\times {10}^{-6}$ with a significance of $4.2\sigma$, and the branching fraction $\mathcal{B}\mathbf{(}{B}^{\pm }\to a_1^0(1260){\pi }^{\pm }\mathbf{)}\times \mathcal{B}\mathbf{(}{a}_1^0(1260)\to {\pi }^{-}{\pi }^{+}{\pi }^0\mathbf{)}=(20.4\pm 4.7\pm 3.4)\times {10}^{-6}$ with a significance of $3.8\sigma$, where the first error quoted is statistical and the second is systematic.

Figure 1

Projections of (a) $\Delta E$, (b) $m_{\mathrm{ES}}$, (c) $m_{a_1}$, and (d) $\mathcal{F}$ for $B^{+}\to a_1^{+}{\pi }^0$. Points represent on-resonance data, dashed lines the signal, dotted lines the continuum, dash-dotted lines the $B\overline{B}$ charm background, the filled region the $a_2$ background, and solid lines the full fit function. These plots are made with a requirement on the signal likelihood to enhance the signal, and thus do not show all events in the data sample.

Figure 2

Projections of (a) $\Delta E$, (b) $m_{\mathrm{ES}}$, (c) $m_{a_1}$, and (d) $\mathcal{F}$ for $B^{+}\to a_1^0{\pi }^{+}$, using the same criteria and line styles as Fig. 1.