Search for the decay $B^0\to a_1^{\pm }{\rho }^{\mp }$

We present a search for the rare $B$-meson decay $B^0\to a_1^{\pm }{\rho }^{\mp }$ with $a_1^{\pm }\to {\pi }^{+}{\pi }^{-}{\pi }^{\pm }$. We use $(110\pm 1.2)\times {10}^6\mathit{{\rm Y}}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We obtain an upper limit of $30\times {10}^{-6}(90\%\mathrm{C}.\mathrm{L}.)$ for the branching fraction product $\mathcal{B}(B^0\to a_1^{\pm }{\rho }^{\mp })\mathcal{B}(a_1^{\pm }\to {\pi }^{+}{\pi }^{-}{\pi }^{\pm })$, where we assume that the $a_1^{\pm }$ decays exclusively to ${\rho }^0{\pi }^{\pm }$.

Figure 1

The true signal (top) and continuum (bottom) distributions for (left to right) $m_{\mathrm{ES}}$, $\Delta E$, $m_{a_1^{+}}$ using the weighting technique described in Ref. [20]. The points represent the weighted data, and solid curves represent the corresponding PDFs.

Figure 2

The $-\ln (L/L_{\max })$ distribution from the fit to data with $f_L=1.0$ (fixed). This distribution has been corrected for fit bias. The solid curve is for statistical errors only, and the dashed curve includes systematic errors.