Branching fraction limits for $B^0$ decays to ${\eta }^{\prime }\eta$, ${\eta }^{\prime }{\pi }^0$ and $\eta {\pi }^0$

We describe searches for decays to two-body charmless final states ${\eta }^{\prime }\eta$, ${\eta }^{\prime }{\pi }^0$ and $\eta {\pi }^0$ of $B^0$ mesons produced in $e^{+}{e}^{-}$ annihilation. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent $232\times {10}^6$ produced $B\overline{B}$ pairs. The results for branching fractions are, in units of ${10}^{-6}$ (upper limits at 90% C.L.): $\mathcal{B}(B^0\to {\eta }^{\prime }\eta )={0.2}_{-0.5}^{+0.7}\pm 0.4(<1.7)$, $\mathcal{B}(B^0\to \eta {\pi }^0)={0.6}_{-0.4}^{+0.5}\pm 0.1(<1.3)$, and $\mathcal{B}(B^0\to {\eta }^{\prime }{\pi }^0)={0.8}_{-0.6}^{+0.8}\pm 0.1(<2.1)$. The first error quoted is statistical and the second systematic.

Figure 1

Plots of the $B^0\to {\eta }_{\eta \pi \pi }^{\prime }{\pi }^0$ data distribution projected on each of the fit variables: (a) $\Delta E$, (b) $m_{\mathrm{ES}}$, (c) ${\eta }^{\prime }$ mass, and (d) $\mathcal{F}$. The solid line represents the result of the fit, and the dashed line the background contribution. (The absence of signal here nearly hides the dashed curve.) The dotted line illustrates the expected shape for signal, with a normalization, chosen for clarity, that corresponds to a branching fraction of $50\times {10}^{-6}$.

Figure 2

The likelihood ratio ${\mathcal{L}}_{\mathrm{sig}}/[{\mathcal{L}}_{\mathrm{sig}}+\sum _{}^{}{\mathcal{L}}_{\mathrm{bkg}}]$ for $B^0\to {\eta }_{\eta \pi \pi }^{\prime }{\pi }^0$. The open circles represent a simulated signal component (normalized as the signal curves in Fig. 1), the solid points represent the data, the solid histograms are from samples of simulated background (shaded) and background plus signal (white, barely visible in the right-most bins, given the small signal yield).