Search for $B^{+}\to \varphi {\pi }^{+}$ and $B^0\to \varphi {\pi }^0$ decays

A search has been made for the decays $B^{+}\to \varphi {\pi }^{+}$ and $B^0\to \varphi {\pi }^0$ in a data sample of approximately $232\times {10}^6$ $B\overline{B}$ pairs recorded at the ${\rm Y}(4S)$ resonance with the BABAR detector at the PEP-II $B$-meson Factory at SLAC. No significant signals have been observed, and therefore upper limits have been set on the branching fractions: $\mathcal{B}(B^{+}\to \varphi {\pi }^{+})<2.4\times {10}^{-7}$ and $\mathcal{B}(B^0\to \varphi {\pi }^0)<2.8\times {10}^{-7}$ at 90% probability.

Figure 1

Feynman diagram for $B\to \varphi \pi$ and $B\to \varphi K$.

Figure 2

Distribution of $m_{\mathrm{miss}}$ (top) and $m_B$ (bottom) for reconstructed $B^0\to \varphi {\pi }^0$ (left), $B^{+}\to \varphi {\pi }^{+}$ (middle) and $B^{+}\to \varphi h^{+}$ ($h=\{\pi ,K\}$) (right), after applying a requirement on the ratio of signal likelihood to signal-plus-background likelihood to enhance the signal. The curves are projections from the likelihood fit for total yield (solid line), for the continuum background (fine dashed line) and for continuum plus S-wave component (dashed line). For $B^{+}\to \varphi h^{+}$ decay we do not apply any particle identification criteria and assign the pion mass to the primary track. For this reason, the $m_B$ distribution for $B^{+}\to \varphi K^{+}$ events is shifted with respect to the nominal $B^{+}$ mass (positive bump in bottom middle and bottom right plot), while it peaks at the nominal value for $B^{+}\to \varphi {\pi }^{+}$ events (negative bump in bottom middle plot).

Figure 3

Likelihood distribution, $L_{\mathcal{B}}(\mathcal{B})$, for $\mathcal{B}(B^{+}\to \varphi {\pi }^{+})$ (left) and $\mathcal{B}(B^0\to \varphi {\pi }^0)$ (right) in arbitrary units. The upper boundary of the dark region represents the 90% probability upper limit.