Observation of $B\to {\eta }^{\prime }{K}^{*}$ and Evidence for $B^{+}\to {\eta }^{\prime }{\rho }^{+}$

We present an observation of $B\to {\eta }^{\prime }{K}^{*}$. The data sample corresponds to $232\times {10}^6$ $B\overline{B}$ pairs collected with the BABAR detector at the PEP-II asymmetric-energy $B$ factory at the Stanford Linear Accelerator Center. We measure the branching fractions (in units of ${10}^{-6}$) $\mathcal{B}(B^0\to {\eta }^{\prime }{K}^{*0})=3.8\pm 1.1\pm 0.5$ and $\mathcal{B}(B^{+}\to {\eta }^{\prime }{K}^{*+})={4.9}_{-1.7}^{+1.9}\pm 0.8$, where the first error is statistical and the second systematic. A simultaneous fit results in the observation of $B\to {\eta }^{\prime }{K}^{*}$ with $\mathcal{B}(B\to {\eta }^{\prime }{K}^{*})={4.1}_{-0.9}^{+1.0}\pm 0.5$. We also search for $B\to {\eta }^{\prime }\rho$ and ${\eta }^{\prime }{f}_0(980)(f_0\to {\pi }^{+}{\pi }^{-})$ with results and 90% confidence level upper limits $\mathcal{B}(B^{+}\to {\eta }^{\prime }{\rho }^{+})={8.7}_{-2.8-1.3}^{+3.1+2.3}$ ($<14$), $\mathcal{B}(B^0\to {\eta }^{\prime }{\rho }^0)<3.7$, and $\mathcal{B}\mathbf{(}{B}^0\to {\eta }^{\prime }{f}_0(980)(f_0\to {\pi }^{+}{\pi }^{-})\mathbf{)}<1.5$. Charge asymmetries in the channels with significant yields are consistent with zero.

Figure 1

$B$ candidate $m_{\mathrm{ES}}$ (left) and $\Delta E$ (right) projections obtained with a cut on the likelihood (see text) for $B^0\to {\eta }^{\prime }{K}^{*0}$ (top), $B^{+}\to {\eta }^{\prime }{K}^{*+}$ (middle), and $B^{+}\to {\eta }^{\prime }{\rho }^{+}$ (bottom). Submodes have been combined. The data are represented by points with uncertainties, full fit functions by solid curves, $B\overline{B}$ background by dashed curves, continuum by dotted curves, and signal by dotted-dashed curves. Depending on the decay, the plots contain 63%–85% of all signal events.

Figure 2

Distributions of the $K\pi$ mass (left) and helicity (right) for the decay $B^0\to {\eta }^{\prime }{K}^{*0}$. Points with error bars: data, background subtracted with the event-weighting technique described in Ref. [13]; solid curve: signal PDF.