Two-Body $\mathit{B}$ Meson Decays to $\eta$ and ${\eta }^{\prime }$: Observation of $\mathit{B}\to \eta {\mathit{K}}^{*}$

In a sample of $19\times {10}^6$ produced $B$ mesons, we have observed the decays $B\to \eta K^{*}$ and improved our previous measurements of $B\to {\eta }^{\prime }K$. The branching fractions we measure for these decay modes are $B(B^{+}\to \eta K^{*+})=({26.4}_{-8.2\mathrm{}}^{+9.6\mathrm{}}\pm 3.3)\times {10}^{-6\mathrm{}}$, $B(B^0\to \eta K^{*0\mathrm{}})=({13.8}_{-4.6\mathrm{}}^{+5.5\mathrm{}}\pm 1.6)\times {10}^{-6\mathrm{}}$, $B(B^{+}\to {\eta }^{\prime }{K}^{+})=({80}_{-9\mathrm{}}^{+10\mathrm{}}\pm 7)\times {10}^{-6\mathrm{}}$, and $B(B^0\to {\eta }^{\prime }{K}^0)=({89}_{-16\mathrm{}}^{+18\mathrm{}}\pm 9)\times {10}^{-6\mathrm{}}$. We have searched with comparable sensitivity for related decays and report upper limits for these branching fractions.