Measurement of charmless $B$ Decays to $\eta K^{\ast }$ and $\eta \rho$

Abstract

We report measurements of branching fractions and CP asymmetries for $B\to \eta K^{\ast }$ and $B\to \eta \rho$ decays. These results are obtained from a $414{\mathrm{fb}}^{-1}$ data sample collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We measure the following branching fractions: $\mathcal{B}(B^0\to \eta K^{\ast 0})=(15.2\pm 1.2\pm 1.0)\times 10^{-6}$ and $\mathcal{B}(B^{+}\to \eta K^{\ast +})=(19.3_{-1.9}^{+2.0}\pm 1.5)\times 10^{-6}$, where the first error is statistical and the second systematic. We also find a $2.7\sigma$ excess in the $B^{+}\to \eta {\rho }^{+}$ mode and measure $\mathcal{B}(B^{+}\to \eta {\rho }^{+})=(4.1_{-1.3}^{+1.4}\pm 0.4)\times 10^{-6}<6.5\times 10^{-6}$ at 90% confidence level. For $B^0\to \eta {\rho }^0$ decays, we determine the upper limit $\mathcal{B}(B^0\to \eta {\rho }^0)<1.9\times 10^{-6}$ at 90% confidence level. The partial rate asymmetries are ${\mathcal{A}}_{CP}(\eta K^{\ast 0})=0.17\pm 0.08\pm 0.01$, ${\mathcal{A}}_{CP}(\eta K^{\ast +})=0.03\pm 0.10\pm 0.01$, and ${\mathcal{A}}_{CP}(\eta {\rho }^{+})=-0.04_{-0.32}^{+0.34}\pm 0.01$.

9 pages, 6 figures, 3 tables, to be submitted to PRD, journal version of ICHEP06 conference paper hep-ex/0608034 with refinement of analysis