Improved Measurement of $B^{+}\to {\rho }^{+}{\rho }^0$ and Determination of the Quark-Mixing Phase Angle $\alpha$

Abstract

We present improved measurements of the branching fraction $\mathcal{B}$, the longitudinal polarization fraction $f_L$, and the direct {\ensuremath{CP}\xspace} asymmetry {\ensuremath{{\cal A}_{CP}}\xspace} in the $B$ meson decay channel $B^{+}\to {\rho }^{+}{\rho }^0$. The data sample was collected with the {{\slshape B\kern-0.1em{\smaller A}\kern-0.1em B\kern-0.1em{\smaller A\kern-0.2em R}}} detector at SLAC. The results are ${\cal B} (\Bp\ra\rprz)=(23.7\pm1.4\pm1.4)\times10^{-6}$, $f_L=0.950\pm 0.015\pm 0.006$, and $\Acp=-0.054\pm0.055\pm0.010$, where the uncertainties are statistical and systematic, respectively. Based on these results, we perform an isospin analysis and determine the CKM weak phase angle $\alpha$ to be $(92.4_{-6.5}^{+6.0}{)}^{\circ }$.

7 pages, 1 figure, short version in Phys. Rev. Lett. (Fig.2 removed), adding color Figure 2 for the earlier versions of arxiv.0901.3522