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

TL;DR

This paper reports improved measurements of the $B^+ o ho^+ ho^0$ decay parameters and uses these results to determine the quark-mixing phase angle $oldsymbol{ extalpha}$, enhancing understanding of CP violation and CKM matrix constraints.

Contribution

The study provides more precise measurements of branching fraction, polarization, and CP asymmetry in $B^+ o ho^+ ho^0$ decays, leading to a refined determination of the CKM phase angle $oldsymbol{ extalpha}$.

Findings

Branching fraction ${ m f B}$ measured as $(23.7 extpm1.4 extpm1.4) imes10^{-6}$.

Longitudinal polarization fraction $f_L$ is $0.950 extpm0.015 extpm0.006$.

CKM phase angle $oldsymbol{ extalpha}$ determined as $(92.4^{+6.0}_{-6.5})^ ext{o}$.

Abstract

We present improved measurements of the branching fraction ${\cal B}$, 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 ${\cal B} (\Bp\ra\rprz)=(23.7\pm1.4\pm1.4)\times10^{-6}$, $f_L=0.950\pm0.015\pm0.006$, 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 $(92.4^{+6.0}_{-6.5})^{\circ}$.