Improved measurement of the branching fraction, polarization, and $CP$ asymmetry in $B^+\to\rho^0\rho^+$ decays

Based on data collected at the $\Upsilon(4S)$ resonance by the Babar detector at the PEP-II asymmetric-energy $e^+ e^-$ storage rings at SLAC, we present an improved measurement of the $B^+\to\rho^0\rho^+$ branching fraction, polarization, and direct $CP$ asymmetry. These results can be used to improve the determination of the CKM unitarity angle $\alpha$.