A Study of B0 to rho+rho- Decays and Constraints on the CKM Angle alpha

TL;DR

This paper reports on measurements of B0 to rho+rho- decays, including branching fraction, polarization, and CP violation parameters, to constrain the CKM angle alpha using data from the BaBar experiment.

Contribution

It provides the first precise measurements of B0 to rho+rho- decay parameters and constrains the CKM angle alpha through isospin and SU(3) symmetry analyses.

Findings

Branching fraction B(B0-> rho+rho-) = (25.5 +/- 2.1 (stat) +3.6/-3.9 (syst))*10^-6

Longitudinal polarization fraction f_L = 0.992 +/- 0.024 (stat) +0.026/-0.013 (syst)

CKM angle alpha constrained to [73.1, 117.0] degrees at 68% CL

Abstract

We present results from an analysis of B0 to rho+rho- decays using 383.6 million BB-bar pairs collected by the BaBar detector at the PEP-II asymmetric-energy B Factory at SLAC. The measurements of the B0 to rho+rho- branching fraction, longitudinal polarization fraction f_L, and the CP-violating parameters S_{long} and C_{long} are: B(B0-> rho+rho-) = (25.5 +/- 2.1 (stat) +3.6/-3.9 (syst))*10^-6 f_L = 0.992 +/- 0.024 (stat) +0.026/-0.013 (syst) S_{long} = -0.17 +/- 0.20 (stat) +0.05/-0.06 (syst) C_{long} = 0.01 +/- 0.15 (stat) +/- 0.06 (syst) We determine the unitarity triangle angle alpha, using an isospin analysis of B to rhorho decays. One of the two solutions, alpha = [73.1, 117.0] degrees at 68% CL is compatible with standard model-based fits of existing data. Constraints on the unitarity triangle are also evaluated using an SU(3) symmetry based approach.