Updated Measurement of the CKM Angle alpha Using B0->rho+rho- Decays

TL;DR

This paper reports a precise measurement of the B0->rho+rho- decay parameters, including polarization and CP violation, to refine the determination of the CKM angle alpha, consistent with the Standard Model.

Contribution

It provides updated measurements of B0->rho+rho- decay parameters and a new isospin analysis to determine the CKM angle alpha with improved precision.

Findings

Branching fraction measured as (23.5 +/- 2.2 +/- 4.1) x 10^-6

Longitudinal polarization fraction fL = 0.977 +/- 0.024

CKM angle alpha estimated as [74, 117] degrees at 68% CL

Abstract

We present results from an analysis of B0->rho+rho- using 316fb^-1 of Y(4S) -> B0B0bar decays observed with the BaBar detector at the PEP-II asymmetric-energy B Factory at SLAC. We measure the B0->rho+rho- branching fraction, longitudinal polarization fraction fL, and the CP-violating parameters S_LONG and C_LONG: B(B0->rho+rho-) = (23.5 +/- 2.2 [stat] +/- 4.1 [syst]) * 10^-6, fL = 0.977 +/- 0.024 [stat] +0.015/-0.013 [syst] S_LONG = -0.19 +/- 0.21 [stat] +0.05/-0.07 [syst] C_LONG = -0.07 +/- 0.15 [stat] +/- 0.06 [syst] Using an isospin analysis of B->rhorho decays we determine the angle alpha of the unitarity triangle. One of the two solutions, alpha = [74, 117] degrees at 68% CL, is compatible with the standard model. All results presented here are preliminary.