Constraints on the CKM angle alpha in the B --> rho rho decays

TL;DR

This paper measures CP asymmetries in B0 -> rho+ rho- decays and sets limits on B0 -> rho0 rho0, constraining the CKM angle alpha with data from BaBar at SLAC.

Contribution

It provides the first measurements of time-dependent asymmetries in B0 -> rho+ rho- and limits on B0 -> rho0 rho0, reducing uncertainties on the CKM angle alpha.

Findings

Measured CP asymmetry parameters C_L and S_L with uncertainties.

Set an upper limit on the B0 -> rho0 rho0 branching fraction.

Estimated penguin contribution to alpha uncertainty as 11 degrees.

Abstract

Using a data sample of 122 million Upsilon(4S) -> BBbar decays collected with BaBar detector at the PEP-II asymmetric B factory at SLAC, we measure the time-dependent-asymmetry parameters of the longitudinally polarized component in the B0 -> rho^+ rho^- decay as C_L = -0.23 +/- 0.24 (stat) +/- 0.14 (syst) and S_L = -0.19 +/- 0.33 (stat) +/- 0.11 (syst). The B0 -> rho0 rho0 decay mode is also searched for in a data sample of about 227 million BBbar pairs. No significant signal is observed, and an upper limit of 1.1 * 10-6 (90% C.L.) on the branching fraction is set. The penguin contribution to the CKM angle $\alpha$ uncertainty is measured to be 11 degree. All results are preliminary.