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

TL;DR

This paper improves the measurement of the CKM angle alpha by analyzing B0 -> rho+rho- decays, providing a more precise value consistent with the Standard Model, based on a large dataset from the BABAR experiment.

Contribution

It presents a refined measurement of the CKM angle alpha using B0 -> rho+rho- decays with an isospin analysis, enhancing previous precision and confirming Standard Model predictions.

Findings

Measured the longitudinal polarization fraction f_L = 0.978 +- 0.014

Determined CP-violating parameters SLong and CLong with uncertainties

Estimated the unitarity triangle angle alpha as (100 +- 13) degrees

Abstract

We present results from an analysis of B0 -> rho+rho- using 232 million Upsilon(4S) decays collected with the BABAR detector at the PEP-II asymmetric-energy $B$ Factory at SLAC. We measure the longitudinal polarization fraction f_L = 0.978 +- 0.014 (stat) +0.021 -0.029 (syst) and the CP-violating parameters SLong = -0.33 +- 0.24 (stat) +0.08 -0.14 (syst) and CLong = -0.03 +- 0.18 (stat) +- 0.09 (syst). Using an isospin analysis of B -> rho rho decays we determine the unitarity triangle alpha. The solution compatible with the Standard Model is alpha = (100 +- 13) degrees.