Measurements of the CKM Angle alpha at BABAR

TL;DR

This paper reports precise measurements of CP asymmetries and branching fractions in B meson decays, refining the determination of the CKM angle alpha through multiple decay channels using BaBar data.

Contribution

It provides the first combined measurements of B --> K_1 pi decays and introduces a novel method to determine alpha from these channels, improving the understanding of CP violation.

Findings

Measured CP asymmetries and branching fractions for B0 and B+ decays.

First combined measurements of B --> K_1 pi decays.

Determined alpha angles for rho rho and a_1 pi decay channels.

Abstract

We present improved measurements of the branching fractions and CP-asymmetries in the B0 --> pi+ pi-, B0 --> pi0 pi0, and B+ --> rho+ rho0 decays, which impact the determination of alpha. We find S(pi+ pi-) = -0.68 +/- 0.10 +/- 0.03 C(pi+ pi-) = -0.25 +/- 0.08 +/- 0.02 C(pi0 pi0) = -0.43 +/- 0.26 +/- 0.05 BF(B0 --> pi0 pi0) = (1.83 +/- 0.21 +/- 0.13) x 10^{-6} for B --> pi pi decays, and BF(B+ --> rho+ rho0) = (23.7 +/- 1.4 +/- 1.4) x 10^{-6} f_L(rho+ rho0) = 0.950 +/- 0.015 +/- 0.006 alpha(rho rho) = (92.4 +6.0/-6.5)^{o} for B --> rho rho decays. The combined branching fractions of B --> K_1 pi decays are measured for the first time and allow a novel determination of alpha in the B0 --> a_1(1260)+ pi- decay channel. We obtain BF(B0 --> K_1(1270)+ pi- + K_1(1400)+ pi-) = (3.1 +0.8/-0.7) x 10^{-5} BF(B+ --> K_1(1270)0 pi+ + K_1(1400)0 pi+) = (2.8 +2.9/-1.7) x 10^{-5} alpha(a_1\pi) = (79 +/- 7 +/- 11)^{o}. These measurements are performed using the final dataset collected by the BaBar detector at the PEP-II B-factory.